PIEAS Chemistry MCQs

Mass percent expresses composition on a mass basis.
All component mass percentages sum to 100%.

Mole ratios convert amounts of one substance into another.
They come directly from the balanced equation.

Chemical reactions rearrange atoms but do not create or destroy them.
Therefore total mass remains constant in a closed system.

A pure compound has constant composition.
This is also called the law of constant composition.

Percent composition is calculated from formula mass contributions.
The element percentages sum to approximately 100%.

Stoichiometry uses balanced equations to relate amounts.
It supports mass, mole, particle, and gas calculations.

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.

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.