Relative formula mass Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation

How do you calculate the total relative formula mass on one side of a chemical equation?

Multiply each substance’s $M_r$ by its coefficient, then add the results.

What does conservation of mass imply about the total relative formula masses on the two sides of a balanced equation?

The totals are equal when the coefficients are taken into account.

Why do the total relative formula masses on both sides of a balanced equation match?

The same number of each type of atom is present before and after the reaction.

What does the percentage by mass of an element in a compound represent?

The percentage of the compound’s total relative formula mass contributed by that element.

How do you calculate the percentage by mass of an element in a compound?

$\frac{\text{number of atoms of the element} \times A_r\text{ of the element}}{M_r\text{ of the compound}} \times 100$

How is relative formula mass, $M_r$, calculated from a chemical formula?

Multiply each element’s relative atomic mass by the number of its atoms in the formula, then add the contributions.

What does relative formula mass express about a formula unit?

How heavy it is relative to the atomic mass scale. It is a relative value, not a mass in grams.