C4 Chemical Calculations

Question 1

Why some elements have same relative mass as each other

Answer 1

Although the number of protons in the nucleus is the same for all atoms of the same element, the number of neutrons is not

Question 2

Why some relative atomic masses may not be a whole number

Answer 2

Due to existence of isotopes having different mass numbers

Question 3

Unit for amount of substance

Answer 3

Mole

Question 4

Why chemical equations must be balanced

Answer 4

So it follows the law of conservation of mass

Question 5

The effect of a limiting reactant on the amount of product made

Answer 5

Limits how much product can be formed

Question 6

Limiting reactant

Answer 6

The reactant that gets consumed first in a chemical reaction

Question 7

Theoretical yield

Answer 7

The maximum possible mass of a product that can be made in a chemical reaction

Question 8

Actual yield

Answer 8

The actual mass of a product made in a chemical reaction

Question 9

Percentage yield

Answer 9

(Actual yield ➗ theoretical yield) x 100

Question 10

Why actual yield is often lower than theoretical yield

Answer 10

Some of the reactants do not react to form the product

Question 11

Why percentage yield can never be over 100%

Answer 11

Incomplete reactions, some of reactants don’t react to form the product

Question 12

How to calculate formula mass

Answer 12

Add masses of all atoms

Question 13

Atom economy

Answer 13

A measure of efficiency of a chemical reaction

Question 14

How to calculate atom economy

Answer 14

total number of atoms in the desired product
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 total number of atoms in all the reactants

Question 15

Covalent bond

Answer 15

Chemical bond that involves sharing of electrons to form electron pairs between atoms

Question 16

Covalent

Answer 16

2 or more non-metals

Question 17

Ionic

Answer 17

When a metal reacts with non-metal

Question 18

Why using reactions with high atom economy is important

Answer 18

Uses fewer natural resources

Produce less waste

Better for environment

Question 19

Why the sum of the formula masses of the reactants is the same as the sum of the formula masses of the product

Answer 19

All atoms making up the reactants are still in the products

Question 20

How concentration of solution can be changed

Answer 20

Increasing amount of solute

Question 21

How to calculate concentration of solution

Answer 21

Mass ➗ volume of solution

Question 22

How to calculate a titre

Answer 22

Values added together divide number of readings that were taken

Question 23

Use of pipette for titration

Answer 23

To accurately measure a fixed volume of liquid

Question 24

How an indicator can be used to determine the end point

Answer 24

Helps us spot the equivalence point in an acid-base titration

Question 25

How precise results are obtained in a titration

Answer 25

Relies on accurate volume measurement

Question 26

How accuracy can be improved in a titration

Answer 26

Calibrate your electrode regularly

Question 27

Use of an indicator in an acid-base titration

Answer 27

To signal the end of a titration

Question 28

How the volume of gas would change when temperature was changed

Answer 28

Volume increases as temperature increases

Molecules of gas have more kinetic energy