Acids, Bases and Salts - Numerical Applications
Q. How many grams of sodium chloride are needed to prepare 0.5 L of a 0.2 M solution?
A.
5.84 g
B.
11.68 g
C.
2.92 g
D.
0.58 g
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Solution
Molar mass of NaCl = 58.44 g/mol. Moles needed = 0.2 M * 0.5 L = 0.1 moles. Mass = moles * molar mass = 0.1 * 58.44 g = 5.844 g.
Correct Answer: B — 11.68 g
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Q. How many moles of potassium hydroxide are needed to neutralize 0.1 moles of hydrochloric acid?
A.
0.05
B.
0.1
C.
0.2
D.
0.3
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Solution
The reaction between KOH and HCl is 1:1. Therefore, 0.1 moles of HCl will require 0.1 moles of KOH.
Correct Answer: B — 0.1
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Q. If 25 mL of 0.5 M acetic acid is mixed with 25 mL of 0.5 M sodium acetate, what is the resulting pH of the buffer solution?
A.
4.76
B.
5.00
C.
5.76
D.
6.00
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Solution
Using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). pKa of acetic acid is approximately 4.76. Since [A-] = [HA], pH = 4.76.
Correct Answer: A — 4.76
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Q. If 50 mL of 0.1 M sulfuric acid is neutralized by sodium hydroxide, how many moles of NaOH are required?
A.
0.005
B.
0.01
C.
0.02
D.
0.03
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Solution
H2SO4 dissociates to give 2 H+ ions. Moles of H2SO4 = 0.1 M * 0.050 L = 0.005 moles. Therefore, moles of NaOH required = 0.005 moles * 2 = 0.01 moles.
Correct Answer: B — 0.01
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Q. What is the concentration of hydroxide ions in a solution with a pH of 11?
A.
1 x 10^-3 M
B.
1 x 10^-4 M
C.
1 x 10^-5 M
D.
1 x 10^-6 M
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Solution
pOH = 14 - pH = 14 - 11 = 3. [OH-] = 10^-pOH = 10^-3 M.
Correct Answer: A — 1 x 10^-3 M
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Q. What is the equivalent weight of sulfuric acid (H2SO4) for the purpose of neutralization?
A.
49 g
B.
98 g
C.
24.5 g
D.
196 g
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Solution
Equivalent weight = molar mass / n, where n = number of H+ ions. Molar mass of H2SO4 = 98 g/mol, n = 2. Therefore, equivalent weight = 98 g / 2 = 49 g.
Correct Answer: C — 24.5 g
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Q. What is the molarity of a sodium hydroxide solution if 0.4 moles are dissolved in 2 liters of water?
A.
0.2 M
B.
0.4 M
C.
0.5 M
D.
0.8 M
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Solution
Molarity (M) = moles of solute / liters of solution. Here, M = 0.4 moles / 2 L = 0.2 M.
Correct Answer: B — 0.4 M
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Q. What is the pH of a 0.001 M solution of sodium bicarbonate (NaHCO3)?
A.
8.4
B.
7.0
C.
9.0
D.
6.5
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Solution
Sodium bicarbonate is a weak base. The pH can be estimated to be around 8.4 for a 0.001 M solution.
Correct Answer: A — 8.4
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Q. What is the pH of a 0.01 M hydrochloric acid solution?
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Solution
The pH of a strong acid like HCl can be calculated using the formula pH = -log[H+]. For 0.01 M HCl, pH = -log(0.01) = 2.
Correct Answer: A — 1
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Q. What is the pH of a solution that has a hydrogen ion concentration of 1 x 10^-7 M?
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Solution
pH = -log[H+] = -log(1 x 10^-7) = 7.
Correct Answer: A — 7
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