# 15.1 Precipitation and dissolution  (Page 9/17)

 Page 9 / 17

## Key concepts and summary

The equilibrium constant for an equilibrium involving the precipitation or dissolution of a slightly soluble ionic solid is called the solubility product, K sp , of the solid. When we have a heterogeneous equilibrium involving the slightly soluble solid M p X q and its ions M m+ and X n– :

${\text{M}}_{p}{\text{X}}_{q}\left(s\right)⇌p{\text{M}}^{\text{m+}}\left(aq\right)+q{\text{X}}^{\text{n−}}\left(aq\right)$

We write the solubility product expression as:

${K}_{\text{sp}}={{\text{[M}}^{\text{m+}}\right]}^{p}{{\text{[X}}^{\text{n−}}\right]}^{q}$

The solubility product of a slightly soluble electrolyte can be calculated from its solubility; conversely, its solubility can be calculated from its K sp , provided the only significant reaction that occurs when the solid dissolves is the formation of its ions.

A slightly soluble electrolyte begins to precipitate when the magnitude of the reaction quotient for the dissolution reaction exceeds the magnitude of the solubility product. Precipitation continues until the reaction quotient equals the solubility product.

A reagent can be added to a solution of ions to allow one ion to selectively precipitate out of solution. The common ion effect can also play a role in precipitation reactions. In the presence of an ion in common with one of the ions in the solution, Le Châtelier’s principle applies and more precipitate comes out of solution so that the molar solubility is reduced.

## Key equations

• ${\text{M}}_{p}{\text{X}}_{q}\left(s\right)⇌p{\text{M}}^{\text{m+}}\left(aq\right)+q{\text{X}}^{\text{n−}}\left(aq\right)\phantom{\rule{4em}{0ex}}{K}_{\text{sp}}={\left[\text{M}}^{\text{m+}}{\right]}^{p}{{\left[\text{X}}^{\text{n−}}\right]}^{q}$

## Chemistry end of chapter exercises

Complete the changes in concentrations for each of the following reactions:

(a) $\begin{array}{ccc}\text{AgI}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& {\text{Ag}}^{\text{+}}\left(aq\right)& +\phantom{\rule{0.2em}{0ex}}{\text{I}}^{\text{−}}\left(aq\right)\\ \\ & x& _____\end{array}$

(b) $\begin{array}{ccc}{\text{CaCO}}_{3}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& {\text{Ca}}^{\text{2+}}\left(aq\right)+& {\text{CO}}_{3}{}^{\text{2−}}\left(aq\right)\\ \\ & ____& x\end{array}$

(c) $\begin{array}{ccc}\text{Mg}{\left(\text{OH}\right)}_{2}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& {\text{Mg}}^{\text{2+}}\left(aq\right)+& 2{\text{OH}}^{\text{−}}\left(aq\right)\\ \\ & x& _____\end{array}$

(d) $\begin{array}{ccc}{\text{Mg}}_{3}\left({\text{PO}}_{4}{\right)}_{2}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& 3{\text{Mg}}^{\text{2+}}\left(aq\right)+& 2{\text{PO}}_{4}{}^{\text{3−}}\left(aq\right)\\ \\ & & x_____\end{array}$

(e) $\begin{array}{cccc}{\text{Ca}}_{5}\left({\text{PO}}_{4}{\right)}_{3}\text{OH}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& 5{\text{Ca}}^{\text{2+}}\left(aq\right)+& 3{\text{PO}}_{4}{}^{\text{3−}}\left(aq\right)+& {\text{OH}}^{\text{−}}\left(aq\right)\\ \\ & _____& _____& x\end{array}$

(a) $\begin{array}{ccc}\text{AgI}\left(s\right)⇌& {\text{Ag}}^{\text{+}}\left(aq\right)+& {\text{I}}^{\text{−}}\left(aq\right)\\ \\ & x& \underset{_}{x}\end{array}$
(b) $\begin{array}{ccc}{\text{CaCO}}_{3}\left(s\right)⇌& {\text{Ca}}^{\text{2+}}\left(aq\right)+& {\text{CO}}_{3}{}^{\text{2−}}\left(aq\right)\\ \\ & \underset{_}{x}& x\end{array}$
(c) $\begin{array}{lll}\text{Mg}{\left(\text{OH}\right)}_{2}\left(s\right)⇌\hfill & {\text{Mg}}^{\text{2+}}\left(aq\right)\hfill & +\phantom{\rule{0.2em}{0ex}}2{\text{OH}}^{\text{−}}\left(aq\right)\hfill \\ \hfill & x\hfill & \underset{_}{\text{2}x}\hfill \end{array}$
(d) $\begin{array}{ccc}{\text{Mg}}_{3}{\left({\text{PO}}_{4}\right)}_{2}\left(s\right)⇌& {\text{3Mg}}^{\text{2+}}\left(aq\right)+& {\text{2PO}}_{4}{}^{\text{3−}}\left(aq\right)\\ \\ & \underset{_}{3x}& 2x\end{array}$
(e) $\begin{array}{cccc}{\text{Ca}}_{5}\left({\text{PO}}_{4}{\right)}_{3}\text{OH}\left(s\right)⇌& {\text{5Ca}}^{\text{2+}}\left(aq\right)+& {\text{3PO}}_{4}{}^{\text{3−}}\left(aq\right)+& {\text{OH}}^{\text{−}}\left(aq\right)\\ \\ & \underset{_}{5x}& \underset{_}{3x}& x\end{array}$

Complete the changes in concentrations for each of the following reactions:

(a) $\begin{array}{ccc}{\text{BaSO}}_{4}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& {\text{Ba}}^{\text{2+}}\left(aq\right)+& {\text{SO}}_{4}{}^{\text{2−}}\left(aq\right)\\ \\ & x& _____\end{array}$

(b) $\begin{array}{ccc}{\text{Ag}}_{2}{\text{SO}}_{4}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& 2{\text{Ag}}^{\text{+}}\left(aq\right)+& {\text{SO}}_{4}{}^{\text{2−}}\left(aq\right)\\ \\ & _____& x\end{array}$

(c) $\begin{array}{ccc}\text{Al}{\left(\text{OH}\right)}_{3}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& {\text{Al}}^{\text{3+}}\left(aq\right)+& 3{\text{OH}}^{\text{−}}\left(aq\right)\\ \\ & x& _____\end{array}$

(d) $\begin{array}{cccc}\text{Pb}\left(\text{OH}\right)\text{Cl}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& {\text{Pb}}^{\text{2+}}\left(aq\right)+& {\text{OH}}^{\text{−}}\left(aq\right)+& {\text{Cl}}^{\text{−}}\left(aq\right)\\ \\ & _____\phantom{\rule{0.2em}{0ex}}& x& _____\end{array}$

(e) $\begin{array}{ccc}{\text{Ca}}_{3}\left({\text{AsO}}_{4}{\right)}_{2}\left(s\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}& 3{\text{Ca}}^{\text{2+}}\left(aq\right)+& 2{\text{AsO}}_{4}{}^{\text{3−}}\left(aq\right)\\ \\ & 3x& _____\end{array}$

How do the concentrations of Ag + and ${\text{CrO}}_{4}{}^{\text{2−}}$ in a saturated solution above 1.0 g of solid Ag 2 CrO 4 change when 100 g of solid Ag 2 CrO 4 is added to the system? Explain.

There is no change. A solid has an activity of 1 whether there is a little or a lot.

How do the concentrations of Pb 2+ and S 2– change when K 2 S is added to a saturated solution of PbS?

What additional information do we need to answer the following question: How is the equilibrium of solid silver bromide with a saturated solution of its ions affected when the temperature is raised?

The solubility of silver bromide at the new temperature must be known. Normally the solubility increases and some of the solid silver bromide will dissolve.

Which of the following slightly soluble compounds has a solubility greater than that calculated from its solubility product because of hydrolysis of the anion present: CoSO 3 , CuI, PbCO 3 , PbCl 2 , Tl 2 S, KClO 4 ?

#### Questions & Answers

given that 32.og sulphur contains 6.02×10 ^23 sulphur atoms how many atoms are there in 2.70g of aluminum. (A=27 s =32 )
0.602*10^23=6.02×10^22
galina
Correct 👍... Its 1/10 of the mass number of Al which is 27
Karim
show the steps pls
Faith
correct
Collins
2.7g of Al - 6.02×10^23×2.7/27=0.602×10^23
galina
thanks
Faith
An aqueos solution of sodium hydroxide containing 2g in 200cm3 of solution has a concentration of (NaOH=40).
0.25 mol/dm3
David
0.25M
David
what is the meaning of the term an orbital?
Orbital mathematical function that describes the wave-like behavior of an electron, electron pair, or (less commonly) nucleons. An orbital may also be called an atomic orbital or electron
Emmanuel
orbitals describe where an electron is likely to be found in an atom. Molecular orbitals perform the same role in molecules
Danny
why is alkynes more reactive than alkenes and alkanes
Alkenes and alkynes are generally more reactive than alkanes due to the electron density available in their pi bonds.
Danny
What are molecules
a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction
Danny
True
David
exactly
Harriet
true
lucy
were is ruth
Danny
Perfect
BISWAJIT
what is partial pressure law
what is the structural formular for 2,3-dimethylbutane?
name the following compound (COOH)2
Mercy
CH3-CH(CH3)-CH(CH3)-CH3 this is 2,3-dimethylbutane
galina
(COOH)2 is oxalic acid
thiru
what is chemistry
chemistry is the study of chemical reactions
lucy
Chemistry is the study of matter, its properties, how and why substances combine or separate to form other substances, and how substances interact with energy.
Danny
chemistry is the study of matter, it's properties and composition
alexandra
am from Abuja and am in ss1
lucy
ss1 some one translate that for me we use grades in my country
Danny
lucy
okay am a chemistry and biology teacher from Zambia
Danny
should be grade 10 I think
alexandra
thats good Mr mwanza
Harriet
harriet you in grade what
Danny
GCE 12
Harriet
lusaka
Harriet
yes sir
lucy
me ss2
Richard
so are a final year student
kabu
What is the chemical formula for alcohol? is the chemical formula for alcohol?
CH3CH2OH
Anupam
20 element are what element?
What is Chemistry?
studying about chemical reactions
thiru
You are right Vengada
Esther
studying about the rate of chemical is ?
thiru
Chemistry is the branch of sciences dealing with the composition of substances and their properties and reaction.
Jeremiah
chemical reaction is the process in which one or more chemical substances react with other chemical substance and converted one or more different substances.
Aisha
what is isotopy
Isotopy is one of two or more atoms having the same atomic numbers but different mass number.
Esther
is phenomenon where by atom of an element exhibit different mass number but have the same atomic number
lucy
same number of electrons and protons but different number of neutrons
galina
is an atom which has different number of protons but same number of electron such as carbon -12 and corbon 12
Collins
carbon-12 and carbon-13 have 6 electrons and 6 protons but carbon-12 has 6 neutrons and carbon-13 has 7 neutrons. Isotopes have different amount of neutrons
galina
Molar mass of Chlorine
molar mass of chlorine 35.5
lucy
what is chemistry
Molar mass of Chlorine atom
Sakyi
chem is the study of structure, properties of matter and changes that matter undergo
Sheila
m.m of Cl is 35.5
Sheila
SYOPI chemistry is the study of changes in the study of matter
syopi
what is an acid
example, HCl, H2SO4, HNO3
galina
an acid is a substance that dissolves in water to give hydrogen oins as the only negatively charged ions
Sheila
Galina is correct those are some examples of acids , others are ethanedioic acid, ethanoic acid , methanoic acid ma ans above is tha definition of an acid
Sheila
An acid is a substance with particular chemical properties including litmus red, neutralizing alkalis and dissolving some metals.
Esther
Shelia is also right 💯💯
Esther
what is hydrocarbon?
Edgar
is a group of carbon atoms that is bonded with an alkyl group eg methyl butane
Sheila
A hydrocarbon is a compound that contains only hydrogen and carbon atoms
martha
it means only carbon and hydrogen atoms are bonded..
Edgar