Qualitative analysis

Question 1

Reagent for carbonate test

Answer 1

Any acid

Question 2

Products for carbonate test with acid

Answer 2

Carbon dioxide and water

Question 3

Observation for carbonate test

Answer 3

Effervesence (CO2(g))

Question 4

To confirm the gas is carbon dioxide…

Answer 4

…bubble through limewater.

Question 5

What is limewater?

Answer 5

A saturated solution of calcium hydroxide, Ca(OH)2(aq).

Question 6

Carbon dioxide and limewater reaction products

Answer 6

White precipitate of calcium carbonate (CaCO3)

Question 7

BaSO4 in water is very…

Answer 7

…insoluble.

Question 8

Reagent used in sulfate test

Answer 8

Soluble barium compound, e.g; Ba(NO3)2(aq)

Question 9

Reagent for halide test

Answer 9

Acidified silver nitrate solution: AgNO3(aq)

Question 10

Ionic equ between chloride and silver nitrate

Answer 10

Ag+(aq) + Cl-(aq) …. AgCl(s)

Question 11

Colour of precipitate for chloride and silver nitrate reaction

Answer 11

White

Question 12

Solubility of AgCl(s) in NH3(aq)

Answer 12

Soluble in dilute NH3(aq)

Question 13

Ionic equ between bromide and silver nitrate

Answer 13

Ag+(aq) + Br-(aq) …. AgBr(s)

Question 14

Colour of precipitate for bromide and silver nitrate reaction

Answer 14

Cream

Question 15

Solubility of AgBr(s) in NH3(aq)

Answer 15

Soluble in concentrated NH3(aq)

Question 16

Ionic equ between iodide and silver nitrate

Answer 16

Ag+(aq) + I-(aq) …. AgI(s)

Question 17

Colour of precipitate for iodide and silver nitrate reaction

Answer 17

Yellow

Question 18

Solubility of AgI(s) in NH3(aq)

Answer 18

Insoluble on concentrated NH3(aq)

Question 19

Sequence of tests

Answer 19

1. Carbonate test: CO3^2-
2. Sulfate test: SO4^2-
3. Halide test: Cl-, Br-, I-

Question 20

Only carbonate produce…

Answer 20

…bubbles of gas wen an acid is added.

Question 21

What is expected when Ba^2+(aq) ions are added?

Answer 21

A white precipitate of barium sulfate will form, if SO4^2(aq) ions are present.

Question 22

Describe a false positive for the sulfate test

Answer 22

If carbonate ions are present, a white precipitate of barium carbonate, BaCO3(s), will form as it is also soluble. This is a flase positive.

Question 23

What is expected when Ag+(aq) are added to a halide solution?

Answer 23

A precipitate of a silver halide is expected.

Question 24

What happens if a carbonate or sulfate are present in a halide test?

Answer 24

A precipitate will be seen as CO3^2- and SO4^2- are also insoluble.

Question 25

Describe the carbonate test

Answer 25

Add any acid until effervesence stops. Effervesence shows carbonate present. Adding the acid to excess removes the carbonate prior to the sulfate test.

Question 26

Why is acid added in excess during the carbonate test?

Answer 26

To remove all the carbonate prior to the sulfate test.

Question 27

Describe the sulfate test

Answer 27

Add barium nitrate,. Any white precipitate formed (indicating the presence of a sulfate) should be removed via filtration.

Question 28

Describe the halide test

Answer 28

Add silver nitrate solution. A precipitate will form if a halide is present. Add ammonia solution to confirm which halide it is.

Question 29

Reagent to test for ammonium- NH4+

Answer 29

Sodium hydroxide, NaOH(aq)

Question 30

Describe the test for identifying ammonium

Answer 30

Heat aqueous ammonium ions and aqueous hydroxide ions together as they will react to form ammonia gas, NH3(g).

Question 31

Obs for ammonium test

Answer 31

Ammonia gas is produced which turns damp red litmus paper blue.

Question 32

Ionic equ for ammonium test

Answer 32

NH4+(aq) + OH-(aq) .... NH3(g) + H2O(l)

Question 33

Colour of copper II (Cu2+) solution

Answer 33

Blue

Question 34

Colour and formula of copper II (Cu2+) precipitate

Answer 34

Light blue Cu(OH)2(s)

Question 35

Colour of iron III (Fe3+) solution

Answer 35

Pale yellow (pale violet)

Question 36

Colour and formula of Fe3+ precipitate

Answer 36

Rusty brown Fe(OH)3(s)

Question 37

Colour of iron II Fe2+ solution

Answer 37

Pale green

Question 38

Colour and formula of Fe2+ precipitate

Answer 38

Green, goes orange/brown when exposed to air. Fe(OH)2(s) / Fe(OH)3(s)

Question 39

Colour of maganese II Mn2+ solution

Answer 39

Very pale pink, virtually colourless

Question 40

Colour and formula of Mn2+ precipitate

Answer 40

Pale brown. Surface darkens on exposure to air. Mn(OH)2(s) / Mn(OH)3(s)

Question 41

Colour of chromium III Cr3+ solution

Answer 41

Green

Question 42

Colour and formula of Cr3+ precipitate

Answer 42

Green/grey. Dissolves in excess to form green solution. Cr(OH)3(s) / [Cr(OH)6]^3-(aq)