Relative Masses and MolesAQA GCSE Chemistry: Flashcards

Card 1 of 120 of 12 known

Question

What is relative formula mass (Mr)?

Tap or press Space to reveal

Tap card or press Space to flip

See all 12 cards

What is relative formula mass (Mr)?: The sum of the relative atomic masses of all the atoms shown in a compound's formula.
Calculate the Mr of CO2 (Ar: C=12, O=16).: 12 + (16 × 2) = 44
Calculate the Mr of H2O (Ar: H=1, O=16).: (1 × 2) + 16 = 18
What is a mole?: The unit used to measure the amount of a substance; one mole contains 6.02 × 10²³ particles.
What is the Avogadro constant?: 6.02 × 10²³ particles per mole.
How is the mass of one mole of a substance related to its Mr?: The mass of one mole, in grams, is numerically equal to the substance's relative formula mass.
Write the formula linking moles, mass and Mr.: Moles = mass (g) ÷ Mr
How many moles are in 22 g of CO2 (Mr = 44)?: 22 ÷ 44 = 0.5 mol
What is the mass of 2 moles of CO2 (Mr = 44)?: 2 × 44 = 88 g
How do you find the mass of a product from the mass of a reactant using a balanced equation?: Convert the reactant's mass to moles, use the equation's mole ratio to find the product's moles, then convert back to mass using its Mr.
Why must you convert to moles rather than working directly with masses when using a balanced equation?: Because the balancing numbers in an equation represent ratios of moles (particles), not ratios of mass.
How can masses of reactants and products be used to help balance an equation?: Convert the given masses to moles, then find the simple whole number ratio between them to determine the balancing numbers.