Question

Solid Ba(NO3)2 is gradually dissolved in 1.0 × 10–4 M Na2CO3 solution. At what concentration of Ba2+ will a precipitate begin to form ? (Ksp for BaCO3 = 5.1 × 10–9) :

• A. 5.1 × 10–5 M
• B. 8.1 × 10–8 M
• C. 8.1 × 10–7 M
• D. 4.1 × 10–5 M

Answer 1

Answer: (A)

5.1 × 10–5 M

Answer 2

Na2CO3 ¾¾® 2Na+ + CO32–

1 × 10–4M 1 × 10–4M 1 × 10–4 M

Ksp[BaCO3] = [Ba+2] [CO32–]

5.1 × 10–9 = [Ba+2] × 1 × 10–4

[Ba+2] = 5.1 × 10–5M