Section 3- Equations, Calculations and Electrolysis P1

Question 1

Define RAM or Aᵣ:

Answer 1

The average mass of an atom of an element taking into account the ISOTOPE MASSES AND ABUNDANCES.

Question 2

What do equations show?

Answer 2

The reactants and products of a reaction

Question 3

What are the four state symbols?

Answer 3

s - solid
l - liquid
g - gas
aq - aqueous (dissolved in water)

Question 4

How do you balance symbol equations?

Answer 4

By making sure you have the same number of atoms of each element on each side

Question 5

How do you calculate relative formula masses(RFM or Mᵣ)?

Answer 5

You break up the formula in elements

(Mass of E1 x amount of E1)+(Mass of E2 x amount of E2)+….. = RFM

Question 6

What is a mole?

Answer 6

‘The mole’ is the unit for the amount of a substance

Question 7

What is the significance of using moles?

Answer 7

One mole of atoms or molecules of any substance will have a mass in grams equal to the relative particles mass (Aᵣ or Mᵣ) for that substance.

Question 8

What is molar mass measured in?

Answer 8

grams

Question 9

What would one mole of a substance equal?

Answer 9

The Aᵣ or Mᵣ of a substance in grams

Question 10

How do you calculate the amount of moles of a substance in a given mass?

Answer 10

Moles = Mass(g) ÷ Mᵣ

Question 11

How can you calculate the amount of product you will have from the mass of a reactant?

Answer 11

• write out the balanced equation for the reaction
• work out the Mᵣ of the reactant and product you are interested in
• use moles = mass ÷ Mᵣ and the mole ratio to work out the moles of the given mass one and compare that using the mole ratio to the other
• use moles x Mᵣ = mass, to work out the mass

Question 12

How do you calculate percentage compositions (%compositions)?

Answer 12

You need to have the RFM/Mr

(Mass of E1 x amount of E1) ÷ RFM

Question 13

What do you need to work out the empirical formula?

Answer 13

A percentage or mass of the elements and RAM of the elements

Question 14

How do you calculate the empirical formula?

Answer 14

1)for each element do:
% or mass ÷ RAM
2)then divide through by the smallest value from 1
3)the answer from two should give you an integer ratio or a .5 which would mean you have to double all the numbers
4)you then write out the formula using the element symbols and the ration as small numbers

Question 15

How do you calculate the molecular formulae?

Answer 15

You need to have the empirical formula first

1) you work out the RFM of your empirical formula
2) then you have the RFM of a substance
3) RFM of the substance ÷ RFM of the empirical formula
4) you then with what answer you get from 3 times the ratio of the empirical formula by it and then write the formula with the ratio you just calculated

Question 16

How do you work out percentage yields?

Answer 16

(Actual yield ÷ Theoretical yield) x 100

Question 17

What is the difference between the theoretical yield and the percentage yield?

Answer 17

• the theoretical yield is the calculated mass yield you work out through calculations
• however the actual percentage yield compares the actual yield you got from physically doing the experimented to the yield you calculated

Question 18

Describe an experiment of how you can find the empirical formulae using combustion:
By using magnesium reacting with oxygen:

Answer 18

• weigh the crucible and lid
• put the magnesium in the crucible with the lid on and weigh it
• heat the magnesium opening the lid occasionally to let oxygen in
• once the magnesium has stopped flaring leave the lid off
• after 5 mins weigh the crucible with its lid on and content
• heat again and re weigh until a consistent mass is reached

Question 19

When you have a equation what numbers represent the mole ratio numbers?

Answer 19

The big number before each substance shows the mole ratio

Question 20

Describe an experiment of how you can find the empirical formulae using reduction:
By using copper(II) oxide:

Answer 20

• place a rubber bung with a tube it into a test tube {with a small hole in the end through} and weigh it (using a mass balance)
• put copper(II) oxide in it and re-weigh
• attach the bung tube to the gas and then get a lit splint and light the small hole in the end of the tube
• use a Bunsen burner to heat the copper(II) oxide for 10 mins (colour change from black to brownish)
• turn the Bunsen burner off and leave it to cool and re-weigh the tube and bung and contents

Question 21

How do you find a formula of a hydrated compound?

Answer 21

You need to have the mass of the compound and of the water
1)for both the compound and water you do
Mass ÷ RFM of the compound
2)then divide through by the smallest
3)you will have to get a integer ratio from the answers to 2
4)you then write out the formula with the ratio before the compounds, you write:
_Formula of compound. _Water

Question 22

What are two types of salts?

Answer 22

Hydrated (containing water of crystallisation)

Anhydrous

Question 23

What is the water in a salt lattice called?

Answer 23

Water of crystallisation

Question 24

What is the structure of all solid salts?

Answer 24

All solid salts consist of a lattice of positive and negative ions