Chemical Tests

Question 1

How do you test for halides in a solution

Answer 1

Add silver nitrate + nitric acid

Question 2

Why add nitric acid when testing for halides within a solution

Answer 2

Remove any carbonates which could react with the halide solutions

Question 3

Sodium nitrate + nitric acid -> halide precipitates

Answer 3

Cl- -> white
Br- -> cream
I- -> yellow

Question 4

Halide in solution precipitates + dilute NH3

Answer 4

AgCl —> soluble (dissolves)
AgBr + AgI —> insoluble

Question 5

Halide in solution precipitates + conc NH3

Answer 5

AgBr —> soluble (dissolves)
AgI —> insoluble

Question 6

How to test for sulphates

Answer 6

Aqueous barium chloride + dilute HCl

Question 7

Why add dilute HCl in test for sulfates

Answer 7

So only the sulfate anion will form as the precipitate

Question 8

Test for sulphates precipitates

Answer 8

SO4^2- —> white
SO3^2- —> white
CO3^2- —> White

Question 9

Test for sulfates precipitates + HCl

Answer 9

BaSO4 —> insoluble
BaSO3 —> dissolves
BaCO3 —> dissolves

Question 10

How to test for solid halide

Answer 10

Add a few drops of conc HCl to the halide

Question 11

Test for solid halide: chloride (observation + inference)

Answer 11

• steamy fumes
• HCl (g)

Question 12

Test for solid halide: Bromide (observation + inference)

Answer 12

• Steamy fumes - HBr
• brown vapour - Br2
• SO2 (colourless)

Question 13

Test for solid halide: iodide (observation + inference)

Answer 13

• steamy fumes - HI
• purple vapour - I2
• black solid - S
• yellow solid
• H2S (colourless)

Question 14

Halide displacement observations - Cl- (+)

Answer 14

Cl2 - no reaction, pale green solution
Br2- no reaction, pale red-brown solution
I2 - no reaction, brown solution

Question 15

Halide displacement observations - Br- (+)

Answer 15

Cl2- red-brown solution, yellow-orange organic layer
Br2- no reaction, pale red-brown solution
I2- no reaction, brown solution

Question 16

Halide displacement observations - I- (+)

Answer 16

Cl2- brown solution, black solid, purple organic layer
Br2- brown solution, black solid, purple organic layer
I2- no reaction, brown solution

Question 17

Difference between I2, Br2 + Cl2 (halide displacement)

Answer 17

Br2 + I2 - add organic solvent such as Hexane, will dissolve in the organic layer

Question 18

If CO2 gas given off when heated what could this be

Answer 18

Group 2 carbonate, lithium carbonate

Question 19

If O2 gas given off when heated what could this be

Answer 19

Group 1 nitrates (except lithium nitrate)

Question 20

If O2 + NO2 gas given off when heated what could this be

Answer 20

Group 2 nitrates or lithium nitrate

Question 21

Chemical tests: shake with bromine water

Answer 21

• yellow solution decolorised- alkene
• yellow solution decolorised + white precipitate form- phenol

Question 22

Chemical tests: warm with aqueous, acidified potassium dichromate (VI)

Answer 22

Colour change orange-green —> primary or secondary alcohol, aldehyde

Question 23

Chemical tests: warm with ethanol + aqueous silver nitrate

Answer 23

• white precipitate- choloralkane
• cream precipitate- bromoalkane
• yellow precipitate- iodoalkane

Question 24

Chemical tests: warm with ethanol + add a few drops of conc H2SO4. Pour into an aqueous solution of sodium carbonate

Answer 24

• ester smell (e.g. glue smell) - carboxylic acid

Question 25

Chemical tests: phosphorus (V) chloride

Answer 25

• produce steamy fumes that turn damp blue litmus paper blue —> OH group In alcohols, carboxylic acids

Question 26

Chemical tests: warm with Tollens reagent

Answer 26

Silver mirror —> aldehyde

Question 27

Chemical tests: heat with Fehlings/Benedict’s reagent

Answer 27

Red precipitate —> aldehyde

Question 28

Chemical tests: 2,4-DNPH

Answer 28

Orange precipitate —> C=O group in aldehydes, ketones

Question 29

Chemical tests: iodine in alkaline solution

Answer 29

Pale yellow precipitate —> methyl ketone or ethanal, methyl secondary alcohol or ethanol