Formulae, Equations & Calculations

Question 1

How are atomic masses defined?

Answer 1

In terms of a standard atom - the unified atomic mass unit
Mass of a single atom is too small to weigh directly

Question 2

What is the unified atomic mass?

Answer 2

One-twelfth of the mass of a carbon-12 isotope

Question 3

What is the symbol for unified atomic mass?

Answer 3

u

Question 4

What is the relative atomic mass (Ar) of an element?

Answer 4

The average mass of an atom of an element on a scale in which the mass of a carbon-12 atom is 12

Question 5

How is relative atomic mass calculated?

Answer 5

Average mass of an atom divided by one twelfth of the mass of one carbon-12 atom

Question 6

What is relative isotopic mass?

Answer 6

The mass of an atom of an isotope on a scale in which the mass of a carbon-12 atom is 12

Question 7

What are isotopes?

Answer 7

Atoms of the same element with a different number of neutrons

Question 8

How is average relative atomic mass calculated from isotopes?

Answer 8

Atomic mass and percentage abundance multiplied for each isotope
Total is divided by 100

Question 9

What is relative molecular mass (Mr)?

Answer 9

The average mass of a molecule of a molecular compound on a scale in which the mass of a carbon-12 atom is 12

Question 10

How is Mr calculated?

Answer 10

Weighted average mass of molecules is divided by one twelfth of carbon-12 atom

Question 11

How can Mr be found from Ar?

Answer 11

By adding the relative atomic masses (Ar) of all atoms present in molecule

Question 12

What is molecular formula?

Answer 12

Shows the number and type of each atom in molecule

Question 13

What is empirical formula?

Answer 13

Simplest whole number ratio of elements present in one molecule of a compound

Question 14

What is used to calculate empirical formula?

Answer 14

The ratio of masses of each element in compound

Question 15

How is empirical formula calculated?

Answer 15

Calculate the number of moles of each element
Divide the moles of each element by the small number of moles calculated
Convert to whole number ratio

Question 16

How is molecular formula found?

Answer 16

Divide the relative formula mass of molecular formula by relative formula mass of empirical
Multiply number of each element present in empirical formula by this number

Question 17

What do the roman numerals represent for transition elements?

Answer 17

The charge or oxidation state as it may vary

Question 18

What is the formulae for Silver (I)?

Answer 18

Ag⁺

Question 19

What is the formulae for Ammonium?

Answer 19

NH₄⁺

Question 20

What is the formulae for Zinc (II)?

Answer 20

Zn²⁺

Question 21

What is the formulae for Hydroxide?

Answer 21

OH⁻

Question 22

What is the formulae for Nitrate?

Answer 22

NO₃⁻

Question 23

What is the formulae for Sulfate?

Answer 23

SO₄²⁻

Question 24

What is the formulae for Carbonate?

Answer 24

CO₃²⁻

Question 25

What is the formulae for Hydrogen Carbonate?

Answer 25

HCO₃-

Question 26

What is the formulae for Phosphate?

Answer 26

PO₄³⁻

Question 27

What is a symbol equation?

Answer 27

Shorthand used to describe a chemical reaction using chemical symbols to show number and type of each atom in reactants and products

Question 28

What is a word equation?

Answer 28

Longer way of describing a chemical reaction using only words to show reactants and products

Question 29

Name the rules of balancing equations.

Answer 29

Don't change formulae Put numbers used to balance in front of formulae In combustion reactions, balance C then H then O

Question 30

Describe how to balance an equation.

Answer 30

Write formulae of reactants and products Count number of atoms in each reactant and product Balance the atoms one at a time until all are balanced Use appropriate state symbols in equation

Question 31

What is the purpose of state symbols?

Answer 31

To specify the physical state of reactants and products

Question 32

What are the four state symbols?

Answer 32

(s) solid (l) liquid (g) gas (aq) aqueous

Question 33

What happens to ionic compounds in aqueous solutions?

Answer 33

Dissociate into ions

Question 34

What are spectator ions?

Answer 34

The ions in solution that do not take part in chemical reaction

Question 35

What is an ionic equation?

Answer 35

Shows only ions and particles taking part in reaction, not spectator ions

Question 36

What factors mean not all reactants react to form products in a reaction?

Answer 36

Other reactions taking place simultaneously Reaction does not go to completion Reactants or products lost to atmosphere

Question 37

What is percentage yield?

Answer 37

Shows how much of a particular product is formed from reactants compared to theoretical

Question 38

How is percentage yield calculated?

Answer 38

Actual yield divided by theoretical yield

Question 39

What is meant by actual yield?

Answer 39

Number of moles or mass of product obtained experimentally

Question 40

What is meant by predicted yield?

Answer 40

Number of moles or mass of product obtained by calculation

Question 41

How is predicted yield calculated?

Answer 41

Mass of substance divided by molar mass

Question 42

What is the limiting reagent?

Answer 42

Reactant not in excess

Question 43

How can the limiting reagent be determined?

Answer 43

Number of moles of each reactant calculated Ratio of reactants accounted for

Question 44

What is atom economy?

Answer 44

Shows how many atoms used in reaction become desired product

Question 45

How is atom economy calculated?

Answer 45

Molecular mass of desired product divided by sum of molecular masses of all reactants Multiply by 100

Question 46

What atom economy do addition reactions have?

Answer 46

Always 100%

Question 47

What atom economy do reactions with one product have?

Answer 47

Always 100%

Question 48

What does a high atom economy mean?

Answer 48

Efficient and sustainable Uses fewer resources Creates less waste

Question 49

What is water of crystallisation?

Answer 49

When some compounds can form crystals which have water as part of their structure

Question 50

What is a hydrated compound?

Answer 50

A compound that contains water of crystallisation

Question 51

How is water of crystallisation represented in formula?

Answer 51

Separated from main formula by a dot

Question 52

What is an anhydrous compound?

Answer 52

A compound which doesn't contain water of crystallisation

Question 53

What is the degree of hydration?

Answer 53

The amount of water molecules a substance is hydrated by

Question 54

How can degree of hydration be calculated?

Answer 54

Measure mass of hydrated salt Heat salt until constant mass Difference in mass and constant mass can be used to calculate moles