Maths In Chemistry

Question 1

1

Calculate concentration from moles

Answer 1

Concentration=mole÷volume
Volume in dm^3
Cm^3÷1000

Question 2

1&2

Calculating mass of reactants and products

Answer 2

1) underline substance of given mass and substance whose mass you are finding
2) find Mr for each substance
3) work out molar ratio
4) divide Mr of unknown mass by Mr of known mass
5) × by known mass

Question 3

1

Calculate relative formula mass from relative mass and abundance of isotopes

Answer 3

Total mass of atoms÷number of atoms(100)

Question 4

1&2

Calculate empirical formula from mass

Answer 4

1) find Ar of each element
2) divide mass of each element by its Ar
3) divide the answers by smallest value to find ratio
4) write out empirical formula

Question 5

1H

Calculate molar gas volume

Answer 5

Molar volume=24dm^3

Volume=moles×molar volume

Question 6

1&2H

Calculate the number of particles

Answer 6

Number of particles=moles×avogadro constant (6.02×10^23)

Question 7

1

Calculate the theoretical yield

Answer 7

1) underline substances in equation questioned
2) calculate Mr of all substances
3) find mass made by 1g of reactant
4) ×mass by mass of reactant in question

Question 8

1&2

Calculate molecular formula from empirical formula

Answer 8

1) find Ar of each element
2) calculate Mr of empirical formula
3) divide molecular formula Mr by empirical formula Mr
4) times formula by value to get molecular formula

Question 9

1&2H

Calculate limiting reactants

Answer 9

1) balance the symbol equation
2) calculate the moles of each substance
3) find molar ratio
4) calculate number of moles used in reactants ( its why you balanced)
5) state limiting reactant

Question 10

1&2

Calculating relative formula mass Mr

Answer 10

Sum of Ar of all atoms in a compound or molecule

Question 11

1

Calculating converting concentration in gdm^-3 to moldm^-3

Answer 11

Conc moldm^-3=conc in gdm^-3÷Mr of solute

Question 12

1&2

Calculate concentration from mass

Answer 12

Conc=mass÷volume

Volume in dm^3

Question 13

1

Calculate atom economy

Answer 13

(Mr of desired product÷sum of Mr of all reactants) ×100

Question 14

2H

Calculating bond energies

Answer 14

1) draw structural formula
2) calculate energy in to break bonds
3) calculate energy out during bond formation
4) calculate energy difference- exo+endo

Question 15

1H

Titration calculations

Answer 15

1) write out balanced equation
2) underline reactants needed
3) deduce molar ratio
4) convert volume to dm^-3
5) draw table and substitute values
6) find moles of known conc
7) use molar ratio to find moles of unknown substance
8) substitute values into table
9) find conc of unknown substance

Question 16

1

Calculate percentage yield

Answer 16

%yield=(actual÷theoretical)×100

Question 17

1

Calculate rf

Answer 17

Rf=distance moved by solute÷distance moved by solvent

Question 18

1&2H

Calculating moles

Answer 18

Mass=Mr×moles

Question 19

1&2H

Deduce balanced equations glfrom mass

Answer 19

1) find number of moles of substances with known masses
2) divide by smallest value
3) write formulae & known balanced number
4) finish balancing equations