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gcse chemistry > topic 4 > Flashcards

topic 4 Flashcards

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1
Q

What is an indicator

A

a dye that changes colour depending on whether its above or below a certain pH

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2
Q

What can be used to measure the pH electronically

A

A pH probe attached to a pH meter

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3
Q

What is an acid

A

A substance that forms aqueous solutions with a pH of less than 7

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4
Q

What is a base

A

A substance with a pH greater than 7

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5
Q

Acid + base ——>

A

Salt + water

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6
Q

What ions do alkalis form in water

A

OH^-

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7
Q

What ions do acids form in water

A

H^+

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8
Q

What do acids do in water

A
  • They ionise in aqueous solution

- they produce protons in water

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9
Q

What type of acids ionise completely in water

A

Strong acids

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10
Q

Weak acids do not fully ionise in solutions what does this mean for some acid particles

A

They dissociate to release H^+ ions

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11
Q

What is an electrolyte

A

A molten or dissolved ionic compound

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12
Q

What happens in electrolysis

A

An electric current is passed through an electrolyte

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13
Q

What do ions do in electrolysis

A

They move towards the electrodes, where they react, and the compound DECOMPOSES

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14
Q

What do positive ions do in the electrolyte

A

Move towards the cathode (-ve electrode) and gain electrons (they are REDUCED)

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15
Q

What type electrode do positive ions move towards

A

-ve electrode

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16
Q

What do the negative ions do in the eoectrolyte

A

Move towards the anode (+ve electrode) and lose electrons (they are OXIDISED)

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17
Q

What type of electrode do the negative ions move towards

A

+ve electrode

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18
Q

As ions travel to the electrodes what happens

A

It creates a flow of charge through the electrolyte

19
Q

What happens as ions gain or lose electrons

A

They form the uncharged element and are discharged from the electrolyte

20
Q

Why can’t an ionic solid be electrolysed

A

Because the ions are in fixed positions and can’t move

21
Q

Why can molten ionic compounds be electrolysed

A

Because the ions move freely snd conduct electricity

22
Q

What type of ionic compound can be electrolysed

A

Molten ionic compound

23
Q

Positive METAL ions are … to the element at the …

A
  • reduced

- cathode

24
Q

Negative NON-METAL ions are …. to the element at the …

A
  • oxidised

- anode

25
Q

What method is used if a metal is “too reactive to be reduced with carbon or reacts with carbon”

A

Electrolysis

26
Q

What is the main draw back of electrolysis and why

A

It is expensive as lots of energy is required to melt the ore and produce the required current

27
Q

What ore is aluminium extracted from

A

Bauxite by electrolysis

28
Q

What dies bauxite contain

A

Aluminium oxide (Al2O3)

29
Q

What is electrolysis

A
  • Extracting metal using electricity

- the ore is melted to produce the required current

30
Q

As aluminium oxide has a high melting temperature what is it mixed with

A

Cryolite to lower the melting point

31
Q

In aluminium oxide what dies the molten mixture contain

A

Free ions so it will conduct electricity

32
Q

What are the positive Al3+ ions attracted to

A

To the negative electrode is where they each pick up 3 electrons and turn into neutral aluminium atoms

33
Q

What are the negative O2- ions attracted to

A

The positive electrode where they each lose 2 electrons

The neutral oxygen atoms will combine to from O2 molecules

34
Q

Aluminium oxide —->

A

Aluminium + oxygen

35
Q

What is reduction

A

A gain of electrons

36
Q

What is oxidation

A

Loss of oxygen

37
Q

A more reactive metal will …

A

Displace a less reactive metal from its compound

38
Q

What happens if you put a reactive metal into the solution of a dissolved metal compound

A

The reactive metal will replace the less reactive metal in the compound

39
Q

What always electrons in displacement reactions

A

The metal ion-so it is reduced

40
Q

What is oxidised in displacement reactions

A

The metal atoms as they lose electrons

41
Q

What is a reduction reaction

A

A reaction that separates a metal from its oxide

42
Q

Formation of metal ore

Oxidation=

A

Gain of oxygen

43
Q

Extraction of metal

Reduction =

A

Loss of oxygen

gcse chemistry (15 decks)

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