Topic 3 - Chemical changes

Question 1

Charges of acids & alkalis in aqueous solutions

Answer 1

• acids produce H+ ions

- alkalis produce OH-

Question 2

Colours of Phenolphthalein

Answer 2

Phenolphthalein

• Alkaline = pink
• Acidic = colourless

Question 3

Colours of Methyl orange

Answer 3

Methyl orange

• Alkaline = yellow
• Acidic = red

Question 4

Litmus solution and litmus paper

Answer 4

Litmus solution
-Alkaline = blue
- Acidic = red
○ Litmus paper
- Blue litmus paper goes red in acidic & stays blue in alkaline
- Red litmus paper goes blue in alkaline & stays red in acidic

Question 5

What does does a strong acid and alkali mean ?

Answer 5

-higher concentration of H+ ions makes a strong acid
- higher concentration of OH- ions mean
solution is more alkaline, having a higher pH

Question 6

Explain the terms concentrated and dilute

Answer 6

• concentrated is the larger amount of substance in a volume of a solution
  ▪ Dilute is the lesser amount of substance in a volume of a solution

Question 7

acid + metal reaction

Answer 7

acid + metal -> salt + hydrogen gas

Question 8

acid + metal oxide

Answer 8

acid + metal oxide -> salt + water

Question 9

What is a weak acid?

Answer 9

• a weak acid partially dissociates – doesn’t produce many H+ ions, so reaction w/

Question 10

What is a weak acid?

Answer 10

• a weak acid partially dissociates – doesn’t produce many H+ ions, so reaction w/ substance is slow

Question 11

acid + metal hydroxide

Answer 11

acid + metal hydroxide -> salt + water

Question 12

acid + metal carbonate

Answer 12

acid + metal carbonate -> salt + carbon dioxide

Question 13

Test for hydrogen

Answer 13

• burning splint held at open end of a test tube of the gas

- Creates ‘squeaky pop’ sound

Question 14

Test for carbon dioxide

Answer 14

• Bubble the gas through the limewater (calcium hydroxide solution) and will turn milky (cloudy)

Question 15

Neutralisation reaction equation

Answer 15

H+ (aq) + OH- (aq) -> H20 (l)

Question 16

Explain how to make copper sulfate crystals

Answer 16

• add excess of copper oxide (insoluble) to acid
• use filter and filter paper to filter off any copper oxide that hasn’t reacted
• evaporate off water by placing final solution in water bath

Question 17

how to carry out acid-alkali titration, using burette, pipette
and indicator, to prepare salt

Answer 17

• Wash burette using acid and
• Fill burette with acid
• Use pipette to add alkali into conical flask, drawing alkali using a pipette filler
• Add phenolphthalein to conical flask
• use white tile
• Add acid from burette to alkali carefully and swirl till reaches endpoint (turns light purple)
• Repeat experiment to gain more precise results
• warm salt solution in water bath to evaporate the water– crystals will form

Question 18

What is titre (titration experiment)?

Answer 18

-difference between first and second readings on burette

Question 19

solubility of common sodium, potassium and ammonium

in water

Answer 19

• all are soluble in water

Question 20

solubility of common chlorides in water

Answer 20

• are soluble except silver and lead,

Question 21

solubility of common sulfates in water

Answer 21

-are soluble except lead, barium and calcium,

Question 22

solubility of common carbonates and hydroxides are

Answer 22

-insoluble except sodium, potassium and ammonium

Question 23

how to prepare pure, dry sample of an insoluble

salt

Answer 23

• mix two solutions needed to form salt
• filter mixture using filter paper, which insoluble salt will be left on
• wash salt using distilled water
• leave salt to dry on filter paper

Question 24

What is an electrolyte?

Answer 24

-When an ionic substance is melted or dissolved & ions are free to move about within liquid or solution

Question 25

What is electrolysis?

Answer 25

- process which electrical energy, from a direct current supply decomposes electrolytes - Passing current through substances that are molten or solution means that solution can be broken down into elements-- that's electrolysis, and substance being broken down is the electrolyte

Question 26

What is the movement of ions in electrolysis?

Answer 26

- positively charged ions (cations) move to negative electrode (cathode) - negatively charged ions (anions) move to positive electrode (anode). - Ions then discharged at electrodes producing elements

Question 27

Explain what happens at the cathode during electrolysis?

Answer 27

- at cathode (-): ○ hydrogen (from H+ in water) is produced UNLESS positive ions in ionic compound are from a metal less reactive than hydrogen ○ if the metal is less reactive, it will be produced instead

Question 28

What happens at anode during electrolysis?

Answer 28

- at anode (+): ○ oxygen (from OH- in water) will be produced UNLESS ionic compound contains halide ions (Cl-, Br-, I-) ○ if there are halide ions, the halogen will be produced instead (e.g. Cl2)

Question 29

What is a halide ion ?

Answer 29

- halogen atom w/ a negative charge

Question 30

List of halide ions

Answer 30

- fluoride, chloride, bromide, iodide and astatide

Question 31

Electrolysis of copper chloride solution?

Answer 31

- Cu+ ions got to the cathode | - Cl- ions go to anode

Question 32

Electrolysis of sodium chloride solution

Answer 32

H+ ions go to cathode | - Cl-ions go to anode

Question 33

Electrolysis of Water acidified with sulfuric acid

Answer 33

- H+ to cathode, | - OH- to anode

Question 34

Electrolysis of Molten lead bromide

Answer 34

- Pb2+ to cathode, Pb is produced (not in solution so these are the only + ions present) - Br- to anode

Question 35

What is the reactivity series (most reactive to least)

Answer 35

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

Question 36

Half equation of a negative electrode

Answer 36

X+ + e- -> X, electrons gained, so positive ions are reduced

Question 37

Half equation of positive electrode

Answer 37

X- -> e- + X, electrons are lost, so negative ions are oxidised

Question 38

where does oxidation and reduction occur?

Answer 38

- oxidation at anode – loss of electrons | - reduction at cathode – gain of electrons

Question 39

How can electrolysis purify copper (experiment)?

Answer 39

-anode is made of impure copper ○ cathode is made of pure copper ○ the solution is copper sulfate - Cu2+ ions from anode move to cathode, where they gain electrons and discharged as pure copper ○ impurities form as sludge below the anode - cathode will increase in mass as it gains pure copper -- anode will lose mass as copper ions are lost -- replace ones from CuSO4 solution & so are impurities

Question 40

Why isn't universal indicator used in titration experiments

Answer 40

- doesn't show clear/ distinct change in colour