Chemical Changes C4

Question 1

What is oxidation/reduction

Answer 1

Oxidation Is loss of electrons and reduction is gain of electrons

Question 2

What’s a displacement reaction

Answer 2

Where a more reactive metal displaces a less reactive metal from a compound

Question 3

General equation for a reaction between metals and acids

Answer 3

Metal + acid -> salt +hydrogen

Question 4

What are bases?

Answer 4

Compounds that neutralise acids

Question 5

What are acids and alkalis

Answer 5

Acids produce hydrogen ions aq.
Alkalis are soluble bases and produce hydroxide ions aq.

Question 6

What colour and number is neutral on the ph scale

Answer 6

Green, 7

Question 7

What is a strong acid and what is a weak acid

Answer 7

Strong acid is completely ionised in aq solution
Weak acid is partially ionised in aq solution

Question 8

What happens to ph as concentration of h+ increases

Answer 8

Ph decreases

Question 9

What is electrolysis

Answer 9

Electrolysis involves using electricity to break down electrolytes to form elements.

Question 10

What is an electrolyte

Answer 10

The liquid/solution that conducts electricity

Question 11

What happens at the Cathode and anode and which is positive and negative

Answer 11

Cathode is negative electrode, Anode is positive
Reduction occurs at the cathode
Oxidation occurs at the anode

Question 12

What is cryolites purpose

Answer 12

Lowers the melting point of aluminium oxide, reducing energy cosfs

Question 13

Define Conservation of mass

Answer 13

the total mass of the reactants in a chemical reaction is equal to the total mass of the products

Question 14

What is relative formula mass?

Answer 14

The sum of the relative atomic masses of the atoms in a formula

Question 15

What could happen to the mass if the product or reactant is a gas

Answer 15

The mass could be less because the gas has seemingly escaped into the atmosphere.
The gas’s weight may not be taken into account.

Question 16

What is the formula to Calculate the volume of a gas

Answer 16

No of moles of gas or mass of gas = volume of gas (dm3) / 24dm3

Question 17

What is the limiting reactant

Answer 17

The reactant that is completely used up and limits the amount of product that can be made

Question 18

Define concentration

Answer 18

the amount of solute there is in a specific volume of the solvent.

Question 19

Units for concentration

Answer 19

Mol/dm3

Question 20

Define mole

Answer 20

The mass of 1 mole of a substance in grams is equal to its relative formula mass. For example water has an RFM of 18 and 1 mole of water has a mass of 18g.

Question 21

How to work out number of moles

Answer 21

Number of Moles = Mass / RFM

Question 22

How to calculate concentration (2 ways)

Answer 22

Concentration (g/dm3) = mass of solute (g) / volume of solution (dm3)
Concentration (mol/dm3) = no. Of moles / volume of solution (dm3)

Question 23

Describe the steps of the making salts RPA (6 marks)

Answer 23

1. Add fixed volume of dilute acid into a beaker
2. Heat acid into almost boiling.
3. Asmall amount of copper oxide and the stir using a glass rod.
4. Keep adding copper oxide into powder remains after stirring. This means all of the acid has reacted and the reaction has stopped.
5. Use filtration to remove unreactive copper using filter paper and conicle flask.
6. Play solution in an evaporating basin and heat gently over beaker of boiling water.
7. leaves solution in a cool place for 24 hours to allow crystals to form.