What are we going to discuss? Tables K and L in the Reference Tables list a few of the most common Acids and Bases, but what are Acids and Bases. Acids and Bases have easy to identify properties. In this unit will learn about these properties, and the important reactions that occur between acids and bases.
Properties of Acids They are electrolytes, that break up into ions in water, that conduct electricity in aqueous solutions ○ Strong acid: good conductor ○ Weak acid: poor conductor Sour Taste React with most metals to produce H 2 (g) React with bases to form H 2 O and salt React with indicators to change color turn litmus red phenolphthalein turns colorless pH values are 0.0-6.9 see Table M for others
Properties of Bases Electrolytes conduct electricity in aqueous solutions ○ Strong base: good conductor Bitter Taste Feel slippery (like soap) React with acids to form H 2 O and salt React with indicators to change color litmus turns blue phenolphthalein turns pink pH values are 7.1-14
Arrhenius’ Theory on Acids and Bases Arrhenius Acid Definition: a substance that ionizes in water to give hydrogen ions (proton) or a Hydronium ion: H + or H 3 O+ Ex: Hydrochloric acid, HCl (a strong acid). HCl (g) H + (aq) + Cl - (aq) ACIDIC solutions are formed when an acid transfers a proton to water.
Hydronium Ion The H + interacts strongly with a lone pair of electrons on the oxygen of a water molecule. The resulting ion, H 3 O + is called the hydronium ion. Ex: HCl + H 2 O H 3 O +1 + Cl -1
Arrhenius’ Bases Definition: a substance that ionizes in water to give hydroxide ions: OH- Example: NaOH, NH 3 NaOH (s) Na+(aq) + OH - (aq) NH 3 + H 2 O NH 4 +1 + OH -
SALTS A salt is an ionic compound that does not produce an H+ ion or OH- ion when dissolved in water. Salts are not acids or bases they are neutral substances. Ex. ○ NaCl ○ MgCl 2
Table K and Table L These two tables list the most common acids and bases. The top 4 acids on table K are all strong acids while the last 2 are weak acids. The top 3 bases on table L are strong bases while that last 1 is a weak base.
Strengths of Acids Strong acids: ionize completely which means if 100 molecules dissolve in water all 100 will break up into ions Examples: HCl H + + Cl - H 2 SO 4 2H + + SO 4 -2
Strengths of Acids Weak acids: ionize slightly or only a small percentage will break up into ions Example: acetic acid (vinegar) CH 3 COOH CH 3 COO - + H + ****note if an organic compound ends in COOH it’s a weak acid!!!
Strengths of Bases Strong bases: ionize completely Example: NaOH Na + +OH -
Strengths of Bases Weak base: ionizes slightly Example: ammonia NH 3 + H 2 O NH 4 + + OH -
Acid and Base Reactions You will need to be familiar with 2 reactions that involve acids and bases. The first reaction only involves an acid with a metal. The second reaction deals with reacting an acid with a base to produce a salt and water or neutralization.
Neutralization Reaction In a neutralization reaction an Acid will react with a base to produce salt and water. Three ways we can express neutralization reactions: 1. Word equation 2. Formula equation 3. Net ionic equation A net ionic equation has only the ions that have taken part in the reaction. In the reaction the ions that do not change are omitted, these ions are called spectator ions. See example
Neutralization HCl + NaOH acid + base water + a salt HOH + NaCl Hydrochloric Acid + Sodium Hydroxide yields Water + Sodium Chloride H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq) H 2 O + Na + (aq) + Cl - (aq) H + (aq) + OH - (aq) H2OH2O This is the net ionic equation for all neutralization reactions this equation shows how the ions are neutralized.
Try This One H 2 SO 4 + 2NaOH 2H 2 O + Na 2 SO 4 2H + + SO 4 -2 + 2Na + + 2OH - 2H 2 O + 2Na + + SO 4 -2 H + + OH - H2OH2O Sulfuric acid + sodium hydroxide yields water + sodium sulfate
Concentration of H + in Acids A. 1.0 M HCl (monoprotic acid) HCl H + + Cl - Produces 1 H + so the concentration of H + is 1.0 M [H + ] = 1.0 M
Concentration of H + in Acids B. 1.0 M H 2 SO 4 (diprotic acid) H 2 SO 4 2H + + SO 4 -2 Produces 2 H + so the concentration of H + is 2(1.0 M) [H + ] = 2.0 M
Concentration of OH - in Bases A. 1.0 M KOH KOH K + + OH - Produces 1 OH - so the concentration of OH - is 1.0 M. [OH - ] = 1.0 M
Concentration of OH - in Bases B. 1.0 M NaOH NaOH Na + + OH - Produces 1 OH - so the concentration of OH - is 1.0 M. [OH - ] = 1.0 M
Concentration of OH - in Bases C. 1.0 M Ca(OH) 2 Ca(OH) 2 Ca +2 + 2OH - Produces 2 OH - so the concentration of OH - is 2(1.0 M). [OH - ] = 2.0 M
Concentration of OH - in Bases D. 1.0 M Mg(OH) 2 Mg(OH) 2 Mg +2 + 2OH - Produces 2 OH - so the concentration of OH - is 2(1.0 M). [OH - ] = 2.0 M
Titration An Acid-Base titration is a lab technique used find the concentration of an acid or a base by neutralizing it. During a titration you add volumes of a base to an acid until it is neutralized. Using the Acid-Base titration formula listed on Table T you can solve for your unknown concentration.
Acid- Base Titrations M a V a = M b V b (Table T) M a = molarity of H + V a = volume of acid M b = molarity of OH - V b = volume of base
Titrations (Neutralization) Problems Ex. What volume of 0.50M HCl is required to neutralize 100mL of 2.0M NaOH? M a V a = M b V b M a =.5M V a = ?? M b = 2.0M V b = 100mL Plug in and solve 0.5(x) = 2.0(100) X = 400mL HCl Try the rest on your own!!!
pH Scale A scale, called the pH scale, has been developed to express [H+] as a number from 0 to 14. A pH of 0 is strongly acidic A pH of 7 is neutral A pH of 14 is strongly basic
Acid – Base Indicators An indicator is something that changes its color when it gains or loses a proton or an H+ ion. There are several different indicators and they change differently when exposed to different pH values. On your reference tables there is a list of common indicators that show the color changes at varying pH values. See Table M You can use multiple indicators to find the approximate pH of a substance