chemical changes Flashcards
(88 cards)
1
Q
what is sued to measure the acidicy or how alkaline a solution is
A
ph scale
2
Q
The pH scale ranges from:
A
0-14
3
Q
is the ph of a solution is lower what is it
A
more acidic
4
Q
if teh ph of a solution is higher what is it
A
more alkaline
5
Q
what is the ph of a neutral substance
A
7
6
Q
example of a neutral substance with the ph of 7
A
pure water
7
Q
what is a indicator
A
a dye that changes colour dependingif its above or below a certain PH
8
Q
what is a Ph probe and why is it more useful than a indicator
A
- Ph probe attached to Ph meter and measures it electronically - probe is placed in the solution you are measuring and the Ph is given on a digital display as a numerical value
9
Q
what type of ions do acids form in water
A
H+
10
Q
what is a acid
A
a substance that forms a aqeuous solution with a pH of less than 7
11
Q
what is a base
A
any substance that reacts with an acid to form a salt
12
Q
what is a alkali
A
a base that dissolves in the water to form a solution with a pH greater than 7
13
Q
A
14
Q
what type of ions do alkais form in water
A
OH-
15
Q
what is the reaction between acids and bases called
A
neutrilisation
16
Q
show nuetrilisation as a word equation
A
acid + base = salt + water
17
Q
show nuetralisation in terms of O+ and OH-
A
H+ + OH- = H20
18
Q
what happens when acids ionise in aqueous solutions
A
they form hydrogen ions H+
19
Q
do strong acids ionise completely or partually in water
A
completely
- all particles dissocate to release H+ ions
20
Q
do weak acids ionise completely in water
A
they do not completely ionise
- only a small proportion of acid particles dissocate to release H+ ions
21
Q
what are some examples of strong acids
A
hydroclauric acid
nitric acid
sulfuric acid
22
Q
what is the dissocation of weak acids
A
a reversible reaction meaning the products can be put back together to form the acid
23
Q
for weak acids what position does the equilibrium lie
A
to the left
24
Q
what are examples of weak acids
A
citric acid
ethanol
carbonic acid
25
what does the strength of an acid refer to
how well it ionises when its added to water
26
what does concentration of acids refer to
how much acid there is in a certain volume
27
what is the ph of a acid or alkali
a measure of the concentration of H+ ions in the solution
28
what happens when you decrease 1 on the pH scale e.g 5 to 4
the concentration of H+ ions increases by a factor of 10
29
what happens when metal oxides and metal hydroxides react with acid
they always form salt + water
30
what is the balanced equation for hydrochloric acid and copper oxide
2HCL + CuO = CuCl2 + H20
31
what is the balanced equation for sulfuric acid and zinc oxide
H2SO4 + ZnO = ZnSO4 + H20
32
what is the balanced equation for nitric acid and magnesium oxide
2HNO3 + MgO = Mg(NO3) + H20
33
equation for nitric acid and potassium hydroxide
HNO3 + KOH = KNO3 + H20
34
formula for a acid and a metal carbonate
acid + metal carbonate = salt + water + carbon dioxide
35
example of a acid and metal carbonate reaction
2HCL + Na2CO3 = 2NaCl + H20 + CO2
36
make soluble salts using a insoluble base practical
1 choose right acid and a insoluble base
2 gently warm dilute acid using a bunsen burner then turn it off
3. add insoluble base to acid , acid will be neutralised when excess solid will just sink to the bottom
4. filter out excess soild to get salt solution
5. to get pure solid crystals gentley heat solution then leave solution to cool, crystals should form
37
what is the reactivity series
it lists metals in order of their reactivity towards substances
38
what
39
is a metal is higher up the reactivtiy series what is it
more reactive and looses electrons easily
40
what is the order of the reactivity series
potassium
sodium
lithium
calcium
magnesium
carbon
zinc
iron
hydrogen
copper
41
what hapens when metals react with acids
they produce salt and hydrogen
42
what is the speed of reaction indicated by in reactions of metals and acids
how quickly the hydrogen bubbles are given off
43
what happens when magnesium reacts with acid
reacts vigorously and produces lots of bubbles
44
how does zinc and iron react with acid
react fairly slowly but more strongly if you heat them up
45
how can you test hydrogen is present when reacting magnesium,iron or zinc with acid
the burning splint test
46
what happens when metal reacts with water
metal + water = metal hydroxide + hydrogen
47
what are some metals that will react with water
potassium,sodium,lithium and calcium
48
what are some metals that dont react with water
iron,copper,zinc
49
what is oxidation
the gain of oxygen
e.g magnesium can be oxidised to made magnesium oxide
50
what is reduction
the loss of oxygen
e.g copper oxide reduced to copper
51
what do metals higher than carbon in the reactivity series have to be extracted by
electrolsysis
52
what can metals lower than carbon in the reactivity series be extracted by
by reduction with carbon
53
why cant reduction by carbon not extract things higher than it in the reactivity series
because carbon can only take the oxygen away from metals which are less reactive
54
what is an example of a unreactive metal that is found in the earth as metal itself
Gold
55
what is a loss of electrons called
oxidation
56
what is a gain of electrons called
reduction
57
why are redox reaction called redox reactions
because reduction and oxidation happen at the same time
58
what is a example of a metal and acid redox reaction
iron and dilute sulfuric acid
- iron atoms loose electrons and become iron ions and are oxidised
- hydrogen ions gain electrons to become hydrogen atoms and are reduced
59
Which metals could be reduced from their oxides, by reacting them with carbon?
zinc
copper
iron
60
what does electrolysis mean
splitting up with electricity
61
what are the different parts involved in electrolysis
- electrolyte
- electrodes - cathode + anode
- wire joining cathode and anode so electrons can flow between them
- power supply like battery in wire to drive flow of electrons
62
what is a electrolyte
a molten or dissolved ionic compound - must be molten or dissolved so the ions are free to move
63
what is the negative electrode called
cathode
64
what is the positive electrode called
anode
65
why can't a ionic solid be electrolysed
because the ions are in fixed positions and can't move
66
describe electrolysis in terms of molten lead bromide
- negative bromide ions will be attracted to the positive anode and they become discharged - this will cause them to pair up and form bromide gas
- the positive led ions will be attracted to the negative cathode and become discharged forming pure lead which will fall to the bottom and form a layer of molten lead
67
what does discharged mean
the ion changes from a charged ion to neutral atom
68
In electrolysis, which direction do the electrons travel?
anode to cathode
69
what material should electrodes be made out of and why
an insert material so they don't react with the electrolyte
70
what observations can be made when sodium reacts with oxygen
- sodium melts
- yellow flame
71
observations of potassium and oxygen
liliac flame
more vigorous reaction
white solids form
72
example of a inert metal used for electrolysis
platinum
73
what happens when potassium reatcs with water
the metal whizzes around on the surface, and the hydrogen gas catches fire violently.
74
what happens when magnesium reacts with water
When magnesium reacts with water, bubbles form on the surface but there is no flame.
75
What would happen if iron and lithium sulfate were mixed together?
nothing because iron is less reactive than lithium so it cant displace t
76
why is electrolysis expensive
because lots of energy is required to melt the ore and produce the required current
77
how does electrolysis work for aluminium oxide
- aluminium oxide has very high melting temp so its mixed with croylite to lower the melting point
- the moltern mixture contains free ions- so it conducts electricty
- the positive Al3+ are attracted to the negotove electrode where they each pick up 3 electrons and turn neutral into aluminum ions - they then sink to the bottom of the tank
- the negative O2- ions are attracted to the positve electrode where they each loose two electrons - the neutral oxygen atoms will then join to form O2 molecules
78
why is croylite added aluminium oxide in electroysis
aluminium oxide has a very high melting point so its mixed with croylite to lower it
79
formula for aluminium oxide
Al2O3
80
what is aluminium extracted from
bauxite
81
which electrode do metals go to
metals form psoitive ions so they got o the negitive electrode
non-metals form negitive ions so they go to the positive electrode
82
in electrolysis of aqueous solutions other than ions from the compound what ions will be there
hydrogen ions and hydroxide ions from the water
83
what happens at the cathode if metal ions and H+ ions are present
a hydrogen gas will be formed if teh metal ions form a elemental metal that is more reactive than hydrogen
if the metal ions form a elemental metal that is less reactive than hydrogen a solid layer of pure metal will be produced instead which will coast the cathode
84
what happens at the anode if halide ions and OH- ions are present
molecules of chlorine,bromine or iodine will be formed
if no halide ions are present then the OH- ions from the water will be discharged and oxygen gas will be formed + water
85
electrolysis of copper sulfate solution
copper sulphaye solution contains
Cu SO4 H+ and OH-
- copper metal is less reactive than hydrogen so at teh cathode a solid layer of copper metal is produced and coats the cathode
- there is no halide ions so at the anode oxygen and water is produced - oxygen can be seen as bubbles
86
what are the halide ions in terms of electrolysis
Cl-
Br-
I-
87
electrolysis of sodium chloride solution
solution of sodium chloride contains
Na Cl H+ OH-
- sodium metal is more reactive than hydrogen so hydrogen gas is produced at the cathode
- chlorine ions are present so at the anode chlorine gas is produced
88
after doing the electrolysis experiment how can you test any gaseous products to work out what had been produced at which electrode
chlorine bleaches damp litmus paper - turning it white
hydrogen makes a " squeaky pop" with a lighted splint
oxygen will relight a glowing splint
