Pakistan MCQs

An excess reactant is supplied beyond the stoichiometric requirement.
Some remains when the reaction is complete.

Compounds have definite formulas and characteristic properties.
Their components can be separated only by chemical means.

Theoretical yield assumes complete reaction and no losses.
It is calculated from the limiting reactant.

Mixture components retain much of their individual identity.
They can often be separated by physical methods.

Actual yield is measured after the experiment.
It is usually lower than theoretical yield.

Solutions are homogeneous mixtures.
Any sampled portion has approximately the same composition.

Percent yield measures reaction and recovery efficiency.
Values below 100% commonly result from losses or incomplete reaction.

Heterogeneous mixtures contain distinguishable regions or phases.
Examples include sand in water and granite.

Molarity is a common concentration unit.
Its value changes with temperature because solution volume can change.

A physical change alters form or state without changing chemical identity.
Ice and liquid water are both H2O.

Molality is based on solvent mass.
It is largely independent of temperature.

Rusting forms new iron oxide substances.
Chemical changes involve rearrangement of atoms and new products.