Mole Concept

Question 1

What is the method to calculating the mass of the product when given the mass of the reactant or the mass of the reactant when given the mass of a product for a reaction?

Answer 1

1. Firstly, write the equation of the reaction.
2. Balance the equation + add state symbols
3. Calculate the molar mass of the substance that you were given the mass of.
4. Take the mass divide by molar mass to find the number of mole for that substance.
5. Derive the ratio of the reactant to the product/product to the reactant. Find the number of mole for the product/reactant.
6. Calculate the molar mass of the product/reactant.
7. Multiply the molar mass and the the number of mole to derive the mass of the product/reactant that you were asked to find.

Question 2

What are two important facts about any chemical equations?

Answer 2

1. All the atoms present in the reactants are also present in the products.
2. A balanced equation shows the number of molecules, atoms or ions taking part in the reaction.

These facts allow the masses of substances involved in reactions to be calculated.

Question 3

The molar mass of a substance is numerically the same as the relative atomic or molecular mass of the substance but ______________________.

Answer 3

with the unit g mol to the power of -1.

Question 4

To calculate the percentage purity of a substance, we must keep in mind not to ________________

Answer 4

we must keep in mind not to convert the mass/volume of the impure substance into number of moles

Question 5

To calculate the percentage yield of a reaction, we need to work out the expected yield using ________.

Answer 5

mole ratio.

Question 6

When will percentage yield matter more?

Answer 6

In a factory that produces fertilisers, percentage yield matters more than percentage purity because one will want the highest quantity for the lowest cost

Question 7

When will percentage purity matter more?

Answer 7

In a pharmaceutical firm, percentage purity will matter more than percentage yield as the impurities may harm the people using the drug.