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GCSE Chemistry P1 > Topic 3 - Chemical changes > Flashcards

Topic 3 - Chemical changes Flashcards

Learn about acid, alkali and salts

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1
Q

What are the sources of acid and alkali?

A

Acids in a solution are sources of hydrogen ions

Alkalis in a solution are sources of hydroxide ions

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2
Q

What is an acid?

A

An acid is a substance with a pH of below 7. They form H+ ions.

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3
Q

Give examples of acid with their symbols. (5)

A 
Nitric acid - HNO3
Ethanoic acid - CH3CO2H
Hydrochloric acid - HCl
Sulfuric acid - H2SO4
Phosphoric acid - H3PO4
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4
Q

What is a strong acid?examples?

A

A strong acid is a substance that completely splits up into ions. They release all hydrogen ions. Hydrochloric, Nitric and Sulfuric.

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5
Q

What is a weak acid?

A

A weak acid is one where it only partially splits up into ions. They release some hydrogen ions. Ethanoic, lactic and citric.

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6
Q

What is the difference of concentrated vs dilute?

A

A concentrated solution has a greater amount of dissolved solute particles than dilute.

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7
Q

What does a high concentration of hydrogen ions mean?

A

It means that the solution is more acidic which means that the pH will be lower.

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8
Q

What happens as the hydrogen ion concentration in a solution increases by a factor of 10?

A

The pH of the solution decreases by 1

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9
Q

Describe the reactions of acids with metals.

A

Reactive metals react with acids to produce a salt and hydrogen only.

Metal + acid = salt + hydrogen

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9
Q

Describe the reaction of acid with metal hydroxides.

A

A salt and water are produced when acids react with metal hydroxides. Metal hydroxides are bases because they neutralise acids.

acid + metal hydroxide → salt + water

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9
Q

Describe the reaction of acid with metal oxides.

A

A salt and water are produced when acids react with metal oxides. Metal oxides are bases, because they neutralise acids.

acid + metal oxide → salt + water

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10
Q

Describe the reaction of acid with metal carbonates.

A

Metal carbonates react with acid to produce a salt, water and carbon dioxide.

Metal carbonate + acid = salt + water + carbon dioxide

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12
Q

What is a base?

A

A base is any substance that reacts with an acid to produce salt and water only. An alkali is soluble base.

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14
Q

What are other bases?

A

Metal oxides

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15
Q

What does high concentration of hydroxide ions mean?

A

This means the solution is more alkaline and therefore a higher pH.

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16
Q

What is neutralisation?

A

The reaction between an acid and a base which produces salt and water.

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17
Q

What is the ionic equation for neutralisation?

A

H+ + OH- = H20

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18
Q

What colour is litmus at acidic, alkaline and neutral?

A

Acidic - Red
Neutral - Purple
Alkaline - Blue

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19
Q

What colour is methyl orange at acidic, neutral and alkaline?

A

Acidic - Red
Neutral - Yellow
Alkaline - Yellow

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20
Q

What colour is phenolphthalein at acidic, neutral and alkaline?

A

Acidic - Colourless
Neutral - Colourless
Alkaline - Pink

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21
Q

How is a salt formed?

A

A salt forms when hydrogen ions in an acid are replaced by metal ions or ammonium ions. The name of a salt consists of two parts: First part - the metal in the base; Second part - from the acid used.

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22
Q

Describe the investigation of the change in pH for neutralisation. (4)

A

1) Add some dilute hydrochloric acid to the beaker.
2) Measure and record the pH of the contents of the beakers.
3) Add a small mass of calcium hydroxide powder, stir, and then measure and record the pH again.
4) Repeat until the pH no longer changes.

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23
Q

How do you make a soluble salt from an insoluble base? (6)

A

1) Warm the acid to speed up the reaction.
2) Then add the base to the acid. Ensure that the base in excess so there is no leftover acid in the product. You will know that the reaction is complete if there is excess solid at the bottom of the flask.
3) Filter off the excess solid to get a solution containing only the salt and water.
4) Heat the solution using a Bunsen burner to evaporate the water.
5) Leave the solution to cool and allow the salt to crystallise.
6) Filter off the solid salt and leave it to dry.

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24
Q

How do you make a soluble salt from a soluble base using titration? (6)

A

1) Measure out a set amount of acid into a conical flask using a pipette. Add a few drops of indicator.
2) Slowly add alkali to the acid, using a burette, until you reach the end point - this is when the acid’s been exactly neutralised and the indicator changes colour.
3) Repeat until you get concordant results
4) Then, carry out reaction using exactly the same volumes of alkali and acid but with no indicator, so the salt won’t be contaminated with indicator. The solution that remains when the reaction is complete contains only salt and water.
5) Slowly evaporate off some of the water and then leave the solution to crystallise.
6) Filter off the solid and dry it - you will be left with a pure, dry salt.

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25
Q

What are titrations for?

A

Titrations allow you to find out exactly how much acid is needed to neutralise a given quantity of alkali.

26
Q

How do you complete a titration?

A

1) Use the pipette and pipette filler to add a measured volume of alkali to a clean conical flask.
2) Add a few drops of indicator and put the conical flask on a white tile.
3) Fill the burette with acid and note the starting volume.
4) Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5) Stop adding the acid when the end-point is reached (when the indicator first permanently changes colour). Note the final volume reading.
6) Repeat steps 1 to 5 until you get concordant results. More accurate results are obtained if acid is added drop by drop near to the end-point.

27
Q

How do you work out mole concentration?

A

Number of moles divided by volume (dm3)

28
Q

How do you work out mass concentration?

A

Mass (g) divided volume (dm3)

29
Q

How do you work out the number of moles?

A

Concentration x Volume

30
Q

How do you work out mass concentration using mole concentration?

A

Mole concentration x Mass of one mole

31
Q

How do you work out a titration calculation? (4)

A

Find the number of moles of the solution with info
Write out the equation for the reaction
Work out the n.o of moles of the unknown substance
Work out the concentration of the unknown substance

32
Q

How do you work out mass?

A

Mass = N.O of moles x Relative formula mass

33
Q

How do you test for hydrogen?

A

You can use a lighted splint. Place the lighted splint in the container containing the gas. If a squeaky pop is heard, it means hydrogen is present.

34
Q

How do you test for Carbon Dioxide?

A

Bubble the gas through limewater. If the gas is carbon dioxide, the limewater will turn cloudy/milky.

35
Q

Which substance groups are always soluble in water? (4)

A

Common Sodium salts, Potassium salts and Ammonium salts; and Nitrates.

36
Q

What substance groups are always insoluble in water? (2)

A

Common carbonates and hydroxides except those of sodium, potassium and ammonium.

37
Q

Which substance group contain substances that are soluble and insoluble in water? (2)

A

Common chlorides except those of silver and lead; Common sulphates except those of lead, barium and calcium.

38
Q

How do you make an pure, dry insoluble salt? (4)

A

1) Mix together the two suitable solutions.
2) Use filtration to separate the precipitate as a residue from the solution.
3) Wash the precipitate with distilled water while it is in the filter funnel.
4) Leave the washed precipitate aside or in a warm oven to dry.

39
Q

What are electrolytes?

A

Ionic compounds ,in the molten state or dissolved in water, used in electrolysis.

40
Q

What is electrolysis?

A

It is the breaking down of a substance using electricity. An electric current is passed through an electrolyte, causing it to decompose.

41
Q

What happens at the cathode during elctrolysis?

A

The positive ions (cations) in the electrolyte move towards the cathode (negative electrode) as the opposites attract. The cation gains electrons, reduction occurs.

42
Q

What happens at the anode during elctrolysis?

A

The negative ions (anions) in the electrolyte move towards the anode (positive cathode). The anion loses electrons, oxidation occurs.

43
Q

Why must the ionic compounds be molten or dissolved?

A

Solid ionic compounds can’t conduct electricity so electrolysis can’t happen

44
Q

What is the reactivity series (People Say Little Children Make A Zebra Ill Constantly Sniffing Giraffes) ?

A 
Potassium 
Sodium 
Lithium 
Calcium
(CARBON) 
Magnesium 
Aluminium 
(HYDROGEN)
Zinc
Iron
Copper
Silver
Gold 
(Platinum)
45
Q

What ion is at the cathode if the electrolyte is molten?

For H20 with H2SO4; and PbBr2

A

For:
H20 with H2SO4 - Hydrogen gas forms
PbBr2 - Lead (Pb)

46
Q

What ion is at the anode if the electrolyte is molten?

For H20 with H2SO4; and PbBr2

A

For:
H20 with H2SO4 - OH-
PbBr2 - Bromine gas

47
Q

What ion is at the cathode if the electrolyte is a solution?

For CuCl2, NaCl, NaSO4

A

For:
CuCl2 - Hydrogen (copper is less reactive than hydrogen)
NaCl - Sodium
NaSO4 - Sodium

48
Q

What ion is at the anode if the electrolyte is a solution?

For CuCl2, NaCl, NaSO4

A

For:
CuCl2 - Chlorine
NaCl - Chlorine
NaSO4 - Oxygen

If the compound contains Halide (group 7) ions, then the halide ion is discharged instead of the OH- ion.
If the compound contains other negative ions (SO4-), then OH- ion is discharged. This forms oxygen.

49
Q

Write a balanced half equation for the formation of Sodium from Na+?

A

Na^+ + e- = Na

50
Q

Write a balanced half equation for the formation of Chlorine from 2Cl-?

A

2Cl- - 2e-

51
Q

What is oxidation?

A

Loss of electrons

52
Q

What is reduction?

A

Gain of electrons

53
Q

What happens at the anode in the electrolysis of copper?

Half eq

A

The electrical supply pulls electrons off at the anode

Cu (s) = Cu^2+ + CO2 `

54
Q

What happens at the cathode in the electrolysis of copper?

Half eq

A

The electrical supply offers electrons to nearby Cu2+ ions.

Cu^2+ + 2e- = Cu (s)

55
Q

How does the mass of the elctrodes change during the electrolysis of copper?

A

The mass of the anode decreases and the mass of the cathode increases. This is because copper is transferred from the anode to the cathode.

56
Q

Why is electrolysis needed for copper?

A

Copper can be extracted from its ore by reduction with carbon but copper made this way is impure so electrolysis is used to purify it.

57
Q

How is the electrochemical cell set up?

A

Copper electrodes

58
Q

What happens during the electrolysis of copper? (3)

A

1) The impure copper anode is oxidised, dissolving into the electrolyte to form copper ions.
2) The copper ions are reduced at the pure copper cathode, and add to it as a layer of pure copper.
3) Any impurities from the impure copper anode sink to the bottom to form a sludge.

59
Q

What happens at the cathode in the electrolysis of a molten substance?

A

Metal ion usually gets reduced at cathode

60
Q

What happens at the anode in the electrolysis of a molten substance?

A

Non-metal ion is oxidised at the anode.

61
Q

What happens at the cathode in the electrolysis of a solution?

A

If the metal is more reactive than hydrogen, the H+ is reduced to H2. If the metal is less reactive than hydrogen, the metal is reduced.

62
Q

What happens at the anode in the electrolysis of a solution?

A

If a halide is present, the halide ion is oxidised to the halogen and OH- stays in the solution. If a halide isn’t present, OH- is oxidised to H2O and the other non-metal ion stays in the solution.

GCSE Chemistry P1 (5 decks)

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