# Worksheet: Controlling Precipitation with Common Ions

In this worksheet, we will practice calculating the concentrations of common ions required to trigger or prevent the precipitation of a salt.

Q1:

Silver chloride, , has a very low solubility in water, as shown. Adding ammonia significantly increases the solubility of because a complex ion is formed, as shown.

What mass of is required to prepare 1.00 L of a solution that will dissolve 2.00 g of by formation of ?

Q2:

Unexposed silver halides are removed from photographic film when they react with sodium thiosulfate to form the complex ion . What mass of is required to prepare 1.00 L of a solution that will dissolve 1.00 g of by the formation of ?

Q3:

The concentration of ions in a 0.10 M aqueous solution is 0.050 M. What is the minimum concentration of ions required to prevent the precipitation of ?

Q4:

The concentration of ions in a 0.10 M aqueous ammonia solution is 0.10 M. What is the minimum concentration of ammonium ions required to prevent the precipitation of ?

Q5:

Will precipitate when 20 mL of a 0.050 M solution of is added to 80 mL of a 0.50 M solution of ? for is .

• ANo, the reaction quotient, , is greater than , shifting the equilibrium position in favor of the dissolved ions.
• BYes, the reaction quotient, , is less than , shifting the equilibrium position in favor of solid .
• CNo, the reaction quotient, , is less than , shifting the equilibrium position in favor of the dissolved ions.
• DYes, the reaction quotient, , is greater than , shifting the equilibrium position in favor of solid .
• ENo, the reaction quotient, , is equal to , so the position of equilibrium does not shift in either direction.

Q6:

Does silver chloride precipitate when equal volumes of a M solution of and a M solution of are mixed? The solution also contains and ions, but sodium nitrate is very soluble and does not form a precipitate. for is .

• ANo, the reaction quotient, , is greater than , shifting the equilibrium position in favor of the dissolved ions.
• BYes, the reaction quotient, , is less than , shifting the equilibrium position in favor of solid silver chloride.
• CNo, the reaction quotient, , is equal to , so the position of equilibrium does not shift in either direction.
• DNo, the reaction quotient, , is less than , shifting the equilibrium position in favor of the dissolved ions.
• EYes, the reaction quotient, , is greater than , shifting the equilibrium position in favor of solid silver chloride.

Q7:

has a solubility product of . Will calcium hydrogen phosphate precipitate from a solution with = 0.0001 M and = 0.001 M?

• AYes, the reaction quotient, , is greater than , shifting the equilibrium position in favor of solid calcium hydrogen phosphate.
• BNo, the reaction quotient, , is equal to , so the position of equilibrium does not shift in either direction.
• CCalcium hydrogen phosphate is too insoluble for a solution to form.
• DYes, the reaction quotient, , is greater than , shifting the equilibrium position in favor of the dissolved ions.
• ENo, the reaction quotient, , is less than , shifting the equilibrium position in favor of the dissolved ions.

Q8:

The first step in the preparation of magnesium metal is the precipitation of from sea water by the addition of lime, , a readily available inexpensive source of ions. The concentration of in sea water is 0.0537 M. Will precipitate when enough is added to give a hydroxide ion concentration of 0.0010 M?

• ANo, the reaction quotient, , is less than , shifting the equilibrium position in favor of the dissolved ions.
• BYes, the reaction quotient, , is greater than , shifting the equilibrium position in favor of solid .
• CNo, the reaction quotient, , is greater than , shifting the equilibrium position in favor of solid .
• DYes, the reaction quotient, , is less than , shifting the equilibrium position in favor of solid
• ENo, the reaction quotient, , is greater than , shifting the equilibrium position in favor of the dissolved ions.

Q9:

What concentration of is required to reduce to M by precipitation of ? The of is .

• A M
• B M
• C M
• D M
• E M

Q10:

What is the concentration of required to begin precipitation of in a solution that is M in ? The of is .

• A1.3 M
• B M
• C M
• D M
• E M

Q11:

What is the concentration of required to begin precipitation of in a solution with a concentration of 0.015 M? The of is .

• A M
• B M
• C M
• D M
• E M

Q12:

What concentration of is required to reduce to M by precipitation of ? The of is .

• A M
• B M
• C M
• D M
• E M

Q13:

A 0.800 L sample of a M   solution is added to 0.200 L of M. Does precipitate? The of is .

• ANo, the concentrations of and are not high enough: .
• BYes, the concentrations of and are high enough: .
• CYes, the concentrations of and are just high enough to enable precipitation: .

Q14:

A solution contains 0.20 M of both and ions. If ions are added to the solution, what is the concentration of ions when begins to precipitate? The of is and that of is .

• A M
• B M
• C M
• D M
• E M

Q15:

About 50% of kidney stones consist of calcium phosphate, . The typical mass of excreted in urine is 0.10 g per day. The typical amount of urine passed is 1.4 L per day. What is the maximum concentration of phosphate ions that urine can contain before a kidney stone begins to form? The of is .

• A M
• B M
• C M
• D M
• E M

Q16:

The base dissociation constant, , of is and the solubility product, , of is . A 50 mL solution containing 0.95 g is mixed with an equal volume of 1.80 M aqueous . What mass of must be added to the solution to prevent the precipitation of ?

Q17:

Calcium ions in serum, the liquid component of blood, are necessary for coagulation. Adding potassium oxalate () to blood samples prevents coagulation because most of the calcium is removed as a precipitate of , which has a solubility product () of . It is necessary to remove all but 1.0% of the calcium ions in serum in order to prevent coagulation. A blood sample contains 5.50 mL of serum with a calcium concentration of 89 mg/L. What mass of is required to prevent coagulation of this blood sample?