Pakistan MCQs

Percent yield is actual divided by theoretical times 100.
8/10×100 = 80%.

Molarity equals moles divided by liters of solution.
0.50/2.0 = 0.25 M.

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.

Moles equal mass divided by molar mass.
18 g ÷ 18 g/mol = 1 mol.

Mass equals moles multiplied by molar mass.
2×58.5 = 117 g.

Particles equal moles times Avogadro's number.
0.5×6.022×10^23 = 3.011×10^23 molecules.

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

An element cannot be broken down chemically into simpler substances.
Each element is identified by its atomic number.