Solid chromium(III) nitrate is slowly added to 75.0 mL of a 0.0396 M sodium hydr

Question

Solid chromium(III) nitrate is slowly added to 75.0 mL of a 0.0396 M sodium hydroxide solution. The concentration of chromium(III) ion required to just initiate precipitation is  M.

Solid manganese(II) acetate is slowly added to 125 mL of a 0.0316 M sodium carbonate solution. The concentration of manganese(II) ion required to just initiate precipitation is  M.

Solid sodium hydroxide is slowly added to 75.0 mL of a 0.196 M chromium(III) acetate solution until the concentration of hydroxide ion is 0.0336 M. The percent of chromium(III) ion remaining in solution is  %.

Solid sodium carbonate is slowly added to 125 mL of a manganese(II) acetate solution until the concentration of carbonate ion is 0.0610 M. The maximum amount of manganese(II) ion remaining in solution is  M.

Explanation / Answer

1) the Ksp of chromium hydroxide is 6.3*10^-31.

Ksp = [Cr+3] [OH-]3 = 6.3*10^-31.

To start precipitation Ksp < Q

Q > 6.3*10^-31 > [Cr+3] [OH-]3

[Cr+3] [OH-]3 = [Cr+3] [0.0396]3

[Cr+3] = 6.3*10^-31 / [0.0396]3

[Cr+3] = 1. 02 X 10-26 M (minimum concentration )

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