Free response · Unit 4 Beta

Sulfate in a water sample

Short free response · 4 points

The question

Name: ______________________   Date: ____________   Sulfate in a water sample (4 points)

Experimental setup

Precipitating barium sulfate

To find the sulfate concentration in a 50.00 mL water sample, a student adds BaCl₂(aq) until no more white solid forms, then a few drops more. The solid, BaSO₄ (molar mass 233.40 g/mol), is filtered, rinsed, dried to constant mass and found to weigh 0.4668 g. The only sulfate compound in the water is Na₂SO₄.

  1. (a) Write the balanced net ionic equation for the formation of the precipitate. [1 point]

  2. (b) Calculate the molarity of sulfate ions in the water sample. [2 points]

  3. (c) The student skipped rinsing the precipitate, and some dissolved NaCl dried onto the solid. Predict the effect on the calculated sulfate molarity and justify your prediction. [1 point]