IB Docs (2) Team MC test: The pH scale
Multiple choice test on 8.3 The pH scale
Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).
If you get an answer wrong, read through the explanation carefully to learn from your mistakes.
What is the hydrogen ion concentration in a solution with a pH of 8?
pH = −log10[H+(aq)] so if the pH is 8 then [H+(aq)] = 1 x 10−8 mol dm−3
What will be the concentration of hydroxide ions in a solution with a pH of 4?
The ionic product of water = [H+(aq) x [[OH−(aq)] = 1 x 10−14. If the pH = 4 then [H+(aq) = 1 x 10−4 so [OH−(aq)] = 1 x 10−10 mol dm−3.
Which will have a pH of 2?
I. 10.0 cm3 of a solution of 0.01 mol dm−3 hydrochloric acid, HCl(aq).
II. 1000 cm3 of a solution of 0.02 mol dm−3 hydrochloric acid, HCl(aq).
III. 500 cm3 of a solution of 0.01 mol dm−3 hydrochloric acid, HCl(aq).
pH depends only upon the concentration of hydrogen ions in the solution not on the volume of solution.
10.0 cm3 of a strong acid solution has a pH of 3.
What will be the pH of the solution when it is diluted by adding 90.0 cm3 of distilled water?
[H+(aq)] changes from 1 x 10−3 mol dm−3 to 1 x 10−4 mol dm−3, i.e. it is diluted 10 times, so the new pH will be 4.
Which solution will have the highest pH?
Ethanoic acid, CH3COOH and sulfuric acid, H2SO4 are both acids with pH < 7. Distilled water has a pH =7 and ammonia solution is alkaline with a pH > 7.
When the pH of a solution changes from 12 to 9 what is the change in the hydroxide ion concentration?
[H+(aq)] x [OH−(aq)] = 10−14. At pH 12, [H+(aq)] = 10−12 mol dm−3 so [OH−(aq)] = 10−2 mol dm−3 ; at pH 9, [H+(aq)] = 10−9 mol dm−3 so [OH−(aq)] = 10−5 mol dm−3 . The change in [OH−(aq)] is from 10−2 to 10−5 mol dm−3 so it has decreased one thousand times.
Which solution will have the lowest pH?
[H+(aq)] in 0.100 mol dm−3 H2SO4 = 2 x 10−1 mol dm−3, so the pH < 1.
What volume of 0.0200 mol dm−3 sodium hydroxide solution must be added to 25.0 cm3 of a solution of hydrochloric acid with a pH of 2 to produce a solution with a pH of 7?
The pH = 2, so the concentration of the HCl(aq) = 0.0100 mol dm−3. pH 7 is a neutral solution so the volume of 0.0200 mol dm−3 NaOH(aq) required = 12.5 cm3.
Which solution will have a pH greater than 11?
NaCl(aq) is neutral with a pH of 7. [OH−(aq)] for 0.001 mol dm−3 NaOH(aq) = 0.001 mol dm−3 so pH = 11. [OH−(aq)] for 0.001 mol dm−3 Ba(OH)2(aq) = 0.002 mol dm−3 so pH > 11.
What will be the pH of the resulting solution after 25.0 cm3 of 0.100 mol dm−3 sulfuric acid solution, H2SO4(aq) has been added to 25.0 cm3 of 0.200 mol dm−3 potassium hydroxide solution, KOH(aq)?
H2SO4 + 2KOH → K2SO4 + 2H2O. So 25.0 cm3 of 0.200 mol dm−3 KOH will react exactly with 25.0 cm3 of 0.100 mol dm−3 H2SO4 to produce a neutral solution with a pH of 7.
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