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A level Chemistry > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

What is meant by the relative molecular mass ?

A

Mr is the average mass of a molecule relative to one twelfth of the mass of an atom of carbon-12. It is the sum of the relative atomic masses of each atom within the molecule.

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2
Q

What is meant by the relative formula mass ?

A

It is the sum of the relative atomic masses of the atoms present. Compares the mass of a formula unit with 1/12th of the mass of an atom of Carbon-12.

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3
Q

What is another term for the relative molecular mass ?

A

Molar mass

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4
Q

What is meant by a mole of something ?

A

A mole of anything is 6.022 × 10²³ ( Avagadro’s constant ) atoms/particles/molecules

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5
Q

How to calculate the number of particles in a substance ?

A

Number of particles = number of moles x Avagadro’s constant

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6
Q

What is meant by Avagadro’s constant ?

A

The number of particles per mole of substance. 6.022 × 10²³

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7
Q

What equation links moles, molar mass and mass

A

Moles = mass / molar mass

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8
Q

What is meant by molar mass ?

A

It is the mass per mole, units g mol -1 . Molar mass has the same numerical value as the relative atomic masses for a substance.

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9
Q

What is meant by the term molar gas volume ?

A

Gas volume per mole, units dm3 mol -1 )

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10
Q

What is the emperical formula ?

A

It shows the simplest whole number ratio of atoms of each element present in a compound ?

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11
Q

What is the molecular formula ?

A

Shows the actual number and type of atoms of each element in a molecule.

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12
Q

How to calculate the emperical formula.

A

Convert both substance to moles
Write the moles as ratios
Convert the ratio to a whole number

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13
Q

How to calculate the molecular formula.

A

Find the % mass
Find the mass of each substance in a total of 100g
Calculate the moles
Calculate the moles ratio
Find the emperical formula
Calculate the molecular formula.

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14
Q

What is meant by the term hydrated ?

A

( ionic solid ) contains water of crystallisation

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15
Q

What is meant by the term anhydrous ?

A

( ionic solid ) does not contain water of crystallisation

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16
Q

What is meant by the water of crystallisation ?

A

Water molecules in an ionic solid

17
Q

How to calculate the formula of a hydrated salt

A

Calculate the mass of water lost
Convert the residual mass to moles
Convert the mass of water to moles
Write the moles as a ratio
Write as a whole number ratio

18
Q

Percentage uncertainty equation

A

Percentage uncertainty = ( uncertainty / quantity measured ) x 100

19
Q

What is the equation that links moles, concentration and volume

A

Number of moles ( mol ) = Concentration ( mol dm-3 ) x Volume ( dm3 )

20
Q

How can concentration be expressed in g dm-3 ?

A

( Mol dm-3 ) x molar mass = g dm-3

21
Q

How to calculate mass using c = n/v

A

Make sure volume and concentration are in right units
Calculate number of moles required
Calculate molar mass of substance
Calculate mass

22
Q

What is Avagadro’s law ?

A

Equal volumes of all gases at the same temperature and pressure contain an equal number of particles.

23
Q

What is room temperature and pressure ( RTP ) ?

A

20 degrees celsius / 293K
101kPa or 1 atmosphere

24
Q

At RTP, what is the volume of one mole of ideal gas ( molar gas volume ) ?

A

24dm3

25
Q

What does Avagadro’s law allow us to do ?

A

Equal volumes contain equal numbers of particles. This means we can equate the number of moles in a gas reaction with simple volumes.

26
Q

What is the ideal gas equation ?

A

pV = nRT

Pressure , p in Pa (pascals)
Volume, V in m3
Temperature, T in K
R = 8.314 mol-1 K-1

27
Q

What is stoichiometry ?

A

A balanced equation tells you the reacting ratio, in moles, of each substance.

28
Q

How to carry out calculations using the stoichiometry of the reaction ?

A

Write the balanced equation
Convert mass of given substance to moles
Calculate moles of other substance using ratio
Convert moles to mass using molar mass

29
Q

Process to identify an unknown metal

A

If you know the valency of a metal ( which group its in and the charge of the ion ) you can identify it by measuring how much hydrogen gas it produces in excess water/acid
Different stoichiometries depend on the Group of the Metal
Measure volume of hydrogen gas produced and calculate moles
Work out relative atomic mass of metal using moles and mass
Use periodic table to identify the metal

30
Q

Two different methods of measuring volume of hydrogen gas produced

A

Collecting the gas over water - used for larger volumes of gas that are not soluble in water
Using a gas syringe - used for smaller volumes of gas (up to 100cm3)

31
Q

When do limiting reagents occur

A

When reagents are not in there stoichiometric amounts, one of the reagents will be in excess and the other reagent will be limiting

32
Q

Limiting reagents calculations method

A

Calculate number of moles of each substance
Write out balanced equation
Determine which reagent is in excess and which is limiting
Use Avagadro’s law to calculate volume of gas ( if required )

33
Q

What is atom economy and how do you calculate it ?

A

It measures the amount of starting materials that become useful products. High atom economy = most of the starting materials end up as useful products.

% atom economy = ( sum Mr of desired products / sum Mr of all products ) x 100

34
Q

What are the benefits for sustainability of developing chemical processes with a high atom economy ?

A

Produces less waste
Uses fewer natural resources
Has a lower environmental impact
Cheaper to produce - more economical

35
Q

How to calculate percentage yield ?

A

( actual mass/theoretical mass ) x 100
( actual yield/theoretical yield ) x 100
( actual moles/theoretical moles ) x 100

A level Chemistry (8 decks)

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