Limiting reactants | Starter Quiz | Oak National Academy

Match the following terms to the correct definition.

• relative atomic mass

• the average mass of the atoms of an element compared to carbon-12

• relative formula mass

• the sum of the relative atomic masses of all the atoms in a formula

• Avogadro's constant

• the number of particles in one mole of a substance

Answer explanation

The relative atomic mass compares atoms to a twelfth of carbon-12, this is because atoms are so small it is easier to compare them to each other, than give their actual mass.

The formula for ammonium nitrate is NH₄NO₃. Which of the following ratios are correct?

• The ratio of nitrogen to oxygen is 2 : 3.

• The ratio of nitrogen to hydrogen is 1 : 2.

• The ratio of oxygen to hydrogen is 3 : 4.

• The ratio of oxygen to nitrogen is 2 : 3.

Answer explanation

Ratios are used to compare two or more quantities. The ratio needs to be written in the same order as in statement, with the : representing 'to'. For example, the ratio of hydrogen to oxygen would be written hydrogen : oxygen or 4 : 3.

Chemical equations represent how the atoms in the ___ rearrange to form the products.

Answer explanation

No atoms are created or destroyed during a chemical reaction. The atoms in the reactants are rearranged to form the products of the reaction.

Which of the following is the equation which links mass, relative formula mass and amount of substance?

• mass = amount of substance × relative formula mass

• mass = amount of substance ÷ relative formula mass

• amount of substance = relative formula mass × mass

• amount of substance = relative formula mass ÷ mass

Answer explanation

The mass of a substance is equal to the product of the amount of substance in moles and the relative formula mass of the substance.

True of false? The following equation is balanced: C₂H₄ + 2O₂ → 2CO₂ + 2H₂O.

• true

• false

Answer explanation

In the equation the products contain 6 oxygen atoms, but the reactants only contain 4. The correct balanced chemical equation for the reaction is: C₂H₄ + 3O₂ → 2CO₂ + 2H₂O.

Calculate the relative formula mass for calcium carbonate, CaCO₃. Relative atomic masses: Ca = 40; C = 12; O = 16.

Answer explanation

RFM = 40 + 12 + (3 × 16) = 100