KISS Resources for NSW Syllabuses & Australian Curriculum

® KEEP IT SIMPLE SCIENCE keep it simple science Chemistry Module 6 - Reactions WORKSHEETS

Worksheet 1 , Bases & Indicators Part 1 Fill in the blank spaces Student Name...... Acids and bases are chemical a)...... The colour changes for the following indicators If you add one to the other, they b)...... need to be learnt. each other. Indicator Acid Neutral Base

Acidity is measured by the c)...... scale. On this Litmus j)...... purple k)...... scale, a neutral substance has a value of d)...... Phenolphthalein l)...... Values above this indicate e)...... substances, while values below indicate Methyl orange m)...... f)...... substances. Bromothymol n)...... green/blue o)...... Indicators are chemicals which g)...... blue ...... according to the h)...... of the solution they are in. The original indicators were In everyday situations, indicators are used for extracts from i)...... purposes such as p)...... for farming and gardening, q)...... for pools and aquariums, and for monitoring r)...... from industries. Part 2 Practice Questions 1. 2. Each solution listed below has been tested with A household substance most likely to be strongly one or more indicators, and the colour is given. basic is For each, state if it is acidic, neutral or basic. A. vinegar. B. soap. Solution A: Phenolphthalein is clear. C. sugar. Methyl orange is red. D. milk.

3. a) What is meant by an “acid-base indicator”?

Solution B: Phenolphthalein is pink. Methyl orange is yellow.

b) Identify an everyday use of an indicator.

Solution C: Phenolphthalein is clear. Methyl orange is yellow.

Solution D: Bromothymol blue is blue. c) Describe how you could prepare a simple Methyl orange is yellow. indicator from a named natural substance.

Solution E: Phenolphthalein is clear. Litmus is pink.

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® Worksheet 2 Practice Questions keep it simple science Acid-Base Reactions Student Name...... 1. Acid-Alkali Reactions 4. Acid-Metal Reactions a) Name the salt formed in a reaction between: Write a balanced ionic equation (including states) i) hydrochloric acid & calcium hydroxide for each reaction.

a) reacting with zinc metal. ii) & magnesium hydroxide

iii) nitric acid & barium hydroxide

b) Write a balanced equation for the reaction of: b) Calcium metal plus sulfuric acid i) hydrochloric acid and lithium hydroxide

ii) sulfuric acid and sodium hydroxide c) Hydrochloric acid plus magnesium metal.

iii) nitric acid and magnesium hydroxide

d) Lead metal plus nitric acid. 2. Reactions of Basic Oxides Write a balanced equation for the reaction of:

a) sulfuric acid & iron(II) oxide e) (Revision) Assuming all the acids above have the same b) hydrochloric acid & concentration, all metals the same surface area, all reactions at the same temperture, etc., which of the reactions above is likely to proceed most vigorously, and why? c) nitric acid & copper(II) oxide

3. Reactions of Acidic Oxides a) reacts with calcium hydroxide to form water and calcium carbonate. (This is the 5. Acid-Carbonate Reactions “limewater” reaction) Write a balanced equation for Write a balanced “molecular-style” equation the reaction. (including states) for each reaction.

a) nitric acid + copper(II) carbonate

b) P2O5 is an acidic oxide. It reacts with water to form , H3PO4. Write the balanced equation. b) sulfuric acid + potassium carbonate

c) reacts with water to form a strong acid. Write a balanced equation, and name the acid. c) sodium carbonate + hydrochloric acid

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® Worksheet 3 Practice Problems keep it simple science Reaction of Acids & Bases With Water Student Name...... For each substance below, write an equation e) sulfide ion, S2- (base) describing its monoprotic reaction with water, according to Bronsted-Lowry Theory. (In brackets is a description of how the substance behaves in each case) f) cyanide ion, CN- (base)

For each equation, identify the /base of the named species.

a) methanoic acid, HCOOH (acid) g) hydrogen sulfide, H2S (acid)

b) ammonia, NH (base) - 3 h) nitrite ion, NO2 (base)

c) hydrogen phosphate ion, HPO 2-, (acid) + 4 i) ammonium ion, NH4 (acid)

d) hydrogen phosphate ion, HPO 2-, (base) - 4 j) hydrogen sulfite ion, HSO3 (acid)

Worksheet 4 Practice Questions Acid Ionisation & pH Student Name...... 1. Write a balanced equation for the reaction of each acid + 2. Calculating pH from [H3O ] with water. (Assume complete ionisation in each case, Each of the following values is the hydronium ion even though some may be weak acids) concentration of a solution, in molL-1. For each, calculate the pH, and state if the solution is acidic or basic. Monoprotic acids a) HCl a) 0.0675 b) 0.000840 c) 2.50 d) 2.50x10-12 e) 3.5 x 10-3 f) 1.50 x 10-8 b) HBr (hydrobromic)

3. Calculating pH from Acid Concentration c) HCOOH (methanoic) Calculate the pH of each solution, taking into account that some acids may be diprotic or triprotic. (assume total ionisation) d) HCN (hydrocyanic) a) 0.250 molL-1 HCl -1 Diprotic acids b) 0.0750 molL H2SO4. e) H SO -4 -1 2 4 c) 7.50x10 molL H2SO4. -3 -1 d) 4.50x10 molL H3PO4. -1 f) H2CO3 (carbonic) e) 6.00 molL H2SO4.

+ Triprotic acids 4. Calculating [H3O ] from pH. + g) H3PO4 (phosphoric) Find the [H3O ] in each solution. a) pH = 5.30 b) pH = 11.5 h) C6H8O7 (citric) c) pH = -0.40 d) pH = 4.85 e) pH = 8.50 f) pH = 0

Chem Mod.6 “Acid-Base Reactions” Worksheets page 3 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au KISS Resources for NSW Syllabuses & Australian Curriculum ® Worksheet 5 Test-Style Questions keep it simple science Student Name...... O-H Longer Response Questions Multiple Choice Answer on reverse if insufficient space. 1. H The diagram shows a molecule of C 6. the weak acid, methanoic acid. A certain diprotic acid can be represented by the O formula “H A”. (“A” is not the correct symbol) When dissolved in water, one of the bonds in 2 the molecule may ionise, resulting in acid behaviour. a) Write a balanced equation for the complete ionisation of H2A when added to water. The bond most likely to ionise is the Label each species in the equation as acid or base. A. H-C bond B. C=O bond C. O-H bond D. C-O bond

2. If an undissociated molecule of an acid is represented by “H-A”, and the ionised acid by b) If H A is a strong acid, calculate the pH of a + - 2 separate “H ” and “A ” symbols, which diagram solution with concentration [H A] = 0.0250 molL-1. could show a dilute solution of a strong acid? 2 A. B. C. D. - + A H-A H H-A H+ A- A- H+ H-A + A- + H H H+ - H-A A + H-A A- H c) In fact, when this exact concentration solution H+ A- was tested, it was found to have a pH = 2.50. H-A A- H+ H-A What do you conclude from this?

3. In a solution of pH=10, the concentration of hydronium ions is: 7. -1 10 -1 A. 10 molL . B. 10 molL . A certain solution has a pH = 9.5 C. 10-10 molL-1. D. 1 molL-1. a) What is the value of the pOH? 4. If you had 4 solutions of different acids Hydrochloric Nitric b) Find the concentration of: Ethanoic Sulfuric i) hydronium ions. all with exactly the same molar concentration of acid, which two only would you expect to have the same pH? ii) hydroxide ions A. sulfuric and ethanoic B. hydrochloric and nitric C. nitric and sulfuric D. ethanoic and hydrochloric c) The solution contains a single, pure compound dissolved in water at a concentration of 0.002molL-1. 5. A student describes this solution as “a weak In the following equation... solution of a strong base”. The student has made at - - least 2 errors in this description. NO2 (aq) + H2O(l) HNO2(aq) + OH (aq) Give a more accurate description. Justify three parts of your description. ...it is true to say that: A. H2O is a B-L acid. - B. the conjugate base of NO2 is HNO2 - C. the species NO2 is amphiprotic D. HNO2 is a diprotic acid.

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® Worksheet 6 Amphiprotic Ions, Acidic & Basic Salts keep it simple science Practice Problems Student Name......

1. Amphiprotic Substances 2. Acidic and Basic Salts

Each of the substances below is amphiprotic. Each of the following salts dissolves in water, and For each, write TWO equations to show its reaction reacts (as shown in brackets) to form an acidic or + basic solution. i) with H3O ii) with OH- Write a net ionic equation (leave out spectators) to - show the reaction with water. a) dihydrogen phosphate ion, H2PO4

a) potassium ethanoate, CH3COOK (basic)

b) ammonium nitrate, NH4NO3 (acidic)

- b) hydrogen carbonate ion, HCO3

c) sodium nitrite, NaNO2 (basic)

d) potassium hydrogen oxalate, KHC2O4 (acidic) c) hydrogen sulfide ion HS-

e) lithium cyanide, LiCN (basic)

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® Worksheet 7 Practice Problems keep it simple science Titration Student Name...... 1. 3. 25.00mL of an “unknown” NaOH solution was A student wants to make 500mL of a 0.02500molL-1 titrated against standardised HCl, of concentration solution of oxalic acid (COOHCOOH), from the solid = 0.09255 molL-1. The titration was carried out 4 chemical. times, with the end-point titres being 22.50mL, 22.45mL, 23.10mL and 22.50mL. i) What are the characteristics that qualify this chemical as a “primary standard”? Average these results appropriately, then write an equation, and calculate the concentration of the NaOH solution. ii) What mass needs to be accurately weighed out?

iii) Summarise the main steps involved in preparing the solution.

4. The solution, when prepared, was used to determine the concentration of a KOH solution. 25.00mL aliquots of KOH required an average titre of 31.45mL. Find the concentration of the KOH. (hint: oxalic acid is diprotic) 2. Using a 0.05025molL-1 standardised solution of NH4OH (ammonia solution), 25.00mL samples of an unknown H2SO4 solution were titrated. The average titre was 28.32mL

i) Write a balanced equation for the neutralisation.

ii) Find the concentration of the acid. 5. To find the concentration of an ammonia solution (NH4OH), a student has 2 choices of standardised solutions she could use: -1 • 0.7438 molL HNO3 solution -1 or • 0.8863 molL CH3COOH solution i) Which solution should she use in the titration? Explain.

iii) For this titration there were 3 indicators available: ii) Using 10.00mL samples of the ammonia Indicator pH of Colour Change unknown, and titrating with the appropriate acid, the J ≅ 8.7 average titre was found to be 12.76mL. Calculate the K ≅ 6.8 concentration of the ammonia solution. L ≅ 4.2 Which indicator is most appropriate for this titration? Explain your answer.

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® Worksheet 8 Dissociation Constants & pKa keep it simple science Practice Exercises Student Name...... 1. 3. A certain weak acid can be represented by the Benzoic acid (C6H5COOH) is a weak, monoprotic symbols “HZ”, where H is for hydrogen, but “Z” is acid with pKa = 4.20 (at 25oC) not the correct symbol for the other part of the molecule. a) Write an equilibrium equation for its reaction with water. a) Write an equilibrium equation describing how this weak acid reacts with water. States may be omitted. b) What is the pH of a 0.00258 molL-1 solution of benzoic acid at 25oC?

b) Write an expression for its acid “Ka”.

c) Explain why part of the “formal” equilibrium expression seems to be “missing” from Ka.

4. Hypochlorous acid (HOCl) has a pKa = 7.53.

a) Write an equilibrium equation for its reaction o -1 d) At 25 C, a 0.040 molL solution of HZ is found to with water. have a pH = 3.8

Calculate the value of Ka and pKa for this acid. b) If the pH of a solution is 4.75, what is the concentration of the HOCl solution?

2. Calculate the pH of a solution of nitric acid -1 (strong acid) if its concentration is c = 2.50 molL . 5. Calculate the pKa of a weak monoprotic acid if a 1.50 molL-1 solution has a pH = 2.9 at 25oC.

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® Worksheet 9 keep it simple science Acid-Base Theory & Titration Fill in the blank spaces Student Name...... Lavoisier concluded that acids must The “rules” governing this are: contain a)...... Later, Davy • Neutral salts form from the neutralisation described acids as all containing of u)...... acids by v)...... b)...... , and being able to bases. react with c)...... • Acidic salts form from the neutralisation of w)...... acids by The first attempt at a complete acid-base x)...... bases. theory was made by d)...... • Basic salts form from the neutralisation in 1885. According to this theory, all acids of y)...... acids by z)...... produce e)...... in bases. solution. Bases were defined as compounds containing f)...... or All neutralisation reactions (in aqueous ...... ions. This theory was solution) involve the reaction of successful at explaining some acid-base aa)...... and ...... ions behaviour, but failed to take into account to form ab)...... The reaction is the important role of g)...... always ac)...... -thermic.

The h)...... -...... (B-L) ad)...... is a technique Theory is much more useful for explaining used for chemical analysis. A measured things. It defines an acid as a i)...... ae)...... of “unknown” solution is ...... , and a base as a reacted with a “af)...... solution” j)...... , and all until the “ag)...... point” is acid-base reactions involve the reached. The main piece of equipment k)...... of one or more involved is a ah)...... It is l)...... important to choose the ai)...... which will change aj)...... at the pH When an acid loses a proton it forms the of the end-point, depending on the nature “m)...... base”, and when a of the salt formed. base gains a proton it forms the n)...... If the ak)...... is measured during titration and graphed, the graphs generally Water can acts as either o)...... or show an “S” shaped curve. The end-point ...... , depending on the chemical is located in the middle of the environment. The word for this is al)...... part of the curve. “p)...... ” Buffers are solutions containing an Many salts dissolve in water to form acidic equilibrium mixture of a am)...... or basic solutions, because of their ...... and its ...... interaction with q)...... If either acid or base is added, the An example of an acidic salt is equilibrium an)...... (according to r)...... An example of a ao)...... Principle) so that basic salt is s)...... the change in ap)...... is minimized. An example of a neutral salt is Buffers are important in all t)...... aq)...... things, by helping to maintain ar)...... A specific example is as)...... , where the pH is maintained by a mixture of at)...... and ...... ions.

Chem Mod.6 “Acid-Base Reactions” Worksheets page 8 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au KISS Resources for NSW Syllabuses & Australian Curriculum ® Worksheet 10 Test-Style Questions keep it simple science Student Name...... Multiple Choice Longer Response Questions 1. Mark values shown are suggestions only, and are to give 2- you an idea of how detailed an answer is appropriate. The hydrogen phosphate ion, HPO4 is an amphiprotic species. If it were to act as a base, then Answer on reverse if insufficient space. its conjugate acid would be: A. H PO - B. H PO C. PO 3- D. HPO 3- 7. (7 marks) 2 4 3 4 4 3 a) Give the definition of an acid according to the 2. Arrhenius Theory. An ionic “salt” is found to be acidic in water solution. It is likely that this salt is the product of b) Write an equation which Arrhenius might have the reaction between: used to explain why hydrogen chloride gas is an A. a strong acid and a strong base. acid when dissolved in water. B. a weak acid and a . C. a weak acid and a strong base. c) Give the definitions for acid and base according D. a strong acid and a weak base. to the Bronsted-Lowry Theory.

3. d) Write an equation to show why hydrogen chloride The salt mentioned in Q2 was formed during a gas in water is an acid according to the B-L Theory. titration. The most appropriate indicator for the titration would be: 8. (7 marks) a) A solution containing carbonate ions (CO 2- ) is A. bromothymol blue. 3 B. methyl orange. found to be quite strongly basic. C. phenolphthalein. D. universal indicator. Write an equation to explain why, and state the role of the water molecule in this reaction. 4. Which of the following graphs might be the “titration curve” for the titration described in Q2? b) Write TWO different equations to show the amphiprotic nature of the hydrogen carbonate ion, HCO -. A. B. C. D. 3 9. (8 marks) A diluted vinegar sample (CH3COOH solution) was analysed by titration with a standardised solution of KOH with concentration of 0.008263 molL-1.

9.00mL samples of the vinegar solution were used. The titration was done 4 times, giving burette titres of 27.35, 26.70, 26.75 and 26.65mL of KOH. 2 pH 7 12 7 pH 2 2 pH 7 12 7 pH 2 2 pH 7 12 7 pH 2 2 pH 7 12 7 pH 2 a) What is an appropriate indicator for this titration? Vol Base Vol Base Vol Base Vol Base Justify your choice.

5. b) Write a balanced symbol equation for the An appropriate material to use in case of an acid reaction. spill is: A. an amphiprotic substance, e.g. sodium bicarbonate. B. a strong base, like sodium hydroxide. c) Explain how the titration measurements should be C. a , like methanoic/methanoate used. mixture. D. a weak base, like ammonia. d) Calculate the concentration of the diluted vinegar 6. solution. + - In the reaction HBr + NH3 NH4 + Br it is true to say that: 10. (4 marks) a) What are the characteristics of a “buffer A. NH3 is the base, because it has accepted a proton. solution”? B. HBr is the acid, because it has accepted a proton. b) In general terms, what are the usual ingredients of + a buffer solution? Give a specific example. C. NH4 is the conjugate acid of HBr. D. Br- is the conjugate acid of HBr. c) Give an example of a natural buffer system.

Chem Mod.6 “Acid-Base Reactions” Worksheets page 9 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au KISS Resources for NSW Syllabuses & Australian Curriculum ® Answer Section keep it simple science 4. Worksheet 1 c) 2H+ + 2Cl- + Mg Part 1 (aq) (aq) (s) H + Mg2+ + 2Cl- a) opposites b) neutralise 2(g) (aq) (aq) c) pH d) 7 + - e) basic f) acidic d) 2H (aq)+ 2NO3 (aq) + Pb(s) 2+ - g) change colour h) pH (acidity) H2(g)+ Pb (aq)+ 2NO3 (aq) i) plants / lichens j) pink k) blue e) Reaction (b) because of these metals, calcium is l) clear, clear, pink/red m) red, yellow, yellow the most active in the “Activity Series”. n) yellow o) blue p) soil testing q) water testing 5. r) effluents a) 2HNO3(aq) + CuCO3(s) CO + H O + Cu(NO ) Part 2 2(g) 2 (l) 3 2(aq) 1. A = acid. B = base. C = neutral. D = base. E = acid. b) H2SO4(aq) + K2CO3(s) 2. B CO2(g) + H2O(l) + K2SO4(aq) 3. a) A chemical which changes colour depending on c) 2HCl(aq) + Na2CO3(s) the pH of the solution it is in. CO2(g) + H2O(l) + 2NaCl(aq) b) Soil testing, to help gardening or agriculture. c) Put Hydrangea flowers through a blender with a small amount of water and ethanol. Filter the Worksheet 3 mixture. The liquid will act as an acid-base indicator. In each case the conjugate is underlined.

+ - a) CH3COOH(aq)+ H2O(l) H3O (aq)+ CH3COO (aq) Worksheet 2 + - 1. b) NH3(aq) + H2O(l) NH4 (aq) + OH (aq) a) i) calcium chloride 2- 3- + ii) magnesium sulfate c) HPO4 (aq) + H2O(l) PO4 (aq) + H3O (aq) iii) barium nitrate 2- - - d) HPO4 (aq) + H2O(l) H2PO4 (aq) + OH (aq) b) i) HCl + LiOH H2O + LiCl 2- - - e) S (aq) + H2O(l) HS (aq) + OH (aq) ii) H2SO4 + 2NaOH 2H2O + Na2SO4 - - f) CN (aq) + H2O(l) HCN(aq) + OH (aq) iii) 2HNO3 + Mg(OH)2 2H2O + Mg(NO3)2 - + g) H2S(aq) + H2O(l) HS (aq) + H3O (aq) 2. - - a) H2SO4 + FeO H2O + FeSO4 h) NO2 (aq) + H2O(l) HNO2(aq) + OH (aq)

+ + b) 2HCl + MgO H2O + MgCl2 i) NH4 (aq) + H2O(l) NH3(aq) + H3O (aq)

- 2- + c) 2HNO3 + CuO 2H2O + Cu(NO3)2 j) HSO3 (aq) + H2O(l) SO3 (aq) + H3O (aq)

3. a) CO2 + Ca(OH)2 H2O + CaCO3

b) P2O5 + 3H2O 2H3PO4

c) SO3 + H2O H2SO4 (sulfuric acid)

4. + - a) 2H (aq)+ 2NO3 (aq) + Zn(s) 2+ - H2(g)+ Zn (aq)+ 2NO3 (aq)

+ 2- b) 2H (aq)+ SO4 (aq) + Ca(s) 2+ 2- H2(g)+ Ca (aq)+SO4 (aq)

Chem Mod.6 “Acid-Base Reactions” Worksheets page 10 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au KISS Resources for NSW Syllabuses & Australian Curriculum ® Answer Section keep it simple science + b) i) pH = -log[H3O ] Worksheet 4 + so [H3O ] = antilog (-pH) 1. Acid Ionisation in Water -10 -1 + - = 3.16 x 10 molL . a) HCl(g) + H2O(l) H3O (aq) + Cl (aq) ii) pOH = -log[OH-] b) HBr + H O H O+ + Br- (g) 2 (l) 3 (aq) (aq) so [OH-] = antilog (-pOH) -5 -1 + - = 3.16 x 10 molL . c) HCOOH(l) + H2O(l) H3O (aq) + HCOO (aq) c) Correct Description: “This a dilute solution of a d) HCN + H O H O+ + CN- (g) 2 (l) 3 (aq) (aq) weak base”. Justification of the underlined words: e) H SO + 2H O 2H O+ + SO 2- 2 4(l) 2 (l) 3 (aq) 4 (aq) dilute. The concentration is quite low... “dilute”. Do NOT f) H CO + 2H O 2H O+ + CO 2- 2 3(l) 2 (l) 3 (aq) 3 (aq) use “weak” to describe concentrations. g) H PO + 3H O 3H O+ + PO 3- 3 4(l) 2 (l) 3 (aq) 4 (aq) weak The [OH-] concentration (in (b) (ii) above) is well h) C H O + 3H O 3H O+ + C H O 3- 6 8 7(s) 2 (l) 3 (aq) 6 5 7 (aq) below the concentration of the solution itself.

+ Therefore, ionisation is partial. 2. pH from [H3O ] + Therefore, “weak” is the appropriate word. use pH = -log[H3O ] in each case a) 1.17 (acidic) b) 3.08 (acidic) base. c) -0.398 (acidic) d) 11.6 (basic) The pH is above 7, so the dissolved substance has e) 2.46 (acidic) f) 7.82 (just barely basic) reacted as a B-L base with water. 3. pH from Acid Concentration + Worksheet 6 a) [H3O ] = 0.250, so pH = 0.602 1. Amphiprotic Substances + b) [H3O ] = 0.0750 x 2, so pH = 0.824 a) H PO - + H O+ H PO + H O + -4 2 4 (aq) 3 (aq) 3 4(aq) 2 (l) c) [H3O ] = 7.50x10 x 2, so pH = 2.82 + -3 d) [H3O ] = 4.5x10 x 3, so pH = 1.87 H PO - + OH- HPO 2- + H O + 2 4 (aq) (aq) 4 (aq) 2 (l) e) [H3O ] = 6.00 x 2, so pH = -1.08 b) HCO - + H O+ H CO + H O + 3 (aq) 3 (aq) 2 3(aq) 2 (l) 4. [H3O ] from pH use inverse (or 2nd function) log (-pH) on calculator HCO - + OH- CO 2- + H O a) 5.01 x 10-6 molL-1. b) 3.16 x 10-12 molL-1. 3 (aq) (aq) 3 (aq) 2 (l) -1 -5 -1 c) 2.51 molL . d) 1.41 x 10 molL . c) HS- + H O+ H S + H O e) 3.16 x 10-9 molL-1. f) 1.00 molL-1. (aq) 3 (aq) 2 (aq) 2 (l) HS- + OH- S2- + H O Worksheet 5 (aq) (aq) (aq) 2 (l) 1. C 2. D 3. C 4. B 5. A 2. Acidic & Basic Salts a) CH COO- + H O OH- + CH COOH 6. 3 (aq) 2 (l) (aq) 3 (aq) a) H A+ 2HO 2H O+ + A2- 2 2 (l) 3 (aq) (aq) b) NH + + H O NH + H O+ acid base conj.acid conj.base 4 (aq) 2 (l) 3(aq) 3 (aq) - - + -1 c) NO2 (aq) + H2O(l) HNO2(aq) + OH (aq) b) if [H2A] = 0.0250, then [H3O ]= 0.0500 moL pH = -log [H O+] 10 3 d) HC O - + H O C O 2- + H O+ = 1.30 2 4 (aq) 2 (l) 2 4 (aq) 3 (aq) - - e) CN (aq) + H2O(l) HCN(aq) + OH (aq) c) H2A must be a weak acid and has only partially + ionised. The [H3O ] is lower and pH higher than predicted.

7. a) pH + pOH = 14. ∴ pOH = 14-9.5 = 4.5

Chem Mod.6 “Acid-Base Reactions” Worksheets page 11 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au KISS Resources for NSW Syllabuses & Australian Curriculum ® Answer Section keep it simple science 5. Worksheet 7 i) use nitric acid because it is strong acid. Weak 1. acid-weak base titrations have indistinct end- 23.10 omitted point... best avoided. Average titre = (22.50+22.45+22.50)/3 = 22.48mL

ii) HNO3 + NH4OH H2O + NH4NO3 HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) Cb = b x Ca x Va/(Vb x a) Ca x Va = Cb x Vb = 1 x 0.7438 x 12.76/10.00 x1 a b = 0.9491 Cb = b x Ca x Va/(Vb x a) ∴ c(NH OH) = 0.9491 molL-1. = 1 x 0.09255 x 22.48/25.00 x1 4 = 0.08322 Worksheet 8 ∴ c(NaOH) = 0.08322 molL-1. 1. + - a) HZ + H2O H3O + Z 2. i) H SO + 2NH OH 2H O + (NH ) SO + - 2 4 4 2 4 2 4 b) Ka = [H3O ] [Z ] ii) Ca x Va = Cb x Vb [HZ] a b Ca = a x Cb x Vb/(Va x b) c) [H2O] is “missing” because the concentration of = 1 x 0.05025 x 28.32/(25.00 x 2) the water in any aqueous solution is essentially the = 0.02846 same. This constant value has been “absorbed” ∴ c(H SO ) = 0.08322 molL-1. 2 4 into the value of Ka. iii) L is best choice because stong acid-weak base titration has end-point at acidic pH. + d) Since pH = 3.8, then [H3O ] = antilog(-3.8) L changes colour at 4.2. = 1.58 x 10-4 molL-1. ∴ [Z-] = 1.58 x 10-4 and [HZ] ≅ 0.040 3. i) Can be obtained in a pure, dry state. Is stable and ∴ -4 2 -7 Ka = (1.58x10 ) / 0.040 = 6.24 x 10 does not react with gases in air or absorb moisture. and pKa = 6.20

ii) moles required: 2. n = C x V = 0.02500 x 0.5 = 0.01250 mol. Since HNO3 is considered a strong acid, mass required: m = n x MM (MM= 90.04g) dissociation is 100%. = 0.01250 x 90.04 ∴ + -1 [H3O ] = 2.50 molL . mass = 1.126g. So pH = -log(2.50) = -1.40 iii) Weigh out chemical into clean, dry beaker. Add enough pure water, and stir, to dissolve it 3. completely. a) C H COOH + H O H O+ + C H COO- Transfer solution into 500mL volumetric flask. 6 5 2 3 6 5 Rinse beaker with small amounts of extra water and b) Since pKa = 4.20, then Ka = antilog (-4.20) add washings to flask. ∴ K = 6.31 x 10-5 Fill flask to mark with pure water. Use a dropper at a the end to fill exactly to the mark. + let [H3O ] = “x” at equilibrium. Insert stopper and invert repeatedly to mix solution So [C H COO-] = “x” also. thoroughly. 6 5 So, a good approximation is 4. 2 -5 Ka = x / 0.00258 = 6.31x10 C2H2O4 + 2KOH 2H2O + C2O4K2 (or) ∴ -5 COOHCOOH + 2KOH 2H O + COOKCOOK x = 0.00258 x 6.31x10 2 + -4 -1 [H3O ] = 4.03x10 molL . Ca x Va = Cb x Vb + a b pH = - log[H3O ] = 3.39 Cb = b x Ca x Va/(Vb x a) = 2 x 0.02500 x 31.45/25.00 x1 = 0.06290 ∴ c(KOH) = 0.06290 molL-1.

Chem Mod.6 “Acid-Base Reactions” Worksheets page 12 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au KISS Resources for NSW Syllabuses & Australian Curriculum ® Answer Section keep it simple science Worksheet 10 Worksheet 8 (cont.) 1. A 2. D 3. B 4. C 5. A 6. A 4. + - a) HOCl + H2O H3O + OCl 7. a) An acid produces hydrogen ions in solution. b) Since pKa = 7.53, then Ka = antilog (-7.53) b) HCl H+ + Cl- ∴ -8 + - (g) (aq) (aq) Ka = 2.95 x 10 = [H3O ] [OCl ] [HOCl] c) Acids are proton donors. Bases are proton + - -5 -1 acceptors. pH = 4.75, so [H3O ] = [OCl ] = 1.78 x 10 molL . d) HCl + H O Cl- + H O+ Substituting into the Ka expression gives (g) 2 (l) (aq) 3 (aq) -8 -5 2 Ka = 2.95 x 10 = ( 1.78 x 10 ) The HCl molecule has transferred a proton to the [HOCl] water molecule, therefore it is an acid. ∴ [HOCl] = ( 1.78 x 10-5 )2 / 2.95 x 10-8 -1 8. = 0.011 molL . 2- - - a) CO3 (aq) + H2O(l) HCO3 (aq) + OH (aq) 5. Water acts as an acid and donates a proton to the + - In general terms, HA + H2O H3O + A carbonate ion. A hydroxide ion forms, which explains why the solution is basic. + - Ka = [H3O ] [A ] - [HA] b) If the environment is acidic, HCO3 acts as a base: and since pH = 2.9, [H O+ ] = 1.26 x10-3 3 H O+ + HCO - H CO + H O -3 2 -6 3 (aq) 3 (aq) 2 3(aq) 2 (aq) Ka = (1.26 x 10 ) / 1.50 = 1.06 x10 ∴ - pKa = 5.97 If the environment is basic, HCO3 acts as an acid: - - 2- OH (aq) + HCO3 (aq) CO3 (aq)+ H2O(aq) Worksheet 9 9. a) oxygen b) hydrogen a) A weak acid-strong base titration has an end c) metals d) Arrhenius point about pH = 8-10, so phenolphthalein is best. e) hydrogen ions f) hydroxide or oxide b) CH COOH + KOH H O + CH COOK g) the solvent (water) h) Bronsted-Lowry 3 2 3 i) proton donor j) proton acceptor c) The first titre should be discarded because it k) transfer l) protons does not agree closely with the others. The m) conjugate n) conjugate acid remaining 3 should be averaged. o) acid or base p) amphiprotic Average = (26.70+26.75+26.65)/3 = 26.70mL q) water r) any ammonium salt s) sodium carbonate t) sodium chloride/sulfate d) Ca x Va = Cb x Vb u) strong v) strong a b w) strong x) weak Ca = a x Cb x Vb/(Va x b) y) weak z) strong = 1 x 0.008263 x 26.70/(25.00 x 1) aa) hydronium & hydroxide ab) water = 0.008825 ∴ -1 ac) exo- ad) Titration c(CH3COOH) = 0.08322 molL . ae) volume af) standard ag) equivalence (end) ah) burette 10. ai) indicator aj) colour a) A buffer can maintain a constant pH despite ak) pH al) near-vertical addition of acid or base. am) weak acid and its conjugate base b) A (roughly equal) mixture of a weak acid and its an) shifts ao) Le Chatelier’s conjugate base, such as ethanoic acid plus sodium ap) pH aq) living ethanoate (which provides ethanoate ions). ar) constant chemical conditions c) Our blood is buffered by a mixture of bicarbonate as) in the blood at) bicarbonate & carbonate ions and carbonate ions. The blood pH remains quite constant, despite constant changes occurring as gases dissolve, food is absorbed, etc.

Chem Mod.6 “Acid-Base Reactions” Worksheets page 13 Usage & copying is permitted according copyright © 2005-18 KEEP IT SIMPLE SCIENCE to the SITE LICENCE CONDITIONS only www.keepitsimplescience.com.au