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MS1

- Conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. (2)

MS2

- Mass is conserved by ensuring the total mass of the reactants is equal to the total mass of the products. (1)

- Add coefficients to the substances to balance the number of atoms of each element on both sides. (1)

- Ensure the same number of atoms of each element is present before and after the reaction. (1)

MS3

- Calculate moles of Mg: 10.0 g / 24.3 g/mol = 0.412 mol (1)

- So, 0.412 mol of Mg will produce 2 × 0.412 mol = 0.824 mol of MgO. (1)

- Calculate mass of MgO: 0.824 mol × 40.3 g/mol = 33.2 g (1)

MS4

MS5

- During a change of state, atoms/molecules are not lost or gained. (1)

- The change in state only involves a rearrangement of these particles. (1)

- Therefore, the total mass of the substance remains the same. (1)

MS6

- Calculate moles of Na: 5.0 g / 23.0 g/mol = 0.217 mol (1)

- Calculate moles of Cl2: 5.0 g / 71.0 g/mol = 0.070 mol (1)

- Comparing moles of Na and Cl2: 0.217 / 2 > 0.070 / 1 (1)

- Therefore, Cl2 is the limiting reactant. (1)

MS7

- A compound always contains the same elements in the same proportions by mass. (2)

MS8

- Burning a candle in a closed container:

- Measure the mass of the candle, container, and empty syringe. (1)

- Insert the syringe into the container and attach it to the candle. (1)

- Light the candle and observe the syringe as the reaction proceeds. (1)

MS9

- Calculate moles of Na2CO3: 2.0 g / 106.0 g/mol = 0.0189 mol (1)

- From the balanced equation, 1 mol of Na2CO3 produces 1 mol of CO2. (1)

- Calculate moles of CO2 produced: 0.0189 mol (1)

- Calculate mass of CO2 produced: 0.0189 mol × 44.0 g/mol = 0.832 g (1)

- Calculate percentage loss of mass: (0.832 g / 2.0 g) × 100% = 41.6% (1)

MS10

- To calculate the amount of reactants and products needed in chemical processes. (1)

- To monitor chemical reactions and ensure efficiency. (1)

- To prevent waste and optimise production. (1)