2.2 - Amount of substance

Question 1

Define the term ‘Avagadro’s constant’ ?

Answer 1

Avagadro’s constant - The number of atoms per mole of the carbon-12 isotope ( 6.022 x 10^23 mol-1 )

Question 2

Define the term ‘amount of substance’ ?

Answer 2

Amount of substance - The quantity whose unit of the mole, used as a means of counting any species such as atoms, ions and molecules

Question 3

Define the term ‘mole’ ?

Answer 3

Mole - The amount of any substance contain gin as many elementary particles as there are carbon atoms in exactly 12g of carbon-12 isotope ( 6.022 x 10^23 )

Question 4

Define the term ‘Molar mass’ ?

Answer 4

Molar mass - The mass per mole of a substance, in units of gmol-1

Question 5

Define the term ‘Molar gas volume’ ?

Answer 5

Molar gas volume - The volume per mole of gas molecules at a stated temperature and pressure

Question 6

Define the term ‘anhydrous’ ?

Answer 6

Anhydrous - Containing no water molecules

Question 7

Define the term ‘hydrated’ ?

Answer 7

Hydrated - A crystalline compound containing water

Question 8

Define the term ‘water of crystallisation’ ?

Answer 8

Water of crystallisation - Water molecules that are bonded into a crystalline structure of a compound

Question 9

What is the units for molar mass ?

Answer 9

g mol^–1

Question 10

What is molar gas volume ?

Answer 10

Gas volume per mole

Question 11

What are the units for molar gas volume ?

Answer 11

dm^3 mol^-1

Question 12

Define the term ‘Empirical formula’ ?

Answer 12

Empirical formula - The formula that shows the simplest whole number ratio of atoms of each element present in a compound

Question 13

Define the term ‘molecular formula’ ?

Answer 13

Molecular formula - A formula that shows the number and type of atoms of each element present in a molecule

Question 14

Do you know how to calculate the empirical formula and molecular formula ?

Answer 14

Yes

Question 15

Do you know how to do calculations using mass or gas volume or solution volume and concentration ?

Answer 15

Yes

Question 16

What is the ideal gas equation ?

Answer 16

pV = nRT

Question 17

What is a percentage error ?

Answer 17

Percentage error is the error of the actual data recorded

Question 18

What is the equation to calculate percentage error ?

Answer 18

Percentage error = ( uncertainty/ value measured ) x 100

Question 19

What do you times by two when calculating the percentage error of titre from a burette ?

Answer 19

• To achieve a titre from a burette you need to take away the initial reading from the final reading
• Therefore, this involves two values which means there are two uncertainties
• Therefore, you times by two when calculating percentage error

Question 20

How do you find the uncertainty for a particular piece of equipment ?

Answer 20

• Find the lower and upper bound of the data recorded
• Find the difference between actual data and the lower/ upper bound

Question 21

What needs to be considered when designing an experiment ?

Answer 21

• Atom economy ( Ideally one product or market found for by-product so 100% )
• Percentage yield ( Very difficult to have high yield of reaction is reversible )
• Sustainability

Question 22

Define the term ‘percentage yield’ ?

Answer 22

Percentage yield - The ratio of mass of actual product made to the maximum theoretical mass of product

Question 23

Do you know how to calculate the atom economy or percentage yield ?

Answer 23

Yes

Question 24

Define the term ‘atom economy’ ?

Answer 24

Atom economy - The ratio of reactants used to make the desired product. The higher the atom economy, the less waste/ by-product.

Question 25

When is a reaction ‘sustainable’ ?

Answer 25

• When the raw materials are renewable ( eg. Sugarcane, solar panels, water … )
• When the products don’t damage the environment

Question 26

Describe how to produce a standard solution ( 100cm^3, 0.20 mol/dm^-3 of NAv2COv3 )

Answer 26

1 ) Work out the mass of Nav2COv3 required
2 ) Transfer the solid into a small beaker and dissolve in a minimum volume of distilled water, stir with a glass rod
3 ) Transfer via funnel ( to prvenet loss/escape ) into a 100cm^3 volume metric flask
4 ) Rinse stirring rod and beaker three times with distilled water and rinse funnel
5 ) Add distilled water just below the line, then use a dropping pipette to add water until the bottom of the meniscus
6 ) Put a stopper and shake to mix the solution