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Calculate the concentration of Sr 2+ when SrF 2 starts to precipitate from a solution that is 0.0025 M in F .

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Calculate the concentration of PO 4 3− when Ag 3 PO 4 starts to precipitate from a solution that is 0.0125 M in Ag + .

9.2 × 10 −13 M

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Calculate the concentration of F required to begin precipitation of CaF 2 in a solution that is 0.010 M in Ca 2+ .

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Calculate the concentration of Ag + required to begin precipitation of Ag 2 CO 3 in a solution that is 2.50 × 10 –6 M in CO 3 2− .

[Ag + ] = 1.8 × 10 –3 M

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What [Ag + ] is required to reduce [ CO 3 2− ] to 8.2 × 10 –4 M by precipitation of Ag 2 CO 3 ?

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What [F ] is required to reduce [Ca 2+ ] to 1.0 × 10 –4 M by precipitation of CaF 2 ?

6.3 × 10 –4

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A volume of 0.800 L of a 2 × 10 –4 - M Ba(NO 3 ) 2 solution is added to 0.200 L of 5 × 10 –4 M Li 2 SO 4 . Does BaSO 4 precipitate? Explain your answer.

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Perform these calculations for nickel(II) carbonate. (a) With what volume of water must a precipitate containing NiCO 3 be washed to dissolve 0.100 g of this compound? Assume that the wash water becomes saturated with NiCO 3 ( K sp = 1.36 × 10 –7 ).

(b) If the NiCO 3 were a contaminant in a sample of CoCO 3 ( K sp = 1.0 × 10 –12 ), what mass of CoCO 3 would have been lost? Keep in mind that both NiCO 3 and CoCO 3 dissolve in the same solution.

(a) 2.25 L; (b) 7.2 × 10 –7 g

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Iron concentrations greater than 5.4 × 10 –6 M in water used for laundry purposes can cause staining. What [OH ] is required to reduce [Fe 2+ ] to this level by precipitation of Fe(OH) 2 ?

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A solution is 0.010 M in both Cu 2+ and Cd 2+ . What percentage of Cd 2+ remains in the solution when 99.9% of the Cu 2+ has been precipitated as CuS by adding sulfide?

100% of it is dissolved

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A solution is 0.15 M in both Pb 2+ and Ag + . If Cl is added to this solution, what is [Ag + ] when PbCl 2 begins to precipitate?

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What reagent might be used to separate the ions in each of the following mixtures, which are 0.1 M with respect to each ion? In some cases it may be necessary to control the pH. (Hint: Consider the K sp values given in Appendix J .)

(a) Hg 2 2+ and Cu 2+

(b) SO 4 2− and Cl

(c) Hg 2+ and Co 2+

(d) Zn 2+ and Sr 2+

(e) Ba 2+ and Mg 2+

(f) CO 3 2− and OH

(a) Hg 2 2+ and Cu 2+ : Add SO 4 2− .
(b) SO 4 2− and Cl : Add Ba 2+ .
(c) Hg 2+ and Co 2+ : Add S 2– .
(d) Zn 2+ and Sr 2+ : Add OH until [OH ] = 0.050 M .
(e) Ba 2+ and Mg 2+ : Add SO 4 2− .
(f) CO 3 2− and OH : Add Ba 2+ .

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A solution contains 1.0 × 10 –5 mol of KBr and 0.10 mol of KCl per liter. AgNO 3 is gradually added to this solution. Which forms first, solid AgBr or solid AgCl?

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A solution contains 1.0 × 10 –2 mol of KI and 0.10 mol of KCl per liter. AgNO 3 is gradually added to this solution. Which forms first, solid AgI or solid AgCl?

AgI will precipitate first.

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The calcium ions in human blood serum are necessary for coagulation ( [link] ). Potassium oxalate, K 2 C 2 O 4 , is used as an anticoagulant when a blood sample is drawn for laboratory tests because it removes the calcium as a precipitate of CaC 2 O 4 ·H 2 O. It is necessary to remove all but 1.0% of the Ca 2+ in serum in order to prevent coagulation. If normal blood serum with a buffered pH of 7.40 contains 9.5 mg of Ca 2+ per 100 mL of serum, what mass of K 2 C 2 O 4 is required to prevent the coagulation of a 10 mL blood sample that is 55% serum by volume? (All volumes are accurate to two significant figures. Note that the volume of serum in a 10-mL blood sample is 5.5 mL. Assume that the K sp value for CaC 2 O 4 in serum is the same as in water.)

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About 50% of urinary calculi (kidney stones) consist of calcium phosphate, Ca 3 (PO 4 ) 2 . The normal mid range calcium content excreted in the urine is 0.10 g of Ca 2+ per day. The normal mid range amount of urine passed may be taken as 1.4 L per day. What is the maximum concentration of phosphate ion that urine can contain before a calculus begins to form?

1.5 × 10 −12 M

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The pH of normal urine is 6.30, and the total phosphate concentration ( [ PO 4 3− ] + [ HPO 4 2− ] + [ H 2 PO 4 ] + [H 3 PO 4 ]) is 0.020 M . What is the minimum concentration of Ca 2+ necessary to induce kidney stone formation? (See [link] for additional information.)

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Magnesium metal (a component of alloys used in aircraft and a reducing agent used in the production of uranium, titanium, and other active metals) is isolated from sea water by the following sequence of reactions:

Mg 2+ ( a q ) + Ca(OH) 2 ( a q ) Mg(OH) 2 ( s ) + Ca 2+ ( a q )

Mg(OH) 2 ( s ) + 2HCl( a q ) MgCl 2 ( s ) + 2H 2 O ( l )

MgCl 2 ( l ) electrolysis Mg ( s ) + Cl 2 ( g )

Sea water has a density of 1.026 g/cm 3 and contains 1272 parts per million of magnesium as Mg 2+ ( aq ) by mass. What mass, in kilograms, of Ca(OH) 2 is required to precipitate 99.9% of the magnesium in 1.00 × 10 3 L of sea water?

3.99 kg

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Hydrogen sulfide is bubbled into a solution that is 0.10 M in both Pb 2+ and Fe 2+ and 0.30 M in HCl. After the solution has come to equilibrium it is saturated with H 2 S ([H 2 S] = 0.10 M ). What concentrations of Pb 2+ and Fe 2+ remain in the solution? For a saturated solution of H 2 S we can use the equilibrium:

H 2 S ( a q ) + 2H 2 O ( l ) 2H 3 O + ( a q ) + S 2− ( a q ) K = 1.0 × 1 0 26

(Hint: The [ H 3 O + ] changes as metal sulfides precipitate.)

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Perform the following calculations involving concentrations of iodate ions:

(a) The iodate ion concentration of a saturated solution of La(IO 3 ) 3 was found to be 3.1 × 10 –3 mol/L. Find the K sp .

(b) Find the concentration of iodate ions in a saturated solution of Cu(IO 3 ) 2 ( K sp = 7.4 × 10 –8 ).

(a) 3.1 × 10 –11 ; (b) [Cu 2+ ] = 2.6 × 10 –3 ; [ IO 3 ] = 5.3 × 10 –3

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Calculate the molar solubility of AgBr in 0.035 M NaBr ( K sp = 5 × 10 –13 ).

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How many grams of Pb(OH) 2 will dissolve in 500 mL of a 0.050- M PbCl 2 solution ( K sp = 1.2 × 10 –15 )?

1.8 × 10 –5 g Pb(OH) 2

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Use the simulation from the earlier Link to Learning to complete the following exercise:. Using 0.01 g CaF 2 , give the K sp values found in a 0.2- M solution of each of the salts. Discuss why the values change as you change soluble salts.

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How many grams of Milk of Magnesia, Mg(OH) 2 ( s ) (58.3 g/mol), would be soluble in 200 mL of water. K sp = 7.1 × 10 –12 . Include the ionic reaction and the expression for K sp in your answer. ( K w = 1 × 10 –14 = [H 3 O + ][OH ])

Mg(OH) 2 ( s ) Mg 2+ + 2OH K sp = [ Mg 2+ ] [ OH ] 2
1.23 × 10 −3 g Mg(OH) 2

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Two hypothetical salts, LM 2 and LQ, have the same molar solubility in H 2 O. If K sp for LM 2 is 3.20 × 10 –5 , what is the K sp value for LQ?

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Which of the following carbonates will form first? Which of the following will form last? Explain.

(a) MgCO 3 K sp = 3.5 × 1 0 8

(b) CaCO 3 K sp = 4.2 × 1 0 7

(c) SrCO 3 K sp = 3.9 × 1 0 9

(d) BaCO 3 K sp = 4.4 × 1 0 5

(e) MnCO 3 K sp = 5.1 × 1 0 9

MnCO 3 will form first, since it has the smallest K sp value it is the least soluble. MnCO 3 will be the last to precipitate, it has the largest K sp value.

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How many grams of Zn(CN) 2 ( s ) (117.44 g/mol) would be soluble in 100 mL of H 2 O? Include the balanced reaction and the expression for K sp in your answer. The K sp value for Zn(CN) 2 ( s ) is 3.0 × 10 –16 .

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Practice Key Terms 4

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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