What is one mole of a substance?

The amount that contains 6.02 × 10²³ particles of that substance.

How do you calculate relative formula mass, Mr?

Add the relative atomic masses of all the atoms in the formula.

How do you find the number of particles from moles?

Multiply the moles by 6.02 × 10²³.

What units does Mr have?

None: it is a ratio, a relative mass.

How many atoms are in 1 mol of O₂ molecules?

2 × 6.02 × 10²³ = 1.20 × 10²⁴ atoms, because each molecule has two atoms.

How do you deal with brackets when finding Mr of Ca(OH)₂?

Multiply everything inside the bracket by the number outside: 40 + 2 × (16 + 1) = 74.

Relative formula mass and the moleIB MYP Chemistry: Flashcards

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What is the Avogadro constant?

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What is the Avogadro constant?: 6.02 × 10²³ particles per mole.
What is one mole of a substance?: The amount that contains 6.02 × 10²³ particles of that substance.
How do you calculate relative formula mass, Mr?: Add the relative atomic masses of all the atoms in the formula.
What is the Mr of water, H₂O?: 18 (2 × 1 + 16).
What is the Mr of CaCO₃?: 100 (40 + 12 + 3 × 16).
What is the equation linking moles, mass and Mr?: moles = mass ÷ Mr.
How do you find the mass from moles?: mass = moles × Mr.
How do you find the number of particles from moles?: Multiply the moles by 6.02 × 10²³.
What units does Mr have?: None: it is a ratio, a relative mass.
What is the mass of one mole of a substance equal to?: Its Mr in grams.
How many atoms are in 1 mol of O₂ molecules?: 2 × 6.02 × 10²³ = 1.20 × 10²⁴ atoms, because each molecule has two atoms.
How do you deal with brackets when finding Mr of Ca(OH)₂?: Multiply everything inside the bracket by the number outside: 40 + 2 × (16 + 1) = 74.
How many moles are in 36 g of water?: 2.0 mol (36 ÷ 18).

Exam questions on Relative formula mass and the mole

A cement works in Turkey heats limestone, which is mostly calcium carbonate, CaCO₃. A chemist at the works calculates the amounts of substances being used. Relative atomic masses: Ca = 40, C = 12, O = 16.
Calculate the mass of 3.0 mol of calcium carbonate.2 marks
A sports drink company in Australia lists glucose, C₆H₁₂O₆, as an ingredient and also uses large amounts of water, H₂O. Chemists count particles in moles. The Avogadro constant is 6.02 × 10²³ per mole. Relative atomic masses: H = 1, C = 12, O = 16.
Calculate the relative formula mass (Mr) of glucose.2 marks
A teacher gives students samples of four substances and asks them to weigh out one mole of each. The students record the mass of one mole: water, H₂O, 18 g; sodium chloride, NaCl, 58.5 g; magnesium oxide, MgO, 40 g; calcium carbonate, CaCO₃, 100 g. Relative atomic masses: H = 1, C = 12, O = 16, Na = 23, Mg = 24, Cl = 35.5, Ca = 40.
Describe the pattern in the data, verify it using one of the substances, and state a general rule.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).