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Chapter 17: Problem 13

Which of these statements about the common-ion effect is most correct? (a) The solubility of a salt MA is decreased in a solution that already contains either \(\mathrm{M}^{+}\) or \(\mathrm{A}^{-} .\) (b) Common ions alter the equilibrium constant for the reaction of an ionic solid with water. \((\mathbf{c})\) The common-ion effect does not apply to unusual ions like \(\mathrm{SO}_{3}^{2-} .(\mathbf{d})\) The solubility of a salt MA is affected equally by the addition of either \(\mathrm{A}^{-}\) or a noncommon ion.

Short Answer

Expert verified
The most correct statement about the common-ion effect is (a): "The solubility of a salt MA is decreased in a solution that already contains either M+ or A-."

Step by step solution

01

Understanding the Common-Ion Effect

The common-ion effect refers to the decrease in the solubility of a sparingly soluble salt when an ionic compound containing a common ion is added to a solution of the salt. This occurs due to the equilibrium principle which states that when a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust itself to counteract the effect of the change and maintain the new equilibrium. Therefore, adding the common ion to the solution will make the system compensate and shift its equilibrium position, resulting in the decreased solubility of the salt. Now let's analyze each statement against this understanding.
02

Analyzing Statement (a)

Statement (a) says that "The solubility of a salt MA is decreased in a solution that already contains either M+ or A-." This statement is in line with the concept of the common-ion effect, as adding an ion that is already part of the salt MA will shift the equilibrium to reduce the solubility of the salt.
03

Analyzing Statement (b)

Statement (b) says that "Common ions alter the equilibrium constant for the reaction of an ionic solid with water." This statement is incorrect because the common-ion effect only affects solubility and causes a shift in the equilibrium position, but the equilibrium constant itself remains unchanged.
04

Analyzing Statement (c)

Statement (c) says that "The common-ion effect does not apply to unusual ions like SO3^2-." This statement is not correct because the common-ion effect applies to all ionic compounds, whether the ions are "unusual" or not, as long as there is a common ion in the solution.
05

Analyzing Statement (d)

Statement (d) says that "The solubility of a salt MA is affected equally by the addition of either A- or a noncommon ion." This statement is also incorrect because the common-ion effect only applies when a common ion is added to the solution. Adding a noncommon ion will not affect the solubility through a common-ion effect.
06

Conclusion

Based on the analysis of each statement, the most correct statement about the common-ion effect is (a): "The solubility of a salt MA is decreased in a solution that already contains either M+ or A-."

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Most popular questions from this chapter

Assume that \(30.0 \mathrm{~mL}\) of a \(0.10 \mathrm{M}\) solution of a weak base \(\mathrm{B}\) that accepts one proton is titrated with a \(0.10 \mathrm{M}\) solution of the monoprotic strong acid HA. (a) How many moles of HA have been added at the equivalence point? (b) What is the predominant form of B at the equivalence point? (a) Is the \(\mathrm{pH} 7\), less than 7 , or more than 7 at the equivalence point? (d) Which indicator, phenolphthalein or methyl red, is likely to be the better choice for this titration?

Two buffers are prepared by adding an equal number of moles of formic acid (HCOOH) and sodium formate (HCOONa) to enough water to make \(1.00 \mathrm{~L}\) of solution. Buffer A is prepared using 1.00 mol each of formic acid and sodium formate. Buffer B is prepared by using 0.010 mol of each. (a) Calculate the pH of each buffer. (b) Which buffer will have the greater buffer capacity? (c) Calculate the change in \(\mathrm{pH}\) for each buffer upon the addition of \(1.0 \mathrm{~mL}\) of \(1.00 \mathrm{MHCl}\). (d) Calculate the change in \(\mathrm{pH}\) for each buffer upon the addition of \(10 \mathrm{~mL}\) of $1.00 \mathrm{MHCl}$.

A concentration of \(10-100\) parts per billion (by mass) of \(\mathrm{Ag}^{+}\) is an effective disinfectant in swimming pools. However, if the concentration exceeds this range, the \(\mathrm{Ag}^{+}\) can cause adverse health effects. One way to maintain an appropriate concentration of \(\mathrm{Ag}^{+}\) is to add a slightly soluble salt to the pool. Using \(K_{s p}\) values from Appendix \(D\), calculate the equilibrium concentration of \(\mathrm{Ag}^{+}\) in parts per billion that would exist in equilibrium with (a) AgCl, (b) AgBr, (c) AgI.

The value of \(K_{s p}\) for \(\mathrm{Cd}(\mathrm{OH})_{2}\) is $2.5 \times 10^{-14} .(\mathbf{a})$ What is the molar solubility of \(\mathrm{Cd}(\mathrm{OH})_{2} ?(\mathbf{b})\) The solubility of \(\mathrm{Cd}(\mathrm{OH})_{2}\) can be increased through formation of the complex ion \(\mathrm{CdBr}_{4}^{2-}\left(K_{f}=5 \times 10^{3}\right) .\) If solid \(\mathrm{Cd}(\mathrm{OH})_{2}\) is added to a NaBr solution, what is the initial concentration of NaBr needed to increase the molar solubility of \(\mathrm{Cd}(\mathrm{OH})_{2}\) to $1.0 \times 10^{-3} \mathrm{~mol} / \mathrm{L} ?$

Lead(II) carbonate, \(\mathrm{PbCO}_{3}\), is one of the components of the passivating layer that forms inside lead pipes. (a) If the \(K_{s p}\) for \(\mathrm{PbCO}_{3}\) is \(7.4 \times 10^{-14}\) what is the molarity of \(\mathrm{Pb}^{2+}\) in a saturated solution of lead(II) carbonate? (b) What is the concentration in ppb of \(\mathrm{Pb}^{2+}\) ions in a saturated solution? (c) Will the solubility of \(\mathrm{PbCO}_{3}\) increase or decrease as the \(\mathrm{pH}\) is lowered? (d) The EPA threshold for acceptable levels of lead ions in water is 15 ppb. Does a saturated solution of lead(II) carbonate produce a solution that exceeds the EPA limit?
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