University:
High School
Course:
High School Chemistry
Academic year:

2021
Views:

72

Pages:

4
Author:

Quieraaffexuhz4

Ch 16 - Acid-Base Reactions Which acid, together with its sodium salt, would be best for preparing a buffer with a pH = 4.5? (A) HCN (Ka = 4.9 x 10⁻¹⁰) (B) HC₂H₃O₂ (Ka = 1.8 x 10⁻⁵) pKa = 4.88 (C) HF (Ka = 6.8 x 10⁻⁴) (D) ClC₂H₂O₂H (Ka = 1.4 x 10⁻³) What is the pH of a solution that contains 0.50 M benzoic acid and 0.75 M benzoate acid? (Ka = 6.8 x 10⁻⁵) Henderson-Hasselbalch equation pH = -log(Ka) + log ([Base]/[Acid]) pH = -log(6.8 x 10⁻⁵) + log (0.75/0.50) pH = 4.17 - 0.176 pH = 3.99 Which of these solutions, appropriately combined, could be used to produce a buffer? (A) HCl and NaOH - SA + SB - won't make buffer (B) HNO₂ and NaNO₃ - can't use NaNO₃, need NaNO₂ (C) KI and KOH - weak acid + SB - can't make buffer (D) HF and NaOH - weak acid + SB - will work if use as much NaOH as HF Which pair of chemicals would produce a buffer solution when equal numbers of moles of each are mixed? Weak acid HF and conjugate base F⁻ - from NaF (A) HF and NaF (B) HF and HCl (C) HNO₂ and NH₃ (D) HNO₃ and NaOH Which titration will have an equivalence point at the lowest pH? Strong acid with weak base (A) HCl and KOH (B) HF and NaOH (C) HF and NH₃ (D) HCl and NH₃ A 0.100 M solution of acetic acid (Ka = 1.8 x 10⁻⁵) is titrated with a 0.1000 M solution of NaOH. What is the pH when 50% of the acid has been neutralized? When acid is 50% neutralized you have made a buffer! pH = pKa - log(1.8 x 10⁻⁵) = 4.74 (A) 2.38 (B) 4.74 (C) 5.70 (D) 7.00 7. Which indicator is most appropriate for titrating a 0.100 M solution of NH₃ with 0.100 M HNO₃? The equilibrium constant, Kb, for NH₃ equals 1.8 x 10⁻⁵ Strong acid with weak base form acidic solution so indicator needs to be below 7 NH₃ + HNO₃ → NH₄⁺ + NO₃⁻ moles NH₃ = 0.050 mol moles HNO₃ = 0.050 mol KaNH₄⁺ = (1.0 x 10⁻¹⁴)/1.8 x 10⁻⁵ KaNH₄⁺ = 5.56 x 10⁻¹⁰ x²/(0.050) = 5.56 x 10⁻¹⁰ x = 5.27 x 10⁻⁶ pH = 5.28 (A) cresol red 1-2 Too low (B) methyl red 4-6 (C) phenolphthalein 8-10 too high (D) alizarin yellow 10-12 too high 8. When a particular aqueous solution is diluted by a factor of ten with H₂O, the pH increases by one pH unit. This solution most likely contains a Strong acid pH increases 1 pH unit when diluted 10% Weak acid & dissociates slightly pH not change as much (A) weak acid (B) strong base (C) strong acid (D) buffer 9. When 50.0 mL of 0.200 M HCl is mixed with 150.0 mL of 0.100 M NaOH, the reaction is as shown. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) L x M = moles 0.01 moles HCl 0.015 moles NaOH all the HCl is reacted to form 0.010 moles NaOH Divide moles by volume (0.200 L) to get molarity. Also could use ICE box What is the concentration of the resulting solution? (A) 0.0500 M NaCl (B) 0.100 M NaCl (C) 0.0500 M NaCl and 0.0250 M NaOH (D) 0.0500 M NaCl and 0.0500 M NaOH 1 10. Which pair constitutes a buffer? (A) HCl and KCl (B) NaOH and NaCl (C) HNO₂ and NaNO₂ (D) HNO₃ and NH₄NO₃ Weak acid and conjugate base 11. The best acid for preparing a buffer of pH = 3.2 has a Kₐ near (A) 2.0 x 10⁻⁵ (B) 6.0 x 10⁻⁷ (C) 3.2 x 10⁻² (D) 4.0 x 10⁻⁶ pKa of acid should be close to desired pH