Formulae And Expressions

Question 1

How to calculate the number of moles of solute

Answer 1

n = C x V

Step 1: write the chemical equation
Step 2: balance the chemical equation
Step 3: Cross out irrelevant information and write the molar ratio
Step 4: Calculate the number of moles using the information in the question
Step 5: Use the molar ratio to find the number of moles of the unknown variable
Step 6: Calculate the unknown variable

Question 2

SVSDF

Answer 2

Symbol - Write down the symbols of both the elements involved

Valency - Beneath each symbol, write its valency

Swap - Swap the valencies over

Divide - if the valencies can be simplified, divide them both by the smaller of the 2 numbers. If one of the numbers is already 1, then they cannot be divided and simplified any further.

Formula - Write the formula

Question 3

How to calculate the mass of a substance

Answer 3

M= n x GFM

Question 4

How to calculate the number of moles

Answer 4

n = m/GFM

Question 5

How to calculate the gram formula mass of a substance

Answer 5

GFM = m/n

Question 6

How to calculate the concentration of a solution

Answer 6

C = n/V

Question 7

How to calculate the volume of a solution in litres

Answer 7

V = n/C

Question 8

How to calculate the percentage mass

Answer 8

Step 1: Write the chemical formula of the compound

Step 2: Calculate the gram formula mass of the compound

Step 3: For the percentage mass asked in the question, insert the mass of the element and the formula mass of the compound into the formula below:

% mass = mass of element in the compound/ GFM of compound x 100

Question 9

Covalent bonds

Answer 9

Occurs in non-metals

Structures:

• covalent network - unlimited no. of atoms
• discrete molecular - defined no. of atoms e.g. H2O

Question 10

CHO rule

Answer 10

Balance carbon first then hydrogen then oxygen then anything else

Question 11

Ionic bonds

Answer 11

Metal and non-metals e.g. sodium chloride

Structure:
- Ionic lattice

NOTE: When you dissolve an ionic solid the ionic lattice breaks down and the ions are free to move

Conducts when molten/ in solution
Doesn’t conduct when solid

Question 12

Metallic bonds

Answer 12

Occurs in metals

Structure: electrons are delocalised

Question 13

What are isotopes

Answer 13

Isotopes are atoms of the same element which have:
The same atomic number but a different mass number
The same number of protons but a different number of neutrons