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What is the PH of 0.001 moldm-3 solution of sodium hydroxide?

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What is the PH of 0.001 moldm-3 solution of sodium hydroxide?

A. 14

B. 13

C. 12

D. 11

QUICK ANSWER…

D

SOLUTION…  

For sodium hydroxide, its concentration of 0.001 moldm-3 is for hydroxide ion (and not hydrogen ion), this means:

P(OH) = -Log[OH]

P(OH) = -Log[0.001]

P(OH) = -Log[10^-3]

P(OH) = -Log[10]^-3

P(OH) = -(-3) = 3

But we know that P(H) + P(OH) = 14,

Therefore, P(H) = 14 – P(OH) = 14 – 3 = 11

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Now for the right answer to the above question:

  1. Option A is incorrect.
  2. Option B is incorrect.
  3. C is incorrect.
  4. D is the correct answer.

QUICK TIPS…

You may please note these/this:

  • If the concentration of an acid is given, then this concentration is for hydrogen ion, and P(H) = -Log [H].
  • If the concentration of a base is given, then this concentration is for hydroxide ion, and P(OH) = -Log [OH].
  • And PH + POH = 14.

Use the questions and answers session to deal further on this topic…

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/ culled from 2018 JAMB-UTME Chemistry question 33 /

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