3.1 Quantitative chemistry (Combined)
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What is the law of conservation of mass?
The law of conservation of mass states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
Write a balanced equation of magnesium reacting with hydrochloric acid.
Mg + 2 HCl → MgCl2 + H2
Define relative atomic mass and relative formula mass.
Relative atomic mass - average mass of atoms in an element taking into account masses and abundance of its isotopes, relative to Carbon-12. Relative formula mass - sum of the relative atomic mass of all atoms in the formula.
What is the relative formula mass of: CaF2 Ca = 40 F = 19
78
What is the relative formula mass of: C6H12O6 C = 12 H = 1 O = 16
180
The following reaction occurs in a test tube under a Bunsen Burner: 4 MgO(s) + CH4(g) → 4 Mg(s) + 2H2O(g) + CO2(g) The carbon dioxide and water escape from the test tube. Use the equation to explain why.
They are both gases
Suggest how you could increase the precision of results.
Measure to more decimal places or use a more sensitive balance / apparatus
What is Avogadro’s constant? (Higher)
The number of atoms, molecules or ions in a mole of a given substance. The value of the constant is 6.02 x 10^23
What is the formula that links mass, molecular mass and moles together? (Higher)
Mass = Mr x Moles
What is the mass of 20 moles of calcium carbonate, CaCO3 (Mr is 100)?
2000g
State what is meant by a limiting reactant in a chemical reaction. (Higher)
In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactants are used. The reactant that is completely used up is called the limiting reactant because it limits the amount of products.
Write down the two formulae that link concentration, mass and volume together.
Concentration (g per dm3) = Mass (g)/Volume (dm3) Concentration (mol per dm3) = no of moles/volume (dm3)
What is the molar volume of a gas at room temperature and pressure?
1 mole of a gas at room temperature and pressure occupies 24 dm3