amount of substance

Question 1

define relative atomic mass (Ar)

Answer 1

the average mass of an atom of an element relative to 1/12th the mass of 12C

Question 2

units of relative atomic mass

Answer 2

g mol^-1

Question 3

what are isotopes

Answer 3

atoms with the same number of protons but different number of neutrons

Question 4

calculating relative atomic mass

Answer 4

sum of (isotopic mass x % abundance )/ sum of abundances

Question 5

define relative formula mass and give its units

Answer 5

the mass of the formula relative to 1/12th the mass of 12C (giant ionic compounds/salts)
g mol^-1

Question 6

how to calculate number of atoms or molecules

Answer 6

avagadros constant x number of moles

Question 7

what is water of crystallisation

Answer 7

(xh20) is an amount of water relative to one mole of salt

Question 8

how do you calculate xh20

Answer 8

find the number of moles of both the salt and the water and divide by the smallest value (always the salt) to give a WHOLE NUMBER

Question 9

cm^3 to dm^3

Answer 9

x1000

Question 10

formula linking conc vol and moles

Answer 10

concentration=moles/volume

Question 11

what is volume always measured in

Answer 11

dm^3

Question 12

how do you calculate the limiting reagent when ratio is 1:1?

Answer 12

calculate moles
lowest moles = limiting reagent

Question 13

how do you calculate the limiting reagent when ratio is 2:1?

Answer 13

calculate moles
use ratio to find limiting reagent
eg nNa=0.4 and n S=0.25
ratio is 2:1 respectively so Na needs 0.2 moles of S to react. 0.25 moles available so S is in xs and Na is limiting reactant

Question 14

what does one mole of any gas occupy?

Answer 14

1 mole of any gas will occupy 24dm^3 at standard temperature and pressure

Question 15

how to calculate volume occupied by a gas

Answer 15

volume (dm^3) = number of moles x 24 (dm^3)

Question 16

equation for ideal gas equation?

Answer 16

PV=nRT (pressure x volume = moles x gas constant x temperature)

Question 17

assumptions made when using the ideal gas equation

Answer 17

no intermolecular forces exist between molecules of a gas
volume occupied by gas molecules is negligible

Question 18

units of measurements for ideal gas equation?

Answer 18

volume= m^3 (cm^3/1000000 or dm^3/ 1000)
pressure= Pa (kPa x 1000)
temperature= K (°C +273)

Question 18

define empirical formula

Answer 18

the simplest ratio of elements in a compoundde

Question 19

define molecular formula

Answer 19

the actual number of atoms of each element in each molecule of a substance

Question 20

how to calculate % atom economy

Answer 20

(total molar mass of desired product/ (total molar mass of all reactants) x 100

Question 21

how to calculate % yield

Answer 21

( actual yield/ theoretical yield ) x 100

Question 22

define relative molecular mass and give its units

Answer 22

the mass of a molecule relative to 1/12th the mass of 12C
g mol^-1

Question 23

what is the mass, of one mole of a substance equal to?

Answer 23

its relative atomic mass

Question 24

what is the mass, in g of 2 moles of 12C?

Answer 24

24g

Question 25

what is one mole of any substance equal to?

Answer 25

6.022x10^23 atoms/molecules/ions of that substance

Question 26

formula for calculating the number of atoms or molecules?

Answer 26

number of atoms or molecules = number of moles x 6.022x10^23

Question 27

how do you calculate moles

Answer 27

moles=mass/mr