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1A) How many grams of solid ammonium chloride should be added to 2.00 L of a 0.1

ID: 1031156 • Letter: 1

Question

1A) How many grams of solid ammonium chloride should be added to 2.00 L of a 0.144 M ammonia solution to prepare a buffer with a pH of 10.010 ?

1B) A student measures the CN- concentration in a saturated aqueous solution of nickel(II) cyanide to be 3.81×10-8 M. Based on her data, the solubility product constant for nickel(II) cyanide is ?

1C) A student measures the molar solubility of silver chromate in a water solution to be 1.28×10-4 M. Based on her data, the solubility product constant for this compound is ?

1D) The molar solubility of aluminum hydroxide in a water solution is ? M.

1E) The equilibrium concentration of sulfite ion in a saturated calcium sulfite solution is ? M.

Explanation / Answer

A)

pH = 10.010

pKa = 9.255

pH = pKa + log [base / acid]

10.010 = 9.255 + log [0.288 / NH4Br]

moles of NH4Br = 0.0506

mass of NH4Br = 4.958 g

B)

Ni(CN)2   ----------> Ni+2   +    2 CN-

Ksp = [Ni+2][CN-]^2

      = (1.905 x 10^-8) (3.81 x 10^-8)^2

Ksp = 2.76 x 10^-23

C)

Ag2CrO4 -------------> 2 Ag+   +   CrO42-

Ksp = 4S^3

      = 4 x (1.28 x 10^-4)

Ksp = 8.39 x 10^-12

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