Reactions rearrange matter
Chemical substances are made up of different types of elements, compounds and mixtures, each of which have different properties and uses. Different substances can be made in chemical reactions but the atoms themselves cannot be created or destroyed, only rearranged. There are many different types of chemical reaction, such as synthesis, decomposition and combustion reactions.
In this unit you will be learning about acids and alkalis and how to identify them using different indicators. You will also be learning about reactions between acids and alkalis, particularly neutralisation reactions.
Atoms are the smallest unit of matter. Elements are made up of one type of atom. Compounds are two or more elements chemically bonded together. Mixtures are two or more elements or compounds not chemically bonded together. Solids, liquids and gases can be represented using the particle model.
1. Which statement describes the motion of the particles in a slab of concrete? £ A. They move when the concrete gets heated £ B. They can vibrate £ C. They do not move at all
2. Ice feels solid but water feels runny. Which idea explains this? £ A. Particles in ice are linked more tightly together £ B. Particles in ice are harder than particles in water £ C. Ice is solid particles but water is liquid particles
3. After a hot shower, water vapour from the shower condenses on the glass. Why? £ A. Particles in the water vapour have lost energy £ B. Particles in the water vapour have gained energy £ C. Glass particles in the shower have lost energy
4. Which of the following are all examples of elements. £ A .Oxygen, hydrogen, potassium £ B. Water, carbon dioxide, helium £ C. Protein, oxygen, water
5. Elements are represented by symbols. What is the symbol for sodium? £ A. NA £ B. Na £ C. So
6. The periodic Table is organised into groups and periods. Using your Periodic Table which group and period is Lithium in? £ A. Group 1, Period 2 £ B. Group 2, Period 1 £ C. Group 1, Period 1
7. Which of these is an observation showing that a chemical reaction has taken place? £ A. There was a change in state £ B. There was a colour change £ C. There was a change in texture from hard to runny
8. Which best explains the difference between an element and a compound? £ A. Elements are made up of one type of atom, compounds are 2 or more elements mixed together £ B. Elements are made up of one type of atom, compounds are 2 or more elements chemically bonded together £ C. Compounds are made up of one type of atom, elements are 2 or more compounds mixed together
9. The formula for nitric acid is HNO3. How many atoms of each element are present? £ A. 1 hydrogen atom, 1 nitrogen atom and 3 oxygen atoms £ B. 3 hydrogen atoms, 3 nitrogen atoms and 3 oxygen atoms £ C. 1 hydrogen atom and 3 nitrate atoms
10. Sugar is mixed into a cup of tea. What is the solute and what is the solvent? £ A. Sugar is the solvent, tea is the solute £ B. Sugar is the solute, tea is the solvent £ C. Water is the solute, tea is the solvent
Question Answer What to do next (Fix-It task) 1 B If you answered A or C you need to review the properties of solids. Draw a particle diagram to show the arrangement of particles in a solid and describe the movement of particles. 2 A If you answered B or C you need to review the differences between solids and liquids. Explain the differences between the arrangement of particles in ice and water. 3 A If you answered B or C you need to review the process of condensation. Explain what happens during condensation by referring to the energy of particles and state the name of the opposite process. 4 A If you answered B or C you need to review the difference between elements and compounds. Explain why water and carbon dioxide are not elements. 5 B If you answered A or C you need to review how to use the Periodic Table. Find the symbols for: tin, iron, potassium and lead. 6 A If you answered B or C you need to review the meaning of groups and periods in the Periodic Table. Identify the group and period of oxygen, potassium and chlorine. 7 B If you answered A or B you need to review the differences between a physical and a chemical change. Describe the observations you may see if a chemical change (reaction) has taken place. 8 B If you answered A or C you need to review the difference between elements and compounds. State the definition and an example of each. 9 A If you answered B or C you need to review how to use chemical formulae. Determine how many of each atom are in sulfuric acid (H2SO4), calcium carbonate (CaCO3) and phosphoric acid (H3PO4). 10 B If you answered A or C you need to review the definitions of solute and solvent. State the definitions of solute, solvent, solution and saturated and give an example of a solute being added to a solvent.
Great job! Now you’re ready to start learning about acids and alkalis!
C2.1 Acids and Alkalis Knowledge Organiser
The pH Scale 27. Acids will turn universal indicator red or orange. 1. Substances can be classified into acidic,
alkaline and neutral solutions 28. Neutral solutions will turn universal indicator
green. 2. The pH scale, from 0 to 14, is a measure
of the acidity or alkalinity of a solution 29. Alkaline solutions will turn universal indicator
blue or purple. 3. The pH scale can be measured using
litmus, universal indicator or a pH probe.
4. A solution with pH 7 is neutral.
5. Aqueous solutions of acids have pH values of less than 7
6. Aqueous solutions of alkalis have pH values greater than 7
7. An aqueous solution is any solution in which the solvent is water
Neutralisation
30. In neutralisation reactions an acid reacts
with an alkali to form a salt and water. 8. Strong acids have a pH from 0 to 3.
31. Neutralisation forms a neutral (pH7) 9. Weak acids have a pH of 4 to 6. solution.
10. Strong alkalis have a pH from 11 to 14. 32. A salt is a metal compound made from
acid. 11. Weak alkalis have a pH from 8 to 10.
33. A salt is formed when the hydrogen in an 12. Strong acids and strong alkalis are both acid is replaced by a metal. corrosive.
13. Weak acids and alkalis are less corrosive.
14. Many substances we use every day are acidic or alkaline.
15. Lemon juice is acidic.
16. Bleach (and many other cleaning agents) are alkaline.
C2.1 Acids and Alkalis Knowledge Organiser
Indicators Metal Carbonates
17. Indicators will show the pH of the 34. Metal carbonates react with acids in substance by a colour change. neutralisation reactions to form a salt, water
and carbon dioxide 18. Litmus indicator can show if a solution is
acidic or alkaline.
35. In an open system these products can escape, and the system is neutral
36. In a closed system carbon dioxide reacts with water to form carbonic acid, which makes the system acidic 19. Litmus indicator is red in an acidic solution.
20. Litmus indicator is blue in an alkaline solution.
21. Litmus indicator remains the same colour in a neutral solution.
22. If using litmus paper, blue litmus paper turns red in an acidic solution.
23. Red litmus paper turns blue in an alkaline solution.
24. To remember this, it might be helpful to memorise the rhyme Blue to red, acid is said Red to blue, acid untrue
Acid Alkali 25. Universal indicator is sometimes called UI
26. Universal indicator can be used as a liquid solution or as paper strips to dip into a solution.
Keyword Definition
pH Acid Alkali Acidic Alkaline Solution Universal indicator Litmus paper Salts Chloride Sulphate Nitrate Citrate Carbonate Neutralisation Evaporation Crystallisation Acidification Limewater
The pH Scale
Starter 1. What does this symbol tell you?
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2. What does this mean?
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Foundation: Where might you find this hazard symbol in the lab?
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Stretch: What does this symbol have to do with the title of today’s lesson?
______
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Substances can be classified into acidic, alkaline and neutral solutions, according to the pH scale. The pH scale ranges from 0 to 14, and is a measure of the acidity or alkalinity of a solution.
The pH scale can be measured using litmus, universal indicator or a pH probe.
Note: acids and alkalis are not actually these colours – the colour scale shows the colour that universal indicator turns when a few drops of it are added to an acidic or alkaline solution.
Note: an aqueous solution is any solution in which water is the solvent (the liquid the solute is dissolved in).
A solution with pH 7 is neutral.
Aqueous solutions of acids have Aqueous solutions of alkalis have pH values of less than 7. pH values greater than 7.
1. Determine if the following statements are true or false: a. The pH scale ranges from 1 to 14 b. pH 1-7 indicates an acidic solution c. pH 7 indicates that the solution is both an acid and alkali d. Three ways to measure the pH of a solution are; using litmus indicator, universal indicator or a pH probe
2. Colour the sections to represent each pH, and then use the boxes at the top of the pH scale to label the pH scale. The first one has been done for you.
3. There are many acids and alkalis that we come across all the time in our everyday lives. Below is a table with examples of different substances and their pH. Add these examples to your pH scale in the correct place.
Substance pH Substance pH battery acid 1.0 mineral water 8.0 bee sting 3.5 oven cleaner 13.0 blood 7.5 skin 5.5 distilled water 7.0 tap water 6.0 egg white 9.5 toothpaste 9.0 fizzy drinks 4.5 vinegar 3.0 indigestion powder 8.5 washing up liquid 5.0 kitchen surface cleaner 11.0 washing soda 11.5 lemon juice 2.0 wasp sting 10.0 milk 6.5 Washing powder 10.5
4. Write four sentences to describe the pH scale. Use each of the following words at least once: acids alkalis neutral fourteen indicator substances weak strong
______
1. What does the pH scale tell us? £ A. How acidic a solution is £ B. How alkaline a solution is £ C. How acidic or alkaline a solution is
2. How does universal indicator show us that a solution is acidic/alkaline? £ A. It turns red/yellow if acidic and blue/purple if alkaline £ B It turns red/yellow if alkaline and blue/purple if acidic £ C. The acid or alkali changes colour pH 3. Which of these solutions is the least acidic solution? Solution £ A A 1 £ B B 4 £ C C 6
If you answered A The pH Scale is a measure of the acidity or alkalinity of a substance. The more extreme the pH the more acidic or alkaline the substance is, so the most acidic substances have low pHs (around 1) and the most alkaline substances have high pHs (around 14). These substances are all acidic but a pH of 1 would be the most acidic of these and a pH of 6 would be the least acidic, as it is closest to neutral. State what pH a very alkaline solution would have.
If you answered B The pH Scale is a measure of the acidity or alkalinity of a substance. The more extreme the pH the more acidic or alkaline the substance is, so the most acidic substances have low pHs (around 1) and the most alkaline substances have high pHs (around 14). These substances are all acidic but a pH of 1 would be the most acidic of these and a pH of 6 would be the least acidic, as it is closest to neutral. Suggest the colour that universal indicator would turn when added to each of these substances.
If you answered C The pH Scale is a measure of the acidity or alkalinity of a substance. The more extreme the pH the more acidic or alkaline the substance is, so the most acidic substances have low pHs (around 1) and the most alkaline substances have high pHs (around 14). These substances are all acidic but a pH of 1 would be the most acidic of these and a pH of 6 would be the least acidic, as it is closest to neutral. Suggest which of these substances would be the most harmful and explain why.
Indicators
Starter 1. State the pH of an acid.
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2. State the pH of an alkali.
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3. State the pH of a neutral substance.
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Foundation: Give an example of an acid.
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Stretch: suggest which is more dangerous between a substance that has a pH of 1 and a substance that has a pH of 12.
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Indicators are used to show (which is why they are called indicators) whether a substance is acid, alkaline or neutral. The most common indicators are Universal Indicator and Litmus paper.
Blue litmus indicator (paper) turns red when it is placed in an acidic solution.
Red litmus indicator (paper) turns blue when it is placed in an alkaline solution.
Both red and blue litmus indicators remain the same colour in a neutral solution and do not change.
Universal Indicator colour ranges from red to yellow in an acidic solution. Universal Indicator colour ranges from blue to purple in an alkaline solution. Universal Indicator is green in a neutral solution.
Note: the pH scale is not a linear scale. Each time you go up the pH scale, the scale goes up by 10x.
pH
1. Correct these statements: a. Litmus indicator (paper) is red in alkaline solutions. b. Litmus indicator (paper) is blue in acidic solutions. c. Litmus indicator remains the same colour in a neutral solution but sometimes changes. d. Universal Indicator colour ranges from red to yellow in an alkaline solution e. Universal Indicator colour ranges from blue to purple in an acidic solution f. Universal Indicator is yellow in a neutral solution
Unusual scales
Scientists describe the magnitude (strength) of an earthquake using the Richter Scale. This scale of numbers is unusual because an earthquake that measures 2 on the scale is not double the magnitude of an earthquake measuring 1. It is 10 times the magnitude.
Worked example How much greater is a magnitude 8 earthquake than a magnitude 6 one?
A magnitude 8 earthquake is 10x10 = 100 x greater than a magnitude 6 earthquake.
Practice questions 1. How much greater is a magnitude 6 earthquake than an earthquake that has magnitude 3?
10 x 10 x 10 = x1000
2. How much greater is a magnitude 7 earthquake than an earthquake that has magnitude 2? 10 x 10 x 10 x 10 x 10 = x100 000
The pH scale works in two directions.
pH 1 is 10 times more acidic than pH 2. pH 14 is 10 times more alkaline than pH 13.
Practice questions 1. How much more acidic is pH 1 than pH 4?
2. How much more alkaline is pH 14 than pH 12?
3.How much less acidic is pH 6 than pH 5?
4. How much less alkaline is pH 9 than pH 11?
1. An unknown solution was poured into a test tube. The red litmus paper turned blue. What type of solution is in the test tube? £ A. Acidic solution £ B. Alkali solution £ C. Neutral solution
2. When using Universal Indicator, what range of colours show an acidic solution? £ A. Red to blue £ B. Red to green £ C. Red to yellow
3. As you go from pH 1 to pH 6, the acidity… £ A. Increases by a scale of x10 each time £ B. Doubles each time £ C. Decreases by a scale of x10 each time
If you answered A Universal indicator is used to show whether a substance is acidic or alkaline. Universal indicator turns red or yellow when it is added to an acid, meaning the range of colours in an acid is red to yellow. Universal indicator only turns blue when added to an alkaline solution. Explain how you can tell whether a substance is acidic or alkaline using universal indicator and describe the results you would expect.
If you answered B Universal indicator is used to show whether a substance is acidic or alkaline. Universal indicator turns red or yellow when it is added to an acid, meaning the range of colours in an acid is red to yellow. Universal indicator only turns green when it is added to neutral substances and the range for acids does not include neutral substances. Give examples of substances that would turn universal indicator i) red, ii) green and iii) blue.
If you answered C Universal indicator is used to show whether a substance is acidic or alkaline. Universal indicator turns red or yellow when it is added to an acid, meaning the range of colours in an acid is red to yellow. Suggest what universal indicator would show if an acid and an alkali of equal strength were added together.
Indicators Practical
Starter 1. State three types of indicator.
______
2. Which indicator would give the most useful results?
______
3. Which indicator gives the least information about the pH of a solution?
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Foundation: Which type of indicator would you use if you’re deciding on whether a solution is acid of alkali?
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Stretch: Why would you not use Litmus indicator when deciding whether water has a suitable pH to drink?
______
______
1. Determine if the following statements are true or false: a. Adding universal indicator changes the colour of the solution so that we can identify its pH b. Adding more acidic solution to the Universal indicator will make the solution become darker c. Adding equal amounts of a pH 1 acid and a pH 14 alkali will produce a green colour when adding Universal Indicator.
Traffic Light Challenge
In small groups, your task is to make a red, orange and green coloured solution. Your colour change will happen when you add universal indicator.
Equipment • Universal indicator • Range of acids and alkalis • Pipettes • Test tubes • Test tube rack
It’s more challenging to achieve the orange colour because you’ve got to use specific quantities of acid and alkali. You will need to record your quantities of acid/alkali each time you try because for the final test you will have to make the solutions without checking the colour. Use the table below to record your measurements.
Volume of Name of Volume of acid Colour pH Improvement water (cm3) acid or or alkali (drops) needed alkali
5
5
5
5
5
1. Which of the following statements is true? £ A. Adding equal amounts of weak acid and a weak alkali will give you a neutral solution £ B. Adding a lot of acid to a weak alkali creates a neutral solution £ C. Adding a little bit of acid to a weak alkali creates a neutral solution
2. To make a weak acidic solution more acidic, you: £ A. Add more acid £ B. Add more alkali £ C. Can’t do it
3. To make an alkali with pH 13 weaker, you must: £ A. Add more alkali £ B. Add more acid £ C. Add water
If you answered A Neutral solutions have a pH 7 and turn Universal indicator green when it is added to them. If you added an equal amount of a weak acid and a weak alkali it would give you a neutral solution. Bee stings are acidic. Suggest why baking soda (alkaline) is recommended as a treatment for bee stings.
If you answered B Neutral solutions have a pH 7 and turn Universal indicator green when it is added to them. If you added an equal amount of a weak acid and a weak alkali it would give you a neutral solution. Adding a lot of acid to a weak alkali would still leave you with a more acidic solution. Two equal volumes of acid and alkali were added together and produced a neutral solution. If the acid was pH 5, what pH must the alkali have been?
If you answered C Neutral solutions have a pH 7 and turn Universal indicator green when it is added to them. If you added an equal amount of a weak acid and a weak alkali it would give you a neutral solution. Adding a little bit of acid to a weak alkali may end up creating a neutral solution but you need to know the volumes to be certain. Bee stings are acidic but wasp stings are alkaline. Suggest why baking soda (alkaline) is recommended as a treatment for bee stings but would not help when treating wasp stings.
Neutralisation
Starter 1. What colour would Universal Indicator turn if it was added to a solution of pH 9?
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2. Universal Indicator turns yellow when added to a solution. What is the pH of the solution?
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3. Explain why litmus paper is not as useful as Universal Indicator for determining pH of a substance.
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Foundation: What colour does Universal Indicator turn in neutral solutions?
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Stretch: Equal volumes of an acid (pH 1) and an alkali (pH 12) are added together. Suggest what would happen and describe how you could check the result.
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In neutralisation reactions an acid reacts with an alkali to form a salt and water;
acid + alkali → salt + water
Note: a salt refers to any substance that is produced from the reaction between an acid and a metal. Sodium chloride (table salt) is an example of a salt, but is not the only salt.
Neutralisation forms a neutral (pH7) solution but not all salts produced from a neutralisation reaction are neutral. Only salts produced from a strong acid and a strong alkali are neutral.
A salt is a metal compound made from acid e.g. potassium chloride is a metal compound; the metal is potassium and the acid it is made from is hydrochloric acid. A salt is formed when the hydrogen in an acid is replaced by a metal.
Example:
Potassium hydroxide (alkali) + hydrochloric acid (acid) → Potassium chloride + water
The ‘H’ in ‘HCl’ is replaced with the ‘K’ from ‘KOH’. The OH from the alkali and H from the acid form H2O (water).
1. Determine if the following statements are true or false: a. Neutralisation reactions produce a salt and hydrogen b. Water is produced from a neutralisation reaction because the OH from the alkali and the H from the acid join together c. All acid and alkali reactions produce neutral salts
2. Watch a demonstration of copper carbonate gradually being added to a beaker containing sulfuric acid. Copper sulfate solution is formed.
a. Complete the table below to show what the beaker contains at each stage of the experiment.
Substance Stage 1 Stage 2 Stage 3 Sulfuric acid
Copper carbonate copper sulfate solution
Water
b. Describe how the pH changes during the reaction. The sulfuric acid is pH1. ______
3.We know that neutralisation reactions with hydrochloric acid produce chloride salts, sulphuric acid produces sulphate salts and nitric acid produces nitrate salts. What would the products be for the following neutralisation reactions?
a. Sodium hydroxide + sulphuric acid → b. Barium hydroxide + sulphuric acid → c. Calcium hydroxide + hydrochloric acid → d. Magnesium hydroxide + sulphuric acid →
4. Neutralisation can be useful in everyday life.
a. Colour each everyday problem red if it is caused by an acid or blue if it is caused by an alkali. b. Choose the best remedy for each problem from the list below.
bicarbonate vinegar dock leaves antacid lime toothpaste of soda
c. Colour each remedy red if it is an acid or blue if it is an alkali. d. Using your knowledge of how acids react with alkalis, suggest how each remedy can help solve the everyday problem.
Everyday problem Remedy Suggested explanation
Wasp sting venom is slightly alkaline.
Bee sting venom (pH 5.5) contains several active ingredients including formic acid. The plaque that forms on teeth contains bacteria that break down sugary foods to get energy. At the same time they make acids that attack the tooth surface. Heartburn is a type of indigestion caused when hydrochloric acid from the stomach irritates the lining of the oesophagus. Soil that has a pH below 6 will stunt plant growth. Stinging nettles cause inflammation and pain if they touch your skin.
The graph shows the pH of Sam’s mouth 5. Look at the graph to show the pH
changes in Sam’s mouth as she eats. 8 Sam started to eat
a. Describe what happens to the pH in 7 pH of Sam’s mouth as she eats. the liquid in ______Sam’s 6 mouth
______5 ______4
Time b. Why might this be a problem for Sam? ______
______
______c. What type of food could she have been eating? ______
______d. What will happen to the pH if she brushes her teeth? ______
Extended Response Your science teacher needs your help. There is a clear, odourless liquid spillage in the lab. The previous group working in the lab had been learning about acids and alkalis. The teacher thinks the spillage could be an acid or an alkali. Your teacher needs to clear the spillage up safely. They need your knowledge and advice to help them decide the best way to do this. ______
______
1. Which of the following statements describes the formation of a salt in a neutralisation reaction? £ A. When the hydrogen in an acid is replaced by a metal £ B. When the hydrogen in a metal is replaced by an acid £ C. When the hydroxide (OH) in the alkali is replaced by a metal
2. When we say that an acid has been neutralised, what do we mean? £ A. It has reacted with an alkali to produce a salt £ B. It has reacted with an alkali to produce a salt and water £ C. It has reacted with an alkali to produce a salt and hydrogen
3. During a neutralisation reaction between a strong acid and strong alkali, what happens to the pH of the acid? £ A. It increases £ B. It decreases £ C. It stays the same
If you answered A A neutralisation reaction is a reaction between an acid and an alkali to produce a neutral solution.
The products of these reactions are always a salt and water. Write a word equation to show the reaction between hydrochloric acid and sodium hydroxide.
If you answered B A neutralisation reaction is a reaction between an acid and an alkali to produce a neutral solution. The products of these reactions are always a salt and water. Explain where the salt and water come from in a neutralisation reaction.
If you answered C A neutralisation reaction is a reaction between an acid and an alkali to produce a neutral solution. The products of these reactions are always a salt and water. Write a word equation to show the reaction between potassium hydroxide and hydrochloric acid.
Making Salts Practical
Starter 1. What happens during filtration of a mixture?
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2. What happens during crystallisation?
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Foundation: What is meant by ‘conservation of mass’?
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Stretch: How would you observe conservation of mass when making a salt from an acid and an alkali/base?
______
To make a salt, you must react an acid and an alkali. To ensure that all the acid has reacted, the alkali should be in excess (there should be more alkali than acid). For the reaction to happen quickly, a powdered form of the base is used (this gives it a large surface area for the reaction to happen). Filtration, evaporation and crystallization methods are utilised to separate the products (water and the salt).
An example of a neutralisation reaction is:
Magnesium oxide (alkali) + sulphuric acid (acid) → Magnesium sulphate + water
1. Why must the alkali be in excess during a neutralisation reaction? (Choose 2 answers) a. Because you need it to react with all of the acid b. Because you are unsure how much alkali is required to neutralise the acid c. Because this is the way to make sure that a lot of salt is produced
2. Why is the product of a neutralisation reaction always a solution? a. Because the acid (reactant) is always a liquid b. Because water is the other product c. Because the alkali (reactant) is always a liquid
3.What happens when magnesium oxide is added to sulphuric acid? a. Magnesium oxide dissolves in the acid b. Sulphuric acid dissolves in magnesium oxide c. Magnesium oxide reacts with the sulphuric acid
Name each piece of apparatus you will be using:
Follow the instructions to carry out the practical:
1. Which two reactants would have been used to make the salt potassium nitrate? £ A. Potassium and nitrate £ B. Potassium and nitrogen £ C. Potassium and nitric acid
2. Which processes are used to separate the products of a neutralisation reaction? £ A. Filtration/crystallisation £ B. Evaporation/crystallisation £ C. Evaporation/condensation
3. Why must the reaction be heated? £ A. To get the alkali to react £ B. To activate the acid £ C. To speed up the reaction
If you answered A The products of a neutralisation reaction between an acid and an alkali are a salt and water. The water must be evaporated from the salt in order to separate them, leaving the salt to crystallise, therefore the processes involved are evaporation and crystallisation. Filtration is used to remove excess reactant but it is not used for separation of the products. Suggest how the products formed in this reaction would be different if calcium carbonate was used instead of magnesium carbonate.
If you answered B The products of a neutralisation reaction between an acid and an alkali are a salt and water. The water must be evaporated from the salt in order to separate them, leaving the salt to crystallise, therefore the processes involved are evaporation and crystallisation. Suggest why a Bunsen burner is used to evaporate most of the water. What would happen if this stage was not included?
If you answered C The products of a neutralisation reaction between an acid and an alkali are a salt and water. The water must be evaporated from the salt in order to separate them, leaving the salt to crystallise, therefore the processes involved are evaporation and crystallisation. Condensation would be the cooling of the water vapour to form liquid water again, which is not involved in this process. Describe what happens in the process of crystallisation.
Metal Carbonate reactions with acids
Starter 1. Describe how you can observe if a chemical reaction has taken place.
______
2. What is produced when bubbling is observed?
______
3. What are the products of a reaction between an acid and an alkali?
______
Foundation: What is the pH of an acid?
______
Stretch: Write a word equation to show the products of a reaction between lithium hydroxide and nitric acid.
______
Acids can be neutralised by:
1. Alkalis/bases • Examples of alkalis: sodium hydroxide, potassium hydroxide • Examples of bases: copper oxide, zinc oxide
2. Metal carbonates to produce salts, water and carbon dioxide. • Examples of metal carbonates: calcium carbonate, magnesium carbonate
A metal carbonate is a compound containing a metal, carbon and oxygen, e.g. Sodium + Carbon + Oxygen → Sodium Carbonate
Acids + alkali/base → salt + water Acronym: A + A/B → S + W
Acids + metal carbonates → salt + water + carbon dioxide Acronym: A + C → S + W + C
Note: carbon dioxide is produced when acids react with metal carbonates, as atoms cannot be created or destroyed so the carbon atoms have to be found somewhere in the products. If carbon dioxide has been produced, it shows that an acid has reacted with a metal carbonate.
Limewater can be used to test for carbon dioxide. The chemical reaction should be carried out in a flask with a stopper (pictured), with the gas that is produced able to enter a test tube containing limewater. The gas is bubbled through the limewater and if it turns cloudy/milky (from clear) this shows a positive result and means that carbon dioxide is present, so carbon dioxide was the gas produced in the reaction.
Shell shocked: Emerging impacts of our acidifying seas
Our changing climate is altering the chemistry of the ocean, and some animals are paying the price
BY BETHANY BROOKSHIRE February 28th, 2019
Corals provide the base of a unique community of ocean creatures. But ocean acidification may make it difficult for corals to build their beautiful structures.
In the Pacific Northwest, baby oysters have died off by the billions. Their tiny shells dissolved before they were fully formed. In Australia, scans find there are more female and fewer male Sydney rock oysters — which could affect how many oysters fill the plates of future Australian diners. The cause is ocean acidification. Through their industrial activities and the burning of fossil fuels, people have been pumping more and more greenhouse gases, such as carbon dioxide, or CO2, into the air. The ocean will absorb about one-fourth of that gas. There, it will react with water in ways that make the ocean slightly more acidic.
People might never notice the change when going for a swim, but to organisms that call the sea home, acidification is a source of stress. It puts many of the seafoods we love to eat — such as oysters — at risk. And the only way to stop it is to stop the release of CO2 into the air. Today’s ocean is slightly basic, or alkaline. Scientists use the 14-point pH scale to classify substances from very acid to very alkaline. Pure water is a perfectly neutral 7. Battery acid falls around 1. Soapy water is about 12. Water in the ocean contains salt (sodium chloride) and other chemicals such as calcium and boron. Ocean water is slightly basic, with a pH around 8.2. Or at least, that’s what it used to be.
Around one-fourth of humanity’s emissions of CO2 are being absorbed by the world’s oceans. There, this gas reacts with water molecules and carbonate ions (one carbon and three oxygen atoms). The result is a chemical called bicarbonate — and a bunch of leftover hydrogen ions. Those hydrogen ions add to the hydrogen ions already present, making the seawater more acidic. Since the mid-18th century, when people started burning fossil fuels in huge amounts, the pH of the global ocean has dropped by a tenth of a point. She studies ocean acidification at California State University in Northridge. That tenth of a point may seem small. But pH is measured on a logarithmic scale, where each additional 1 point is equal to a 10-fold increase. A substance with a pH of 8 has 10 times the amount of hydroxide ions as one with a pH of 7. A change from 8.2 to 8.1, then, isn’t so small.
Mussels, oysters, coral and many other organisms in the ocean protect themselves with a tough shell. It’s formed from calcium carbonate. This chemical has one atom of calcium hooked to a carbonate ion. Under normal ocean conditions, a critter can make enough calcium carbonate from calcium and carbonate in the water to build its shell. But as more CO2 from the atmosphere dissolves into the ocean, more bicarbonate forms. That uses up carbonate, leaving shell-building organisms with less shell-building calcium carbonate.
Mussels, oysters and other tide-pool denizens suffer in a more acidic ocean. By day, as plants and other photosynthetic organisms are raising the tide pools’ pH, shell- making organisms build away. At night, as the pH drops, shell-building does too. And the lower the pH gets at night, the less building that takes place. Oysters can handle the wild tidepool pH swings. But only to a point. If the pools don’t get basic enough during the day, they can’t build up enough shell. The term “ocean acidification” brings up visions of acid water eating away at a poor, defenceless oyster. But that’s really not the case, scientists say. “It’s not that they’re getting small because the oysters are dissolving from the outside in,” she explains. “It’s because they’re growing slower from the inside out.” The last time the seas were this acidic, the process had occurred Figure 1- Tide pools are cut off from the ocean when the tide is low. That makes them great places to study how ocean pH slowly, so species had millions of changes, and what makes it vary. years to adapt. What took millions of years then may now develop in only a few decades. And most species likely won’t be able to adapt that quickly. To reduce the effects of ocean acidification some people have suggested dumping chemicals into the ocean to make it less acidic. Others are developing corals that can resist more acidic water. There are lots of things being looked at to try and help reefs
over the next 50 to 100 years, but no one in the scientific community feels that’s going to solve this problem. If we continue to dump CO2 into the air and ocean at our current pace, she notes, no amount of resistant coral or pH-raising chemicals will stand up to our efforts.
The only solution is stopping climate change in the first place.
Answer the following questions in full sentences:
1. What is ocean acidification, and what is causing it? ______
2. What does it mean when the story says that the ocean is “slightly basic”? ______
3. Why does pH and temperature vary during the day in a tide pool?
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4. What is calcium carbonate? ______
5. Describe two ways that ocean acidification can affect oysters. ______
6. How can ocean acidification be stopped? ______
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7. Write the definition for any words in bold. ______
1. Which of the following is the general formula for metal carbonate and acid reactions? £ A. Metal carbonate + acid → salt + water + hydrogen £ B. Metal carbonate + acid → salt + carbon dioxide + water £ C. Metal carbonate + acid → salt + water
2. When adding acid to a carbonate, what evidence would suggest that a gas is produced? £ A. Fizzing £ B. Change of colour £ C. Increase in temperature
3. What effect does increasing carbon dioxide levels have on oceans? £ A. Acidification of the oceans £ B. Neutralisation of the oceans £ C. Pollution
If you answered A Metal carbonates react with acids in neutralisation reactions. The products of this type of reaction are always a salt, water and carbon dioxide. Atoms cannot be created or destroyed so the elements that make up the reactants must be rearranged to form the products. Write a word equation to show the reaction between sodium carbonate and hydrochloric acid.
If you answered B Metal carbonates react with acids in neutralisation reactions. The products of this type of reaction are always a salt, water and carbon dioxide. Atoms cannot be created or destroyed so the elements that make up the reactants must be rearranged to form the products. Suggest how you could use hydrochloric acid and limewater to distinguish between a metal carbonate and a metal hydroxide that are both white powders.
If you answered C Metal carbonates react with acids in neutralisation reactions. The products of this type of reaction are always a salt, water and carbon dioxide. Atoms cannot be created or destroyed so the elements that make up the reactants must be rearranged to form the products. Use the word equation for calcium carbonate reacting with hydrochloric acid to show what happens to each of the elements.
Metal Carbonates and acid reactions practical
Starter 1. What has happened to this statue?
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2. How is this related to acid rain?
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Foundation: What is the name of the processes where carbonate statues are worn down by the action of acid rain?
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Stretch: How does the gaseous product from the above reaction have an effect on the acidity of rain?
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Reacting a metal oxide or metal hydroxide with an acid produces a salt and water. This is a neutralisation reaction. Reacting a metal carbonate with an acid also produces a salt and water, but also produces carbon dioxide. This is also a neutralisation reaction.
If a metal carbonate and acid reaction are in a closed system (where none of the products can escape, e.g. a sealed flask), the carbon dioxide will react with the water to produce carbonic acid which will change the pH of the solution from being neutral to being acidic.
MgCO3(s) + H2SO4 (l) → MgSO4 + H2CO3
1. What is the pH of the products of a calcium carbonate and hydrochloric acid reaction in an open system? a. pH 4 b. pH 7 c. pH 8
2. What is the likely pH of the products of a calcium carbonate and hydrochloric acid reaction in a closed system? a. pH 4 b. pH 7 c. pH 8
3.Which two products cause this change in pH? a. Carbon dioxide and the salt b. Carbon dioxide and water c. Carbon dioxide and the acid
Making a salt using a metal carbonate and acid
Your teacher will tell you which acid and which carbonate to use. Record all your observations during each stage of the practical
Method 1. Using a measuring cylinder, measure 20 cm3 of acid into the beaker. 2. Add half a spatula of one of the metal carbonates into the acid and stir with the glass rod. 3.Continue adding the metal carbonate in small amounts until no more dissolves and there is no more fizzing (this should be most of the solid you have been provided with). 4. Set up a filter funnel and filter paper in a conical flask as shown below. Filter the mixture and discard the unreacted metal carbonate.
5. Pour the filtrate into an evaporating basin and place it on a beaker of water, as shown in the diagram below. Heat the water gently until the volume of the solution in the evaporating dish is halved.
6. Remove from the heat. When it is cool, stand the evaporating basin on a piece of paper with your name on. Your teacher will tell you where you can leave it overnight to crystallise. 7. During the next lesson, remove the crystals from the concentrated solution with a spatula and gently pat them dry between two pieces of filter paper. 8. Show your teacher your crystals, record your observations, and then answer the questions below.
Results Record which salt have you made and what you observed when:
1. The metal carbonate was first added to the acid. 2. Excess carbonate was added. 3.The salt was left to crystallise.
1. What colour would universal indicator change in a closed system where a metal carbonate and acid reacted? £ A. Red £ B. Blue £ C. Green
2. There is always excess metal carbonate because: £ A. Not all of it reacts with the acid £ B. Not all of it is soluble £ C. Not all of it dissolves
3. The products from a metal carbonate + acid reaction are: £ A. Salt + water + carbon dioxide £ B. Salt + carbon dioxide + hydrogen £ C. Salt + water + hydrogen
If you answered A In a closed system no products would be able to escape. The products of a metal carbonate and acid reaction would be a salt, water and carbon dioxide. In the closed system the carbon dioxide would react with the water to form carbonic acid, making the system acidic. This would turn Universal Indicator red. Compare this with what would happen when a metal hydroxide reacted with an acid in a closed system.
If you answered B In a closed system no products would be able to escape. The products of a metal carbonate and acid reaction would be a salt, water and carbon dioxide. In the closed system the carbon dioxide would react with the water to form carbonic acid, making the system acidic. This would turn Universal Indicator red. Write the general equation for metal carbonates reacting with acids.
If you answered C In a closed system no products would be able to escape. The products of a metal carbonate and acid reaction would be a salt, water and carbon dioxide. In the closed system the carbon dioxide would react with the water to form carbonic acid, making the system acidic. This would turn Universal Indicator red. Explain why the Universal Indicator would turn green if this experiment was carried out in an open system (where the products could escape).
Scientist in the Spotlight
Divya Persaud
Planetary Scientist
Divya Persaud is a planetary scientist at Mullard Space Science Laboratory, University College London. At school she studied chemistry, maths and languages and the geology and music composition at university. She was fascinated with geology from a very young age. At the age of 12 became interested in studying planetary surfaces using space missions after seeing a documentary about spacecraft in our solar system. One high point of her research career so far was studying a huge canyon on Mars in 3D and learning what it can tell us about the history of the area on Mars near where the Curiosity Rover was moving around. This also included information from pH probes to determine properties of the surface of Mars.
Being a non-traditional scientist has influenced her research ethics and helps her remain balanced but critical. A typical day for Divya is spent using computers to assess and present her data. She also spends time reading research papers to help write her thesis. On some exciting days at work, Divya travels to Oxford for planetary rover field trials, where she gets to be part of “mission control” and operate the rovers in Spain and Chile remotely.
As a scientist with both physical and mental disabilities, Divya knows the importance of building a community of supportive people so that everyone can achieve their goals. According to Divya, a good scientist should be curious about new things and have a critical eye to problems and solutions. They should also be able to communicate their research to everyone so that it is easily understandable. She believes in the idea of spreading her knowledge because everyone has the right to know about space.
The aspect of her work that she enjoys the most is the opportunity to travel to various places for conferences. She gets to meet people from all over the world and from different walks of life and learn how they think and approach the same problems that she faces. However, it can be quite daunting working independently as there are only a small group of people working in this field of space research, so most of the time it ends up being the first time something is done. At these times, it becomes hard to decide the right course of action and also when is the appropriate time to let go of a problem and move on.
In her work, Divya uses a lot of aesthetic judgement. This means thinking about how one looks at images of space and how it can be portrayed to give useful
information. All of these decisions are governed by creativity. When not doing research, Divya enjoys making music and writing.
Activity
Use the scientist’s profile to answer the following questions:
1. What is the scientist’s job?
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2. Briefly describe what the scientist does in a typical day.
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3. What skills do they need for this job?
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4. What do you think is the most interesting part of their job?
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5. Describe how this job links with the science you have learned in this unit.
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6. State the definition of any words in bold.
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