Tests

Question 1

Halide ions (Cl-, Br-, I-)

Answer 1

a) acidify with dilute HNO3
b) add AgNO3
c) add dilute NH3, then add concentrated NH3
Results:
a) Cl- = white precipitate (dissolves in dilute NH3)
b) Br- = cream precipitate (dissolves in concentrated NH3, not in dilute)
c) I- = yellow precipitate (insoluble in concentrated NH3)

Question 2

SO4^2-

Answer 2

a) acidify with dilute HCl
b) add BaCl
Result
White precipitate of BaSO4

Question 3

CO3^2-

Answer 3

a) add dilute HCl
Result
Effervescence as gas produced turns limewater cloudy (CO2)

Question 4

OH-

Answer 4

a) damp red litmus paper
Result
Turns from red to blue

Question 5

Mg2+

Answer 5

a) add dilute NaOH
b) add dilute H2SO4
Result
a) with OH- = white precipitate
b) with SO4^2- = nvc

Question 6

Flame tests - metal ions

Answer 6

Ca2+ = brick-red / orange-red
Sr2+ = red
Ba2+ = green
Li+ = red
Na+ = yellow
K+ = lilac
Cu2+ = blue-green

Question 7

NH4+

Answer 7

a) add NaOH
b) heat sample
c) hold damp red litmus paper at red tube mouth
Result:
Red to blue

Question 8

Co2+

Answer 8

a) add NH3 drops to excess
b) or add Cl- ions
Results:
Pink to blue green precipitate
Straw-yellow solution
Or pink to blue solution

Question 9

Cu2+ (pale blue solution)

Answer 9

a) Add dilute NaOH = pale blue precipitate
b) add excess NaOH = nvc
c) add dilute NH3 = pale blue precipitate
d) add conc. NH3 = dark blue solution
e) add Na2CO3 = green-blue precipitate
f) add NaCl = yellow solution

Question 10

Fe2+ (green solution)

Answer 10

a) Add dilute NaOH = green precipitate
b) add excess NaOH = nvc
c) add dilute NH3 = green precipitate
d) add conc. NH3 = nvc
e) add Na2CO3 = green precipitate

Question 11

Fe3+ (violet/brown/yellow solution)

Answer 11

a) Add dilute NaOH = orange-brown precipitate
b) add excess NaOH = nvc
c) add dilute NH3 = orange-brown precipitate
d) add conc. NH3 = nvc
e) add Na2CO3 = orange-brown precipitate and effervescence
f) add NaCl = yellow solution

Question 12

Al3+ (colourless solution)

Answer 12

a) Add dilute NaOH = white precipitate
b) add excess NaOH = precipitate dissolves —> colourless solution
c) add dilute NH3 = white precipitate
d) add conc. NH3 = nvc
e) add Na2CO3 = white precipitate and effervescence

Question 13

Alkene
-C=C-

Answer 13

• Shake with bromine water
  Result:
  Solution changes colour from orange to colourless

Question 14

Halogenoalkane

Answer 14

a) add NaOH(aq) and warm
b) acidify with HNO3
c) add AgNO3(aq)
Results:
- AgCl = white precipitate
- AgBr = cream precipitate
- AgI = yellow precipitate

Question 15

Alcohol

Answer 15

Primary & Secondary Alcohol:
a) add acidified potassium dichromate (VI) - K2Cr2O7
Result: orange to green

Tertiary Alcohol:
b) add acidified potassium dichromate (VI) - K2Cr2O7
Result: stays orange

Question 16

Alcohol

Answer 16

Primary, Secondary & Tertiary
a) add metallic Na

Result:
Effervescence

Question 17

Aldehyde
R-CHO

Answer 17

a) warm with Fehling’s solution (contains Cu2+ ions)
Result: Orange-red precipitate forms, so solution turns from BLUE —> RED

b) warm with Tollens’ reagent (AgNO3 + NaOH + dilute NH3)
Result: silver precipitate (mirror) forms

• Note: Ketones don’t react with either

Question 18

Carboxylic Acid
R-COOH

Answer 18

a) add a carbonate, e.g. Na2CO3 or NaHCO3
Result: CO2 released - will turn limewater cloudy