Relative Mass and Amount of Substance

Question 1

What is Ar?

Answer 1

Relative atomic mass

Question 2

What does Ar use?

Answer 2

Elements only

Question 3

Define relative atomic mass

Answer 3

The average mass of an element relative to one twelth of the mass of an atom of carbon-12

Question 4

What is carbon-12 used in Ar?

Answer 4

It is highly abundant and the twelve has very little rounding therefore it is highly accurate

Question 5

What are isotopes?

Answer 5

Atoms with the same number of protons but a different number of neutrons

Question 6

How is Ar calculated?

Answer 6

The sum of (the individual mass of each isotope multiplied by their percentage abundance) divided by the sum of the percentage abundances

Question 7

What are the units for Ar?

Answer 7

grams per mol

Question 8

Define relative molecular mass

Answer 8

The mass of a molecule relative to one twelfth the mass of an atom of carbon-12

Question 9

What is Mr used for?

Answer 9

Simple covalent molecules and diatomic molecules

Question 10

What are the Mr units?

Answer 10

Grams per mole

Question 11

How is Mr calculated?

Answer 11

It is the sum of the Ar values of the elements in the molecule

Question 12

What is the relative formula mass?

Answer 12

The mass of the formula, relative to one twelfth the mass of an atom of carbon-12

Question 13

What is RFM used for?

Answer 13

Giant ionic compounds (salts)

Question 14

What is the mole?

Answer 14

A measure of an amount of a substance and the number of atoms in 12g of carbon - 12

Question 15

What is Avogadros constant

Answer 15

6.02 x 10^23 molecules or atoms in one moles

Question 16

How do you calculate the number of moles?

Answer 16

Number of atoms/molecules divided by avogadros constant

Question 17

How do you calculate the number of atoms or molecules?

Answer 17

The number of moles x avogadros constant

Question 18

How do you calculate avogadros constant?

Answer 18

The number of atoms or molecules divided by the number of moles

Question 19

What is molar mass?

Answer 19

Ar/Mr and RFM

Question 20

What are the molar mass units?

Answer 20

Grams per mole

Question 21

How do you calculate the number of moles?

Answer 21

Mass (g) divided by molar mass

Question 22

What is the water of crystallisation?

Answer 22

The amount of water relative to one mole of salt

Question 23

How is the water of crystallisation calculated?

Answer 23

Find the number of moles of salt and water and divide by the smallest to give the ratio

Question 24

What are the units of concentration?

Answer 24

Mol.dm^-3

Question 25

What are the units of volume?

Answer 25

dm^-3

Question 26

How do you convert between cm and dm?

Answer 26

- Divide cm by 1000 to give dm- 1 dm = 1000 cm

Question 27

What is the equation for the mole and solutions?

Answer 27

Number of moles = Concentration x Volume

Question 28

How many dm^3 does 1 mole of gas occupy?

Answer 28

24

Question 29

How many cm^3 does 1 mole of gas occupy?

Answer 29

24000

Question 30

How can volume of gas be calculated?

Answer 30

Volume of gas (dm^3) = moles x 24 (dm^3)

Question 31

What are the key assumptions the ideal gas equation makes?

Answer 31

- No IMF between gas molecules- Volume occupied by gas molecules is negligible

Question 32

What is the ideal gas equation?

Answer 32

Pv=nRT

Question 33

In the idea gas equation, what is p?

Answer 33

Pressure

Question 34

In the idea gas equation, what is v?

Answer 34

Volume

Question 35

In the idea gas equation, what is n?

Answer 35

Moles

Question 36

In the idea gas equation, what is r?

Answer 36

Ideal gas constant

Question 37

In the idea gas equation, what is t?

Answer 37

Temperature

Question 38

In the idea gas equation, what are the units of p?

Answer 38

pa or nm^-2

Question 39

In the idea gas equation, what are the units of v?

Answer 39

m^3

Question 40

In the idea gas equation, what are the units of n?

Answer 40

There are none

Question 41

In the idea gas equation, what are the units of r?

Answer 41

J.K^-1.Mol^-1

Question 42

In the idea gas equation, what are the units of t?

Answer 42

Kelvin

Question 43

How can you convert between pa and kpa?

Answer 43

pa = kpa x 1000

Question 44

How can you convert between m^3 and cm^3

Answer 44

m^3 = cm^3 x 10^-6

Question 45

How can you convert between m^3 and dm^3

Answer 45

m^3 = dm^3 x 10^-3

Question 46

What is the ideal gas constant?

Answer 46

8.314

Question 47

How can you convert between degrees celcius and kelvin?

Answer 47

+ 273 to degrees celcius to get kelvin

Question 48

What is the % by mass equation?

Answer 48

(Ar of 1 mole of the element) / (Mr/RFM) all multiplied by 100

Question 49

What is the empirical formula?

Answer 49

The simplest whole number ratio of elements in a compound

Question 50

What can the empirical formula be calculated from?

Answer 50

%mass or mass

Question 51

How is the empirical formula calculated?

Answer 51

- %mass or mass / Ar- All Ar's / smallest Ar to give ratio

Question 52

What is the molecular formula?

Answer 52

The actual number of atoms of each element in each molecule of a substance

Question 53

What is the only way of calculating molecular formula from empirical formula?

Answer 53

Using Mr

Question 54

How is the ratio of empirical to molecular formula calculated?

Answer 54

Mr/ Empirical Mr

Question 55

What is the atom economy?

Answer 55

The efficiency of a reaction

Question 56

How is % atom economy calculated?

Answer 56

Total molar mass of desired products divided by the total molar mass of reactants all multiplied by 100

Question 57

Why is a higher atom economy desirable?

Answer 57

There are less waste products which could be harmful to the environment or expensive to dispose of therefore a higher atom economy will be industrially more economic and safer to the environment

Question 58

How is percentage yield calculated?

Answer 58

Actual yield / theoretical yield