A student investigates the solubility of silver bromide, AgBr, at 25 °C.
The student prepares two saturated solutions.
• Solution I: Excess AgBr in 100.0mL of pure water.
• Solution II: Excess AgBr in 100.0mL of 0.0200M NaBr.
After equilibrium is reached, the student filters each mixture, evaporates the filtrate to dryness, and weighs the solid residue.
Collected data:
Mass of residue from Solution I = 2.92×10−4g
Mass of residue from Solution II = 4.25×10−5g
At 25 °C, Ksp for AgBr is 5.0×10−13.
(a) Using the experimental masses, determine the experimental molar solubility of AgBr in each solution.
(b) Calculate the theoretical molar solubility of AgBr in (i) pure water and (ii) 0.0200M NaBr.
(c) For Solution II, compute the percent decrease in solubility relative to pure water for both the experimental and theoretical values.
(d) The experimental percent decrease differs from the theoretical prediction. Identify two plausible experimental errors or assumptions that could account for the discrepancy, and explain how each would affect the calculated solubility.