Quantitative chemistry

Question 1

What is the mr?

Answer 1

Relative formula mas of a compound.

Question 2

What is the relative formula mass of a compound?

Answer 2

This is the sum of the relative atomic mass of all the elements in the compound.

Question 3

What is Ar?

Answer 3

Relative atomic mass.

Question 4

What is avoadros constant?

Answer 4

1 mole= 6.023 x 10^23 atoms/molecules
= Avogadro’s number

Question 5

What is the mr of sodium carbonate(Na2CO3)?

Answer 5

= (23 x 2) + 12 + (16x3) ( Na=23)
= 46+12+48 ( C=12)
= 58+48 ( O=16)
= 106

Question 6

What is the equation to work out the [percentage of an element in a compound?

Answer 6

% of an element in a compound = Ar x number of atoms of the element
——————————————————–
Formula mass

Question 7

Calculate the % of Fe in FeO(IRON OXIDE)

Answer 7

Mr = FeO
= 56+16
= 72 (Fe=56)
(O=16)
%Fe = 56 x 1
———- x 100 = 77.7%
72

Question 8

What is % yield?

Answer 8

% yield is the amount of useful product formed from a chemical reaction.

Question 9

% yield equation?

Answer 9

% yield = Actual amount product obtained
————————————————— x 100
Calculated/Theoretical amount

Question 10

Why is a yield always less than 100%?

Answer 10

1) Not all reactants reacted to give the product eg Inversible reaction
2) Some yield could have burnt
3) Side reactions i.e. reactant react with other chemicals eg O2 in the air
4) Transfer of product eg FILTRATION of the solid
—-> STUCK to the walls of the container

Question 11

What is ATOM ECONOMY?

Answer 11

% Atom economy is the amount of reactants that formed the useful product.

Question 12

What is the equation for % ATOM ECONOMY?

Answer 12

% ATOM ECONOMY = Formula mass of useful product
————————————————- x 100
Sum of the formula masses of
the reactants

Question 13

What is the equation for moles?

Answer 13

Mass=Mr x mol