Chapter 19 Acids & Bases
Properties of Acids and Bases • Acids are sour (do not taste) • e.g. Lemon juice and vinegar are both aqsolns 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 reactwith 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 CH3COOHHCl Acetic Acid Hydrochloric acid Monoprotic acids • only 1 acidic H.
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)
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 Not 100% ionized CH3COOH(s) CH3COO−(aq) + H+(aq) weak < 10% most HCl(g) → H+ (aq) + Cl- (aq) strong 100%
Strong and Weak Bases <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)
Strong Acids HCl(g) + H2O(l) → H3O+(aq) + Cl−(aq) • HCl is a strong acidbecause it ionizes completely. • no un-ionizedHCl molecules are in a aqsoln 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. Un-ionized acid
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 • weakand 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.
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 = 7 pH of a salt solution 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.