A student has equal volumes of $\pu{1.0 mol dm-3}$ sodium hydroxide and ammonia solutions. Which statement about the solutions is correct?

A. Sodium hydroxide has a lower electrical conductivity than ammonia.
B. Sodium hydroxide has a higher hydrogen ion concentration than ammonia.
C. Sodium hydroxide has a higher pH than ammonia.
D. Sodium hydroxide has a higher hydroxide ion concentration than ammonia.

The answer is C, and I understand why. What I do not understand is why D isn't correct also? Could someone clarify this for me?

  • 2
    $\begingroup$ Share some reasoning why C is true and why you think D should be true. $\endgroup$ – bpedit Jan 18 '17 at 4:14
  • $\begingroup$ At first glance I'm inclined to agree with you. Where is this question from? $\endgroup$ – electronpusher Jan 18 '17 at 11:51
  • $\begingroup$ D is also correct but as you know sodium hydroxide is strong base and ammonia solution is a weak base. In weak base solution we must know Kb to calculate hydroxide ion concentration. Although a solution of weak base has lower concentration of hydroxide ion compared to a solution of a strong base having same concentration. $\endgroup$ – narendra kumar Jan 18 '17 at 12:53

See this website. Essentially it's a misprint in the IB Chem testbank.


There's a correct rewording for D that makes C the only correct answer, according to the link I just posted.

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