pH: Quiz

pH: Quiz

7 questions

1. Question 1EasyAt 25 °C, a solution has pH 9. It is…

   AacidicBneutralCbasicDimpossible to tell
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   Answer: basic

   At 25 °C, pH above 7 is basic, below 7 is acidic, and exactly 7 is neutral.

2. Question 2MediumWhat is the pH of 0.0025 M nitric acid, $\ce{HNO3}$ (a strong acid)?

   A2.60B3.40C0.0025D11.40
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   Answer: 2.60

   Strong acid, so $[\ce{H3O+}] = 0.0025$ M and pH = −log(0.0025) = 2.60. The answer 11.40 is the pOH.

3. Question 3MediumWhat is the pH of 0.15 M KOH (a strong base)?

   A0.82B7.15C13.18D14.15
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   Answer: 13.18

   $[\ce{OH-}] = 0.15$ M, so pOH = −log(0.15) = 0.82, and pH = 14.00 − 0.82 = 13.18. The answer 0.82 reports the pOH as the pH.

4. Question 4MediumSolution A has pH 4 and solution B has pH 8. How do their $\ce{H3O+}$ concentrations compare?

   AA has 2 times moreBA has 4 times moreCA has 10,000 times moreDB has 10,000 times more
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   Answer: A has 10,000 times more

   A difference of 4 pH units is a factor of $10^4$ = 10,000, and the lower pH has the higher $[\ce{H3O+}]$.

5. Question 5HardA solution has $[\ce{OH-}] = 2.5 \times 10^{-4}$ M at 25 °C. What is its pH?

   A3.60B7.00C10.40D11.60
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   Answer: 10.40

   pOH = −log(2.5 × 10⁻⁴) = 3.60, so pH = 14.00 − 3.60 = 10.40. (Equivalently, $[\ce{H3O+}] = 1.0 \times 10^{-14} \div 2.5 \times 10^{-4} = 4.0 \times 10^{-11}$ M.)

6. Question 6HardWhat is the pH of 0.020 M $\ce{Ca(OH)2}$?

   A1.40B12.30C12.60D13.30
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   Answer: 12.60

   Each $\ce{Ca(OH)2}$ gives two $\ce{OH-}$: $[\ce{OH-}] = 0.040$ M, pOH = 1.40, pH = 12.60. The answer 12.30 forgets the factor of 2.

7. Question 7Medium0.10 M HCl (pH 1.00) is diluted 10 times with water. What is the new pH?

   A0.10B1.00C2.00D10.0
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   Answer: 2.00

   Diluting 10 times gives 0.010 M HCl, and pH = −log(0.010) = 2.00. A 10-fold dilution of a strong acid raises the pH by 1.