WASSCE Chemistry · Paper 1 style

Qualitative analysis

One sample question with the full working. 7 more in the app, with instant feedback and repair sessions for the traps below.

A solution gives a reddish-brown precipitate with sodium hydroxide solution. The cation present is

AFe²⁺
BZn²⁺
CFe³⁺
DCu²⁺

Show the answer and working

Answer: C

Fe(OH)₃ is reddish-brown.

Trap A Mixes up a pair of similar chemical terms: Keep a list of confusable pairs with one defining feature each and a hook. Underline the key word in the stem and check it against the definition, not the sound of the name.

Trap B Picks a related substance or process with a different role: Learn reagents and processes as one-line 'name → job' cards and contrast neighbours in a table (process | product | catalyst | conditions). Match the job in the stem, not just the topic.

Trap D Qualitative analysis errors: NaOH(aq): Cu²⁺ blue ppt; Fe²⁺ green; Fe³⁺ reddish-brown; Zn²⁺ and Al³⁺ white ppt soluble in excess; Ca²⁺ white insoluble. Ag⁺ + Cl⁻ white ppt; Ba²⁺ + SO₄²⁻ white ppt insoluble in HCl. NH₄⁺ + NaOH warmed → NH₃.

Traps in Qualitative analysis

Mixes up a pair of similar chemical terms
Keep a list of confusable pairs with one defining feature each and a hook. Underline the key word in the stem and check it against the definition, not the sound of the name.
Picks a related substance or process with a different role
Learn reagents and processes as one-line 'name → job' cards and contrast neighbours in a table (process | product | catalyst | conditions). Match the job in the stem, not just the topic.
Qualitative analysis errors
NaOH(aq): Cu²⁺ blue ppt; Fe²⁺ green; Fe³⁺ reddish-brown; Zn²⁺ and Al³⁺ white ppt soluble in excess; Ca²⁺ white insoluble. Ag⁺ + Cl⁻ white ppt; Ba²⁺ + SO₄²⁻ white ppt insoluble in HCl. NH₄⁺ + NaOH warmed → NH₃.
Takes one factor as the whole answer
Ask whether the option is necessary or sufficient. If the stem involves two changes or two conditions, both must appear in the answer.
Uses everyday or macroscopic thinking instead of particles
Ask what the particles, ions or electrons are doing. Properties of a substance come from its particles and bonds, not from how it looks or feels.

Practise Qualitative analysis (7 questions)Send to your class on WhatsApp