2.1.3 Amount of substances

Question 1

the mole is…

Answer 1

the amount of substance in grams that has the same number of particles as there are atoms in 12g of carbon 12

Question 2

relative atomic mass is…

Answer 2

the average mass of an atom compared to the mass of one atom of carbon 12

Question 3

relative molecular mass is …

Answer 3

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

Question 4

molar mass is…

Answer 4

the mass in grams of one mole of substance (gmol-1)

Question 5

avogadro’s constant

Answer 5

the number of particles in one mole

Question 6

mass =

Answer 6

n x Mr

Question 7

no of particles =

Answer 7

n x 6.02 x 10^23

Question 8

volume in (dm^3)

Answer 8

n/C

Question 9

moldm^-3 can be made into gdm^-3 by…

Answer 9

multiplying by the Mr

Question 10

avogadro’s number shows …

Answer 10

that there are 6.02 x 10^23 atoms in 12g of carbon 12

Question 11

xH2O means …

Answer 11

water of crystallisation

Question 12

salts that have water removed are …

Answer 12

anhydrous

Question 13

empirical formula is…

Answer 13

the simplest whole number ratio of atoms in a compound

Question 14

molecular formula is …

Answer 14

the actual number of atoms in a compound

Question 15

how to work out the factor of an empirical formula

Answer 15

factor = mr of molecular formula / mr of empirical formula

Question 16

to work out the molecular formula you …

Answer 16

empirical formula x factor

Question 17

ideal gas equation

Answer 17

P(Pa)V = nRT

Question 18

T=

Answer 18

273 +/- ?°C

Question 19

R =

Answer 19

8.31

Question 20

V (m^3) =

Answer 20

cm^3 / 10^6
or
dm^3 / 1000

Question 21

1 mole of any gas at room temp and room pressure =

Answer 21

25°C and 24dm^3

Question 22

gas volume (dm^3) =

Answer 22

n x 24 (or 24,000 if answer is wanted in cm^3)

Question 23

% yield =

Answer 23

actual yield / theoretical yield x 100

Question 24

name two ways % yield can be lowered

Answer 24

• incomplete reactions
• side reactions
• losses during purification
• transfer of substances

Question 25

% atom economy =

Answer 25

mr or mass of useful products / mr or mass of all reactants x 100

Question 26

name two potential errors when using a gas syringe

Answer 26

• gas escapes before bung is inserted
• syringe sticks
• some gases are soluble so the true amount of gas may not be measured

Question 27

method for titration

Answer 27

1) rinse equipment with distilled water
2) using a pipette put 25cm^3 of alkali into a conical flask and add a few drops of indicator
3) fill burette with acid up to 0 and place flask on top of a white tile underneath the burette
4) add acid whilst swirling flask until colour change is seen and record in a table
5) repeat until two concordance results occur

Question 28

why is a conical flask used instead of a beaker ?

Answer 28

so contents is less likely to be spilled

Question 29

only small amounts of indicator are added because…

Answer 29

they are weak acids so too much would affect the result

Question 30

when working out the average titre you use…

Answer 30

the two concordant results

Question 31

% error =

Answer 31

+/- sensitivity error/ measurement made on apparatus x100

Question 32

name two ways to decrease apparatus errors

Answer 32

• decrease the sensitivity error by using apparatus with a greater resolution
• increase the size of the measurement made