10.E: Exercises
- Page ID
- 83120
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Exercises
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Give two examples of Arrhenius acids and two of Arrhenius bases.
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List the general properties of acids.
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List the general properties of bases.
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Write a balanced chemical equation for the neutralization of Ba(OH)2(aq) with HNO3(aq).
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How many moles of sodium hydroxide (NaOH) are needed to neutralize 0.844 mol of acetic acid (HC2H3O2)? (Hint: begin by writing a balanced chemical equation for the process.)
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Hydrazoic acid (HN3) can be neutralized by a base. (The azide ion, N3-, is a polyatomic ion with three nitrogen atoms and a -1 charge.)
A) Write the balanced chemical equation for the reaction between hydrazoic acid and calcium hydroxide. B) How many milliliters of 0.0245 M Ca(OH)2 are needed to neutralize 0.564 g of HN3? -
Magnesium hydroxide [Mg(OH)2] is an ingredient in some antacids. How is the molarity of 101 mL of Mg(OH)2 solution if it can neutralize 158 mL of 0.106 M HCl(aq)? You will need to write the balanced chemical equation.
Answers
- HCl and HNO3 are acids and NaOH and NH3 are bases. (answers will vary)
- sour taste, react with metals, react with bases, and turn litmus red
- perhaps hydroxic acid
- 2HNO3(aq) + Ba(OH)2(aq) → Ba(NO3)2(aq) + 2H2O(ℓ)
- 0.844 mol
- A) 2HN3(aq) + Ca(OH)2 → Ca(N3)2 + 2H2O; B) 268 mL
- (0.106 mol HCl / L HCl soln) (0.158 L HCl soln) (1 mol Mg(OH)2 / 2 mol HCl) (1 / 0.101 L Mg(OH)2 soln) = 0.0829 mol Mg(OH)2 / L Mg(OH)2 soln = 0.0829 M Mg(OH)2
10.2 Brønsted-Lowry Definition of Acids and Bases
Exercises
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Label each reactant as a Brønsted-Lowry acid or a Brønsted-Lowry base.
HCl(aq) + NH3(aq) → NH4+(aq) + Cl−(aq)
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Explain why a Brønsted-Lowry acid can be called a proton donor.
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Write the chemical equation of the reaction of ammonia in water and label the Brønsted-Lowry acid and base.
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Demonstrate that the dissolution of HNO3 in water is actually a Brønsted-Lowry acid-base reaction by describing it with a chemical equation and labeling the Brønsted-Lowry acid and base.
Answers
- HCl: Brønsted-Lowry acid; NH3: Brønsted-Lowry base
- A Brønsted-Lowry acid gives away an H+ ion—nominally, a proton—in an acid-base reaction.
- NH3 + H2O → NH4+ + OH−; NH3: Brønsted-Lowry base; H2O: Brønsted-Lowry acid
- HNO3 + H2O → H3O+ + NO3−; HNO3: Brønsted-Lowry acid; H2O: Brønsted-Lowry base
10.3 Water: Both an Acid and a Base
Exercises
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Is H2O(ℓ) acting as an acid or a base?
H2O(ℓ) + NH4+(aq) → H3O+(aq) + NH3(aq)
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In the aqueous solutions of some salts, one of the ions from the salt can react with water molecules. In some C2H3O2− solutions, the following reaction can occur:
C2H3O2−(aq) + H2O(ℓ) → HC2H3O2(aq) + OH−(aq)
Is H2O acting as an acid or a base in this reaction?
Answers
- base
- acid
10.4 The Strengths of Acids and Bases
Concept Review Exercises
- Explain the difference between a strong acid or base and a weak acid or base.
- Explain what is occurring when a chemical reaction reaches equilibrium.
- Define pH.
Answers
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A strong acid or base is 100% ionized in aqueous solution; a weak acid or base is less than 100% ionized.
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The overall reaction progress stops because the reverse process balances out the forward process.
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pH is a measure of the hydrogen ion concentration.
Exercises
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Is each compound a strong acid or a weak acid? Assume all are in aqueous solution. (Hint: Consult Table 10.4.1)
(A) HF; (B) HC2H3O2; (C) HCl; (D) HClO4 -
Is each compound a strong base or a weak base? Assume all are in aqueous solution. (Hint: Consult Table 10.4.1)
(A) NH3; (B) NaOH; (C) Mg(OH)2; (D) Cu(OH)2 -
Write the chemical equation for the equilibrium process for HC2H3O2.
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Write the chemical equation for the equilibrium process for NH3.
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Consider two different solutions, 0.15 M HCl and 0.15 M HF. (A) Which would have lower pH? (B) Which would have lower freezing point?
Answers
- (A) weak; (B) weak; (C) strong; (D) strong
- (A) weak; (B) strong; (C) strong; (D) weak
- HC2H3O2(aq) ⇆ H+(aq) + C2H3O2−(aq)
- NH3(aq) + H2O ⇆ NH4+(aq) + OH−(aq)
- (A) The HCl solution will have lower pH ( because larger concentration of H+). (Both are the same concentration, but HF is a weak acid so does not ionize completely so there will be a lower [H+] and thus higher pH for HF.) (B) The HCl will have lower freezing point because there is a larger concentration of dissolved particles (since it completely ionizes).
10.5: Buffers
Concept Review Exercise
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Explain how a buffer prevents large changes in pH.
Answer
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A buffer has components that react with both strong acids and strong bases to resist sudden changes in pH.
Exercises
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Describe a buffer. What two related chemical components are required to make a buffer?
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Which solute combinations can make a buffer? Assume all are aqueous solutions.
A) HCl and NaCl; B) HNO2 and NaNO2; C) NH4NO3 and HNO3; D) NH4NO3 and NH3 -
For each combination in Exercise 2 that is a buffer, write the chemical equations for the reactions of the buffer components when a strong acid and a strong base is added.
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The complete phosphate buffer system is based on four substances: H3PO4, H2PO4−, HPO42−, and PO43−. What different buffer solutions can be made from these substances?
Answers
- A buffer resists sudden changes in pH. It has a weak acid or base and a salt of that weak acid or base.
- A) not a buffer; B) buffer; C) not a buffer; D) buffer
- #2b: strong acid: H+ + NO2− → HNO2; strong base: OH− + HNO2 → H2O + NO2−; #2d: strong acid: H+ + NH3 → NH4+; strong base: OH− + NH4+ → H2O + NH3
- Buffers can be made by combining H3PO4 and H2PO4−, H2PO4− and HPO42−, and HPO42− and PO43−.