Calculations

Question 1

Formula moles ( concentration )

Answer 1

Moles = vol ( dm3) x conc. ( moldm-3)

Question 2

Formula moles ( mass )

Answer 2

Moles = mass / Mr

massive Mr mole

Question 3

Cm3 to dm3

Answer 3

/1000

Question 4

dm3 to cm3

Answer 4

x1000

Question 5

How many particles does 1 mole of a substance contain

Answer 5

6.02 x 10 ^23

Question 6

What is Avogadro’s number

Answer 6

6.02 x 10^23

Question 7

Formula for no. of particles, atoms, or molecules

Answer 7

Moles x Avogadro’s number

= moles x ( 6.02 x 10^23 )

Question 8

What is Avogadro’s constant

Answer 8

6.02 x 10^23 mol-1

Question 9

Formula for calculating chemical %

Answer 9

( Ar / Mr ) x 100

Eg. ( C / CO2 ) x 100

= % of carbon in carbon dioxide

Question 10

Formula for % yield

Answer 10

% yield = ( actual yield (g) / theoretical yield (g) ) x 100

Question 11

How to work out relative atomic mass ( Ar ) ( of isotopes )

Answer 11

1. Multiply mass of each isotope by relative abundance
2. Add them together
3. Divide by sum of relative abundance’s

Question 12

When will you have to work out the relative atomic masses of isotopes

Answer 12

From a Mass Spectrometry

Question 13

When given a mass spectrometry what do u have to work out

Answer 13

The relative atomic mass from isotopes and there abundances

Question 14

what does emitting an alpha particle ( helium atom ) do to the atomic no. and mass no.

Answer 14

Mass no. = -4

Atomic no. = -2

Question 15

what does emitting a beta particle ( electron ) do to the atomic no. and mass no.

Answer 15

Mass no. = stays the same

Atomic no. = +1

Question 16

Reasons why actual compound mass could be less than theoretical amount

Answer 16

1. Reversible reaction
2. Product lost - when separated from reaction mixture
3. Reactants may react in other reactions

Question 17

Equation for c, speed of light ( spectroscopy )

Answer 17

c=v lamda

Speed of light = frequency x wavelength ( m )

Question 18

1st equation for E, Energy (J)

Spectroscopy

Answer 18

E=hv

Energy = planks constant x frequency

Question 19

2nd equation for E, energy (J) when only given wavelength

Answer 19

E= hc/ lamda

Energy (J) = ( planks constant x speed of light ) / wavelength

Question 20

How to go from J -> KJmol^-1

Answer 20

Divide by 1000
Then…
Multiply by Avogadros constant

Question 21

How to go from KJmol^-1 -> J

Answer 21

Divide by Avogadros constant
Then….
Multiply by 1000

Question 22

How to calculate empirical formula (5)

Answer 22

1. List all elements in compound
2. Write mass/ % of each element
3. Divide each element by Ar = moles
4. Divide each element by smallest no. of moles
5. Get ratio in simplest whole no. form ( by x or / )

Question 23

In a water of crystallisation calculation what does the x stand for

Answer 23

Ratio moles of water

Question 24

Equation for heat energy transferred ( given out / absorbed )

Answer 24

q=mcAT

Question 25

What does each letter stand for in q= mcAT

Answer 25

• q= heat energy transferred ( J )
• m= mass of substance ( liquid / solution ) heated
• c = specific heat capacity ( 4.18)
• AT (delta T ) = change in temp ( in K but no conversions required )

Question 26

Equation for (molar) enthalpy change ( per mole )

Answer 26

Delta H = q(KJ) / no. of moles reacting