Quantitative chemistry

Question 1

Mr

Answer 1

Relative formula mass

Mass of all atoms in formula

Question 2

Ar

Answer 2

Relative atomic mass

Mass of individual atoms

Question 3

Relative formula mass

Answer 3

Mr

The relative atomic mass of a compound

Question 4

Relative atomic mass

Answer 4

Ar

An average mass of an element

Question 5

RAM of an Element equation

Answer 5

RAM=
sum of (atomic mass x % of each element
————————————————————
100

Question 6

RAM of an element example

Copper 63 70% copper 65 30%

Answer 6

63 x 70 = 4410
65 x 30 = 1950
= 6360 
   ——- = 63.6
     100

Question 7

How to find out the percentage mass of an element in a compound

Answer 7

Ar x number of atoms of that element
—————————————x100
Mr of the compound

Question 8

% mass of an element in a compound example

Find % mass of Na in Na2CO3
Na= 23(46) C=12 O= 16(48) Mr= 106

Answer 8

46
—- x 100 = 43%
106

Question 9

Mole

Answer 9

An amount of substance
Carbon has an Ar of 12
One mole of carbon weighs 12g

Question 10

Equation linking mass moles and Ar/Mr

Answer 10

Number of moles=
Mass
———
Mr/Ar

Question 11

Change in mass

Answer 11

Happens when reaction vessel is unsealed
Mass increases- one of the reactants is a gas that’s found in air and all the products are s l or a
Decreases- one of the products is a gas and all the reactants s l or a
Product gas can escape

Question 12

Big numbers before chemical formula

Answer 12

Number of moles

Question 13

When do reactions stop

Answer 13

When one reactant is used up
Any other reactant is excess
They’re usually added in excess to make sure that the other is used up

Question 14

Limiting reactant

Answer 14

The reactant that’s used up

It limits the amount of product that’s formed

Question 15

Volume of gas equation

Answer 15

Volume =

Moles x 24(000cm3)dm3

Question 16

Concentration equation

Answer 16

Mass
———
Volume

Moles
———
Volume

Question 17

Atom economy

Answer 17

Tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as the desired product

Question 18

Atom economy equation

Answer 18

Relative formula mass of desired product
—————————————-x100
Relative formula mass of all reactants

Question 19

Yield

Answer 19

Amount of product you get

Question 20

Percentage yield equation

Answer 20

Mass of product actually made
—————————————x100
Max theoretical mass of product

Question 21

What is the conservation of mass?

Answer 21

The total mass of reactants is equal to the total amount of product

Question 22

What must we do to chemical equations to show the conservation of mass?

Answer 22

Balance it

Question 23

Why is % yield never 100%?

Answer 23

Some product could be lost, if it is reversible it may not go through to completion, some reactants may react differently than expected E.g side reaction. And you lose some product when you separate it from the reaction mixture

Question 24

Why do scientists try and choose pathways with high atom economy?

Answer 24

Economic reasons, sustainable development- more made, less wasted