10 questions🇬🇧English
⚗️ Buffers & pH Calculations – A-level
Chemistry · A-level — practises pH, Ka, Kw, buffer calculations and titration curves
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Questions
What is the pH of 0.010 mol dm⁻³ hydrochloric acid?
0.010
1.00
12.00
2.00
20s
Four weak acids have these pKa values. Which value belongs to the strongest acid?
9.3
10.0
3.2
4.8
20s
Which conjugate acid–base pair is mainly responsible for keeping blood pH close to 7.4?
NH₄⁺ / NH₃
HCO₃⁻ / CO₃²⁻
H₂CO₃ / HCO₃⁻
H₃PO₄ / H₂PO₄⁻
20s
What is the pH of 0.050 mol dm⁻³ sodium hydroxide at 298 K? (Kw = 1.00 × 10⁻¹⁴ mol² dm⁻⁶)
12.30
12.70
1.30
13.30
30s
A weak acid HA has Ka = 1.0 × 10⁻⁵ mol dm⁻³. What is the pH of a 0.10 mol dm⁻³ solution of HA?
6.00
3.00
5.00
1.00
30s
A little acid is added to a buffer of ethanoic acid and sodium ethanoate. How is most of the added H⁺ removed?
H⁺ combines with CH₃COOH to form CH₃COOH₂⁺
H⁺ combines with Na⁺ ions to form NaH
H⁺ reacts with water and is fully neutralised
H⁺ combines with CH₃COO⁻ to form CH₃COOH
30s
Ethanoic acid (pKa = 4.76) is titrated with sodium hydroxide. What is the pH at the half-equivalence point?
4.76
8.72
7.00
2.38
30s
At 50 °C the pH of pure water is about 6.6. Why is the water still neutral at this temperature?
[H⁺] equals [OH⁻]
Ionisation of water decreases when heated
[OH⁻] is greater than [H⁺]
Kw is unchanged at 50 °C
30s
A buffer contains 0.20 mol of weak acid HA (Ka = 2.0 × 10⁻⁵) and 0.10 mol of NaA in 1 dm³. What is its pH? (log 2 = 0.30)
5.00
4.40
4.70
4.10
60s
Which indicator is most suitable for titrating ethanoic acid with sodium hydroxide solution?
Methyl orange
Methyl red
Phenolphthalein
Bromophenol blue
30s