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AQA Physical Chemistry > Relative Mass and Amount of Substance > Flashcards

Relative Mass and Amount of Substance Flashcards

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1
Q

What is Ar?

A

Relative atomic mass

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2
Q

What does Ar use?

A

Elements only

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3
Q

Define relative atomic mass

A

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

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4
Q

What is carbon-12 used in Ar?

A

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

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5
Q

What are isotopes?

A

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

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6
Q

How is Ar calculated?

A

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

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7
Q

What are the units for Ar?

A

grams per mol

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8
Q

Define relative molecular mass

A

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

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9
Q

What is Mr used for?

A

Simple covalent molecules and diatomic molecules

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10
Q

What are the Mr units?

A

Grams per mole

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11
Q

How is Mr calculated?

A

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

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12
Q

What is the relative formula mass?

A

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

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13
Q

What is RFM used for?

A

Giant ionic compounds (salts)

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14
Q

What is the mole?

A

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

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15
Q

What is Avogadros constant

A

6.02 x 10^23 molecules or atoms in one moles

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16
Q

How do you calculate the number of moles?

A

Number of atoms/molecules divided by avogadros constant

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17
Q

How do you calculate the number of atoms or molecules?

A

The number of moles x avogadros constant

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18
Q

How do you calculate avogadros constant?

A

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

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19
Q

What is molar mass?

A

Ar/Mr and RFM

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20
Q

What are the molar mass units?

A

Grams per mole

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21
Q

How do you calculate the number of moles?

A

Mass (g) divided by molar mass

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22
Q

What is the water of crystallisation?

A

The amount of water relative to one mole of salt

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23
Q

How is the water of crystallisation calculated?

A

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

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24
Q

What are the units of concentration?

A

Mol.dm^-3

25
Q

What are the units of volume?

A

dm^-3

26
Q

How do you convert between cm and dm?

A
  • Divide cm by 1000 to give dm- 1 dm = 1000 cm
27
Q

What is the equation for the mole and solutions?

A

Number of moles = Concentration x Volume

28
Q

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

A

24

29
Q

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

A

24000

30
Q

How can volume of gas be calculated?

A

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

31
Q

What are the key assumptions the ideal gas equation makes?

A
  • No IMF between gas molecules- Volume occupied by gas molecules is negligible
32
Q

What is the ideal gas equation?

A

Pv=nRT

33
Q

In the idea gas equation, what is p?

A

Pressure

34
Q

In the idea gas equation, what is v?

A

Volume

35
Q

In the idea gas equation, what is n?

A

Moles

36
Q

In the idea gas equation, what is r?

A

Ideal gas constant

37
Q

In the idea gas equation, what is t?

A

Temperature

38
Q

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

A

pa or nm^-2

39
Q

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

A

m^3

40
Q

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

A

There are none

41
Q

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

A

J.K^-1.Mol^-1

42
Q

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

A

Kelvin

43
Q

How can you convert between pa and kpa?

A

pa = kpa x 1000

44
Q

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

A

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

45
Q

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

A

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

46
Q

What is the ideal gas constant?

A

8.314

47
Q

How can you convert between degrees celcius and kelvin?

A

+ 273 to degrees celcius to get kelvin

48
Q

What is the % by mass equation?

A

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

49
Q

What is the empirical formula?

A

The simplest whole number ratio of elements in a compound

50
Q

What can the empirical formula be calculated from?

A

%mass or mass

51
Q

How is the empirical formula calculated?

A
  • %mass or mass / Ar- All Ar’s / smallest Ar to give ratio
52
Q

What is the molecular formula?

A

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

53
Q

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

A

Using Mr

54
Q

How is the ratio of empirical to molecular formula calculated?

A

Mr/ Empirical Mr

55
Q

What is the atom economy?

A

The efficiency of a reaction

56
Q

How is % atom economy calculated?

A

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

57
Q

Why is a higher atom economy desirable?

A

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

58
Q

How is percentage yield calculated?

A

Actual yield / theoretical yield

AQA Physical Chemistry (12 decks)

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