Formulae And Amounts Of Substances

Question 1

Definition of molecular formula

Answer 1

Formula which shows the actual number if atoms of each element in a molecule

Question 2

Definition of empirical formula

Answer 2

Formula which shows the simplest WHOLE NUMBER ratio of atoms of each element in a compound

Question 3

Definition of molar gas volume

Answer 3

The volume of one mole of gas under specified conditions of temperature and pressure

Eg 24dm^3 at 20C and one atmospheric pressure

Question 4

How do you calculate the empirical formula

Answer 4

Divide the masses/% masses by the RFM of the element
Divide all answers by the smallest answer
Write out the formula (may have to multiply by a certain number in order to get a WHOLE NUMBER ratio)

Question 5

How do you work out the molecular formula?

Answer 5

1. Empirical formula calculated
2. Divide RFM by empirical formula ➡️ gives scale factor
3. Multiply all numbers in empirical formula by this scale factor

Question 6

Write the combustion equation

Answer 6

See notes

Question 7

How do you work out the number of moles of a gas (mol)

Answer 7

Volume of gas (dm^3)
——————————
Molar volume (dm^3 mol^-1)

Question 8

How do you work out the volume of a gas?

Answer 8

Moles of gas x 24 (vol in dm)

Question 9

How to figure out an unknown hydrocarbon

Answer 9

Burn completely in oxygen and measure volume of everything

Question 10

What does NaOH do in combustion questions?

Answer 10

Absorbs CO2

Question 11

How to work out unknown volume of O2 in combustion hydrocarbon Qs

Answer 11

See equation pg 14 ALL IN VOLUMES

Question 12

What is the theoretical yield

Answer 12

Max possible amount of products formed from the reactants used

Question 13

Reasons for theoretical being more than the actual yield

Answer 13

Impure reactants
Reaction may not go to completion
Competing side reactions
Product left in container

Question 14

Percentage yield equation

Answer 14

(Actual yield/theoretical yield) x 100

Question 15

What is atom economy an indication of

Answer 15

Measure of efficiency of converting reactants to desired products
Can be used to compare efficiency of diff reactions
High % ➡️ more efficient and less waste

Question 16

Equation for the % atom economy

Answer 16

RFM of desired product
——————————— x100
Total mass of reactants

Question 17

What is the formula for Ammonium

Answer 17

NH4^+

Question 18

What is the formula for hypochlorite

Answer 18

ClO^-

Question 19

What is the formula for hydroxide

Answer 19

OH-

Question 20

What is the formula for Nitrite

Answer 20

NO2^-

Question 21

What is the formula for nitrate

Answer 21

NO3^-

Question 22

What is the formula for Chlorate

Answer 22

ClO3^-

Question 23

What is the formula for Hydrogencarbonate

Answer 23

HCO3^-

Question 24

What is the formula for hydrogenaulfate

Answer 24

HSO4^-

Question 25

What is the formula for Permanganate

Answer 25

MnO4^-

Question 26

What is the formula for Carbonate

Answer 26

CO3^2-

Question 27

What is the formula for Chromate

Answer 27

CrO4^2-

Question 28

What is the formula for Dichromate

Answer 28

Cr2O7^2-

Question 29

What is the formula for Sulfate

Answer 29

SO4^2-

Question 30

What is the formula for sulfite

Answer 30

SO3^2-

Question 31

What is the formula for Thiosulfate

Answer 31

S2O3^2-

Question 32

What is the formula for phosphate

Answer 32

PO4^3-