Problem: A 4.36-g sample of an unknown alkali metal hydroxide is dissolved in 100.0 mL of water. An acid-base indicator is added and the resulting solution is titrated with 2.50 M HCl (aq)solution. The indicator changes color signaling that the equivalence point has been reached after 17.0 mL of the hydrochloric acid solution has been added.What is the molar mass of the metal hydroxide?

FREE Expert Solution

Recall that at the equivalence point of a titration:


moles acid=moles base


Also, recall that:

  • moles = molarity × volume
  • moles = molarity × molar mass

For alkali metal (Group 1A) hydroxide → There is 1 OH 

This means:


MVacid=molesbase


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Problem Details

A 4.36-g sample of an unknown alkali metal hydroxide is dissolved in 100.0 mL of water. An acid-base indicator is added and the resulting solution is titrated with 2.50 M HCl (aq)solution. The indicator changes color signaling that the equivalence point has been reached after 17.0 mL of the hydrochloric acid solution has been added.

What is the molar mass of the metal hydroxide?

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Our tutors have indicated that to solve this problem you will need to apply the Equivalence Point concept. If you need more Equivalence Point practice, you can also practice Equivalence Point practice problems.