quantative chemistry

Question 1

Mole

Answer 1

A mole is just number but because particles are very small this number is very large.
1 mole = 6.02 x 10^23
This is known as Avagadro’s number.

Question 2

Relative atomic mass (Ar)

Answer 2

Average mass of an atom - top number in periodic table

Question 3

Relative formula mass / molecular mass (Mr)

Answer 3

Sum of all the masses of all the atoms in the formula
e.g.CaCO3 – 40(Ca) + 12(C ) + 48(O3) = 100

Question 4

How to calculate moles of atoms/formula

Answer 4

Moles of atoms or formula = mass(g) / Ar or Mr

Question 5

Calculating the percentage mass of a element in a compound

Answer 5

Calculate percentage mass of Na in Na2CO3
mass of Na in Na2CO3 = 2 x 23 = 46
RFM of Na2CO3 = (2 x 23) + 12 + (3 x 16) = 106
% = 46/106 = 43.4%

Question 6

Calculating empirical formulae

Answer 6

the empirical formula over compound is the simplest ratio of atoms of each element in it.
It can be calculated if you know either the mass or percentage of each elements in a compound.

Question 7

how to calculate the number of water molecules for crystalisation

Answer 7

Question 8

calculating masses of reacting substances in chemical reactions

Answer 8

Question 9

calculating % yield

Answer 9

% yield = actual yield (usually given in question) / theoretical yield (needs to be calculated)

Question 10

reasons for not getting 100% yield in a chemical reaction

Answer 10

Reversible
incomplete
side reaction
impurities