Ions In Solids And Solutions, Ppt Reactions

Question 1

Name all soluble compounds

Answer 1

• all K+, Na+, NH4+ compounds
• all nitrates (NO3-)
• all sulphates (SO4 2-)
• all Cl-, Br- and I- compounds
• only Na+, K+, NH4+ carbonates (CO3 2-)
• only Na+, K+, NH4+, Sr2+, Ba2+ hydroxides (OH-)

Question 2

Name all insoluble compounds

Answer 2

• only Ca2+, Sr2+, Ba2+, Ag+, Pb2+ sulphates
• only Ag+, Pb2+ when in Cl-, Br-, I- compounds
• all other carbonates
• all other hydroxides

Question 3

Silver nitrate + ammonium chloride

Answer 3

Ppt: Yes, silver chloride

Question 4

Copper (II) sulphate + sodium bromide

Answer 4

Ppt: no

Question 5

Magnesium nitrate + sodium carbonate

Answer 5

Ppt: yes, magnesium carbonate

Question 6

Ammonium hydroxide + potassium carbonate

Answer 6

Ppt: no

Question 7

Zinc sulphate + barium chloride

Answer 7

Ppt: yes, barium sulphate

Question 8

What happens to ionic substances in solution?

Answer 8

Ions separate completely from each other, each becoming surrounded by water molecules. They are said to be hydrated ions
E.g. MgCl2 + (aq) => Mg2+ (aq) + 2Cl- (aq)

Question 9

What happens when 2 soluble ionic compounds are mixed?

Answer 9

A precipitate sometimes forms. This only happens if the combination produces an insoluble product.

Question 10

How do you write an ionic equation for a precipitation reaction?

Answer 10

1. Write the balanced equation
2. Rewrite the equation showing any aqueous ionic substances as separate ions
3. Look for any ions which remain unchanged, these are spectator ions. Rewrite the equation without them.

Question 11

Flame test colours

Answer 11

• Li+: red
• Na+: yellow
• K+: lilac
• Ca2+: orange
• Ba2+: green
• Cu2+: blue/green

Question 12

Adding OH- as a cations test

Answer 12

Transition metals give a coloured ppt
Cu2+: blue ppt of Cu(OH)2
Fe2+: dirty green ppt of Fe(OH)2
Fe3+: foxy brown ppt of Fe(OH)3
Other metal ions will give a white ppt

Question 13

Adding CO3 2- (sodium carbonate)

Answer 13

Most carbonates are insoluble so most metal ions will give a ppt, coloured if it’s a transitions metal, otherwise white.

Question 14

Addition of Pb2+

Answer 14

Give a bright yellow ppt if iodide ions are present, the ppt is PbI2

Question 15

Adding an acid solution (H2SO4) for anion testing

Answer 15

CO3 2- fizzes as CO2 (g) is given. this test must be done first as CO3 2- would give a white ppt in the other 2 tests (AgNO3 and Ba2+) hence confusing the answer

Question 16

Addition of AgNO3 (silver nitrate solution)

Answer 16

Cl-: white ppt of AgCl
Br-: cream ppt of AgBr
I-: yellow ppt of AgI (if Pb2+ added, bright yellow ppt forms)

Question 17

Adding a solution containing Ba2+ ions

Answer 17

SO4 2- gives a white ppt of BaSO4