Question

What percentage of Ca2+ remains unprecipitated when 50.0mL of 0.10M CaCl2 is mixed with 25.0mL of 0.40 M Na2SO4? Ksp CaSO4 = 2.4*10^-5

Answer 1

Here is how we can solve this problem:

• Calculate the moles of CaCl₂ you have (concentration * volume in L). Moles of CaCl₂ = moles of Ca⁺² per the chemical formula.
• Then calculate the moles of Na₂SO₄ you have. That will tell you how many moles of Ca⁺² can be reacted based on the equation.
• Remaining moles of Ca⁺² = original moles of Ca⁺² - moles of Ca⁺² that reacted
• remaining moles of Ca⁺² / original moles of Ca⁺² * 100 is the percentage remaining.

Moles of CaCl₂ = 0.050 L x 0.10M = 0.005 moles

Moles of Na₂SO₄ = 0.025 L x 0.40M = 0.01 moles

Remaining moles of Ca⁺² = 0.01 - 0.005 => 0.005

Percentage remaining =

• remaining moles of Ca⁺² / original moles of Ca⁺² * 100 is the percentage remaining.
• 0.005/0.01 x 100 = 50%