Maths equations in chemistry

Question 1

Relative atomic mass (Ar)

Answer 1

Average mass of the isotopes of an element compared to 1/!2 the mass of an atom of 12C

Question 2

Relative molecular mass (Mr)

Answer 2

Sum of relative atomic masses of all the atoms in one molecule of the compound

Question 3

A mole

Answer 3

A mole is the Ar or Mr expressed in grams e.g. 1 mole of carbon-12 is equal to 12 grams.

1 mole also occupies a volume of 24dm^3 at room temperature and pressure.

Question 4

avogrados constant

Answer 4

The number is 6.02 x 10^23

fun fact this is more than the grains of sand on the planet

Question 5

Number of moles formula

Answer 5

Amount of substance = Mass / molar mass

Amount of substance (mol)
Mass (g)
Molar mass (g/mol)

Question 6

Number of moles in a aqueous solution

Answer 6

moles = concentration x volume

moles (mol)
concentration (mol/dm^3)
volume (24dm^3)

Question 7

Moles of gases

Answer 7

volume = No. of moles x 24dm^3 at r.t.p

1dm^3 = 1000cm^3

Question 8

Moles calculation in Acid-base titration

Answer 8

concentration x volume (cm^3)/1000

Question 9

Empirical formula

Answer 9

This is the simplest ratio of atoms in a compound for example:

molecular formula of ethane = C2H6
Empirical formula of ethane = CH3

To find out the empirical formula you:
Make the percent ratio in the simplest whole number ratio (NOTE: if given %s, use them in grams)
Divide the coefficients of each element symbol by the lowest coefficient

Question 10

Molecular formulae

Answer 10

It shows the actual number of atoms in one mole of a substance

Question 11

Percentage Purity and yield

Answer 11

Percentage purity:

Mass of product (pure) / mass of compound (impure)

all times by 100x for the percentage

Percentage yield:

Actual mass object / calculated/theoretical mass x100 for the percentage

Question 12

Percentage composition by mass

Answer 12

(mass of element/molecular mass) x 100