Question

An experiment is conducted in two steps. In step 1, a black solid compound is heated in a test

tube. The reaction produces a colourless gas that re-lights a glowing splint. Remaining in the

bottom of the test tube is a reddish-brown coloured solid metal. In step 2, the metal resulting

from step 1 is added to a tube of hydrochloric acid, and no reaction is observed.

a. Name the gas produced in step 1.

b. What type of reaction occurred in step 1? Provide a piece of evidence from the experiment

to support your answer.

Write the complete equation of the chemical reaction that occurred in step 1 only. Include

state symbols. Assume the cation in the reactants has the higher of its two possible charges.

Answer 1

a) Oxygen

b) Thermal decomposition.

Thermal decomposition is the process where two or more products form from a single reactant upon heating the reactant.

Copper(ii) oxide forms:

$O_2$ Which relights a glowing splint

and copper metal ( a reddish brown solid which do not react with HCl)

$2CuO_s\>\underrightarrow{heat}\>2Cu_s+O_{2(g)}$