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Chemistry GCSE > Acids & Electrolysis Topic 3 > Flashcards

Acids & Electrolysis Topic 3 Flashcards

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1
Q

What does a strong acid contain

A

Lots of H+ ions

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2
Q

What is pH a measure of

A

How many H+ ions are present in the solution
The more H+ ions the lower the pH ( more acidic)

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3
Q

What does a low pH mean

A

Acidic

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4
Q

What does a high pH mean

A

Alkali

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5
Q

Metal + acid =

A

Salt + hydrogen

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6
Q

When an ACID is added to LITMUS INDICATOR what colour change is seen

A

Dark red

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7
Q

When an ALKALI is added to LITMUS INDICATOR what colour change is seen

A

No colour change - stays dark blue

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8
Q

When an ACID is added to PHENOPHTHALEIN INDICATOR what colour change is seen

A

No change - stays colourless

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9
Q

When an ALKALI is added to PHENOPHTHALEIN INDICATOR what colour change is seen

A

bright pink

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10
Q

When an ACID is added to METHYL ORANGE INDICATOR what colour change is seen

A

Red

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11
Q

When an ALKALI is added to METHYL ORANGE INDICATOR what colour change is seen

A

Yellow

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12
Q

What is a concentrated acid

A

More H+ ions per volume of solution

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13
Q

What is a dilute acid

A

Less H+ ions per volume of solution (more water)

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14
Q

What is a base

A

Substances that neutralise acids to form a salt and water only

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15
Q

Give the generic equation for the neutralisation of an acid using a base

A

Metal oxide + acid ——> salt + water

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16
Q

Describe what happens during a neutralisation reaction with a metal oxide

A

During neutralisation hydrogen ions in the acid combine with oxide ions to form water. This removes the hydrogen ions and so the pH increases (becomes more neutral)

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17
Q

Give the products of the neutralisation reaction :
Tin oxide + hydrochloric acid

A

Tin chloride + water

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18
Q

How many times more hydrogen ions are there in an acid with a pH of 4 compared to an acid with a pH of 2

A

100 (every jump in pH is x10)

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19
Q

When obtaining dry crystals of copper sulphate why is the copper oxide added in excess

A

To make sure all the acid has reacted

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20
Q

What is the final step to get the dry salt crystals (neutralisation reaction)

A

Scrape out onto filter paper and blot them dry

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21
Q

Metal + acid =

A

Salt + hydrogen

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22
Q

Metal carbonate + acid =

A

Salt + carbon dioxide + water

23
Q

What is titration a method of

A

Neutralisation

24
Q

How do you obtain a soluble salt from an alkali (neutral solution left over from titration)

A

By crystallisation

25
Q

Are nitrates soluble in water

A

Yes all of them

26
Q

Are chlorides soluble in water

A

Yes most
apart from silver and lead chlorides (insoluble)

27
Q

Are sulphates soluble in water

A

Most
apart from lead, barium and calcium sulphates (insoluble)

28
Q

Are carbonates soluble in water

A

Most are INSOLUBLE
apart from sodium, potassium and ammonium carbonates

29
Q

Are hydroxides soluble in water

A

Most are IBSOLUBLE
Apart from sodium, potassium and ammonium hydroxides

30
Q

Are salts soluble in water

A

Yes all common sodium potassium and ammonium salts are

31
Q

What is the method to form an INSOLUBLE SALT from two soluble salts

A

Mix the two soluble salts in a beaker and then filter.
Rinse beaker with distilled water and pour through funnel
Pour distilled water over precipitate in funnel
Carefully remove filter paper and dry in warm oven

32
Q

What is the method to form a soluble salt
Core practical

A

Add excess metal oxide to acid
Gently warm in a water bath to speed up the reaction
Filter to remove the unreacted solid from the solution
Heat the solution to evaporate water and concentrate the salt solution
Leave to crystallise

33
Q

Concentration =

A

no.moles ÷ volume (dm^3)

34
Q

Why must titration be used to obtain a solution of a salt and water only, when using an acid and an alkali?

A

Because there is no insoluble excess reactant that could be removed by filtration.

35
Q

Describe the method of a titration

A

Use the pipette and pipette filler to ADD a MEASURED VOLUME OF ALKALI TO a CONICAL FLASK
ADD a few DROPS of INDICATOR and put the CONICAL FLASK ON a WHITE TILE
FILL the BURETTE with ACID and NOTE the start VOLUME.
SLOWLY ADD ACID from the burette TO THE ALKALI in the conical flask, SWIRLING to mix.
STOP WHEN the indicator first PERMENANTLY CHANGES COLOUR). NOTE the FINAL VOLUME.
REPEAT steps 1 to 5 until you get concordant titres (2dp).
More accurate if added drop by drop.

36
Q

What criteria do the products need to fulfil if a precipitate is to form

A

If AT LEAST 1 of the products meets the insoluble rule a precipitate will form

37
Q

What are ionic compounds made out of

A

Charged particles (anions & cations)

38
Q

When can ionic compounds conduct electricity and why

A

They can conduct electricity only when molten or dissolved
Can’t conduct when in a solid state as their ions are in fixed positions

39
Q

What charge does the cathode have

A

Negative

40
Q

What charge does the anode have

A

Positive

41
Q

Would Chlorine be attracted to the anode or the cathode

A

Anode because chlorine is negatively charged and so would be attracted to positively charge anode

42
Q

What is electrolysis

A

Electrolysis is a process in which electrical energy, from a direct current supply, decomposes electrolytes.

43
Q

At which of the electrodes will an oxidation reaction occur

A

At the positively charged ANODE
(OILRIG)
Oxidation is loss of electrons

44
Q

At which of the electrodes does a reduction reaction occur 

A

At the negatively charged CATHODE
(OILRIG)
Reduction is gain of electrons

45
Q

When the substance is electrolysed IN SOLUTION what does it mean

A

That an extra OH- and H+ are produce (water)

46
Q

What is the rule at the cathode for electrolysis in solution

A

Cation that is less reactive is reduced
Eg. If metal is lower than hydrogen in the reactivity series you get the metal
If hydrogen is lower then you get hydrogen instead of the metal

47
Q

What is the rule at the anode for electrolysis IN SOLUTION

A

If you have halides (group 7 ions) the halogen is produced
With other common negative ions you get oxygen

48
Q

What do you have to remember about group 7 molecules when balancing half equations

A

They are DIATOMIC (eg. Not Cl but Cl2)

49
Q

What are the 3 elements less reactive than hydrogen on the reactivity series

A

Copper
Silver
Gold
(These are the only 3 elements that would win and be part of the half equation for electrolysis in solution)

50
Q

Describe the method for electrolysis using copper electrodes

A

Pour copper sulphate solution into beaker
Measure and record mass of 2 copper (foil) electrodes
Attach one to the positive terminal and one to the negative terminal (making sure you know which one correspond to which mass)
Turn on power supply & leave for 20 mins
Remove 1 of the electrodes, rinse with distilled water and then dip it into propanone. Then lift it out and allow liquid to evaporate until dry.
Repeat with other electrode
Record mass of each and then calculate change in mass
You can repeat this experiment at different currents

51
Q

Which of the copper electrodes gains mass?

A

Cathode (negative electrode) COPPER IS DEPOSITED

52
Q

Which of the copper electrodes loses mass?

A

Anode (positive electrode) COPPER DISSOLVES

53
Q

For the electrolysis with copper electrodes describe the change in mass as the current is increased

A

As the current is increased the change in mass of the electrodes becomes greater

54
Q

Why are copper electrodes used in electrolysis

A

To purify copper

Chemistry GCSE (15 decks)

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