Topic 4 - Chemical Changes

Question 1

acid + alkali ->

Answer 1

acid + alkali -> salt + water

Question 2

Acid + Metal →

Answer 2

Acid + Metal → Metal salt + hydrogen(g)

Question 3

Acid + Metal Carbonate →

Answer 3

Acid + Metal Carbonate → Metal salt + carbon dioxide + water

Question 4

Acid + metal oxide →

Answer 4

Acid + metal oxide → Salt + Water

Question 5

metal + oxygen →

Answer 5

metal + oxygen → metal oxide

Question 6

What is the name given to a reaction that involves losing oxygen?

Answer 6

reduction

Question 7

REACTIVITY SERIES

purple
slime
can
make
a 
careless
zebra
insane
try 
learning
how
camels
surprise
gorilla
parties

Answer 7

Potassium
Sodium
Calcium
Magnesium
Aluminium
(Carbon)
Zinc
Iron
Tin
Lead
(Hydrogen)
Copper
Silver
Gold 
Platinum

Question 8

describe the observations of water reacting with potassium, lithium, sodium

Answer 8

Potassium, sodium and lithium all react quickly with cold water to produce a metal hydroxide and hydrogen gas.
2
Potassium
Potassium is the most reactive so reacts very quickly. The hydrogen produced ignites instantly and the metal also sets alight, sparking and burning with a lilac flame.
3
Sodium
Sodium fizzes rapidly and melts to form a ball that moves around on the water surface.
4
Lithium
Lithium fizzes steadily and floats, becoming smaller until it eventually disappears.

Question 9

when do displacement reactions occur?

Answer 9

Displacement reactions occur when a more reactive metal reacts to displace a less reactive metal in a compound.

Question 10

When zinc is reacted with calcium carbonate, no reaction occurs. Explain why.

Answer 10

Zinc does not react with calcium carbonate because zinc is not as reactive as calcium.

Question 11

what are all the diatomic elements?

Answer 11

Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Fluorine (F2)
Chlorine (Cl2)
Iodine (I2)
Bromine (Br2)

Question 12

what group are halogen ?

Answer 12

7

Question 13

describe what happens at each electrode in electrolysis in aqueous solutions

Answer 13

At the cathode (negative electrode)

What is formed at the cathode depends on the reactivity of the metal:
Hydrogen is produced if the metal is higher than hydrogen in the reactivity series.
The metal is produced if the metal is lower than hydrogen in the reactivity series.

At the anode (positive electrode)

What is formed at the anode depends on if there are halide ions present:
If there are halide ions present, the respective halogen forms.
If there are no halide ions, oxygen forms.

Question 14

does reduction or oxidation take place at the anode?

Answer 14

oxidation

Question 15

does reduction or oxidation take place at the anode?

Answer 15

oxidation

Question 16

does reduction or oxidation take place at the cathode?

Answer 16

reduction

Question 17

An aqueous solution of copper(II) sulfate (CuSO4) contains Cu2+, SO42-, H+ and OH- ions. What happens when it is electrolysed?

Question 18

What characterises a more reactive metal?

Answer 18

a metal that forms positive ions more easily

Question 19

Which of the following would you observe when adding potassium to water?

Answer 19

lilac flame
very quick reaction
sparks

Question 20

Give 2 reasons why carbon is used to extract metals from their oxides:

Answer 20

1Carbon is cheap
2Carbon is abundant
3 cheap

Question 21

State 2 metals that would react with dilute acid but not water.

Answer 21

Magnesium
Zinc
Iron
Aluminium
Lead

Question 22

what are the obsevations when sodium is added to water?

Answer 22

melts into a ball
lots of fizzing
orange flame
moves around on surface

Question 23

what are the observations when lithium is added to water?

Answer 23

floats on surface
fizzes steadily
gets smaller and smaller

Question 24

what are the observations when calcium is added to water?

Answer 24

fizzing

cloudy precipitate

Question 25

Describe strong acids

Answer 25

•Ionise completely in water •All acid particles dissociate to release H+ ions = higher conc of H+ ions so rate of reaction will be faster.

Question 26

Describe weak acids

Answer 26

-Don' t fully ionise in solution - only small number of acid particles dissociate to release H+ ions . The ionisation of weak acid is a reversible reaction,which sets up an equilibrium between the undissociated and dissociated acid. Due to only a few of the acid particles release H+ ions, the position at equilibrium lies to the left

Question 27

What is pH?

Answer 27

measure of the conc of H+ ions in solution. For every decrease of 1 on pH scale H+ ions increase by a factor at 10. so pH 4 acid has ten times more conc of H+ Ions as pH 5 acid. Factor H+ ion conc changes by = 10^-x So if ph decreased from 5 to 2 there would be a decrease of -3 so 10^-(-3)+ 10^3

Question 28

Which factor determines the reactivity of a metal?

Answer 28

How easily the atoms of that element lose their outer electrons

Question 29

what is a displacemtn reaction?

Answer 29

When a more reactive metal displaces a less reactive metal

Question 30

Which group of metals are the most reactive?

Answer 30

Group 1

Question 31

When metals react, do the atoms become positive or negative ions?

Answer 31

positive

Question 32

In electrolysis, which direction do the electrons travel?

Answer 32

Anode ➔ Cathode

Question 33

The electrodes in an electrolysis cell are normally made of inert carbon. What does the term 'inert' mean?

Answer 33

It is unreactive, so will not take place in the reaction.

Question 34

In electrolysis, why does the compound you're trying to separate need to be molten or dissolved?

Answer 34

So that the ions are free to move around (and go to their respective electrode)

Question 35

Why is electrolysis not used to extract all metals?

Answer 35

Electrolysis is expensive because it requires a large amount of electricity, metals less reactive than carbon can be reduced

Question 36

Why is electrolysis used to extract aluminium from its ores?

Answer 36

more reactive than carbon

Question 37

What is the name of the substance that is mixed with aluminium oxide to lower its melting point?

Answer 37

Cryolite

Question 38

Balance the equation below for the separation of aluminium from oxygen. Al2O3 ➔ Al + O2

Answer 38

2Al2O3 ➔ 4Al + 3O2

Question 39

In the electrolysis of aqueous solutions, what is the rule for determining which ion will be oxidised (lose electrons) at the anode (positive electrode)?

Answer 39

It will always be the OH-, unless there is a halide ion (such as Cl-, or Br-) present remember all halide ions are diatomic

Question 40

In the electrolysis of aqueous solutions, what is the rule for determining which ion will be reduced (gain electrons) at the cathode (negative electrode)?

Answer 40

It will always be the H+ ion, unless Cu2+ is present (another way of phrasing it would be that it is always the ion of the least reactive element)

Question 41

In the electrolysis of aqueous sodium chloride, NaCl (aq), which four ions would be present in the electrolyte?

Answer 41

Sodium ions (Na+) Chloride ions (Cl-) Hydrogen ions (H+) Hydroxide ions (OH-)

Question 42

In the electrolysis of aqueous sodium chloride, NaCl (aq), which of the four ions will be oxidised at the anode (positive electrode)?

Answer 42

Chloride ions (Cl-)

Question 43

In the electrolysis of aqueous sodium chloride, NaCl (aq), which of the four ions will be reduced at the cathode (negative electrode)?

Answer 43

Hydrogen ions (H+)