Testing for ions and gases

Revision notes on testing for ions and gases :) 

HideShow resource information
Preview of Testing for ions and gases

First 279 words of the document:

Testing for ions and gases
Test's for positive ions / cations
Li+, Na+, K+, Ca2+, Cu2+ - FLAME TESTS
A platinum or nichrome wire is cleaned by dipping it into
concentrated HCl and holding it in a Bunsen flame.
This is repeated until no more colour is seen.
The wire is dipped back into the acid, then into the solid and back
into the flame.
Li+ - red
Na+- orange
K+- lilac
Ca2+- brick - red
Cu2+ - green
Cu2+, Fe2+, Fe3+ - SODIUM HYDROXIDE
Add a spatula of the solid to a test tube.
Add about 3cm3 water and shake well until all the solid has dissolved.
Add about 1cm3 sodium hydroxide solution, place a bung in the test tube,
and shake the tube.
Observe the colour of the precipitate formed.
Cu2+ - blue precipitate formed (copper hydroxide)
Fe2+ - dark green precipitate formed (ironII hydroxide)
Fe3+ - orange ­ brown precipitate formed (ironIII hydroxide)
The precipitates were gelatinous.
NH4+ (ammonium)- SODIUM HYDROXIDE
Add a spatula of solid to the test tube.
Add about 3cm3 water and shake well until all the solid has dissolved.
Add about 1cm3sodium hydroxide solution to the test tube, insets a bung,
and shake the tube.
Remove the bung and carefully smell the air around the top of the test
tube.
It should smell pungent.
If so, gently warm the tube and its contents using a Bunsen burner until
the solution just starts to boil.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Remove from the heat, and place some damp red litmus paper over the
top of the tube to test the gas being released.
Testing for negative ions (anions)
Cl-, Br-, I- - DILUTE NITRIC ACID AND SILVER NITRATE SOLUTION
The acid is only added to remove any substance that might produce a
precipitate with silver nitrate solution. It is not part of the reaction.
In a test tube, dissolve half a spatula of the solid in 1cm3 water.…read more

Page 3

Preview of page 3

Here's a taster:

Testing for gases
Collecting:
1) Downward delivery into a test tube / gas jar
Suitable for gases denser than air ­ Carbon dioxide (CO2), Chlorine (Cl2)
2) Upward delivery into a test tube / gas jar
Suitable for gases less dense than air ­ Hydrogen (H2), Ammonia (NH3)
3) Over water
Suitable for gases which are not very soluble­Hydrogen (H2), Oxygen
(O2)
4) In a gas syringe
For almost any gas - Hydrogen (H2), Oxygen (O2), Ammonia (NH3),
Carbon dioxide (CO2), Chlorine (Cl2)…read more

Page 4

Preview of page 4

Page 5

Preview of page 5

Here's a taster:

H2 = 2H2 (g) + O2 (g) 2H2O (l)
CO2 = Ca(OH)2 (aq) + CO2 (g) CaCO3 (s) + H2O (l)
H2 ­ Test with a lighted splint
Hold a lighted splint over a test tube of gas. If there is a squeaky pop
hydrogen is present.
O2 ­ Test with a glowing splint
Hold a glowing splint over a test tube of gas. If the splint re-lights oxygen
is present.…read more

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »