Chapter 19 Salt Analysis (flame test, testing for anions and cations)

Question 1

What does the flame test work well for

Answer 1

Works well metal cations - esp group 1.

Question 2

Steps for flame test

Answer 2

1) Clean a platinum/nichrome wire. Dip the wire into concentrated HCl. Hold it in a hot bunsen flame

2) Moisten the wire by dipping it in the HCl again. Dip the wire in some salt. some salt would stick to the wire

3) Hold the wire in the clear blue part of the bunsen burner flame and observe the colour change

Question 3

Colour of lithium ion in flame test

Answer 3

Red

Question 4

Colour of sodium ion in flame test

Answer 4

Yellow

Question 5

Colour of potassium ion in flame test

Answer 5

Lilac

Question 6

Colour of calcium ion in flame test

Answer 6

orange-red

Question 7

Colour of barium ion in flame test

Answer 7

Light green

Question 8

Colour of copper(II) ion in flame test

Answer 8

blue-green

Question 9

How to test for ammonium ion
chemical formula for ammonium ion
what happens if it is present what does it turn litmus
ionic equation

Answer 9

Add diluted aqueous sodium hydroxide
NH4+
if present - ammonia gas is given off (turns litmus blue)
NH4+ (aq) + OH- (aq) —> NH3 (g) + H2O (l)

Question 10

How to test iron (II)ion

Answer 10

Add diluted aqueous sodium hydroxide or aqueous ammonia
Fe2+
if present - pale green precipitate forms
Fe2+ (aq) + 2OH- —> Fe(OH)2 (s)

Question 10

How to test iron (iii) ion

Answer 10

Fe3+
Add diluted aqueous sodium hydroxide or aqueous ammonia
red-brown precipitate forms
Fe3+ + 3OH- —> Fe(OH)3 (s)

Question 11

How to test zinc ion

Answer 11

Zn +2
Add diluted aqueous sodium hydroxide or aqueous ammonia
if present - white precipitate forms
dissolves if u add excess of either

Zn2+ (aq) + 2OH- (aq) —> Zn(OH)2 (s)

Question 12

How to test Aluminium ion

Answer 12

Al3+
make 2 portions of it:

portion 1: Add diluted aqueous sodium hydroxide to one, white precipitate forms. If excess aq NaOH is added then the precipitate dissolves

portion 2: and aqueous ammonia to the other, white precipitate forms, nothing happens if excess ammonia is added

Al3+ (aq) + 3OH- (aq) —-> Al(OH)3 (s)

Question 13

How to test for calcium ion

Answer 13

Ca2+
make 2 portions of it:

portion 1: Add diluted aqueous sodium hydroxide to one, white precipitate forms. If excess aq NaOH is added then nothing happens

portion 2: and aqueous ammonia to the other, very slight or no white precipitate is formed

Ca +2 (aq) + 2OH- (aq) —> Ca(OH)2 (s)

Question 14

How to test for copper (II) ion

Answer 14

Cu2+

make 2 portions of it:

portion 1: Add diluted aqueous sodium hydroxide to one, pale blue precipitate forms. If excess aq NaOH is added then nothing happens

portion 2: and aqueous ammonia to the other, pale blue precipiate is formed. Dissolves in excess ammonia to give a deep blue solution. This is because a soluble complex ion forms

Cu+2 (aq) + 2OH- (aq) —> Cu(OH)2 (s)

Question 15

How to test for Chromium (III) ion

Answer 15

make 2 portions of it:

portion 1: Add diluted aqueous sodium hydroxide to one, green precipitate forms. If excess aq NaOH is added then the precipitate dissolves

portion 2: and aqueous ammonia to the other, grey-green precipitate forms, nothing happens if excess ammonia is added

Cr3+ (aq) + 3OH- (aq) —> Cr(OH)3 (s)

Question 16

General method to test for halide ions (Cl-, Br-, I-)

Answer 16

Add dilute nitric acid
add aqeous silver nitrate

If the anion is present then a precipitate will form

Question 17

Colour and eqn of chlorine ion precipitate

Answer 17

white
Ag+ (aq) + Cl- (aq) —> AgCl(s)

Question 18

Colour and eqn of bromide ion precipitate

Answer 18

cream
Ag+ (aq) + Br- (aq) —> AgBr(s)

Question 19

Colour and eqn of iodide ions precipitate

Answer 19

Yellow
Ag+ (aq) + I- (aq) —> AgI(s)

Question 20

How to test for sulfate ions
ion symbol
colour of precipitate
eqn

Answer 20

(SO4)-2
Add dilute nitric acid then baruim nitrate solution
White precipitate forms
Ba+2 (aq) + So4 -2 (aq) —> BaSo4 (s)

Question 21

How to test for sulfite ions
ion symbol
colour change
eqn

Answer 21

SO3)-2
Add acidifed aqueous potassium maganate (VII) = Purple in colour
Solution turns colourless (sulfite gets oxidised)

5SO3 -2 (aq) + 2MnO4- (aq) + 6H+ (aq) —> 5SO4-2 (aq) + 2Mn2+ (aq)

Question 22

How to test for Nitrate ions
ion symbol
eqn

Answer 22

Add a little dilute aqueous sodium hydroxide and then small pieces of aluminium foil

heat gently

If ammonia gas is given out then the solution contains nitrate ions

the nitrate ions are reduced

Question 23

How to test for Carbonate ions
ion symbol
colour change
eqn

Answer 23

Add a little dilute HCl
If the substance bubbles and the gas turns lime water milky white then contains carbonate ions
2H+ (aq) + CO3 -2 (aq) —> CO2 (g) + H20 (l)