WASSCE Chemistry · Paper 1 style

Chemical change

One sample question with the full working. 1 more in the app, with instant feedback and repair sessions for the traps below.

Which of the following is a chemical change?

Amelting ice
Bdissolving salt
Cboiling water
Dburning paper

Show the answer and working

Answer: D

New substance formed = chemical change.

Trap A Confuses elements, compounds and mixtures: Element: one kind of atom. Compound: elements chemically combined in fixed proportions, new properties (water, NaCl). Mixture: components not chemically combined, variable composition, separable physically (air, sea water, brass).

Trap B Reverses a trend, direction or effect: State the rule with its direction before looking at the options (down group 1 reactivity INCREASES; exothermic forward reaction: heating shifts LEFT). An option that is the mirror image of the rule is the trap.

Trap C 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.

Traps in Chemical change

Confuses elements, compounds and mixtures
Element: one kind of atom. Compound: elements chemically combined in fixed proportions, new properties (water, NaCl). Mixture: components not chemically combined, variable composition, separable physically (air, sea water, brass).
Reverses a trend, direction or effect
State the rule with its direction before looking at the options (down group 1 reactivity INCREASES; exothermic forward reaction: heating shifts LEFT). An option that is the mirror image of the rule is the trap.
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.

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