Free response · Unit 7 Beta

Strontium fluoride: Ksp and a common ion

Short free response · 4 points

The question

Name: ______________________   Date: ____________   Strontium fluoride: Ksp and a common ion (4 points)

Experimental setup

A slightly soluble fluoride

Strontium fluoride, SrF2, is slightly soluble in water: SrF2(s) ⇌ Sr2+(aq) + 2 F−(aq). At 25 °C, Ksp = 4.3 × 10−9. NaF is a soluble salt.

  1. (a) Write the expression for Ksp of SrF2. [1 point]

  2. (b) Calculate the molar solubility of SrF2 in pure water at 25 °C. [1 point]

  3. (c) Calculate the molar solubility of SrF2 in 0.10 M NaF at 25 °C. [1 point]

  4. (d) A student claims that NaF lowers the solubility of SrF2 because it lowers the value of Ksp. Explain what is wrong with the claim, using Q and Ksp. [1 point]