NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Chemistry MCQs (Practice_Test 6 of 31)
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- Hypochlorite ion (OCl-) is the conjugate base of hypochlorous acid (HOCl, Ka = 3.5 × 10 − 8) . What is the value of the base ionization equilibrium constant, Kb, for hypochlorite ion?
- 3.5 × 10 − 22
- 3.5 × 10 − 8
- 2.9 × 10 − 7
- 2.9 × 107
- 4.7 × 109
- Calculate the pH of an aqueous solution prepared to contain 1.3 × 10 − 3 M sodium nitrite (NaNO2) if the acid dissociation equilibrium constant, Ka, for nitrous acid (HNO2) is 5.1 × 10 − 4.
- 3.1
- 5.1
- 7.0
- 7.3
- 10.9
- Calculate the carbonate ion concentration in a 0.10 M solution of the weak acid, carbonic acid (H2CO3) . The stepwise dissociation constants of carbonic acid are Ka1 = 4.5 × 10 − 7 and Ka2 = 4.7 × 10 − 11.
- 4.7 × 10 − 11 M
- 1.0 × 10 − 7 M
- 4.5 × 10 − 7 M
- 2.1 × 10 − 4 M
- 3.5 × 10 − 3 M
- The very first disinfectant used by Joseph Lister was called “carbolic acid” This substance is now known as phenol (PhOH) . What is the H3O + ion concentration in a 0.10 M solution of phenol? [PhOH: Ka = 1.0 × 10 − 10]
- 1.0 × 10 − 11
- 3.2 × 10 − 5
- 5.0 × 10 − 12
- 3.2 × 10 − 6
- The sweetener, saccharin, is a weak monoprotic acid with Ka = 2.1 × 10 − 12. Calculate the H3O + concentration in a solution that contains 1.0 × 10 − 2 mole of saccharin in 1.00 L of otherwise pure water.
- 1.4 × 10 − 7
- 1.8 × 10 − 7
- 2.1 × 10 − 12
- 2.1 × 10 − 14
- When would the pH of a solution prepared by adding sodium formate to formic acid be equal to the pKa of formic acid, HCO2H?
- when [HCO2H] < [HCO2-]
- when [HCO2H] = [HCO2-]
- when [HCO2H] > [HCO2-]
- the pH of this buffer will never equal the pKa of formic acid.
- Calculate the pH of a buffer prepared by mixing 0.10 mol of sodium formate and 0.05 mol of formic acid in 1.0 L of solution. [HCO2H: Ka = 1.8 × 10 − 4]
- 1.8 × 10 − 4
- 3.44
- 4.05
- 5.31
- none of these
- For a weak diprotic acid, H2A, for which Ka1 = 2.1 × 10 − 7 and Ka2 = 4.3 × 10 − 13, the A2-ion concentration at equilibrium will be:
- approximately equal to the initial concentration of H2A.
- roughly equal to Ka2.
- roughly equal to the HA-concentration.
- much larger than the HA-concentration.
- approximately equal to the H3O + concentration.
- Many insects discharge sprays containing weak acids as a means of defense. For example, some ants discharge a spray that contains the weak acid, formic acid (HCO2H) . Calculate the pH of a 0.14 M solution of formic acid. Ka (HCO2H) = 1.8 × 10 − 4.
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- Calculate the pH of a solution prepared by dissolving 0.20 moles of benzoic acid (abbreviated HOBz) and 0.15 moles of sodium benzoate (abbreviated NaOBz) in enough water to make 1.0 L of solution. The acid-dissociation equilibrium constant for benzoic acid is Ka = 6.3 × 10 − 5.
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- Consider an aqueous solution of a weak acid. Explain why the contribution of hydronium ion from the dissociation of water (i.e. … [H3O +] water) to the total hydronium ion concentration is not equal to that for pure water (i.e.. . . 1.0 × 10 − 7 M) .
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- Calculate the [OH-] (in M) for an acetic acid solution (Ka = 1.8 × 10 − 5) having a pH of 6.32.
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- Ascorbic acid is also known as Vitamin C.In a 0.10 M solution of ascorbic acid 2.8% of the ascorbic acid will dissociate. Consider the pH you would measure for a 0.25 M solution of ascorbic acid. Which of the following statements is true?
- The pH would show that the %-dissociation would be the same in both ascorbic acid solutions.
- The pH would show that the %-dissociation would be twice as much in the more concentrated acid solutions.
- The pH of the more concentrated solution would be lower.
- You must know the Ka value for ascorbic acid before determining which of the above selections is true.
- A buffer can be prepared by mixing:
- a strong acid and its conjugate base.
- a strong base and its conjugate acid.
- a weak acid and its conjugate base.
- a weak acid and a strong acid.
- all responses above are correct.
- Calculate the pH of a solution containing 0.1 M formic acid (a monoprotic weak acid with Ka = 1.8 × 10 − 4) and 0.1 M sodium formate.
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- N⟋A