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Acids and Bases What Is an Acid and Base?

Acids and Bases What Is an Acid and Base?

Acids and Bases What is an and ?

and bases are special types of solutions  Remember a solution is a mixture of a solute and a  Acids and Bases are extremely useful to us in our everyday life. Common Acids

 Citrus fruits – citric acid and ascorbic acid  Dairy products – lactic acid

 Vinegar – (CH3COOH)

 Car Batteries – (H2SO4)  Stomach Acid - (HCl)

 Acid Rain – Nitric Acid (HNO3)

 Coke – Phosphoric acid (H3PO4) Properties of Acids

Sour  (Conduct Electricity)  Have no characteristic feel  Turns blue red  Produces hydrogen gas when reacted with a certain  Produce dioxide gas when reacted with carbonate compounds.  Corrosive Common Bases

 Drain Cleaner –  Baking soda – Sodium hydrogen carbonate  –  Glass cleaner –  Antacid Tablets – Hydroxide Properties of Bases

 Taste Bitter  Electrolyte (Conduct electricity )  Feel slippery  Turn red litmus paper blue  Do not react with active metals  Do not react with carbonate compounds  Corrosive  Solutions that are basic are also called alkaline Ion

 An ion that forms when a (H+) gets added to a molecule +  Hydronium ion = H3O  In chemical reactions involving acids and bases the hydronium ion is often shown as H+ for simplicity

+ -  HCl + H2O → H + Cl (does not take water into account) OR + -  HCl + H2O → H3O + Cl Acid and Base Theories

1. Arrhenius Theory of Acids and Bases - Early theory proposed in 1884 - (aq) – a solution in which water is the dissolving medium or solvent. - Acid is a substance that adds hydronium ions + (H3O ) to an aqueous solution. - Base is a substance that adds hydroxide ions (OH-) to an aqueous solution + - - HCl(aq) → H3O (aq) + Cl (aq) (HCl = acid) + - - NaOH(aq) → Na + OH (NaOH = base) 2. Bronsted-Lowry Theory of Acid and Bases - Arrhenius did not explain how substances without hydroxide ions, in their formula, like

ammonia (NH3) can be bases. Acid – A substance that can donate a (H+) to another substance. Base – A substance that can accept a proton (H+) from another substance. + - Ex// NH3(g) + H2O(l) → NH4 (aq) + OH (aq)

NH3 accepts proton = base

H2O donates proton = acid Strong vs Weak Acids  The strength of an acid is determined by its ability to dissociate in water to produce Hydrogen/Hydronium ions.  Therefore strong are strong acids  For example Hydrochloric Acid (HCl) is a strong acid because every HCl molecule dissociates into H+  HF is a weak acid because it doesn’t dissociate well in water Strong vs Weak Bases

 The strength of a base is based on the concentration of dissociated OH- (hydroxide ions)  Therefore strong electrolytes are strong bases  Strong bases can also be described as having a high  Those bases that are not soluble in water and don’t dissociate well are weak bases.  NaOH (sodium hydroxide) is a strong base because it dissociates well into Na+ and OH- ions.

 Ammonia (NH3+) is a because most of its molecules do not react with water to form ions. Strength Versus Concentration

❖The terms weak and strong are used to compare strengths of acids and bases ❖The terms dilute and concentrated are used to describe the concentration ❖For example it is possible to have a concentrated solution of a weak acid or base or a dilute solution of a weak acid or weak base. pH scale

 The pH scale is a number line that assigns number values from 0 – 14 to acids and bases.  pH is measuring the concentration of hydrogen ions (H+ in the solution  As the concentration of H+ increases the pH decreases  Although pH is a measure of H+ ions you can also determine the OH- concentration because if H+ concentration is high the OH- concentration is low.  Therefore a pH of 0 has a high concentration of H+ ions.  Acids:  pH value of 0-6  The lower the number the stronger the acid  Bases:  pH value of 8-14  The higher the number the stronger the base  Neutral:  pH value of 7  Water is neutral

How would the pH of HCl change if water was added to it?

 The pH would increase  By adding water to HCl you are decreasing the concentration of H+ ions.  Since pH is inversely related to the concentration of H+ ions if H+ concentration decreases the pH increases. Indicators  An indicator is a chemical that change color when they come in contact with an acid or base.  Types of indicators 1. pH paper / Universal Indicator – This yellow paper will change color depending on whether it is an acid or base - The color corresponds to a specific pH so you can also determine the pH of the substance 2. Litmus Paper - Two pieces of paper where one is blue and one is red - Acid turns blue litmus paper red - Base turns red litmus paper blue 3. - Turns from a clear solution to a purple solution when a base is present

4. Red Cabbage Juice - Turns pink in an acid - Turns green in the presence of a base - Remains purple is a neutral solution Conjugate Acids and Bases  The Bronsted-Lowry definitions of acids and bases provide a basis for studying proton – transfer reactions.  Suppose that a Bronsted Lowry acid gives up a proton; the remaining ion or molecule can re-accept that proton and thus act as a base.  Such a base is known as a CONJUGATE BASE  Thus, the species that remains after a Bronsted-Lowry acid has given up a proton is the conjugate base of that acid.  The species that is formed when a Bronsted-Lowry base gains a proton is the of that base.  In general, Bronsted-Lowry acid-base reactions are equilibrium systems meaning that both the forward and reverse reactions occur.  They involve two acid-base pairs, known as conjugate acid-base pairs.  In this example:  HCl is the acid in the forward direction because it + donates the H while H2O is the base because it accepts the H+. +  H3O is the conjugate acid because it donates the H+ in the reverse direction, while Cl- is the conjugate base because it accepts the H+

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