Calculations

Question 1

What is the relative atomic mass also known as?

Answer 1

Ar

Question 2

What does relative atomic mass represent?

Answer 2

The weighted average mass of an atom, taking into account the abundance of all the isotopes of that element.

Question 3

How is relative atomic mass calculated?

Answer 3

Relative atomic mass = (mass of 1st isotope x abundance) + (mass of 2nd isotope x abundance) / Total abundance of isotopes

Question 4

What is another name for relative formula mass?

Answer 4

Mr

Question 5

How is relative formula mass calculated?

Answer 5

Relative formula mass = sum of all the Ars (listed on periodic table) of the atoms in the formula.

Question 6

What is the relationship between total Mrs on both sides of a chemical equation?

Answer 6

Total Mrs on both sides of the equation are the same.

Question 7

What does percentage composition of an element in a formula allow us to determine?

Answer 7

How much of a certain element is present in a formula unit by mass.

Question 8

How is the percentage composition of an element in a compound calculated?

Answer 8

Percentage composition = (Sum of the A of a particular element / M of compound) x 100%

Question 9

What is the definition of one mole?

Answer 9

One mole is the amount of substance which contains 6.02 x 10^23 particles.

Question 10

How do you calculate moles?

Answer 10

Moles = Mass in grams / Mr

Question 11

What is the mass in grams of one mole of atoms or molecules equal to?

Answer 11

The relative formula mass (Ar or Mr).

Question 12

What can be calculated from balanced symbol equations?

Answer 12

The masses of reactants and products.

Question 13

What do the balancing numbers in a chemical equation represent?

Answer 13

The ratios of moles of the substances.

Question 14

What is the first step in reacting masses calculations?

Answer 14

Use the given mass of the substance and its M to work out its moles.

Question 15

How do you determine the moles of other substances in a reaction?

Answer 15

Using the mole ratio / balancing numbers.

Question 16

What is necessary to work out the mass in grams of other substances?

Answer 16

Using their Mr.

Question 17

What can be determined if the masses of the reactants and products are known?

Answer 17

The chemical equation with balancing numbers.

Question 18

What is the first step to balance an equation using moles?

Answer 18

Calculate the moles of each substance using the mass and Mr.

Question 19

How do you write the ratios for balancing the equation?

Answer 19

Write these in a ratio.

Question 20

What should you do to get whole number ratios?

Answer 20

Divide all the numbers in the ratio by the smallest number.

Question 21

True or False: Total relative formula mass is always conserved in a chemical reaction.

Answer 21

True

Question 22

What is the empirical formula?

Answer 22

The simplest whole number ratio of the elements in a compound

It is determined by calculating the moles of each element and dividing by the smallest number of moles.

Question 23

How can you determine the empirical formula from a mole ratio?

Answer 23

Divide the mole ratio by the smallest number

For example, magnesium chloride has a mole ratio of 1:2, resulting in the formula MgCl.

Question 24

What is the volume occupied by 1 mole of any gas at room temperature and pressure?

Answer 24

24 dm³ or 24,000 cm³

This is a standard volume for gases under these conditions.

Question 25

How do you calculate gas volume in dm³?

Answer 25

Gas volume (dm³) = moles x 24 dm³ ## Footnote This formula is used for calculating the volume occupied by a given number of moles of gas.

Question 26

What is the formula to calculate percentage yield?

Answer 26

Percentage yield = (actual yield / theoretical yield) x 100% ## Footnote This calculation helps to evaluate the efficiency of a chemical reaction.

Question 27

What factors can prevent achieving 100% yield in practice?

Answer 27

Side reactions, incomplete reactions, transfer losses ## Footnote These factors can lead to discrepancies between actual and theoretical yields.

Question 28

What is atom economy?

Answer 28

Atom economy = (sum of Mₘ of useful products / sum of Mₘ of all reactants) x 100% ## Footnote It measures the efficiency of a reaction in terms of the amount of useful products generated.

Question 29

When does a reaction have 100% atom economy?

Answer 29

When there is only one product ## Footnote This indicates that all reactants are converted into the desired product without waste.

Question 30

Why is higher atom economy beneficial?

Answer 30

It leads to better profits and sustainability by using fewer natural resources and creating less waste ## Footnote More product made means more money can be made from the same raw materials.

Question 31

What is a limiting reactant?

Answer 31

The reactant in a chemical reaction that is completely consumed first ## Footnote It determines the amount of product formed in the reaction.

Question 32

True or False: Equal numbers of moles of any gas occupy different volumes at room temperature and pressure.

Answer 32

False ## Footnote Equal moles of gases occupy the same volume under these conditions.

Question 33

What is the reactant that is completely used up in a chemical reaction called?

Answer 33

Limiting reactant ## Footnote The limiting reactant limits any further products being made when it is used up.

Question 34

What is the term for the reactant that is not fully used up in a chemical reaction?

Answer 34

Reactant in excess ## Footnote This reactant remains after the reaction has completed.

Question 35

What are the steps to determine the limiting reactant?

Answer 35

1. Work out how many moles there are of each reactant. 2. Consider the balancing numbers to identify the limiting reactant.

Question 36

To calculate the amount of product formed in a reaction, which reactant's moles should be used?

Answer 36

Moles of the limiting reactant ## Footnote The amount of product depends on the limiting reactant.

Question 37

Fill in the blank: The limiting reactant is important because it _______ any further products being made.

Answer 37

limits

Question 38

True or False: The reactant in excess is used up completely during the reaction.

Answer 38

False ## Footnote The reactant in excess is not fully used up.