c3 Flashcards

(100 cards)

1
Q

during a chemical reaction, what happens to mass?

A

mass is always conserved

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2
Q

what has happened if a mass seems to change in a chemical reaction?

A

there is usually a gas involved
if mass increases - reactant is a gas, before reaction gas was floating and mass didn’t count
if mass decreases - product is a gas and will escape

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3
Q

ion for Lithium

A

Li+

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3
Q

ion for sodium

A

Na+

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4
Q

ion for calcium

A

Ca 2+

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4
Q

ion for potassium

A

K+

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5
Q

ion for magnesium

A

Mg2+

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6
Q

ion for carbonate

A

CO3 2-

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7
Q

ion for sulphate

A

SO4 2-

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8
Q

ion for oxide

A

O2-

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9
Q

ion for sulphide

A

S2-

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10
Q

ion for hydroxide

A

OH-

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11
Q

ion for nitrate

A

NO3 -

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12
Q

ion for fluoride

A

F-

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13
Q

ion for chlorine

A

Cl-

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14
Q

ion for bromide

A

Br-

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15
Q

ion for iodide

A

I-

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16
Q

formula for water

A

H2O

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17
Q

formula for ammonia

A

NH3

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18
Q

formula for carbon dioxide

A

CO2

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19
Q

formula for hydrogen

A

H2

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20
Q

formula for chlorine

A

Cl2

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21
Q

formula for oxygen

A

O2

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22
Q

what are the state symbols?

A

(l) - liquid
(s) - solid
(g) - gas
(aq) - aqueous

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23
what are half equations?
show electrons transferred during reactions .only use half equations for chemical reactions where oxidation and reduction happen
24
what is Avogadro's constant
1 mole = 6.02 * 10 ^23
25
formula for working out moles?
moles = mass (g) ---------------- Mr
26
when does a reaction stop?
when one reactant is used up any other reactants are in excess
27
what s the reactant that is used up in a reaction called?
limiting reactant
28
what is the leftover reactant in a reaction called?
in excess
29
what do reaction profiles show?
energy levels of reactants and products in a reaction. .use them to work out if energy is released or taken in
29
what is the limiting reactant directly proportional to? why?
amount of product formed because if you add more of the limiting reactant there will be more reactant particles to take part in reaction, which means more product particles are made.
30
what is an endothermic reaction?
takes IN energy from surroundings in from of heat, decrease in temp
31
what is an exothermic reaction?
gives OUT energy to surroundings. in form of heat, increase in temp
32
exothermic reaction profile. describe
.reactants - top left higher energy . bump goes over .products - bottom right lower energy .difference in height represents energy given OUT during reaction
32
endothermic reaction profile. describe
reactants - bottom left lower energy levels . up to a bump .products - top right higher energy levels .difference in height shows energy taken IN during reaction
33
what is the activation energy?
minimum amount of energy needed for bonds to break .on a reaction profile its the difference between REACTANTS and top of bump
34
how to break bonds?
energy must be supplied to break bonds so must be ENDOthermic
35
bonds making and breaking how to calculate overall energy change?
= energy to break bonds - energy released forming bonds
35
how to form bonds?
energy is released to form new bonds so must be EXOthermic
36
what is a pH scale?
way of measuring how alkaline or acidic a solution is
37
what pH is a neutral substance?
7
37
what pH is an acidic substance?
0-7
38
what ion do acids form in water?
H+
39
what pH does a base/alkali have?
7-14
40
what is a base (alkali)?
substance with a pH over 7
41
what is an alkali (base)?
a base that dissolves in water
42
what ions do alkalis form in water?
OH-
43
what is the value of pH inversely proportional to?
concentration of hydrogen ions in a solution concentration as H+ increases, the pH decreases (higher conc of H+ more acidic something is = lower pH)
44
(dis)advantages of a pH probe?
+provide quantitative readings +more accurate that indicator +can't be affected by human error (colour blindness) -fragile -easily broken by humans or if exposed to corrosive substances -need rinsing in deionising water inbetween readings (might forgot to do this)
44
how to measure pH?
.universal indicator -dye that changes colour when dropped in solution and you compare to a chart .pH probe -electronically, placed in solution
45
(dis)advantages of universal indicator?
+ approximate value of pH - not very accurate
46
what do acids and bases do to each other?
neutralise
47
H + OH →
H2O
48
what do titration curves show?
pH changes with volume
49
what is a titration used for?
to find out concentration of an unknown acid or base
50
on a titration curve what is the vertical point?
end point where the solution in neutral
51
what is the equation for moles (conc)?
moles = concentration * volume
51
method of a titration? using example sodium hydroxide, unknown conc 0.750 mol/dm^3 of HCl
1. take a known substance which will neutralise the unknown substance 2. measure 25.0cm^3 of NaOH using a volumetric pipette into a conical flask 3. add indicator and swirl 4. fill a burette with HCl 5. add HCl drop by drop until the indicator changes colour (END POINTT) 6. record volume of acid needed 7. repeat until you have 3 concordant results within 0.1 cm^3 of each other 8. find the mean of results (that is volume of HCl) 9. using equation, ratio... work out conc (0.544 mol/dm^3 is ANSWER)
52
what is concentration measured in?
mol/dm^3
53
what do acids produce in water?
protons HCl → H+ + Cl-
54
what is a strong acid?
they ionise almost completely in water .most acid molecules dissociate to release H+ ions low pH (0-2)
55
examples of strong acids?
sulfuric acid hydrochloric acid nitric acid
56
what are weak acids?
do not fully ionise in solution only a few of acid molecules dissociate to release H+ ions pH around (2-6)
57
examples of weak acids?
ethanoic acid citric acid carbonic acid
58
what are concentrated acids?
measures how much acid there is in a litre of water.
59
if the concentration of H+ ions increase by a factor of 10 what happens to Ph?
decreases by 1
60
acid + metal →
salt + hydrogen
61
what salt does hydrochloric acid give?
metal chloride
62
what salt does sulfuric acid produce?
metal sulphate
63
what salt does nitric acid produce?
metal nitrate
63
acid + metal carbonate →
salt + water + carbon dioxide
63
how are soluble salts made?
in acid/ alkali reactions
64
acid + alkali →
salt + water
65
practical for making soluble salts using acid and alkalis?
1. can't tell whether reaction is finished or not, no sign acid has been neutralised 2. add right amount of alkali to neutralise the acid, carry out titration to work out exact amount needed 3. use no indicator, so it doesn't contaminate salt 4. solution that remains is salt and water. 5. slowly evaporate some water then leave solution to crystalise, filter off solid you'll be left with pure, dry salt
66
how to make soluble salts using an acid and an insoluble reactant?
1.react acid with insoluble base 2.acid + metal/ insoluble base 3. add base to acid, they will react and produce a soluble salt (+water) 4.you know when acid is neutralised because excess solid will sink 5. filter off excess solid to get a solution of salt + water 6. heat solution gently to slowly evaporate off some water 7. allow salt to crystalise, filter off solid
67
how to make an insoluble salt
using precipitation reactions .using correct 2 soluble salts, react to get insoluble salt
68
what is a precipitation reaction?
react to aqueous substances and they form a solid called precipitate
69
how does concentration affect rate of reaction?
increasing conc of reactant means there are more particles in the same volume. more frequent collisions. rate of reactions is the also increased
70
if electrons are transferred what type of reaction is it?
REDOX reaction
71
what is oxidation?
reaction with or addition of OXYGEN loss of electrons
72
what is reduction?
removal of OXYGEN gain electrons
73
what is an oxidising agent?
accepts electrons and gets reduced (gain electrons, loses oxygen)
74
what do half equations show?
if things have been oxidised or reduced .show how electrons move in a reaction
74
what is a reducing agent?
donates electrons and gets oxidised (loses electrons and gains oxygen)
74
process of electrolysis?
1. electric current passed through an electrolyte causing it to decompose 2. positive ions (cations) in electrolyte will move towards cathode (-) and are reduced. 3. anions (-) in electrolyte will move towards anode (+) and are oxidised 4. as ions gain or lose electrons they from undercharged substances and are discharged from solution 5. electrochemical cell is a circuit, made up of anode, cathode, electrolyte, power source, wire connecting electrodes
75
why can't an ionic solid be electrolysed?
ions are in a fixed position and can't move
76
what is produced at cathode?
POSITIVE ATTRACT hydrogen is produced if the metal is more reactive than hydrogen
76
why can molten ionic compounds be electrolysed?
ions move freely and conduct electricity
77
what is produced at the anode?
NEGATIVE ATTRACT Oxygen is produced (from hydroxide ions), unless halide.
77
electrolysis- aqueous solution what is produced at cathode?
.cathode if H+ ions and metal ions are present, HYDROGEN gas will be produced IF metal is MORE reactive than hydrogen
78
electrolysis- aqueous solution what is produced at anode?
.anode, if halide ions are present (Cl-, Br-, I-) molecules of chorine, bromine and iodine will be formed if NO HALIDE ions are present OXYGEN will be formed from hydroxide ions
79
how to set up an electrochemical cell?
1. 2 electrodes (INERT), clean surface of electrodes using emery paper 2. place both electrodes into beaker filled with the electrolyte 3. connect electrodes to a power supply using crocodile clips and wires
80
what is an electrolyte?
an ionic compound that is molten or dissolved in water that conducts electricity and is decomposed by it
81
what is an electrode?
a rod of metal or graphite through which an electric current flows into or out of an electrolyte
82
what is electrolysis?
using electricity to break down electrolytes to form elements
83
what can non-inert electrodes do?
decompose into electrolyte
84
which electrode increases mass in electrolysis?
cathode increase in mass
85
how long should you leave cell running for in electrolysis?
15min - hour for a decent change in mass
86
how to measure mass of electrodes to see if it has changed?
measure mass before you begin pat electrodes dry measure mass