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Chemistry Exam Questions > Topic 3 – Chemical Changes > Flashcards

Topic 3 – Chemical Changes Flashcards

1
Q

Explain the meaning of weak acid

A

• partially ionised
• concentration of H+ ions lower

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2
Q

Define electrolytes

A

Ionic compound in molten state/dissolved in water

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3
Q

Define electrolysis

A

A process in which electrical energy/ electricity (from a direct current supply) decomposes electrolytes

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4
Q

Cations (positively charged ions) move towards the…

A

Cathode (negative electrode)
• REDUCED (gains electrons) so mass increases

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5
Q

Anions (negatively charged ions) move towards the…

A

Anode (positive electrode)
• OXIDISED (loses electrons) so mass decreases

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6
Q

What ions are present at the cathode?

A

H+ and metal ions

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7
Q

When is hydrogen produced at the cathode?

A

Hydrogen produced if metal is more reactive than hydrogen (e.g. sodium)

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8
Q

When are metals produced at the cathode?

A

Metal produced if it’s less reactive than hydrogen (e.g. copper, silver)

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9
Q

What happens when OH- & halide ions are present at the anode?

A

• if ionic compound contains halide ions, the halogen is produced (Cl2)

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10
Q

What happens when OH- & halide ions are NOT present at the anode?

A

• Oxygen produced if no halide ions are present (Cl, Br, I)

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11
Q

What are the products formed when a sample of molten potassium bromide is electrolysed?

A

Potassium & bromine

• Potassium (more reactive than Hydrogen)
• Bromine (halide ion)

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12
Q

Test for Hydrogen

A

• Lit splint
• Burns with a squeaky pop

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13
Q

State why it is important that the electrodes are inert

A

inert electrodes do not react with the electrolyte

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14
Q

Explain, in terms of structure, how graphite conducts electricity

A

• electrons
• move (through graphite)
• are delocalised/ free to move

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15
Q

Explain why mass decreases at anode

A

• Atoms become ions
• Atoms are oxidised (lose electrons)
• ions move into solution

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16
Q

Explain why mass increases at cathode

A

• Ions become atoms
• Ions are reduced (gain electrons)
• Ions move out of solution

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17
Q

Molten lead bromide can be electrolysed to form molten lead and bromine gas. Explain how a student can set up an apparatus to carry out this electrolysis (2)

A

• Use a crucible (instead of beaker)
—> so it doesn’t break (when heated strongly)

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18
Q

Explain what should be done to copper electrodes before their masses are determined

A

• Electrodes should be cleaned (using emery paper)
• to remove impurities

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19
Q

Explain how Hydrogen gas is formed at the cathode

A

• hydrogen ions attracted to cathode
• hydrogen ions are reduced (gain 2 electrons)

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20
Q

State what equipment could be used to measure the volume of a gas

A

• measuring cylinder
• burette
• gas syringe

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21
Q

State what could be added into the circuit to show a current is flowing during electrolysis

A

• ammeter
• light bulb/lamp

22
Q

State how hydrochloric acid and base can be measured accurately

A

• HCL - Burette, pipette, measuring cylinder
• Base - balance, scales, weigh out amount

23
Q

Colour change of phenolphthalein indicator

A

Start: colourless
End: pink

24
Q

Explain why pH increases during neutralisation

A

• H+ ions neutralised/reacted
• more concentration of OH- ions

25
Q

Test for carbon dioxide

A

• Bubble gas through limewater
• limewater turns milky/cloudy

26
Q

Test for oxygen

A

• glowing splint
• relights

27
Q

Describe what you would see when copper carbonate powder is added to a beaker of dilute sulfuric acid

A

• powder disappears/dissolved in acid
• effervescence/fizzing/bubbles
• blue solution forms

28
Q

Describe how pure, dry crystals are obtained from a solution (2 marks)

A

• Heat solution/leave water to evaporate
• Filter off/dry crystals formed

29
Q

Describe how a sample of pure, dry crystals can be obtained from the filtrate

A

• heat solution (to concentrate)
• pat dry between filter papers
• dry in oven

30
Q

Copper carbonate + sulfuric acid —> copper sulfate + carbon dioxide + water. State two observations that would show the reaction had finished

A

• no more fizzing/bubbles
• no further change in colour
• solid (copper carbonate) remains at bottom of flask / no more solid dissolves

31
Q

Explain why dilute hydrochloric acid is described as a strong acid

A

• fully dissociates/ionises
• to form H+ ions

32
Q

Explain why the new mixture was evaporated rather than the original mixture from the titration (2)

A

• solution from titration contains an indicator
• therefore second solution used with no indicator

• original mixture was contaminated by indicator so doesn’t form a pure salt (2)

33
Q

Equipment that can measure pH

A

• pH meter
• pH probe

34
Q

Explain how pH changes as magnesium hydroxide is added to dilute hydrochloric acid

A

• pH increases
• until pH above 7
• magnesium hydroxide neutralises the acid
• so hydrogen ions concentration is reduced/all H+ ions reacted/there is an excess of hydroxide ions

35
Q

The hydrogen ion concentration in a solution is decreased by a factor of 10.
State how the pH of this solution changes.

A

pH increases by 1

36
Q

Explain why litmus paper would not be a suitable indicator to use

A

• litmus paper only shows if solution is acidic/alkaline
• does not show how acidic / alkaline solution is

37
Q

Suitable indicators for titrations

A

• phenolphthalein
• methyl orange

NOT UNIVERSAL INDICATOR

38
Q

Why is universal indicator not a suitable indicator to use in an acid-alkali titration?

A

• does not show sharp colour change at end point
• not known which colour change gives correct end point

39
Q

Describe how to obtain a pure, dry sample of the precipitate of copper hydroxide from the reaction mixture

A

• Filter mixture using filter paper
• residue (solid) is rinsed/washed (using distilled water)
•(scrape copper hydroxide onto fresh filter paper)
• dry in oven

40
Q

What element promote plant growth?

A

• Nitrogen
• Phosphorus
• potassium

41
Q

What colour is methyl orange in acid, neutral & alkaline?

A

ACID - red
NEUTRAL - yellow
ALKALINE - yellow

42
Q

What colour is phenolphthalein in acid, neutral & alkaline?

A

ACID - colourless
NEUTRAL - colourless
ALKALINE - pink

43
Q

What colour is litmus in acid, neutral & alkaline?

A

ACID - red
NEUTRAL - purple
ALKALINE - blue

44
Q

Acid + Metal Oxide produces…

A

Salt + water

45
Q

Acid + Metal Hydroxide produces…

A

Salt + water

46
Q

Acid + Metal produces…

A

Salt + Hydrogen

47
Q

Acid + Metal Carbonate produces…

A

Carbon dioxide + Salt + Water

48
Q

What 3 salts are soluble?

A

• sodium
• potassium
• ammonium

49
Q

Are all nitrates soluble / insoluble?

A

Soluble

50
Q

Name 2 insoluble chlorides

A

• Silver chloride
• Lead chloride

51
Q

Name 3 insoluble sulfates

A

• Lead sulfate
• Barium sulfate
• Calcium sulfate

52
Q

Name 3 soluble carbonates & hydroxides

A

• Ammonium carbonate/hydroxide
• Sodium carbonate/hydroxide
• Potassium carbonate/hydroxide

Chemistry Exam Questions (3 decks)

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