17.4.5 The Effects of pH on Solubility Flashcards
Oysters, chalk, and sea urchin shells are comprised primarily of calcium carbonate, CaCO3(s). Calcium carbonate is a sparingly soluble salt, with a Ksp value of 3.9 × 10−9.
(Reaction 1)
CaCO3(s) Ca^2+(aq) + CO3^2-(aq)
When acid (in the form of H3O+ ) is added to CaCO3(s), it reacts much more, yielding bicarbonate and water.
(Reaction 2)
CO3^2-(aq) + H3O^+(aq) HCO3-(aq) + H2O(l)
Which statement about these reactions is not correct?
By Le Châtelier’s principle (applied to both Reaction 1 and Reaction 2), a decrease in [CO32− ] will cause an increase in [CaCO3 ].
The type of sparingly soluble salt that is more soluble in acidic solution than in pure water is one that ________________
yields a basic anion.
One common commercial antacid product uses calcium carbonate, CaCO3, to relieve the symptoms from an excess of H + acid in the stomach. CaCO3 is a sparingly soluble salt. However, in a solution that has an acidic pH, it dissociates to an appreciable extent. An alternative way to show this reaction is:
CaCO3(s) + 2H^+(aq) Ca2+(aq) + H2O(l) +CO2(g)
Which statement is not correct about this reaction?
In the reaction for the dissociation of CaCO3(s) in pure water,
CaCO3(s) Ca2+(aq) + CO3^2-(aq)
the products are strongly favored at equilibrium.
Look at the dissociation of Mg(OH)2(s) in pure water.
(Reaction 1)
Mg(OH)2(s) Mg2+(aq) + 2OH-(aq)
where Ksp = 1.2 × 10−11
Notice from the Ksp value that Mg(OH)2(s) does not dissociate very much in water. We saw this in the lesson when Mg(OH)2(s) in water was a milky white suspension. We can add acid by the following reaction:
(Reaction 2)
2H^+(aq) + 2OH-(aq) 2H2O(l)
where K = (1 / KW )2 and Kw = 1 × 10−14
The K value for this reaction is very high. Combining Reaction 1 and Reaction 2, we get the Final Reaction:
(Final Reaction)
Mg(OH)2(s) + 2H+(aq) Mg^2+(aq) + 2H2O(l)
What is the solubility, S, of Mg2+, in a solution that has been buffered to a pH of 4?
1.2 × 10^9 M
Oyster and sea urchin shells are made up primarily of calcium carbonate, CaCO3(s). Calcium carbonate is a sparingly soluble salt, with a Ksp value of 3.9 × 10−9.
CaCO3(s) Ca2+(aq) + CO3^2+(aq)
Which statement about this equilibrium reaction is not correct?
A neutral solution (such as pure water) is an excellent solvent for the dissociation of CaCO3(s).
A solution of CaCO3(s) in water is a milky white suspension. Which statement best explains why this occurs?
CaCO3(s) does not dissolve very much in water. As a result, it is suspended in solution when it is mixed with water.
Adding HCl (an acid) to a solution of CaCO3(s) in water causes the CaCO3(s) to dissolve very quickly. Which statement about this event is not correct?
By Le Châtelier’s principle, we can state that the [CaCO3 ] increased as a result of a stress put on the system.
Bicarbonate (HCO3− ) and water are produced when H3O+ (aq) interacts with carbonate CO32−:
CO3^2-(aq) + H3O+(aq) HCO3-(aq) + H2O(l)
HCO3− (aq) then reacts with the hydrogen ion, H +, to form carbonic acid.
HCO3-(aq) + H^+(aq) H2CO3(aq)
Because H2CO3 (carbonic acid) is just CO2 in equilibrium with H2O, this adds to the (unfavorable) greenhouse effect in the atmosphere. Which of the following statements is not correct?
A decrease in the [CO32− ] causes a decrease in the [H3O+ ].
As a general rule, sparingly soluble salts (like CaCO3(s)) that yield a basic anion are more soluble in acidic solution. Which of the following statements concerning this premise is not correct?
Increasing the pH of a solution will cause a sparingly soluble salt to dissolve more in solution.
Which of the following is not a (very) basic anion?
bromide, Br−
