# 0.8 Reactions in aqueous solutions  (Page 8/10)

 Page 8 / 10

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.

${\mathrm{Cl}}^{-}+{\mathrm{Ag}}^{+}+{\mathrm{NO}}_{3}^{-}\to \mathrm{AgCl}+{\mathrm{NO}}_{3}^{-}$
( $\mathrm{AgCl}$ is white precipitate)
${\mathrm{CO}}_{3}^{2-}+2{\mathrm{Ag}}^{+}+2{\mathrm{NO}}_{3}^{-}\to {\mathrm{Ag}}_{2}{\mathrm{CO}}_{3}+2{\mathrm{NO}}_{3}^{-}$
( ${\mathrm{Ag}}_{2}{\mathrm{CO}}_{3}$ 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.

$\mathrm{AgCl}+{\mathrm{HNO}}_{3}\to$ (no reaction; precipitate is unchanged)

${\mathrm{Ag}}_{2}{\mathrm{CO}}_{3}+2{\mathrm{HNO}}_{3}\to 2{\mathrm{AgNO}}_{3}+{\mathrm{H}}_{2}\mathrm{O}+{\mathrm{CO}}_{2}$ (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.

${\mathrm{SO}}_{4}^{2-}+{\mathrm{Ba}}^{2+}+{\mathrm{Cl}}^{-}\to {\mathrm{BaSO}}_{4}+{\mathrm{Cl}}^{-}$ ( ${\mathrm{BaSO}}_{4}$ is a white precipitate)

${\mathrm{CO}}_{3}^{2-}+{\mathrm{Ba}}^{2+}+{\mathrm{Cl}}^{-}\to {\mathrm{BaCO}}_{3}+{\mathrm{Cl}}^{-}$ ( ${\mathrm{BaCO}}_{3}$ 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).

${\mathrm{BaSO}}_{4}+{\mathrm{HNO}}_{3}\to$ (no reaction; precipitate is unchanged)

${\mathrm{BaCO}}_{3}+2{\mathrm{HNO}}_{3}\to \mathrm{Ba}{\left({\mathrm{NO}}_{3}\right)}_{2}+{\mathrm{H}}_{2}\mathrm{O}+{\mathrm{CO}}_{2}$ (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.

$\mathrm{Acid}+{\mathrm{CO}}_{3}^{2-}\to {\mathrm{CO}}_{2}$

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

${\mathrm{Ca\left(OH\right)}}_{2}+{\mathrm{CO}}_{2}\to {\mathrm{CaCO}}_{3}+\mathrm{H}{}_{2}\mathrm{O}$ (It is the insoluble ${\mathrm{CaCO}}_{3}$ 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 ( ${\mathrm{CCl}}_{4}$ ).

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 ( ${\mathrm{AgNO}}_{3}$ ) reacts with potassium chloride ( $\mathrm{KCl}$ ) 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.
1. Write a balanced equation for the reaction that takes place.
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. $\mathrm{NaI}$
2. $\mathrm{KCl}$
3. ${\mathrm{K}}_{2}{\mathrm{CO}}_{3}$
4. ${\mathrm{Na}}_{2}{\mathrm{SO}}_{4}$
(IEB Paper 2, 2005)

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Renato
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why we need to study biomolecules, molecular biology in nanotechnology?
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Kyle
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Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
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Abigail
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NANO
what is fullerene does it is used to make bukky balls
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s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
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is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
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What is lattice structure?
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Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
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Cied
what is biological synthesis of nanoparticles
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What makes metals better to use as wires than non-metals? (please link to bonding type)??? HELP