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Section 4.3

Section 4.3. Acid-Base Reactions. Acids:. Substances that increase the concentration of H + when dissolved in water (Arrhenius). Proton donors (Brønsted–Lowry). Acids. Monoprotic : yield one H+ per molecule of acid HCl Diprotic : yield two H+ per molecule of acid H 2 SO 4

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Section 4.3

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  1. Section 4.3 Acid-Base Reactions

  2. Acids: • Substances that increase the concentration of H+ when dissolved in water (Arrhenius). • Proton donors (Brønsted–Lowry).

  3. Acids • Monoprotic: yield one H+ per molecule of acid • HCl • Diprotic: yield two H+ per molecule of acid • H2SO4 • Ionization is two steps

  4. Acids There are only seven strong acids: • Hydrochloric (HCl) • Hydrobromic (HBr) • Hydroiodic (HI) • Nitric (HNO3) • Sulfuric (H2SO4) • Chloric (HClO3) • Perchloric (HClO4)

  5. Bases: • Substances that increase the concentration of OH− when dissolved in water (Arrhenius). • Proton acceptors (Brønsted–Lowry).

  6. Bases The strong bases are the soluble salts of hydroxide ion: • Alkali metals • Calcium • Strontium • Barium

  7. Identifying Strong and Weak Electrolytes

  8. Acid-Base Reactions In an acid-base reaction, the acid donates a proton (H+) to the base.

  9. Generally, when solutions of an acid and a base are combined, the products are a salt and water. HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) Neutralization Reactions

  10. When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq) Na+ (aq)+ Cl- (aq)+ H2O (l) Neutralization Reactions

  11. When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH-(aq) Na+ (aq)+ Cl- (aq)+ H2O (l) H+ (aq)+ Cl- (aq)+ Na+ (aq) + OH- (aq) Na+ (aq) + Cl- (aq) + H2O (l) Neutralization Reactions

  12. Neutralization Reactions Observe the reaction between Milk of Magnesia, Mg(OH)2, and HCl.

  13. These metathesis reactions do not give the product expected. The expected product decomposes to give a gaseous product (CO2 or SO2). CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l) NaHCO3 (aq) + HBr (aq) NaBr (aq)+ CO2 (g) + H2O (l) SrSO3 (s) + 2 HI(aq) SrI2 (aq) + SO2 (g) + H2O (l) Gas-Forming Reactions

  14. This reaction gives the predicted product: a gas Just as in the previous examples, a gas is formed as a product of this reaction: Na2S (aq) + H2SO4 (aq) Na2SO4 (aq) + H2S (g) Gas-Forming Reactions

  15. SAMPLE EXERCISE 4.5 Comparing Acid Strengths The following diagrams represent aqueous solutions of three acids (HX, HY, and HZ) with water molecules omitted for clarity. Rank them from strongest to weakest. Solution Analyze: We are asked to rank three acids from strongest to weakest, based on schematic drawings of their solutions. Plan: We can examine the drawings to determine the relative numbers of uncharged molecular species present. The strongest acid is the one with the most H+ ions and fewest undissociated acid molecules in solution. The weakest is the one with the largest number of undissociated molecules. Solve: The order is HY > HZ > HX. HY is a strong acid because it is totally ionized (no HY molecules in solution), whereas both HX and HZ are weak acids, whose solutions consist of a mixture of molecules and ions. Because HZ contains more H+ ions and fewer molecules than HX, it is a stronger acid.

  16. Homework • 4.29-4.31; 4.36-4.38 on page 159

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