Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AQA Chemistry > Topic 4- Chemical Changes > Flashcards

Topic 4- Chemical Changes Flashcards

1
Q

What is the pH scale?

A

• A measure of how acidic or alkaline a solution is.
• The lower the pH of a solution, the more acidic it is.
• The higher the pH of a solution, the more alkaline it is.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What pH does a neutral substance have?

A

7

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is an indicator?

A

• A dye that changes colour depending on whethee it’s above or below a certain pH.
• Some indicatoes contain a mixture of dyes that means they gradually change colour over a broad range of pH.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a pH probe?

A

• pH probe attached to a pH meter can be used to measure the pH electronically.
• The pH is given on a digital display as a numerical value, meaning it’s more accurats than an indicator.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is an acid?

A

• A substance that forms aqueous solutions with a pH of less than 7.
• Acids form H+ ions in water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a base?

A

A substance with a pH greater than 7.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is an alkali?

A

• A base that dissolves in water to form a solution with a pH greater than 7.
• Alkalis form OH- ions in water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is neutralisation?

A

• The reaction between acids and bases.
• Acid + Base —> Salt + Water
• Neutralisation can be seen in terms of H+ and OH- ions like this:
H+ (aq) + OH- (aq) —> H2O (l)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens when an acid neutralises a base?

A

• The products are neutral, i.e. they have a pH of 7.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Required practical: titration

A
  1. Using a pipette and a pipette filler, add a set voluke of the alkali to a conical flask. Add two or three drops of indicator too.
  2. Use a funnel to fill a burette with some acid of known concentration. Make sure you do this BELOW EYE LEVEL. Record the initial volume of the acid in the burette.
  3. Using the burette, add the acid to the alkali a bit at a time- giving the conical flask a regular swirl. Go especially slowly when you think the end point is about to be reached.
  4. The indicator changes colour when all the alkali has been neutralised.
  5. Record the final volume of acid in the burette, and use it, along with the intial reading, to calculate the volume of acid and to neutralise the alkali.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How do you increase the accuracy of your titration?

A

• You need several consitent readings to spot any anomalous results.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why is universal indicator used to estimate the pH of a solution?

A

• Because it can turn a variety of colours.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why is single indicator used in titrations?

A

• Because you want to see a sudden colour change at the end-point.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are strong acids?

A

• Acids that ionise completely in water.
• All acid particles dissociate to release H+ ions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are weak acids?

A

• Do not fully ionise in solution.
• Only a small proportion of acid particles dissociate to release H+ ions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do weak acids ionise?

A

• It is a reversible reaction, which sets up an equilibrium between the undissociated and dissociated acid.
• Since only a few acid particles release H+ ions, the position of equilibrium lies well to the left.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do you find the factor that the H+ ion concentration changes by?

A

factor the H+ ion concentration changes by= 10^-X
e.g. for a decrease of 3 the factor is 10^-(-3)=10^3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do metal oxides react with acids?

A

Acid + Metal Oxide —> Salt + Water

19
Q

How do metal hydroxides react with acids?

A

Acid + Metal Hydroxide —> Salt + Water

20
Q

How do metal carbonates react with acid?

A

Acid + Metal Carbonate —> Salt + Water + Carbon Dioxide

21
Q

Required practical: making soluble salts using an insoluble base

A
  1. Pick the right acid and insoluble base.
  2. Gently warm the acid using a Bunsen burnse, then turn off the Bunsen burner.
  3. Add the insoluble base to the acid a bit at a time, until no more reacts (i.e. the base is in excess).
  4. Then filter out the excess solid to get the salt solution.
  5. To get pure, solid crystals of the salt, gently heat the solution using a water bath or an electric heater to evaporate some of the water and then stop heating it and leave the solution to cool. Crystals of the salt should form which can be filtered out of the solution and then dried. This is called crystallisation.
22
Q

What is the reactivity series?

A

• Potassium
• Sodium
• Lithium
• Calcium
• Magnesium
• Aluminium
• Carbon
• Zinc
• Iron
• Lead
• Hydrogen
• Copper
• Silver
• Gold

23
Q

What is the reactivity series based on?

A

• How easily the elements lose electrons to form positive ions.
• The reactivity increases going up.

24
Q

What happens when a metal reacts with acid?

A

• Lose electrons and form positive ions.
• Acid + Metal —> Salt + Hydrogen

25
Q

How is the speed of reaction (acid + metal) determined?

A

• By the rate at which the bubbles of hydrogen are given off.

26
Q

What does a fast reaction between a metal and acid tell you?

A

• The metal is reactive.

27
Q

Word equation for reaction of metal with water

A

Metal + Water —> Metal Hydroxide + Hydrogen

28
Q

Which metals react with water?

A

• Potassium
• Sodium
• Lithium
• Calcium

29
Q

How are metals extracted?

A

• Metals often react with oxygen to form oxides. These oxides are often the ores that metals need to be extracted from.
• A reaction that seperates a metal from its oxide is called a reduction
• Oxidation= Gain of oxygen
• Reduction= Loss of oxygen

30
Q

How can metals be extracted using reduction with carbon?

A

• The ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidised.
• The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon.

31
Q

Can a metal be extracted by reduction with carbon if it is higher than carbon in the reactivity series?

A

• No, metals higher than carbon will have to be extracted using electrolysis.

32
Q

Why can only metals below carbon in the reactivity series by extracted by reudction with carbon?

A

• This is because carbon can only take the oxygen away from metals which are less reactive than carbon itself.

33
Q

Why are some metals found in the elemental form?

A

• Because they are so unreactive.
• e.g. gold is mined in its elemental form.

34
Q

What does OIL RIG stand for

A

• Oxidation is Loss (of electrons) Reduction is Gain (of electrons).
• REduction and OXidation happen at the same time, REDOX.

35
Q

What is a displacement reaction?

A

• Where one metal is replaced out of a compound.
• A more reactive metal will displace a less reactive metal from its compound.

36
Q

What happens during the reaction of iron with copper sulfate?

A

• Iron displaces copper to give iron sulfate.
• Iron will lose 2 electeoms to become a 2+ ion, its oxidised.
• Copper gains these 2 electrons to become a copper atom, it’s reduced.

37
Q

What happens during electrolysis?

A

• When an electric current passed through an electrolyte. The ions move towards the electrodes, where they react, and the compound decomposes.
• The positive ions in the electrolyte will move gowards the cathode (+ve electrode) and lose electrons (they are oxidised).
• The negative ions in the electrolyte will move towards the anode (+ve electrode) and lose electrons (they are oxidised).
• This creates a flow of charge through the electrolyte as ions travel to the electrodes.
• As ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte.

38
Q

Why can an ionic solid not be electrolysed?

A

• The ions are in fixed positions and can’t move.
• Molten ionic compounds can be electrolysed because the ions can move freely and conduct electricity.

39
Q

How are metals extracted from their ores using electrolysis?

A
  1. Aluminium is extracted from the ore bauxite by electrolysis. Bauxite contains aluminium oxide, Al2O3.
  2. Aluminium oxide has a very high melting temperature so it’s mixed with cryolite to lower the melting point.
  3. The molten mixture contains free ions, so it’ll conduct electricity,
  4. The positive Al3+ ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms. These then sink to the bottom of the electrolysis tank.
  5. The negative O2- ions are attracted to the positive electrode where they each lose two electeoms. The neutral oxygen atoms will then combine to form O2 molecules.
40
Q

What are the rules at the cathode?

A

• Ion of the least reactive element will be discharged first, followed by hydrogen.

41
Q

What are the rules at the anode?

A

• If a halide is present, it is discharged first at the anode followed by OH- ions and then by nitrates and sulfates.

42
Q

How are reduction and oxidation written as an ionic equation?

A

• Gain= L.H.S, e.g. Pb2+ +2e —> Pb
• Loss= R.H.S, e.g. 2Br- —> Br2 + 2e-

43
Q

Electrolysis of lead bromide

A

• Molten lead bromide is used as electrolyte.
• Lead ions with charge Pb2+ are attracted towards negative electrode.
• Lead ions gain 2 electrons to become lead atom.
• Bromdide ion, which is negative, is attracted towadds negative electrode.
• Each beomide ion loses 1 electron to form each bromine atom Br2 which is diatomic.

AQA Chemistry (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions