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Assuming that no equilibria other than dissolution are involved, calculate the concentration of all solute species in each of the following solutions of salts in contact with a solution containing a common ion. Show that changes in the initial concentrations of the common ions can be neglected.
(a) TlCl( s ) in 1.250 M HCl
(b) PbI 2 ( s ) in 0.0355 M CaI 2
(c) Ag 2 CrO 4 ( s ) in 0.225 L of a solution containing 0.856 g of K 2 CrO 4
(d) Cd(OH) 2 ( s ) in a solution buffered at a pH of 10.995
Assuming that no equilibria other than dissolution are involved, calculate the concentration of all solute species in each of the following solutions of salts in contact with a solution containing a common ion. Show that it is not appropriate to neglect the changes in the initial concentrations of the common ions.
(a) TlCl( s ) in 0.025 M TlNO 3
(b) BaF 2 ( s ) in 0.0313 M KF
(c) MgC 2 O 4 in 2.250 L of a solution containing 8.156 g of Mg(NO 3 ) 2
(d) Ca(OH) 2 ( s ) in an unbuffered solution initially with a pH of 12.700
(a) [Cl
– ] = 7.6
10
−3
M
Check:
This value is too large to drop
x . Therefore solve by using the quadratic equation:
[Ti
+ ] = 3.1
10
–2
M
[Cl
– ] = 6.1
10
–3
(b) [Ba
2+ ] = 7.7
10
–4
M
Check:
Therefore, the condition is satisfied.
[Ba
2+ ] = 7.7
10
–4
M
[F
– ] = 0.0321
M ;
(c) Mg(NO
3 )
2 = 0.02444
M
Check:
The condition is satisfied; the above value is less than 5%.
[Mg
2+ ] = 0.0244
M
(d) [OH
– ] = 0.0501
M
[Ca
2+ ] = 3.15
10
–3
Check:
This value is greater than 5%, so a more exact method, such as successive approximations, must be used.
[Ca
2+ ] = 2.8
10
–3
M
[OH
– ] = 0.053
10
–2
M
Explain why the changes in concentrations of the common ions in [link] can be neglected.
Explain why the changes in concentrations of the common ions in [link] cannot be neglected.
The changes in concentration are greater than 5% and thus exceed the maximum value for disregarding the change.
Calculate the solubility of aluminum hydroxide, Al(OH) 3 , in a solution buffered at pH 11.00.
Refer to Appendix J for solubility products for calcium salts. Determine which of the calcium salts listed is most soluble in moles per liter and which is most soluble in grams per liter.
CaSO 4 ∙2H 2 O is the most soluble Ca salt in mol/L, and it is also the most soluble Ca salt in g/L.
Most barium compounds are very poisonous; however, barium sulfate is often administered internally as an aid in the X-ray examination of the lower intestinal tract ( [link] ). This use of BaSO 4 is possible because of its low solubility. Calculate the molar solubility of BaSO 4 and the mass of barium present in 1.00 L of water saturated with BaSO 4 .
Public Health Service standards for drinking water set a maximum of 250 mg/L (2.60 10 –3 M ) of because of its cathartic action (it is a laxative). Does natural water that is saturated with CaSO 4 (“gyp” water) as a result or passing through soil containing gypsum, CaSO 4 ·2H 2 O, meet these standards? What is in such water?
4.8 10 –3 M = = [Ca 2+ ]; Since this concentration is higher than 2.60 10 –3 M , “gyp” water does not meet the standards.
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