1.10 quantitive analysis

Question 1

Testing for Hydrogen, H2
include property, chemical test and observation

Answer 1

Properties: Colourless gas, odourless gas, less dense than air
Chemical test: Place a burning splint in an inverted test tube filled with the gas
Observations: The gas burns with a ‘squeaky pop’ sound (2H2 + O2 —>2H2O)

Question 2

Testing for Oxygen, O2
include properties, chemical test and observation

Answer 2

Properties: Colourless gas, odourless gas
Chemical test: Place a glowing splint in an inverted test tube filled with the gas
Observations: The gas relights a glowing splint

Question 3

Testing for Chlorine, Cl2
include properties, test and observation

Answer 3

Properties: Green-yellow gas, pungent odour of ‘bleach’, denser than air
Chemical test: Bring the gas into contact with damp blue litmus paper or damp
Universal Indicator paper.
Observations: Turns the damp indicator red then bleaches the paper

Question 4

Testing for Aqueous Iodine, I2
include properties, test and observation

Answer 4

Properties: Yellow solution (dilute)
Chemical test: Add several drops of starch solution
Observations: A blue-black coloured solution is formed

Question 5

Testing for Carbon Dioxide, CO2
including properties, test and observations

Answer 5

Properties: Colourless gas, odourless gas, denser than air, soluble in water
Chemical test: Bubble the gas through colourless limewater (aqueous calcium
hydroxide solution)
Observations: The colourless solution changes to milky. Prolonged exposure leads
to the formation of a colourless solution (Ca(OH)2 + CO2 —> CaCO3 + H2O). The
calcium carbonate produced is insoluble and so the milky colour is due to the white
ppt of calcium carbonate

Question 6

Testing for Hydrogen Chloride, HCL
include properties, test and observation

Answer 6

Properties: Colourless gas, pungent odour, denser than air, soluble in water
Chemical test: Bring the gas into contact with a glass rod dipped in concentrated
ammonia solution
Observations: White fumes/smoke of solid ammonium chloride are formed
(HCl + NH3 —> NH4Cl)

Question 7

Testing for Ammonia, NH3
include properties, test and observation

Answer 7

Properties: Colourless gas, pungent odour, less dense than air, soluble in water
Chemical test: Bring the gas into contact with a glass rod dipped in concentrated
hydrochloric acid
Observations: White fumes/smoke of solid ammonium chloride are formed
(HCl + NH3 —> NH4Cl)

Question 8

method of a flame test

Answer 8

1. Make a loop on the end of a piece of nichrome wire.
2. Dip wire into concentrated hydrochloric acid.
3. Dip wire into the salt to be tested.
4. Place in blue Bunsen flame.
5. Record colour of flame.

Question 9

lithium ion and flame colour

Answer 9

Li+ crimson

Question 10

sodium ion and flame colour

Answer 10

Na+ orange

Question 11

potassium ion and flame colour

Answer 11

K+ lilac

*The flame produced by potassium ions appears pink if viewed through blue glass.

Question 12

barium ion and flame colour

Answer 12

Ba2+ green

Question 13

copper ion and flame colour

Answer 13

Cu2+ blue-green

Question 14

why is nichrome wire used?

Answer 14

Nichrome wire is used because it has a high melting point and is unreactive.

Question 15

why is conc HCL used

Answer 15

Concentrated hydrochloric acid is used because it cleans the wire, helps the solid stick to the wire produces more volatile chlorides in a Bunsen flame.

Question 16

testing for ammonium ion (NH4+)

Answer 16

Confirming the presence of ammonium ion in solution:
Method:
1. Add a spatula of solid to a test tube containing 4-5 cm3 of dilute sodium hydroxide solution.
Observation: Solid dissolves to give a colourless solution.
2. Warm the mixture gently and test any gas evolved using a glass rod dipped in concentrated hydrochloric acid.
Observation: Pungent smell. White fumes of ammonium chloride formed

Question 17

calcium ion and flame colour

Answer 17

Ca2+ brick-red

Question 18

testing for sulfate ions

Answer 18

Method:
1. Make up a solution of the sample to be tested in water.
2. Acidify with dilute HCl or HNO3 (this removes any carbonate ions which
may be present – if effervescence occurs then there is carbonate ion present,
no effervescence then no carbonate ion present).
Observation: solid dissolves
3. Add a few drops of barium chloride solution and shake to mix.
Observation: White precipitate forms which indicates the presence of a
sulfate ion.

Question 19

testing for Carbonate Ion (CO32-)

Answer 19

Confirming the presence of carbonate ion:
Method:
1. Add dilute hydrochloric acid to the sample (usually solid).
Observation: Effervescence, colourless gas produced.
2. Effervescence will occur and test the gas produced by bubbling into
colourless limewater which will change to milky if the gas is carbon dioxide
and the solid contains the carbonate ion.
(H+ + CO32- ->H2O + CO2)

Question 20

halide ion half equations

Answer 20

Ag+(aq) + Cl-
(aq) → AgCl(s)
white ppt

Ag+(aq) + Br-
(aq) → AgBr(s)
cream ppt

Ag+(aq) + I-
(aq) → AgI(s)
yellow ppt

Question 21

method for carrying out the test for a halide ion

Answer 21

1. Add a spatula of the solid to a test tube containing 2-3 cm3 of water and shake to mix.
2. Add 1 cm3 of dilute nitric acid followed by 3-4 drops of silver nitrate solution.
3. Add 4-5 cm3 of dilute ammonia solution and shake to mix.
4. If precipitate does not dissolve repeat step 2 then add 4-5 cm3 of concentrated ammonia solution and shake to mix.

Question 22

observation of chloride ions

Answer 22

White precipitate forms
that redissolves in
dilute and
concentrated ammonia
solution to form a
colourless solution

Question 23

observations of bromide ions

Answer 23

Cream precipitate
forms that
does not redissolve in
dilute ammonia
solution but does
redissolve in
concentrated
ammonia solution to
form a colourless
solution.

Question 24

observations for iodide ions

Answer 24

Yellow precipitate
forms that does not
redissolve in either
dilute ammonia
solution or
concentrated ammonia
solution.