Q: What is the difference between relative formula mass (Mr) and relative molecular mass?
A: Relative formula mass refers to ionic compounds; relative molecular mass refers to covalent compounds (but the calculation method is the same).
Q: How do you calculate the relative formula mass (Mr) of a compound?
A: Add together the relative atomic masses (Ar) of all the atoms in the formula
Q: What is the mole (mol)?
A: The unit for the amount of substance; 1 mole = 6.022 × 10²³ particles (Avogadro’s number).
Q: What is the formula linking moles, mass, and Mr?
moles= Mass (g) /mr
Q: What is the formula linking moles, particles, and Avogadro’s number?
A: Number of particles/ 6.022 x 10 to the power of 23
How do you create reacting masses from balancing equations?
- Write a balanced chemical equation.
- Work out the Mr of substances.
- Use moles = mass ÷ Mr to find moles.
- Use mole ratios to find unknowns.
- Convert back to mass if needed.
Q: What is the formula for percentage yield?
A: Percentage yield = actual yield/ theoretical yield x 100
Q: How can the formula of a metal oxide be obtained experimentally?
A: By measuring mass changes when a metal is burned in oxygen or reduced from its oxide.
Q: How can you find the formula of salts with water of crystallisation?
A: Heat to remove water, measure mass before and after, and calculate ratio of water to salt.
Q: What is the empirical formula?
A: The simplest whole-number ratio of atoms in a compound.
Q: What is the molecular formula?
A: The actual number of atoms of each element in a molecule.
Q: How do you calculate the empirical formula from data?
A:
1. Convert mass/percentage to moles.
2. Divide by the smallest number of moles.
3. Write ratio as whole numbers
Q: How do you calculate the molecular formula from the empirical formula?
A:
Molecular formula= Empirical formula x MR (molecular)/ MR( empirical)
Q: How can you find the formula of magnesium oxide experimentally?
A: Burn magnesium in oxygen, measure mass before and after, and calculate ratio of Mg:O.
Q: How can you find the formula of copper(II) oxide experimentally?
A: Reduce copper(II) oxide with hydrogen, measure mass loss (oxygen removed), then find ratio of Cu:O.
Q: What is the molar volume of a gas at rtp?
A: 24 dm³ (24,000 cm³) per mole.
Q: What is the formula linking moles, gas volume, and molar volume?
Moles = volume of gas (dm)/24
or volume of gas (cm) / 24000
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Matter and separating techniques20
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Atomic structure & bonding21
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2.44 test for gasses5
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periodic TABLE22
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periodic table9
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chem gases tests6
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rates of reaction12
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How much?17
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Y10 test One5
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test for ions24
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Test for ions24
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Energetics36
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Energetics19
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Energetics calculations10
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Energetics experiments9
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polyatomic Ions9
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The Models of Matter- Topic 170
