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, A g C l , has a very low solubility in water, as shown. A g C l ( ) A g ( ) + C l ( ) s a q a q + – s p 𝐾 = 1 . 6 × 1 0    Adding ammonia significantly increases the solubility of A g C l because a complex ion is formed, as shown. A g ( ) + 2 N H ( ) [ A g ( N H ) ] ( ) + 3 3 2 + f a q a q a q 𝐾 = 1 . 7 × 1 0 

What mass of N H 3 is required to prepare 1.00 L of a solution that will dissolve 2.00 g of A g C l by formation of [ A g ( N H ) ] 3 2 + ?

Q2:

Unexposed silver halides are removed from photographic film when they react with sodium thiosulfate ( N a S O ) 2 2 3 to form the complex ion [ A g ( S O ) ] 2 3 2 3 – . A g B r ( ) A g ( ) + B r ( ) A g ( ) + 2 S O ( ) [ A g ( S O ) ] ( ) s a q a q a q a q a q + – s p + 2 3 2 – 2 3 2 3 – f , 𝐾 = 5 . 0 × 1 0 , 𝐾 = 4 . 7 × 1 0      What mass of N a S O 2 2 3 is required to prepare 1.00 L of a solution that will dissolve 1.00 g of A g B r by the formation of A g ( S O ) 2 3 2 3 – ?

Q3:

The concentration of Z n 2 + ions in a 0.10 M aqueous H S 2 solution is 0.050 M. What is the minimum concentration of H O 3 + ions required to prevent the precipitation of Z n S ? Z n S ( ) Z n ( ) + S ( ) 2 H O ( ) + H S ( ) 2 H O ( ) + S ( ) s a q a q l a q a q a q + 2 2 – s p 2 2 3 + 2 – 𝐾 = 1 . 0 × 1 0 𝐾 = 1 . 0 × 1 0      

Q4:

The concentration of M g 2 + 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 M g ( O H ) 2 ? M g ( O H ) ( ) M g ( ) + 2 O H ( ) N H ( ) + H O ( ) N H ( ) + O H ( ) 2 2 + – s p 3 2 4 + – b s a q a q a q l a q a q , 𝐾 = 8 . 9 × 1 0 , 𝐾 = 1 . 8 × 1 0     

Q5:

Will K C l O 4 precipitate when 20 mL of a 0.050 M solution of K + is added to 80 mL of a 0.50 M solution of C l O 4 – ? 𝐾 s p for K C l O 4 is 1 . 0 5 × 1 0   .

  • ANo, the reaction quotient, 𝑄 , is less than 𝐾 s p , shifting the equilibrium position in favor of the dissolved ions.
  • BYes, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of solid K C l O 4 .
  • CYes, the reaction quotient, 𝑄 , is less than 𝐾 s p , shifting the equilibrium position in favor of solid K C l O 4 .
  • DNo, the reaction quotient, 𝑄 , is equal to 𝐾 s p , so the position of equilibrium does not shift in either direction.
  • ENo, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of the dissolved ions.

Q6:

Does silver chloride precipitate when equal volumes of a 2 . 0 × 1 0   M solution of A g N O 3 and a 2 . 0 × 1 0   M solution of N a C l are mixed? The solution also contains N a + and N O 3 – ions, but sodium nitrate is very soluble and does not form a precipitate. 𝐾 s p for A g C l is 1 . 6 × 1 0    .

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

Q7:

C a H P O 4 has a solubility product of 7 × 1 0   . Will calcium hydrogen phosphate precipitate from a solution with [ C a ] 2 + = 0.0001 M and [ H P O ] 4 2 – = 0.001 M?

  • ACalcium hydrogen phosphate is too insoluble for a solution to form.
  • BNo, the reaction quotient, 𝑄 , is less than 𝐾 s p , shifting the equilibrium position in favor of the dissolved ions.
  • CNo, the reaction quotient, 𝑄 , is equal to 𝐾 s p , so the position of equilibrium does not shift in either direction.
  • DYes, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of solid calcium hydrogen phosphate.
  • EYes, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of the dissolved ions.

Q8:

The first step in the preparation of magnesium metal is the precipitation of M g ( O H ) 2 from sea water by the addition of lime, C a ( O H ) 2 , a readily available inexpensive source of O H – ions. M g ( O H ) ( ) M g ( ) + 2 O H ( ) 2 2 + – s p s a q a q , 𝐾 = 8 . 9 × 1 0    The concentration of M g ( ) 2 + a q in sea water is 0.0537 M. Will M g ( O H ) 2 precipitate when enough C a ( O H ) 2 is added to give a hydroxide ion concentration of 0.0010 M?

  • ANo, the reaction quotient, 𝑄 , is less than 𝐾 s p , shifting the equilibrium position in favor of the dissolved ions.
  • BNo, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of solid M g ( O H ) 2 .
  • CYes, the reaction quotient, 𝑄 , is less than 𝐾 s p , shifting the equilibrium position in favor of solid M g ( O H ) . 2
  • DNo, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of the dissolved ions.
  • EYes, the reaction quotient, 𝑄 , is greater than 𝐾 s p , shifting the equilibrium position in favor of solid M g ( O H ) 2 .

Q9:

What concentration of [ A g ] + is required to reduce [ C O ] 3 2 – to 2 . 8 × 1 0   M by precipitation of A g C O 2 3 ? The 𝐾 s p of A g C O 2 3 is 8 . 1 × 1 0    .

  • A 4 . 8 × 1 0    M
  • B 1 . 7 × 1 0   M
  • C 6 . 6 × 1 0   M
  • D 4 . 0 × 1 0   M
  • E 2 . 9 × 1 0   M

Q10:

What is the concentration of A g + required to begin precipitation of A g C O 2 3 in a solution that is 2 . 5 0 × 1 0   M in C O 3 2 – ? The 𝐾 s p of A g C O 2 3 is 8 . 1 × 1 0    .

  • A 1 . 8 × 1 0   M
  • B 1.3 M
  • C 4 . 6 × 1 0   M
  • D 7 . 8 × 1 0   M
  • E 3 . 2 × 1 0   M

Q11:

What is the concentration of F – required to begin precipitation of C a F 2 in a solution with a C a 2 + concentration of 0.015 M? The 𝐾 s p of C a F 2 is 4 . 0 × 1 0    .

  • A 2 . 7 × 1 0   M
  • B 1 . 9 × 1 0   M
  • C 7 . 1 × 1 0   M
  • D 3 . 3 × 1 0    M
  • E 5 . 2 × 1 0   M

Q12:

What concentration of [ F ] – is required to reduce [ C a ] 2 + to 1 . 0 × 1 0   M by precipitation of C a F 2 ? The 𝐾 s p of C a F 2 is 4 . 0 × 1 0    .

  • A 6 . 3 × 1 0   M
  • B 4 . 0 × 1 0   M
  • C 4 . 0 × 1 0   M
  • D 5 . 1 × 1 0   M
  • E 4 . 0 × 1 0   M

Q13:

A 0.800 L sample of a 2 . 8 × 1 0 M B a ( N O ) 2 . 8 × 1 0 M B a ( N O )     3 2 3 2 2 . 8 × 1 0 M B a ( N O )   3 2 2 . 8 × 1 0 M B a ( N O )   3 2 solution is added to 0.200 L of 4 . 8 × 1 0 M L i S O 4 . 8 × 1 0 M L i S O     2 4 2 4 4 . 8 × 1 0 M L i S O   2 4 4 . 8 × 1 0 M L i S O   2 4 . Does B a S O 4 precipitate? The 𝐾 s p of B a S O 4 is 2 . 3 × 1 0   .

  • AYes, the concentrations of S O 4 2 – and B a 2 + are just high enough to enable precipitation: 𝑄 = 𝐾 s p .
  • BNo, the concentrations of S O 4 2 – and B a 2 + are not high enough: 𝑄 < 𝐾 s p .
  • CYes, the concentrations of S O 4 2 – and B a 2 + are high enough: 𝑄 > 𝐾 s p .

Q14:

A solution contains 0.20 M of both P b 2 + and A g + ions. If C l – ions are added to the solution, what is the concentration of A g + ions when P b C l 2 begins to precipitate? The 𝐾 s p of P b C l 2 is 1 . 6 × 1 0   and that of A g C l is 1 . 6 × 1 0    .

  • A 1 . 8 × 1 0   M
  • B 1 . 6 × 1 0   M
  • C 1 . 0 × 1 0    M
  • D 7 . 1 × 1 0   M
  • E 5 . 1 × 1 0   M

Q15:

About 50% of kidney stones consist of calcium phosphate, C a ( P O ) 3 4 2 . The typical mass of C a 2 + 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 𝐾 s p of C a ( P O ) 3 4 2 is 1 . 3 × 1 0    .

  • A 2 . 3 × 1 0    M
  • B 7 . 3 × 1 0    M
  • C 9 . 1 × 1 0    M
  • D 1 . 5 × 1 0    M
  • E 1 . 7 × 1 0    M

Q16:

The base dissociation constant, 𝐾 b , of N H 3 is 1 . 8 × 1 0   and the solubility product, 𝐾 s p , of M g ( O H ) 2 is 8 . 9 × 1 0    . A 50 mL solution containing 0.95 g   M g C l 2 is mixed with an equal volume of 1.80 M aqueous N H 3 . What mass of N H C l 4 must be added to the solution to prevent the precipitation of M g ( O H ) 2 ?

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.