Calculations Involving Masses

Question 1

Substance that are made of simple molecules also have a molecular formula. What does the molecular formula represent?

Answer 1

Represents the actual number of atoms in one molecule

Question 2

What is the relative formula mass?

Answer 2

The relative formula mass (Mr), of a substance is the sum of the relative atomic masses (Ar) of all the atoms or ions in its formula

Question 3

How can you find the empirical formula?

Answer 3

The empirical formula can be calculated from the masses of the elements used to make it

Question 4

Go to p73

Answer 4

And look at the empirical formula table

Question 5

How do you work out the relative atomic mass?

Answer 5

(Mass ✖️ atomic number) ✖️ (mass ✖️ atomic number) ➗ 100

Question 6

What the the law of conservation of mass?

Answer 6

When a solute is dissolved in a solvent to make a solution, the mass of the solution is equal to the mass of the solvent and the mass of the solute, the overall mass of the substance does not change.

Question 7

What is concentration?

Answer 7

The amount of solute dissolved in a stated volume of a solution. The units are usually grams per cubic decimetre written as g dm 3. 1 dm3 is the same as 1 litre or 1000 cm3

Question 8

How do you calculate the concentration of a solution?

Answer 8

Concentration = mass of solute in g ➗ volume of solution in dm3

Question 9

In concentration if the solution is given in cm3 what do you need to do?

Answer 9

Convert it to dm3 by dividing by 1000

Question 10

What is closed system?

Answer 10

When substances cannot enter of leave an observed environment

Question 11

What is a non-closed system?

Answer 11

Another term for an open system

Question 12

What happens in all systems?

Answer 12

The mass of the products is always the same as the mass of the reactants

Question 13

Go to page 75

Answer 13

See how to work out the masses of reactants

Question 14

What is the Avogadro constant (or 1 mol)

Answer 14

6.02 ✖️ 10 to the power of 23

Question 15

How do you work out the number of moles in a substance?

Answer 15

Mass of a substance (g) ➗ Ar or Mr

Question 16

What is the limiting reactant?

Answer 16

The amount of product formed determined by the amount of product formed that is not in excess

Question 17

What is the empirical formula?

Answer 17

This is the simplest whole number of ratio of atoms or ions of each element in a substance

Question 18

If you know the mass of each substance in a reaction what can you calculate?

Answer 18

You can calculate the number of moles of each and deduce the balanced equation. The ratio of the moles of each substance is the stoichometry of the reaction

Question 19

Go to page 77

Answer 19

And look at the example

Question 20

What is the stoichometry?

Answer 20

The molar ratio of the reactants and products in a chemical reaction