Question

Explain how each of the following would affect the percent sulfate you calculated, i.e., too low, too high, no effect. Be specific. 3. You added 15 mL (instead of 10 mL) of 0.25 M BaCI, to your unknown. a. You were in a hurry to get out of lab, so you did not rinse the last traces of solid BaSO, from the reaction beaker into the funnel. b.

Answer 1

a) Adding more volume of BaCl₂   increases the moles of Ba²⁺which react with more sulphate ions.which inturn form more BaSO₄ . This means, the values you get are higher than expected.(too high)

b) If last traces of solid BaSO₄ are not properly rinsed, then some of them will be left in funnel. This makes you calculate less amount of BaSO₄ (too low)

Answer 2

a) BaCl₂ reacts with sulfate, SO₄^2- anion on a 1:1 molar ratio. The reaction can be denoted as

BaCl₂ (aq) + SO₄^2- (aq) --------> BaSO₄ (s) + 2 Cl^- (aq)

Since there is a 1:1 molar ratio between BaCl₂ and SO₄^2-, hence, using a higher volume of BaCl₂ will have no effect on the percent sulfate. This is due to the fact that with excess BaCl₂, SO₄^2- will become the limiting reactant and hence, the yield of BaSO₄ will be governed by the amount (mass/moles) of SO₄^2-. Since the amount of SO₄₂^- remains unaffected, the percent sulfate will remain unchanged.

b) The percent sulfate is calculated from the mass of BaSO₄ obtained. Since solid BaSO₄ was not completely filtered and some BaSO₄ remained in the beaker, hence the recorded mass of BaSO₄ will be too low and consequently, the calculated percent sulfate will be too low.

C) The filter paper remained damp because the precipitate wasn’t completely dried. Consequently, the mass of precipitated BaSO₄ was recorded too high. Since the percent sulfate is calculated from the mass of BaSO₄ precipitated, hence, the percent sulfate will be too high.