<< Chapter < Page Chapter >> Page >

Salts of carbonates, phosphates, oxalates, chromates and sulphides are generally insoluble.

Testing for common anions in solution

It is also possible to carry out tests to determine which ions are present in a solution. You should try to do each of these tests in class.

Test for a chloride

Prepare a solution of the unknown salt using distilled water and add a small amount of silver nitrate solution. If a white precipitate forms, the salt is either a chloride or a carbonate.

Cl - + Ag + + NO 3 - AgCl + NO 3 -
( AgCl is white precipitate)
CO 3 2 - + 2 Ag + + 2 NO 3 - Ag 2 CO 3 + 2 NO 3 -
( Ag 2 CO 3 is white precipitate)

The next step is to treat the precipitate with a small amount of concentrated nitric acid . If the precipitate remains unchanged, then the salt is a chloride. If carbon dioxide is formed, and the precipitate disappears, the salt is a carbonate.

AgCl + HNO 3 (no reaction; precipitate is unchanged)

Ag 2 CO 3 + 2 HNO 3 2 AgNO 3 + H 2 O + CO 2 (precipitate disappears)

Test for a sulphate

Add a small amount of barium chloride solution to a solution of the test salt. If a white precipitate forms, the salt is either a sulphate or a carbonate.

SO 4 2 - + Ba 2 + + Cl - BaSO 4 + Cl - ( BaSO 4 is a white precipitate)

CO 3 2 - + Ba 2 + + Cl - BaCO 3 + Cl - ( BaCO 3 is a white precipitate)

If the precipitate is treated with nitric acid, it is possible to distinguish whether the salt is a sulphate or a carbonate (as in the test for a chloride).

BaSO 4 + HNO 3 (no reaction; precipitate is unchanged)

BaCO 3 + 2 HNO 3 Ba ( NO 3 ) 2 + H 2 O + CO 2 (precipitate disappears)

Test for a carbonate

If a sample of the dry salt is treated with a small amount of acid, the production of carbon dioxide is a positive test for a carbonate.

Acid + CO 3 2 - CO 2

If the gas is passed through limewater and the solution becomes milky, the gas is carbon dioxide.

Ca(OH) 2 + CO 2 CaCO 3 + H 2 O (It is the insoluble CaCO 3 precipitate that makes the limewater go milky)

Test for bromides and iodides

As was the case with the chlorides, the bromides and iodides also form precipitates when they are reacted with silver nitrate. Silver chloride is a white precipitate, but the silver bromide and silver iodide precipitates are both pale yellow. To determine whether the precipitate is a bromide or an iodide, we use chlorine water and carbon tetrachloride ( CCl 4 ).

Chlorine water frees bromine gas from the bromide and colours the carbon tetrachloride a reddish brown.

Chlorine water frees iodine gas from an iodide and colours the carbon tetrachloride purple.

Precipitation reactions and ions in solution

  1. Silver nitrate ( AgNO 3 ) reacts with potassium chloride ( KCl ) and a white precipitate is formed.
    1. Write a balanced equation for the reaction that takes place.
    2. What is the name of the insoluble salt that forms?
    3. Which of the salts in this reaction are soluble?
  2. Barium chloride reacts with sulphuric acid to produce barium sulphate and hydrochloric acid.
    2. Does a precipitate form during the reaction?
    3. Describe a test that could be used to test for the presence of barium sulphate in the products.
  3. A test tube contains a clear, colourless salt solution. A few drops of silver nitrate solution are added to the solution and a pale yellow precipitate forms. Which one of the following salts was dissolved in the original solution?
    1. NaI
    2. KCl
    3. K 2 CO 3
    4. Na 2 SO 4
    (IEB Paper 2, 2005)

Questions & Answers

what is the stm
Brian Reply
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
what is differents between GO and RGO?
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
Damian Reply
absolutely yes
Akash Reply
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
what is the actual application of fullerenes nowadays?
Smarajit Reply
Privacy Information Security Software Version 1.1a
What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP
Yash Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Chemistry grade 10 [caps]. OpenStax CNX. Jun 13, 2011 Download for free at http://cnx.org/content/col11303/1.4

Notification Switch

Would you like to follow the 'Chemistry grade 10 [caps]' conversation and receive update notifications?