Chapter 19 Acids & Bases

Properties of Acids and Bases Acids are sour (do not taste) e.g. Lemon juice and vinegar are both aq solns of acids. Bases taste bitter. Bases have a slippery feel. (not a safe chem test)

Definitions of Acid and Bases Acids: H+ donating substances e.g. HCl → H+ + Cl- Bases: H+ accepting substances.

Rxns with Metals and Carbonates Simple tests that distinguishes acids from bases 1. the rxn of acids with carbonate ions (CO32- )or hydrocarbonate ions, (HCO3-), to form CO2 gas, water, and another cpd. e.g. HCl (aq) + Na2CO3 → CO2 + H2O + 2NaCl e.g. HCl(aq) + NaHCO3 → NaCl(aq) + CO2 + H2O bases do not react with carbonates and …

Rxns with Metals and Carbonates 2. Add a small piece of metal (above H in the activity series of metals) in an acid, hydrogen gas bubbles will be formed. 2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g) ** no rxn with bases.

Submicroscopic Behavior of Acids The simplest definition of an acid a sub that produces (H+) when it dissolves in water. Acidity of a soln depends on the [H+] in the soln

Submicroscopic Behavior of Acids e.g. HCl(g) is an acid as it produces H+ when dissolved in water. HCl(aq) Hydrochloric acid

Acidic Hydrogen Atoms In an acid, any H atom that can be transferred to H2O is called an acidic hydrogen. e.g. HCl, HNO3, H2SO4, CH3COOH Can’t be transferred HC2H3O2

Acidic Hydrogen Atoms To help distinguish acids from other H-containing molecules, acidic H are written first in the formula. e.g. HCl(aq), HNO3(aq) , H2SO4 (aq)

Monoprotic Acids Acetic Acid Hydrochloric acid Monoprotic acids CH3COOH HCl Acetic Acid Hydrochloric acid Monoprotic acids only 1 acidic H. H2SO4 Sulfuric acid a diprotic acid H3PO4 Phosphoric acid a triprotic acid

Submicroscopic Behavior of Bases A base a subs that produces, OH –, when dissolves in H2O. e.g. NaOH (aq) → Na+ + OH- Hydroxide ion ionization ionic covalent Acids, Bases, salts, ionic cpds (dissolved) are electrolytes (polar)

all (100% turns into ions in water). Strong Acids and Bases NaOH is a strong base because all (100% turns into ions in water). NaOH(aq) → Na+ (aq) + OH- (aq) All ions No un-ionized NaOH ‘strong’ ≠ high [ ] 10 M HCl(aq) is not stronger than 0.1M HCl(aq) The ionization of the base is complete.

Strong and Weak Acids Hydrochloric acid Acetic acid Sulfuric acid Strong Acids Weak Acids Hydrochloric acid Acetic acid Sulfuric acid Carbonic acid H2CO3 Nitric acid Not 100% ionized CH3COOH(s) CH3COO−(aq) + H+(aq) weak < 10% most HCl(g) → H+ (aq) + Cl- (aq) strong 100%

NH3(g) + H2O (l) NH4+(aq) + OH−(aq) Strong and Weak Bases Strong Bases Weak Bases Sodium hydroxide Ammonia (NH3; NH4OH) Potassium hydroxide Aluminum hydroxide <10% ionized NH3(g) + H2O (l) NH4+(aq) + OH−(aq) NaOH(aq) → Na+ (aq) + OH- (aq) 100% ionized

Strong Bases strength of a base based on the % of units ionized, not the # of OH– ions produced. ([OH-]) e.g. NaOH ionizes 100%; about 10% of NH4OH ionizes (about 90% remains as molecules)

HCl(g) + H2O(l) → H3O+(aq) + Cl−(aq) Strong Acids HCl(g) + H2O(l) → H3O+(aq) + Cl−(aq) HCl is a strong acid because it ionizes completely. no un-ionized HCl molecules are in a aq soln of HCl. i.e. 100 % ionized.

Weak Acids Acetic acid, CH3COOH, is a weak acid. CH3COOH ↔ CH3COO- + H+ Unionized molecules ions Partially ionizes A soln of weak acid contains a mixture of un-ionized acid molecules, H3O+ and ….

Weak Acids The [ ] of the un-ionized acid is always the greatest.

Weak Bases NH3 is a weak base because most of its molecules do not react with H2O to form ions. NH3 (g) + H2O (l) NH4+ (aq) + OH- (aq) Un-ionized molecules ions Other examples: Al(OH)3, and Fe(OH)3.

Strength Is Not Concentration Strength concentration weak and strong : compare the strengths of acids and base (degree of ionization). dilute and concentrated :describe the [ ] of solns. (molarity) The combn of strength and [ ] ultimately determines the behavior of the soln.

Strength ≠ Concentration e.g. a 10 M CH3COOH(aq). A conc weak acid e.g. 0.001 M NaOH (aq) A dilute strong base

The pH Scale pH a math scale in which the [H+] in a soln is expressed as a # from 0 to 14.

Measuring pH Indicators register different colors at different pHs. pH meters are instruments that measure the exact pH of a soln.

Interpreting the pH Scale pH of 7 is neutral, A pH < 7 is acidic, a pH > 7 is basic.

pH of Common Materials

Types of Acid-Base Reactions Neutralization rxn The rxn of an acid and a base to produce a salt and water only. NaOH(aq) + HCl(aq) → NaCl(aq) + H2O (l) Mg(OH)2(aq) + H2SO4(aq) → MgSO4(aq) + H2O (l)

Salt Hydrolysis pH of a salt solution pH = 7 pH < 7 pH > 7

CST example 1 Equal volumes of 1 M hydrochloric acid (HCl) and 1 M sodium hydroxide base (NaOH) are mixed. After mixing, the soln will be A strongly acidic B weakly acidic C nearly neutral D weakly basic

CST example 2 Which of the following is an observable property of many acids? A they become slippery when reacting with water. B they react with metals to release hydrogen gas. C they produce salts when mixed with other acids. D they become more acidic when mixed with a base.

CST example 3 Potassium hydroxide (KOH) is a strong base because it A easily releases hydroxide ions. B does not dissolve in water. C reacts to form salt crystals in water. D does not conduct an electric current.

CST example 4 Of four different laboratory solutions, the solution with the highest acidity has a pH of A 11 B 7 C 5 D 3

CST problem 5 Which would be most appropriate for collecting data during a neutralization rxn? A a pH probe B a statistics program C a thermometer D a graphing program

CST problem 6 Copper (II) nitrate and sodium hydroxide solns react in a test tube as shown below. Cu(NO3)2(aq) + 2NaOH(aq) Cu(OH)2(s) + 2NaNO3(aq) If nitric acid is added to the test tube, the amt of (s) ppt decreases. The best explanation for this is that the acid A dilutes the soln making the ppt dissolve. B reacts with the copper (II) nitrate, pushing the eqm to the left. C will dissolve most solids, including sodium nitrate. D will react with the copper (II) hydroxide to form water and soluble copper (II) nitrate.

The End