Pakistan MCQs

A molecular formula is a whole-number multiple of the empirical formula.
It applies to substances composed of discrete molecules.

Balancing follows conservation of atoms and mass.
Coefficients change amounts, not chemical formulas.

Equation coefficients give stoichiometric ratios.
They may be interpreted as molecule or mole ratios.

Once the limiting reactant is used up, no more product can form.
Other reactants may remain in excess.

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

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

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

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

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.

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

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