chemical changes Flashcards
1
Q
molecule formed by acids and alkalis
A
acids ionise to produce H+ ions in aqueous solutions
alkalis produce OH- ions in aqueous solutions
2
Q
what is a base
A
any chemical that neutralises an acid to form salt and water
3
Q
what is an alkali
A
a base that can dissolved in water to form a solution
4
Q
how can you measure pH
A
- universal indicator: changes colour
- pH probe: electronic
5
Q
what colour are acids on the pH scale
A
0 - 6
dark red - yellow
6
Q
what colour is water on a pH scale
A
Green
7
Q
what colour is alkali on the pH scale
A
8 - 14
blue - purple
8
Q
what makes something a salt?
A
contains a positive ion from the metal and a negative ion from the acid
9
Q
what is a neutralisation reaction
A
reactions between an acid and a base
10
Q
equations for neutralisation
A
H+ (from acid) + OH- (from alkali) –> H2O
acid + base –> salt + water
11
Q
oxidation vs reduction in terms of oxygen
A
when an element gains oxygen - oxidation
when an element loses oxygen - reduction
12
Q
metal + oxygen
A
metal oxide
13
Q
metal + water
A
metal hydroxide + hydrogen
14
Q
how is reactivity series determined
A
reactivity with water or dilute acids
15
Q
what determines how rapidly a metal reacts
A
how easily they lose electrons to form positive ions
16
Q
why do some metals need to be extracted
A
- only unreactive metals, eg gold, can be found as pure metal
- most have reacted with oxygen and are found as compounds
17
Q
how are metals extracted from their metal oxides
A
reduction with carbon
carbon displaces metal as it is more reactive
18
Q
what is oxidation and reduction in terms of electrons
A
oxidation is loss
reduction is gain
19
Q
how do metals react with acid (with equation!!)
A
they displace the hydrogen found in acids
- more reactive = faster reaction
acid + metal = salt + hydrogen
20
Q
how do metals react with acids in terms of electrons
A
- metal ion oxidised: loses 2 electrons to form metal2+
- hydrogen ions reduced: gain 2 electrons to form hydrogen gas H2
- more reactive = faster reaction
21
Q
what salts will form when an acid reacts with hydrochloric acid or sulfuric acid or nitric acid
A
metal chloride
metal sulfate
metal nitrate
22
Q
when given a word equation, what does “oxide” or “hydroxide” tell you about the compound
A
it is alkali
23
Q
how do acids react with a base/alkali
A
neutralisation
positive ion from alkali and negative ion from acid for salt
acid + base = salt + water
24
Q
how do metal carbonates react with acids
A
neutralisation
acid + metal carbonate = salt + water + co2
25
how can you make pure, crystals of copper sulphate from copper oxide and dilute sulphuric acid
* pour fixed volume of acid into beaker - the limiting reactant
- gently heat over bunsen burner until small bubbles visible
* add small amount of oxide using spatula and stir
* continue adding until excess can be seen, which ensures all the acid has reacted
* using filter funnel and filter paper, use filtration to remove excess, leaving copper sulphate solution
* heat in evaporating basin over boiling water, until half of solution remains
* leave for 24 hours for crystals to form
* pat dry with paper towels
26
What do titrations do?
allow you to find out concentrations needed neutralisation
27
How do you do a titration?
PIPFRACRU
say you want to find out the concentration of some alkali
• use a pippette and a pippette filler to add a 25cm cubed of the alkaline to a conical flask - meniscus exactly at 25cm^3
• indicator - five drops of phenothalein
• place on white tile so colour change can be observed
• Funnel to fill a burette with hydrochloric acid until meniscus is at 0cm^3
• record initial volume in burette
• first do rough titration: add bit by bit, occasionally swirling flask. when neutralisation has occured, colour will change. record volume in burette and calculate change to find rough titre value
• repeat again, ensuring all values are measured at meniscus
• this time, when volume in burette reaches around 5cm^3 before the rough titre value, add add drop by drop, swirling in between to find exact value of acid needed
• record new volume and calculate acid used
• repeat two more times to find an average, dont include rough titre when calculating mean
28
how can you make copper sulphate crystals using copper oxide and sulphuric acid
• gently heat the acid until small bubbles visible
• add small amount of oxide using spatula and stir
• continue adding until excess can be seen, which ensures all the acid has reacted
• using filter funnel and filter paper, use filtration to remove excess, leaving copper sulphate solution
• heat in evaporating basin over boiling water, until half of solution remains
• leave for 24 hours for crystals to form
• pat dry with paper towels
29
what is a strong acid, how can you identify one, and give examples
in aqueous solutions, acid fully ionises to produce H+
one-way arrow
hydrochloric, sulfuric, nitric
30
what is a weak acid, how can you identify one, and give examples
in aqueous solutions, acid partially ionises to produce H+
reversible reaction arrow
carbonic, ethanoic, citric
31
what is concentration of an acid
amount of acid molecules in given volume of solution, even if strength is the same
32
how is the pH scale actually organised
conc of H+ ions
when pH decreases by 1 unit, H+ conc increases by one order of magnitude (10x)
33
what is the purpose of a titration
find out conc in neutralisation reaction
34
how to do a titration
PIPFRACRU
say you want to find out the concentration of some alkali
* use a pippette and a pippette filler to add a 25cm cubed of the alkaline to a conical flask - meniscus exactly at 25cm^3
* indicator - five drops of phenothalein
* place on white tile so colour change can be observed
* Funnel to fill a burette with acid until meniscus is at 0cm^3
* add acid bit by bit, occasionally swirling flask
* when alkali starts to turn pink, add add drop by drop, still swirling
* record volume of acid added from burette at meniscus
* repeat several times, until you get at least two readings within 0.1cm^3 from each other
* calculate mean from these
35
three examples of indicators you can use in titrations , their colour change (acid —> alkali)
phenolphthalein: colourless -> pink
litmus: red -> blue
methyl orange: red -> yellow
36
how to do titration calculation
- write c=, v=, amd m= under both reactants and fill in conc, vol, and mol
- find missing values using mol = conc x vol
- multiply mol by scale factor to find mols of other reactant
- find missing values
37
how to convert mol/dm^3 to g/dm^3
conc in mol/dm^3 x Mr
38
how to remember the reactivity series
people say little children may cause zesty inmates happy cocks
39
what is the reactivity series
potassium
sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper
40
how are metals extracted
Above carbon: electrolysis
Below carbon: reduction with carbon
41
What is a redox reaction?
Reduction and oxidation happening at the same time
42
why can ionic compounds be split via electrolysis
they contain two ions - one positive and one negative
43
what state must the ionic compound be in order for electrolysis to occur
molten or dissolved in water, as forces of attraction are broken and ions are free to move and carry electricity as electrolytes
44
describe the electrodes in electrolysis of molten compounds
made from conducting material eg graphite or a metal
- cathode is negative and is covered in electrons
- anode is positive and has a lack of electrons
45
explain what happens in electrolysis of molten compounds
- Positive attracted to cathode (-)
- gain electrons (reduction) to form atoms
- negative attracted to anode (+)
- lose electrons (oxidisation) to form
46
what must be done to aluminium oxide before electrolysis and why
aluminium has high MP so is mixed with cryolite to lower it
- reduces energy needed to melt it, saving money
47
describe electrodes for electrolysis of aluminium oxide and why
made from graphite
- good conductor of electricity
- high MP so it can be used at high temps
- must be replaced regularly, as oxygen molecules produced at anode react with carbon from the graphite electrodes, forming co2
48
how is aluminium extracted from aluminium oxide
- mixed w/ cryolite and melted
- Al3+ ions attracted to cathode, where they gain 3 electrons to become aluminium atoms
- 02- ions attracted to anode, where they lose 2 electrons to become oxygen atoms
- electrodes must be replaced regularly, as oxygen molecules produces at anode react with carbon from the graphite electrodes, forming co2
49
half equations for aluminium oxide electrolysis
Al3+ + 3e- —(reduction)—> Al
202- - 4e- —(oxidation)—> 02
50
why is electrolysis expensive
- melting compound requires energy, which is expensive
- electric current requires energy, which is expensive
51
explain what happens in electrolysis of aqueous solutions
- Positive attracted to cathode (-)
- gain electrons (reduction) to form atoms
- H+ ions from water also go here
- ion with lowest reactivity produced
- negative attracted to anode (+)
- lose electrons (oxidisation) to form atoms
- OH- ions from water also go here
- oxygen or halogen produced
52
how do you predict what products you will get at cathode for electrolysis of aqueous solutions
If the metal is more reactive than hydrogen, hydrogen (H2) is produced
If it is less reactive, pure metal is produced
53
how do you predict what products you will get at anode in electrolysis of aqueous solutions
if a halide ion is present, the halogen will be produced
if halide ion is not present, oxygen and water is produced
54
describe electrodes for electrolysis of aqueous solutions
must be inert - not react with chemical made
often platinum
55
half equations for electrolysis of copper sulfate solution
cathode:
cu2+ + 2e- —> Cu
anode:
4OH- —> 02+ 2H2O + 4e-
56
half equations for electrolysis of sodium chloride solution
cathode:
2H+ + 2e- —> H2
anode:
2Cl- - 2e- —> Cl2
57
how to carry out electrolysis of copper chloride
- pour 50cm3 copper(II) chloride solution into a beaker
- place plastic petri dish with two holes over beaker
- insert graphite rods into each hole, which will be the inert electrodes as they are unreactive. make sure they are not touching to avoid making circuit
- connect rods to low V power supply and set to 4V
- observe electrodes: cathode will become coated with copper, anode produces bubbles of gas (chloride)
- test gas using damp blue litmus paper; paper should bleach white
58
how to test what is produced at cathode for electrolysis of sodium chloride
gas bubbles will form
- collect and test with a lit splint; hydrogen will burn with a squeaky pop
59
how to convert from cm^3 to dm^3
divide by 1000
60
how to convert from dm^3 to cm^3
times by 1000
