Chemical changes

Question 1

What is produce when metals react with oxygen?

Answer 1

metal oxides

Question 2

Describe reduction and oxidation in terms of loss or gain of oxygen

Answer 2

oxidation is loss of electrons, gain of oxygen or loss of hydrogen
reduction is gain of electrons, loss of oxygen or gain of hydrogen

Question 3

Why do displacement reactions occur?

Answer 3

when a metal is more reactive than another metal

Question 4

State the reactivity series

Answer 4

potassium
sodium
calcium
magnesium
aluminium
carbon
zinc
iron
tin
lead
hydrogen
copper
silver
gold
platinum

Question 5

Why are some metals such as gold found in the earth as metal itself but most are found as compounds?

Answer 5

they have reacted with other elements as they are more reactive

Question 6

What determines whether a metal can be extracted from its oxide by reduction?

Answer 6

if a metal is less reactive than carbon

Question 7

What is produces when acids react with some metals?

Answer 7

salts and hydrogen

Question 8

When acids are neutralised by alkalis and bases what is produced?

Answer 8

salts and water

Question 9

When acids are neutralised by metal carbonates what is produced?

Answer 9

salts, water and carbon dioxide

Question 10

What salts are produced in neutralisation reactions?

Answer 10

metal + ide or ate (taken from the acid)

Question 11

What can reactions be used to make?

Answer 11

soluable salts

Question 12

What do acids produce in aqueous solutions?

Answer 12

hydrogen ions

Question 13

What do aqueous solutions of alkalis contain?

Answer 13

hydroxide ions

Question 14

What is the ph scale and how is it used?

Answer 14

range from 0-14
1-6 = acid
7 = neutral
8-14 = alkaline

Question 15

What happens in a neutralisation reaction between an acid and an alkali?

Answer 15

hydrogen ions react with hydroxide ions to produce watee

Question 16

what is the ionic equation for a neutralisation reaction?

Answer 16

NaOH+HCl ->H2O & NaCl

Question 17

what is the use of universal indicator?

Answer 17

shows us how acidic or alkaline a solution is

Question 18

What can the volumes of acid and alkali solutions that react with eachother be measured by?

Answer 18

titration using a suitable indicator

Question 19

How do you carry out titrations?

Answer 19

1. fill up a burette with acid
2. use a pipette to add alkali to conical flask
3. Add an indicator to the alkali
4. slowly add the acid into the alkali
5. slow the adding of acid when the indicator changes colour
6. Stop adding when there is a permanent colour change

Question 20

How do you calculate the chemical quantities in titrations? ( involving concentrations in mol/dm3 and g/dm3 )

Answer 20

amounts of solute in moles = concentration x volume

Question 21

What is a strong acid? give an example

Answer 21

an acid that breaks down completely
sulphuric acid or hydrochloric acid

Question 22

what is a weak acid? give an example

Answer 22

partially dissociates
ethanoic acid

Question 23

What happens as the pH decreases by one unit?

Answer 23

the hydrogen ion concentration of the solution increases by a factor of 10

Question 24

What happens to the ions in an ionic compound when it is melted or dissolved in water?

Answer 24

ions are free to move from place to place

Question 25

What is an electrolyte?

Answer 25

substances that have a natural positive or negative charge when dissolved in water

Question 26

What happens to ions during electrolysis?

Answer 26

positive ions move to the cathode
negative ions move to the anode

Question 27

What happens during the electrolysis of molten compounds?

Answer 27

positively charged ions move to the cathode, they receive electrons and are reduced.

Question 28

Why is electrolysis used to extract some metals?

Answer 28

when a metal is more reactive than carbon it is cheaper to extract by electrolysis

Question 29

Why are large amounts of energy used in the extraction process?

Answer 29

to melt the compounds and to produce the electrical current

Question 30

How is aluminium extracted using electrolysis?

Answer 30

positively charged ions gain electrons from the cathode and form molten aluminium

Question 31

Why is a mixture used as the electrolyte during the extraction of aluminium?

Answer 31

to allow the movement of free ions

Question 32

Why must the positive electrode be continually replaced during the extraction of aluminium?

Answer 32

the oxygen reacts with the carbon of the positive electrodes forming CO2 so they gradually burn away

Question 33

What do ions discharges when an aqueous solution is electrolysed using inert electrodes depend on?

Answer 33

the relative reactivity of the elements involved

Question 34

What will be produced at the negative electrode (cathode) and how is this linked to the break down of water molecules?

Answer 34

hydrogen is produced if the metal is more reactive than hydrogen

Question 35

What will be produced at the positive electrode (anode) and how is this linked to the break down of water molecules?

Answer 35

oxygen is produced

Question 36

What happens at the cathode and anode in terms of electrons, oxidation and reduction?

Answer 36

reduction happens at the negative cathode because this is where positive ions gain electrons.
oxidation happens at the positive anode because this is where the negative ions lose electrons

Question 37

How do you write half equations?

Answer 37

1. write down the reactant and the product
2. balance the atoms
3. write the total charge underneath each species in the equation
4. balance the charge by adding electrons