Maths In Chemistry

Question 1

Calculate molecular formula from empirical formula

Answer 1

1. Find Ar of each element
2. Calculate Mr of empirical formula
3. Divide molecular formula Mr by empirical formula Mr
4. Times formula value to get molecular formula

Question 2

P1

Calculate Theoretical yield

Answer 2

1. Underline substances in equation questioned
2. Calculate Mr of substances
3. Find mass made by 1g of reactant
4. X mass by mass of reactants in question

Question 3

P1&2

Calculating relative formula mass Mr

Answer 3

Sum of Ar of all atoms in a compound or molecule.

Question 4

P1&2 H

Calculating number of particles

Answer 4

Number of particles = moles x avagadros constant

Avogadro (6.02 x 10^23)

Question 5

P1 H

Calculate molar gas volume

Answer 5

Molar volume = 24dm^3

Volume = moles x molar volume

Question 6

P1&2

Calculate empirical formula from mass

Answer 6

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 7

P1

Calculate relative formula mass from relative mass & abundance of isotopes

Answer 7

(Total mass of atoms ÷ number of atoms) x 100

Question 8

P1&2

Calculating mass of reactants from products

Answer 8

1. Underline substance of given mass & substance whose mass you are finding
2. Find Mr for each substance
3. Workout molar ratio
4. Divide Mr of unknown mass by Mr of known mass
5. x by known mass

Question 9

P1

Calculate concentration from moles

Answer 9

Conc = moles ÷ volume

Volume in dm^3

Cm^3 ÷1000

Question 10

P1

Calculating converting conc in gdm^3 to mol dm^3

Answer 10

Conc mol dm^3 = conc in gdm^3 ÷ Mr of solute

Question 11

P1&2

Calculate conc from mass

Answer 11

Conc = mass ÷ volume

Volume in dm^3

Question 12

P1

Rf value

Answer 12

Rf = distance moved by solute÷ distance moved by solvent

Question 13

P1

Calculate % yield

Answer 13

% yield = (actual÷theoretical)x100

Question 14

P1&2 H

Calculating moles

Answer 14

Mass=mr x moles

Question 15

P2 H

Calculating Bond energies

Answer 15

1. Draw structural formula
2. Calculate energy in to break bonds
3. Calculate energy out during bond formations
4. Calculate energy difference -exo + endo

Question 16

P1 H

Titration calculations

Answer 16

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 concentration
7. Use molar ratio to find moles of unknown substance
8. Substitute values into table
9. Find conc of unknown substance

Question 17

P1&2 H

Deduce balanced equations from mass

Answer 17

1. Find number of moles of substance with known masses
2. ÷ by smallest value
3. Write formulae & known balanced number
4. Finish balancing equations

Question 18

P1

Calculate atom economy

Answer 18

(Mr of desired product÷sum of Mr of all reactants) x100