Chemical Changes

Question 1

The reactivity series

Answer 1

Potassium, sodium, and calcium are at the top with transition metals such as gold and silver at the bottom

Question 2

Displacement reactions

Answer 2

When a more reactive metal displaces the less reactive metal

Question 3

Extracting metals

Answer 3

The less reactive metals are usually extracted by carbon reduction (heat a metal with carbon) (redox reaction)

More reactive metals are extracted by electrolysis

Question 4

Making salts

Answer 4

Salts are the compounds formed when acids are neutralised

Question 5

Bases (alkalis)

Answer 5

Bases are chemicals that neutralise acids to make a salt and water

Question 6

Reaction of metals with oxygen

Answer 6

Metal + oxygen = metal oxide

Oxidation reaction as the metal gains oxygen

Question 7

Reaction of metals with acids

Answer 7

Metal + acid = salt + hydrogen

Question 8

Reaction of metal oxides with acids

Answer 8

Metal oxide + acid = salt + water

Question 9

Reaction of metal carbonates with acids

Answer 9

Metal carbonate + acid = salt + carbon dioxide + water

Question 10

Neutralisation reaction

Answer 10

A reaction between an acid and a base (alkalis)

Question 11

Neutralisation reaction balanced equation

Answer 11

H⁺(aq) + OH⁻(aq) → H₂O(l)

Question 12

Dilute solutions

Answer 12

A dilute solution contains relatively small amount of dissolved solute

Question 13

Concentrated solutions

Answer 13

A concentrated solution contains a relatively large amount of dissolved solute

Question 14

Strong acids

Answer 14

Strong acids completely dissociate into ions (H⁺) in solution

It ionises completely

Question 15

Weak acids

Answer 15

Weak acids partially dissociate into ions (H⁺) in solution

It partially ionises

Question 16

pH and universal indicator

Answer 16

Acidic - red, pH < 7

Neutral - green, pH = 7

Alkaline - purple, pH = 14

Question 17

pH and hydrogen ion concentration

Answer 17

The higher the concentration of H+ ions in an acidic solution, the lower the pH

The lower the concentration of H+ ions in an acidic solution, the higher the pH

Question 18

Preparation of soluble salt

Answer 18

Add powdered insoluble reactant to acid in a beaker

Add until excess

Filter the mixture into a beaker to remove the excess

Pour the filtrate into an evaporating basin

Place on a water bath, and stop until small crystals start to appear

Dry the crystals using a towel and place on the windowsill

Question 19

Titrations

Answer 19

Used to measure accurately what volume of acid and alkali react completely

Question 20

Titrations practical

Answer 20

Use the pipette and pipette filler to add 25 cm3 of alkali to a conical flask

Add a few drops of indicator and put the conical flask on a white tile

Fill the burette with acid and note the starting volume

Open the tap and allow the acid to enter the conical flask drop by drop

Swirl the conical flask, slowly

Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour)

Question 21

Electrolysis

Answer 21

The breakdown of a compound using an electrical current

Question 22

PANIC

Answer 22

Positive anode, negative is cathode

Question 23

OILRIG in terms of electrons

Answer 23

Oxidation is loss (of electrons), reduction is gain (of electrons)

Question 24

OILRIG in terms of oxygen

Answer 24

Oxidation is gain (of oxygen), reduction is loss (of oxygen)

Question 25

Products at the cathode

Answer 25

If the metal is more reactive than hydrogen, H⁺ ions will be produced

Question 26

Products at the anode

Answer 26

If no halide ions are present then O₂ is produced

Question 27

Electrolysis practical

Answer 27

Add about 50cm³ of copper chloride solution to a beaker Add the lid and insert electrodes through the holes making sure the electrodes don’t touch Attach crocodile leads to the electrode and connect the rods to the DC terminals of 4V Using the forceps hold the litmus paper near the positive electrode Observe the negative electrode

Question 28

Test for hydrogen

Answer 28

A burning splint held at the open end of a test tube of the gas Hydrogen burns rapidly with a pop sound

Question 29

Test for oxygen

Answer 29

The test for oxygen uses a glowing splint inserted into a test tube of the gas The splint relights in presence of oxygen

Question 30

Test for carbon dioxide

Answer 30

When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)

Question 31

Test for chlorine

Answer 31

Damp blue litmus paper turns red and is then is bleached and turns white

Question 32

Half equations

Answer 32

2H⁺ + 2e⁻ → H₂