amount of substances in all papers (3.1.2)

Question 1

what is the relative atomic mass (Ar)?

Answer 1

the average mass of one atom compared to one twelfth of the mass of one atom of carbon 12.

no units.

Question 2

what is the relative molecular mass (Mr) ?

Answer 2

the average mass of a molecule compared to one twelfth of the mass of one atom of carbon 12.

for covalent compounds

no units

Question 3

what is the avogadros constant?

Answer 3

the number of particles in a mole.
(6.022x10^23)

Question 4

how do you work out the number of moles in pure solids and liquids?

Answer 4

moles= mass/Mr

units: grams
mol

Question 5

how do you work out the number of moles in pure solids and liquids?

Answer 5

moles= mass/Mr

units: grams
mol

Question 6

how do you work out the mass of 1 mole of pariticles?

Answer 6

avogadros constant X mass of 1 parrticle.

Question 7

how to work out the number of particles?

Answer 7

number of moles x avogadros constant

Question 8

how do you convert kPa to Pa?

Answer 8

x1000

Question 9

how do you convert cm^3 to m^3?

Answer 9

divide by 10^6 or x10^-6

Question 10

how do you convert dm^3 to m^3?

Answer 10

divide by 10^3 or x10^-3

Question 11

how do u convert C to kelvins?

Answer 11

add 273

Question 12

how do you work out the empirical formula and molecular formula from it?

Answer 12

1: set out the elements with
their masses/percentage.
2: divide each mass by their Mr.
3: divide all them by the smallest
value.
4: give whole number ratio in
empirical formula.
5: molecular formula =
n(empirical formula)

Question 13

explain the water of crystallisation practical (hydrated salt)

Answer 13

• weigh an empty crucible.
• add 2g of hydrated calcium
  sulfate to the crucible and
  weigh again.
• heat with a bunsen burner for
  5 mins and let it cool.
• weigh the crucible and
  contents again.
• heat and reweigh again until
  you reach a constant mass to
  ensure salt has become
  anhydrous.

Question 14

how do you work out atom economy?

Answer 14

mass of desired product
————————————–x100
total mass of reactants

Question 15

how do you work out percentage yield?

Answer 15

actual mass of product
————————————–x100
maximum theorectical mass of product

Question 16

why might a chemical reaction not give a 100% percentage yield?

Answer 16

• reactants react in a different way.
• reaction doesnt go to completion, the reaction is reversible.
• some reactant or product is lost during reaction or seperation or purification.

Question 17

define the concentration of a solution?

Answer 17

• the number of moles of solute in 1dm^3 of solution?

Question 18

how do you calculate the number of moles in a solute in a given volume?

Answer 18

• moles = concentration x volume

Question 19

list the steps of titration?

Answer 19

• pipette 25cm^3 of the HCL into the conical flask.
• add the indicator
• fill the buette with the NaOH solution.
• make sure the jet space in the burette in the solution and air bubbles are removed.
• take the initial burette reading
• add the NaOH
• stop adding NaOH when the indicator changes colour and record the final burette reading.
• work out titre volume.

Question 20

titration

how do you record the volume

decimals

Answer 20

• to 2 d.p

Question 21

titration

how do you work out the titre volume?

Answer 21

final burette reading - initial burette reading

Question 22

titration

when do you have concordant results?

Answer 22

• when you have 2 titre volumes within 0.1

Question 23

titration

why is a conical flask used instead of a beaker?

Answer 23

• to prevent loss of solution from splashing.

Question 24

titration

why should we only add a few drops of indicator?

Answer 24

• its slightly acidic, too much will interfer with results.

Question 25

titration

why does adding distilled water not affect titration reading?

Answer 25

• because the number of moles is still the same.

Question 26

how do you make a standard solution?

Answer 26

• Weigh the crucible.
  on a 2 dp balance
• Transfer to beaker and reweigh crucible
• Record the difference in mass
• Add 100cm3 of distilled water to the beaker. Use a glass rod to
  stir to help dissolve the solid.
• Pour solution into a 250cm3 graduated flask via a funnel.
• Rinse beaker and funnel and add washings from the beaker
  and glass rod to the volumetric flask. * Make up to the mark with distilled water using a dropping
  pipette for last few drops.
• Invert flask several times to ensure uniform solution.

Question 27

how do you work out percentage error?

Answer 27

maximum error
————————-x100
measurement taken

• if 2 measurements need to be taken in order to obtain the vlaue, the maximum error must be doubled.

Question 28

how can you reduce error in a titration?

Answer 28

• replace measuring cyclinders with pipettes or burettees.
• make the titre volume by:
  . increaing volume and concentration of the substance in the conical flask.
  . or decrease concentration of the substance in the burette.