2.1.3 Amount Of Substances

Question 1

How many particles/atoms/molecules are in a mole?

Answer 1

6.02 x 10 23

Question 2

What is the mass of one mole of carbon?

Answer 2

12g

Question 3

How many atoms in 12g of carbon?

Answer 3

6.02 x 10 23 atoms

Question 4

What is molar mass Mr measured in

Answer 4

gmol-1 or g/mol

Question 5

Moles (mol) =

Answer 5

Mass (g)
————
RFM/Mr (g mol-1)

Question 6

How to work out empirical formula with a given mass or percentage composition by mass

Answer 6

Find the moles by mass / RFM and divide the other moles by the smallest moles to find ratio

Question 7

How many centimetres/millilitres/litres in 1 dm3?

Answer 7

1000cm3 or 1000ml or 1L

Question 8

Concentration (mol dm-3) =

Answer 8

Moles(mol)
——————
Volume(dm3)

Question 9

How to calculate volume (cm3) from moles and concentration

Answer 9

Vol = mol/mol dm-3 = dm3 x 1000 = cm3

Question 10

How to calculate mass from concentration and volume

Answer 10

Find the moles and fill into moles = mass/rfm

Question 11

What is the volume of one mole of a gas molecule at room temperature and pressure

Answer 11

24dm3 / 24000cm3

Question 12

Percentage yield =

Answer 12

Actual yield/ theoretical yield

Question 13

Atom economy =

Answer 13

Sum of Mr of desired products/ sum of Mr of all products

Question 14

pV =
pa x m3

Answer 14

nRT
Mol x r x k

Question 15

How to use ideal gas equation when given density instead of volume and mass

Answer 15

Density = x g dm -3 x grams per 1 dm so our vol is 1 / 1000 for m3 = 0.001
So there are X grams Which can be used to find Mr

Question 16

How to find rfm using ideal gas equation and a mass

Answer 16

Find moles using ideal gas equation and divide from Mass

Question 17

What mass of potassium chlorate (V) must be heated to give 1.00 dm3 of oxygen at 20.0ºC and 0.100 MPa.
2 KClO3(s) → 2 KCl(s) + 3 O2(g)

Answer 17

Use gas equation to find moles = 0.0411 of O2
so 2/3 X moles of O2 = moles of KClO3 = 0.0274 X Rfm = 3.36g

Question 18

K =

Answer 18

C + 273

Question 19

How to convert from cm3 to m3 and dm3 to m3

Answer 19

Divide by 1 million
Divide by 1000

Question 20

how to convert from MPa to Pa and KPa to Pa and atm pressure

Answer 20

MPa X 1,000,000 = pa
kPa X 1,000 pa
atm p = 101,000 pa

Question 21

Gas volume =

Answer 21

Moles x 24dm3 or 24000cm3

Question 22

Concentration of in mass gdm-3 =

Answer 22

Concentration in mol dm-3 (mols/vol) x RFM

Question 23

Why isn’t percentage yield 100%?

Answer 23

• Lost due to mechanical transfer
• Loss whilst separating e.g. filtration funnel
• Side reactions(reactants or products react with something unexpected)
• incomplete/reversible reactions

Question 24

Why are products with higher atom economies better?

Answer 24

They produce a larger proportion of desired products and less unwanted waste products and are important for sustainability as they make the best use of natural resources

Question 25

How many grams in a ton?

Answer 25

1000000

Question 26

What is weighted mean mass

Answer 26

Average mass of an atom or molecule taking into account the abundance of isotopes

Question 27

What does (.xH2O) represent

Answer 27

Water of crystallisation

Question 28

How do you work out moles of water in a hydrated compound given hydrous and anhydrous masses

Answer 28

Anhydrous mass divided by rfm of anhydrous compound equals = moles Hydrated mass divided by Moles = RFM Total RFM - Anhydrous compound RFM = RFM of water Total Rfm of water divided by 18 = moles

Question 29

why is C12 used to compare atomic masses

Answer 29

It is the agreed standard

Question 30

Explain clearly the difference between atom economy and percentage yield

Answer 30

% yield compares the amount produced compared to the amount you should get, atom economy is the proportion of the mass of all the products that is the desired product

Question 31

How to find the number of atoms in a molecule

Answer 31

Find the number of moles and X by 6.02× 10 23

Question 32

What is the apparatus used to measure gas volume produced?

Answer 32

A gas syringe or a conical flask and measuring cylinder

Question 33

What is the equation for complete combustion?

Answer 33

Fuel + O2 = CO2 + H2O

Question 34

What assumptions are we making when working out the formula of a hydrated salt?

Answer 34

All of the water has been lost and no further decomposition has occurred

Question 35

What is made in the ionic equation of acid and hydroxide H+ + OH-

Answer 35

H2O

Question 36

What is made in the Ionic equation For acid and hydrogen carbonate or carbonate 2H+ + CO3 2- or H+ + HCO3-

Answer 36

Water and Carbon dioxide

Question 37

What is made in the ionic equation of acid and ammonia H+ + NH3 =

Answer 37

NH4+

Question 38

density =

Answer 38

mass/volume

Question 39

Why do we measure multiple times in a water of crystallisation experiment?

Answer 39

To make sure all the water has been removed

Question 40

How can we reduce percentage uncertainty in a water of crystallisation reaction?

Answer 40

Use a balance that weighs to more decimal places Use a larger mass of starting reaction

Question 41

How to get a solid from a sample

Answer 41

Filter to obtain the solid precipitate and then dry or evaporate it

Question 42

How to work out the total number of ions in a mass of MgBr2

Answer 42

We have three ions in each mole of MgBr2 so find the number of moles By dividing the must by RFM then multiply by 3 and then by Avogadro Constant

Question 43

What are three ways to separate a mixture?

Answer 43

Fractional distillation Distillation Filtration