Amount of substance

Question 1

What is amount of substance?

Answer 1

Number of moles = n
Units = mol

Question 2

What is Avagadros number

Answer 2

The number of things (atoms, molecules) in one mole of a substance. It is 6.02x10^23

Question 3

What is molar gas volume?

Answer 3

The volume one mole of gas occupies at room temperature and pressure (24cm3)?

Question 4

What is the equation for molar mass?

Answer 4

mass/amount. the unit is gmol-1 or g/mol

Question 5

What is RTP

Answer 5

298K
101KPa

Question 6

What is the ideal gas equation?

Answer 6

pV=nRT
Used to find the mol, volume or pressure (via rearragning) of a gas not at room temp and pressure.
p=pressure=Pa
V=volume=m3
n=mol
R=gas constant=8.
T=temp=K

Question 7

What is room temperature and pressure?

Answer 7

298K (=273 to celsius)
101KPa

Question 8

Convert 1m3 to dm3 then cm3

Answer 8

1m3 is 1000dm3 which is 1,000,000 cm3

Question 9

What is an ideal vs real gas?

Answer 9

Ideal gases do not follow kinetic theory of gases;
moving very fast and randomly, having barely any volume, no intermolecular forces (they don’t repel r attract eachother), no KE is lost during collision and the gas temp is related to the average KE of the gas molecules.
Real gases follow the kinetic theory of gases.

Question 10

Explain the ideal gas law

Answer 10

The volume an ideal gas occupies depends on its TEMP & PRESSURE.
Heater=moreKE=more frequent collisions with container wall.
To keep CONSTANT PRESSURE, molecules move further apart so VOLUME INCREASES.
So, volume is therefore directly proportional to the temperature (at constant pressure).

Question 11

What is the gas constant for the ideal gas equation?

Answer 11

8.31JK-1mol-1

Question 12

What is the equation for concentration of a solution?

Answer 12

Concentration (mol/dm3) = amount (mol)/volume(dm3)

Question 13

How to calculate volumes of gases at room temperature?

Answer 13

Volume (dm3) = amount (mol)/24dm3

Question 14

How to calculate empirical formula?

Answer 14

Divide the mass of each atom in the substance (g) by their atomic masses. Then divide by the smallest figure you get to get the ratio.

Question 15

What is water of crystallisation/

Answer 15

Water molecules exisiting in crystal structures with a salt (hydrous). For every mole of salt is a number of moles of water; .XH20

Question 16

How to use balanced equations to work out theoretical mass?

Answer 16

Write balanced equation
work out Ar or Mr of species involved and write as g.
Convert one side into 1g and multiply by the amount of g that reacts. Repeat to the other side for the answer.

Question 17

How to find molecular formula from empirical formula?

Answer 17

Find the Mr of the empirical formula and divide by Mr of molecular formula. Multiply this with the number of atoms of each element in the empirical formula.

Question 18

What is percentage yield?

Answer 18

Actual yield/theoretical yield x 100%
The theoretical yield is the amount produced assuming no product is lost and all reactants react fully.

Question 19

What is atom economy?

Answer 19

Molecular Mass of desired products in a reaction/total molecular mass of all products x100%
It is a measure of a reaction’s efficiency.

Question 20

List some reasons why 100% percentage yield is impossible?

Answer 20

Not all reactants reacted.
Impurities reacted with reactants forming other products.
Product lost (eg gas escapes) like when transferring from beaker to beaker.

Question 21

Why is atom economy important?

Answer 21

1. When high, raw materials used more efficiently, which is more sustainable.
   2.Companies will tend to use reactions with 100% atom economy
   3.High produces less waste, evironmentall good.
   High = less by product so don’t need to spend money separating products

Question 22

How to find mass of one molecule?

Answer 22

Divide the molecules Mr by avagadros constant.
Or find its no. mols by dividing the number of molecules by avagadros constant to find the moles. Then multiple by the Mr to find the mass.