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4-chemical changes Flashcards

1
Q

explain how the ph scale works

A

it is a measure of how acidic or alkaline a solution is
the lower the ph of a solution the more acidic it is
the higher the ph of a solution, the more alkaline it is
a neutral substance has ph of 7(pure water)

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2
Q

give examples of things with ph 1

A

car battery acid
stomach acid

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3
Q

e.g. things with ph 3

A

vinegar
lemon juice

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4
Q

e.g. things with ph 4

A

acid rain

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5
Q

things with ph 5

A

normal rain

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6
Q

things with ph 9

A

washing up liquid

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7
Q

things with ph 10

A

pancreatic juice

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8
Q

ph 11 examples

A

soap powder

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9
Q

ph 12 examples

A

bleachh

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10
Q

ph 13/14 examples

A

causatic soda (drain cleaner)

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11
Q

what is an indicator

ways to measure pH

A

a dye that changes colour depending on whether its above or below a certain pH
Some indicators contain a mixture of dyes that mean they gradually change colour over a broad range of pH . =WIDE range of indicators, useful for estimating ph of a solution e.g. universal indicator gives colours

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12
Q

how to measure pH
pH probe
why are they more accurate than indicators

A

attached to a pH meter to measure pH electronically
probe is placed in the solution youre measuring and the pH is given on a digital display as a numerical value = more accurate than indicator

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13
Q

what is an acid

A

a substance that forms aqueous solutions with a ph less than 7
acids from H+ ions in water

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14
Q

what is an acid

A

a substance that forms aqueous solutions with a ph less than 7
acids from H+ ions in water

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15
Q

what is an alkali

A

a base is a substance with a ph greater than 7
an alkali is a base that dissolves in water to form a solution with a pH greater than 7
alkalis form OH- ions in water

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16
Q

what is the neutralisation equation
show in terms of words
show in terms of ions

A

acid + base => salt + water
H+(aq)+ OH- (aq)=> H2O(l)

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17
Q

explain what happens in neutralisation

A

when an acid neutralises base
products are neutral with ph of 7
indicator can be used to show that a neutralisation reaction is over
neutralisation reactions of strong acids and alkalis can be used to calculate the concentration of an acid or alkali by titration

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18
Q

acids ionise in aqueous solutions
give example equations

A

HCL => H+ + CL-
HNO3 => H+ + NO3-

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19
Q

explain how strong acids behave in aqueous solutions

A

eg sulfuric,hydrochlric,nitric
ionise completely in water
all acid particles disassociate to release H+ ions

20
Q

explain how weak acids behave in aqueous solutions

A

ethanoic,citric, carbonic
dont fully ionise in solution
only a small proportion of acid particles disassociate to release H+ ions

21
Q

explain ionisation of weak acids

A

reversible reaction
sets up an equilibrium between the undissociated and disassociated acid
since only a few particles release H+ ions, position of equilibruim lies well to the left

22
Q

explain reactions of acids involving H+ ions

A

they react with other substances

if the concentration of H+ ions is higher, the rate of reaction will be faster so strong acids will be more reactive than the weak acids of the same concentration

23
Q

what is the pH of an acid/alkaliis a measure of what

A

the concentration of H+ ions in the solution

24
Q

for every decrease of 1 on the pH scale

A

the concentraition of H+ ions increases by a factor of 10
an acid which the ph of 4 has 10 x the conc of H+ ions of ann acid that has a pH of 5
for a decrease of 2 on the pH scale, the concentration of H+ ions increases by a factor of 100

rule=
factor H+ ion concentration changes by= 10^-x
x is the difference in pH, soif pH falls from 7 to 4, difference is -3
factor increased by is increased by 10-(-3) so 10^3

ph of a strong acid is less than ph of weaker acid if they have same concentration

25
what does strength of acid tell u
acid strength tels you what proportion of acid molecules ionise in water
26
what does the concentration of an acid tell u
it measures how much acid there is in a certain volume of water concentration is basically how watered down your acid is the larger the amount of acid there is in a certain volume of liquid, the more concentrated the acid is you can have dilute but strong acid vice versa ph will decrease with increasing acid conc regardless strong/weak acid
27
what are metal oxides and hydroxides and what they do in water
they are bases that dissolve in water these compounds are alkalis
28
what happens to bases that dont dissolve in water
they take part in neutralisation reactions with acids
29
what do metal oxides and hydroxides form after reacting with acids s
salt and water acid + metal oxide- salt + water acid + metal hydroxide- salt+water
30
explain metal carbonates
reacts with acids to produe acid + metal carbonate- salt + water+ carbon dioxide
30
explain metal carbonates
reacts with acids to produe acid + metal carbonate- salt + water+ carbon dioxide
31
how can you make soluble salts from an insoluble base
gently warm dilute acid with bunsen burner then turn off add insoluble base to acid at a time until no more reacts so base in in excess all acid should be neutralised so excess solid sinks filter out excess solid to get salt solution gently heat solution using water bath/ electric heater to evaporate some water to make it more concentrated . leave to cool crystals formed filter out and dry
32
explain properties of reactivity series
reactivity determined by how easily metal leaves electron to form positive ions the higher up the more reactive metals react with water/acid to make positive ions
33
what is the order of the reacitivity series
potassium sodium lithium calcium magnesium carbon zinc iron hydrogen copper
34
what does acid + metal give
salt + hydrogen
35
from a reaction between an acid and metal, how is speed of reaction indicated
rate at which bubbles of hydrogen are given off more reactive the metak, the faster the reaction will go
36
how could you investigate the reactivity of metals
measure temperature change of reaction with acid/ water over set time period use same mass and surface area of metal each time more reactive metal gives greater temperature change
37
metal + water ? what metals react with water
metal hydroxide + hydrogen e.g. potassium, sodium, lithium, calcium
38
explain oxidation
commmon metals react with oxygen to form oxides , they are often the ores that metals need to be extracted from = gain of oxygen
39
explain reduction
a reaction that separates a metal from its oxide is called a reduction reaction loss of oxygen
40
how can metals be extracted from ores
chemically by reduction using carbon the ore is reduced as oxygen is removed from it carbon gains oxygen so its oxidised position of metal in reactivity series determines whether it can be extracted by reduction with carbon metals higher than carbon is extracted with electrolysis(expensive) -below carbon, extracted with carbon as carbon can only take oxygen away from metals less reactive than carbon itself
41
redox reactions oxidation reduction
oxidation is loss of electrons gain of electrons is reduction OILRIG
42
Give an example of a redox reaction
reduction and oxidation can occur at the same time iron atoms are oxidised to give fe 2+ ions when reacting with dilute acid Fe+2H+->Fe2+ +H2 iron atoms lose electrons, oxidised by hydrogen ions Fe-2e- ->Fe2+ Hydrogen ions gain electrons, reduced by iron atoms 2H+ + 2e- -> H2
43
explain displacement reactions
a more reactive metal will displace a less reactive metal from its compound e.g iron in copper sulfate solution, iron displaces copper= iron sulfate solution + copper iron loses 2 electrons (2+ion)-oxidised copper gains 2 electrons = reduced metal ion always gains electrons and is reduced, metal atom loses electrons and is oxidised
44
what happens during electrolysis
elecric current passsed through electrolyte (molten or dissolved ionic compound) ion moves towards electrodes , where they react and compound decomposes
45
what happens in ions in electrolysis
positive ions in electrolyte move near cathode (-ve ) and gain electrons where reduced negtive ions move to anode (+ve) and loses electrons =oxidised creates flow of charge through electrolyte as ions travel to electrodes = uncharged elements formed and discharged from electrolyte
46
why should electrodes be inert why do ionic compounds have to be molten
electrodes should be inert so they dont react with electrolyte molten ionic compounds can be electrolysed as ions can move freely to conduct electricity molten ionic liquids are always broken up into elements positive metal ions are reduced to element at cathode negative non metal ions are oxidised at anode

chemistry (11 decks)

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