ECAT MCQs

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

Moles equal particles divided by Avogadro's number.
1.2044×10^24 ÷ 6.022×10^23 = 2 mol.

Carbon contributes about 12 and two oxygens contribute 32.
The total molar mass is about 44 g/mol.

Oxygen contributes 16 of the 18 g/mol formula mass.
16/18×100 ≈ 88.9%.

The coefficients of H2 and H2O are equal.
Thus 4 mol H2 produce 4 mol H2O.

The mole ratio H2:NH3 is 3:2.
6 mol H2×2/3 = 4 mol NH3.

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

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

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

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

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.