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Chemistry > topic 4 > Flashcards

topic 4 Flashcards

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1
Q

how do we measure ph

A

indicators-(chemical dyes)
ph probe connected to ph meter

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2
Q

what is an acid

A

any substance that forms an aqeous solution with ph less than 7 which is made acidic from the h+ ions they release in water

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3
Q

what are bases

A

any substance of ph greater than 7

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4
Q

what are alkalis

A

a sub group of bases that are soluble in water- a base that dissolves in water to form a solution with a ph greater than 7

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5
Q

what is an acid +base reaction called and what does it produce

A

a neutralisation reaction
- produces water and salt
-baws

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6
Q

what is the formula for sulfuric and nitric acid

A

-h2so4
-hn03

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7
Q

what are formulas for calcium carbonate /sodium hydroxide

A

NaOH/CaC03

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8
Q

what is a titration

A

an experimental technique to find an unknown conc of an acid or alkali

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9
Q

list equipment needed for titration

A

-a pipette to measure 25cm3 volume of acid or alkali
-conical flask to hold the liquid from the pipette
-a burette to add acid or alkali
-white tile to place conical flask

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10
Q

titration method

A

1) use pipette to add 25cm3 of alkali to conical flask
2)add few drops of indicator and put the conical flask to the white tile
3)fill the burette with acid and note the starting volume by reading it off the burette
4)Add acid from the burette to alkali in conical flask swirling it to mix
5)Stop adding acid when all acid has neutralised alkali and the indicator changes colour
6)Read volume of acid remaining in burette and calculate the volume of acid added
7)Repeat the titration until you get concordant(0.10 cm3 of each other)
8)Find the mean volume of acid required to neutralise the alkali using concordant results

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11
Q

list the indicators and how they would be used

A

-litmus-red in acidic and blue in alkaline
-phenolphthalein-colourless in acidic and pink in alkaline
-methyl orange-red in acidic solutions and yellow in alkaline solutions

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12
Q

list some safety precautions

A

wearing gloves to reduce risk of harm from acid burns

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13
Q

what does the term ionise mean

A

for particles to split or dissasociate to release ions

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14
Q

what are some strong acids vs weak acids

A

strong include sulfuric acid /hydrochloric/nitric
weak acids include ethanoic/citric/carbonic

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15
Q

why are weak acids not completely ionising

A

its ionisation is reversible so there is an equilibrium between the undissociated and dissociated forms of the acid
therefore the equilibrium will lie to the left are there are far more undissociated forms of the acid

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16
Q

what is an acids strength or weakness

A

how much an acid dissasociates

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17
Q

what is the relationship between ph and hydrogen ions

A

the lower ph higher conc of h+ ions

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18
Q

at any concentration what do strong acids have over weak acids

A

At low ph a higher proportion of h+ ions will dissasociate

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19
Q

Mash
what do metal oxides/hydroxide + acid form

A

salt +water

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20
Q

how do we form salts with words

A

take the -ion from acid and combine w +ion from base

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21
Q

cawcs
metal carbonate +acid

A

=h20 +co2 and salt

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22
Q

how do we make soluble salts

A

from an acid + insoluble base

1)put dilute acid(eg hcl in a beaker)
2)gently heat with a bunsen burner
3)add insoluble base(eg copper oxide) a little a time
-it will keep dissapearing but at some point base no longer dissapears so we know base must be in excess so we have neutralised the acid
4)filter out excess base using filter paper and funnel
5)what we have is the dissolved form of soluble salt(copper chloride)
6)gently heat up solution using water bath to evaporate some water off
7)Stop heating it and let it cool
8)Filter crystals out with filter paper and funnel
9)leave it somewhere warm or dab with filter paper

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23
Q

what is the reactivity series

A

potassium
sodium
lithium
calcium
magnesium
CARBON
zinc
iron
HYDROGEN
copper

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24
Q

what is metal +acid

A

salt +hydrogen gas

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25
Q

how do we get the reactivity series

A

by reacting the metals with acid and water to see how violent the reactions are

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26
Q

how does pottasiums reaction with acid differ with copper or magnesium

A

potassium reacts explosively catching fire and whizzing around and producing alot of hydrogen

-magnesium produces a lot of bubbles

-copper doesnt react at all

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27
Q

what is another way we can see how reactive a metal is

A

we can measure the temp change as the most reactive metals produce the most heat

-we must make it a fair test by

-using metals of same mass and sa
-same type and conc of acid each time

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28
Q

metals + water

A

metal hydroxide+hydrogen

however only most reactive metals can do this
mg only reacts slightly

29
Q

what is oxidation and reduction

A

oxidation-gain of oxygen
reduction-loss of oxygen

30
Q

what is an exception to metals reacting with oxygen

A

unreactive metals that havent been oxidised which are found as pure metals

31
Q
A
32
Q

how can we reduce metal oxides to get pure metals and what are the limits to this

A

react it with carbon to form carbon dioxide and leave behind a pure metal

we can only do this to metals less reactive than carbon
zinc
iron
copper

33
Q

what are ores

A

metal rich compounds from rocks in the ground that we can extract our metal from

34
Q

what is the most common ore

A

fe2o3

35
Q

Why do we find pure gold in the ground, but not pure iron?

A

Gold is unreactive, so doesn’t react with any other elements

Iron is reactive enough to react with oxygen so is oxidised to iron oxide

36
Q

what is a redox reaction

A

when oxidation and reduction both occur at the same time

37
Q

what is oilrig in terms of electrons

A

oxidation is loss
reduction is gain

38
Q

where are some places we see redox reactions

A

in displacement reactions where spectator ions are removed if they dont change at all from reactants to products)

39
Q

how do you write half equations and what is the scenario you need to write them in

A

get the reactant element and if it has no charge write an arrow.get the product of the same element and add the electrons it has gained in the form of (e-)

get the reactant element and if it has charge add the number of electrons it will take to become what
it is as a product

This will be after you have cancelled out the spectator ions and have ypur ionic equation

40
Q

what is the half equation for the reduction of oxygen

A

o2 +4e->2o2-

41
Q

in displacement reactions what happens to the metal ions

A

they are reduced

42
Q

in electrolysis what side will the shorter lines of the cells be

A

on the cathode side

43
Q

what equipment is used in electrolysis

A

beaker
electrolyte

44
Q

what is an electrolyte

A

liquid or solution that contains an ionic compound with ions free to move

45
Q

what can we do if our compound is soluble or insoluble

A

dissolve it in water or melt it to make ions free to move

46
Q

what are electrodes

A

solid conductors generally made of metal or carbon

47
Q

what are the left and right electrode

A

cathode on the left is negative
anode on the right is positive

48
Q

after we have a beaker / electrolyte and electrodes what else do we need

A

-power supply like a battery
-wire so electrons can flow in between the cathode and anode

49
Q

what is the meaning of electrolysis

A

splitting up with electricity

50
Q

how does electrolysis split these compounds

A

by using battery to pass current through electrolyte we can seperate our compound
as - ions are attracted to anode and are discharged(turned from charged ions to neutral atom)
if this was bromine atoms would pair up and form bromine gas which would float off

lead would sink to the bottom forming layer of molten lead

51
Q

what happens ions at the electrodes

A

they are reduced and oxidised

52
Q

describe the journey of electrons in electrolysis

A

electrons from the bromide ions at the anode travel through the wires with the battery transported along the wire to the cathode using the power of the battery

53
Q

what is the half equation rule for electrolysis

A

the - ion is oxidised which forms the pure element+the electrons it loses

eg:at the anode - bromide ions loses electrons
2br->br2+2e-

at the cathode-lead ions gains electrons so reduced into pure lead

pb2+ +2e->pb

54
Q

how does electrolysis convert ions in a compounds into their pure elemental forms

A

using electricity by transferring electron from negative ions to positive ions

55
Q

in electrolysis, why does the compound you’re trying to separate need to be molten or dissolved

A

So that the ions are free to move around (and go to their respective electrode)

56
Q

what is bauxite

A

the ore of aluminium oxide

57
Q

what is the step of obtaining aluminium from bauxite

A

1)purify aluminium oxide from bauxite we mine from ground
2)melt aluminium oxide to make it molten(has a melting point of over 2000 degrees)
3)mix cryolite mineral with aluminium oxide which lowers melting point
4)melt it and now we have our molten aluminium oxide

58
Q

what are the steps for the electrolysis of aluminium oxide

A

1)o2- ions will go to anode and be reduced losing 2 electrons and be discharged to neutral oxygen atoms where 2 will combine to form an oxygen molecule and float off into the air

2)The electrons of the oxygen ion will travel through the anode and the wire and reach the cathode on the left attracting the positive aluminium ions.it will donate 3 electrons to each al3+ ion to form aluminium atoms which will then fall to the bottom of the beaker as molten aluminium metal.

59
Q

what are the half equations for the cathode and the anode in the electrolysis of molten aluminium oxide

A

anode- 2o2->o2+4e-
cathode- al3+ +3e->al

60
Q

what is the overall equation for electrolysis of aluminium oxide

A

2al2o3 (l) > 4al (l) +3o2 (g)

61
Q

Why is electrolysis not used to extract all metals?

A

Electrolysis is expensive because it requires a large amount of electricity

62
Q

what are soluble compounds that can be dissolved in water to serve as the electrolyte

A

copper sulfate -cuso4
sodium chloride- nacl

63
Q

why is it difficult to work out which ions would go to each electrode in aq solution

A

there would also be hydroxide ions and hydrogen ions from the water in solution as it splits up when in solution

64
Q

what are rules for electrolysis in aq solutions at the cathode

A

positive ions go to cathode including ion from compound and h+ and the least reactive is the one that will be discharged

eg: if it was copper hydrogen copper would be discharged

at the cathode if a halide is present it will get discharged but if it isnt the hydroxide will always get discharged

65
Q

what happens in electrolysis of copper sulphate

A

copper is formed at the anode and accumulates around the cathode as it is solid

at the anode hydroxide is formed so give up extra electron to anode and form oxygen and water

the equation is
4oh->2h2o +o2 +4e-

66
Q

what happens in the aq electrolysis of nacl

A

na is formed at the cathode
chloride is formed at the anode

67
Q

why does the ph of acids depend on strength and conc of acid

A

General principle
* pH depends on H+ ion concentration
* the higher the concentration of H+ ions the lower the pH
Strength
* the stronger an acid the greater the ionisation / dissociation (in
aqueous solution)
* (so) the stronger the acid the lower the pH
Concentration
* the higher the concentration of an acid the more acid / solute in
the same volume (of solution)
* (so) the higher the concentration of the acid the lower the pH

68
Q

temp change prac

A
  1. Measure 25cm3
    of hydrochloric acid into a polystyrene cup.
  2. Place the cup inside the beaker to make it more stable.
  3. Measure and record the temperature of the hydrochloric acid.
  4. Measure 5cm3
    of sodium hydroxide and add it to the polystyrene cup.
  5. Quickly put a lid on the cup and gently stir the solution with the thermometer through the
    hole of lid.
  6. When the reading on the thermometer stops changing and becomes fairly constant,
    record the temperature.
  7. Repeat steps 4 and 5 to add further 5 cm3
    amounts of sodium hydroxide to the cup. A
    minimum total of 40 cm3
    needs to be added.
  8. Repeat steps 1–7 to ensure reliability of results.
  9. Calculate the mean maximum temperature reached for each of the sodium hydroxide
    volumes

Chemistry (6 decks)

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