<< Chapter < Page Chapter >> Page >

Precipitation of silver halides

A solution contains 0.0010 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?


The two equilibria involved are:

AgCl ( s ) Ag + ( a q ) + Cl ( a q ) K sp = 1.6 × 10 10
AgI ( s ) Ag + ( a q ) + I ( a q ) K sp = 1.5 × 10 16

If the solution contained about equal concentrations of Cl and I , then the silver salt with the smallest K sp (AgI) would precipitate first. The concentrations are not equal, however, so we should find the [Ag + ] at which AgCl begins to precipitate and the [Ag + ] at which AgI begins to precipitate. The salt that forms at the lower [Ag + ] precipitates first.

For AgI: AgI precipitates when Q equals K sp for AgI (1.5 × 10 –16 ). When [I ] = 0.0010 M :

Q = [ Ag + ] [ I ] = [ Ag + ] (0.0010) = 1.5 × 10 16
[ Ag + ] = 1.8 × 10 10 0.10 = 1.6 × 10 9

AgI begins to precipitate when [Ag + ] is 1.5 × 10 –13 M .

For AgCl: AgCl precipitates when Q equals K sp for AgCl (1.6 × 10 –10 ). When [Cl ] = 0.10 M :

Q sp = [ Ag + ] [ Cl ] = [ Ag + ] (0.10) = 1.6 × 10 10
[ Ag + ] = 1.8 × 10 10 0.10 = 1.6 × 10 9 M

AgCl begins to precipitate when [Ag + ] is 1.6 × 10 –9 M .

AgI begins to precipitate at a lower [Ag + ] than AgCl, so AgI begins to precipitate first.

Check your learning

If silver nitrate solution is added to a solution which is 0.050 M in both Cl and Br ions, at what [Ag + ] would precipitation begin, and what would be the formula of the precipitate?


[Ag + ] = 1.0 × 10 –11 M ; AgBr precipitates first

Got questions? Get instant answers now!

Common ion effect

As we saw when we discussed buffer solutions, the hydronium ion concentration of an aqueous solution of acetic acid decreases when the strong electrolyte sodium acetate, NaCH 3 CO 2 , is added. We can explain this effect using Le Châtelier’s principle. The addition of acetate ions causes the equilibrium to shift to the left, decreasing the concentration of H 3 O + to compensate for the increased acetate ion concentration. This increases the concentration of CH 3 CO 2 H:

CH 3 CO 2 H + H 2 O H 3 O + + CH 3 CO 2

Because sodium acetate and acetic acid have the acetate ion in common, the influence on the equilibrium is called the common ion effect    .

The common ion effect can also have a direct effect on solubility equilibria. Suppose we are looking at the reaction where silver iodide is dissolved:

AgI ( s ) Ag + ( a q ) + I ( a q )

If we were to add potassium iodide (KI) to this solution, we would be adding a substance that shares a common ion with silver iodide. Le Châtelier’s principle tells us that when a change is made to a system at equilibrium, the reaction will shift to counteract that change. In this example, there would be an excess of iodide ions, so the reaction would shift toward the left, causing more silver iodide to precipitate out of solution.

Common ion effect

Calculate the molar solubility of cadmium sulfide (CdS) in a 0.010- M solution of cadmium bromide (CdBr 2 ). The K sp of CdS is 1.0 × 10 –28 .


The first thing you should notice is that the cadmium sulfide is dissolved in a solution that contains cadmium ions. We need to use an ICE table to set up this problem and include the CdBr 2 concentration as a contributor of cadmium ions:

CdS ( s ) Cd 2+ ( a q ) + S 2− ( a q )
This table has two main columns and four rows. The first row for the first column does not have a heading and then has the following in the first column: Initial concentration ( M ), Change ( M ), and Equilibrium concentration ( M ). The second column has the header, “C d S equilibrium arrow C d to the second power plus S to the second power superscript negative sign.” Under the second column is a subgroup of three rows and three columns. The first column is blank. The second column has the following: 0.010, x, 0.010 plus x. The third column has the following: 0, x, 0 plus x equals x.
K sp = [ Cd 2+ ] [ S 2− ] = 1.0 × 10 28
( 0.010 + x ) ( x ) = 1.0 × 10 28
x 2 + 0.010 x 1.0 × 10 28 = 0

We can solve this equation using the quadratic formula, but we can also make an assumption to make this calculation much simpler. Since the K sp value is so small compared with the cadmium concentration, we can assume that the change between the initial concentration and the equilibrium concentration is negligible, so that 0.010 + x ~ 0.010. Going back to our K sp expression, we would now get:

K sp = [ Cd 2+ ] [ S 2− ] = 1.0 × 10 28
( 0.010 ) ( x ) = 1.0 × 10 28
x = 1.0 × 10 26

Therefore, the molar solubility of CdS in this solution is 1.0 × 10 –26 M .

Check your learning

Calculate the molar solubility of aluminum hydroxide, Al(OH) 3 , in a 0.015- M solution of aluminum nitrate, Al(NO 3 ) 3 . The K sp of Al(OH) 3 is 2 × 10 –32 .


1 × 10 –10 M

Got questions? Get instant answers now!

Questions & Answers

what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
The eyes of some reptiles are sensitive to 850 nm light. If the minimum energy to trigger the receptor at this wavelength is 3.15 x 10-14 J, what is the minimum number of 850 nm photons that must hit the receptor in order for it to be triggered?
razzyd Reply
A teaspoon of the carbohydrate sucrose contains 16 calories, what is the mass of one teaspoo of sucrose if the average number of calories for carbohydrate is 4.1 calories/g?
ifunanya Reply
4. On the basis of dipole moments and/or hydrogen bonding, explain in a qualitative way the differences in the boiling points of acetone (56.2 °C) and 1-propanol (97.4 °C), which have similar molar masses
Kyndall Reply
Calculate the bond order for an ion with this configuration: (?2s)2(??2s)2(?2px)2(?2py,?2pz)4(??2py,??2pz)3
Gabe Reply
Which of the following will increase the percent of HF that is converted to the fluoride ion in water? (a) addition of NaOH (b) addition of HCl (c) addition of NaF
Tarun Reply
Practice Key Terms 4

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Ut austin - principles of chemistry. OpenStax CNX. Mar 31, 2016 Download for free at http://legacy.cnx.org/content/col11830/1.13
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Ut austin - principles of chemistry' conversation and receive update notifications?