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chemistry > 4-chemical changes > Flashcards

4-chemical changes Flashcards

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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
Q

what does strength of acid tell u

A

acid strength tels you what proportion of acid molecules ionise in water

26
Q

what does the concentration of an acid tell u

A

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
Q

what are metal oxides and hydroxides and what they do in water

A

they are bases that dissolve in water
these compounds are alkalis

28
Q

what happens to bases that dont dissolve in water

A

they take part in neutralisation reactions with acids

29
Q

what do metal oxides and hydroxides form after reacting with acids s

A

salt and water
acid + metal oxide- salt + water
acid + metal hydroxide- salt+water

30
Q

explain metal carbonates

A

reacts with acids to produe
acid + metal carbonate- salt + water+ carbon dioxide

30
Q

explain metal carbonates

A

reacts with acids to produe
acid + metal carbonate- salt + water+ carbon dioxide

31
Q

how can you make soluble salts from an insoluble base

A

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
Q

explain properties of reactivity series

A

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
Q

what is the order of the reacitivity series

A

potassium
sodium
lithium
calcium
magnesium
carbon
zinc
iron
hydrogen
copper

34
Q

what does acid + metal give

A

salt + hydrogen

35
Q

from a reaction between an acid and metal, how is speed of reaction indicated

A

rate at which bubbles of hydrogen are given off
more reactive the metak, the faster the reaction will go

36
Q

how could you investigate the reactivity of metals

A

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
Q

metal + water ?
what metals react with water

A

metal hydroxide + hydrogen
e.g. potassium, sodium, lithium, calcium

38
Q

explain oxidation

A

commmon metals react with oxygen to form oxides , they are often the ores that metals need to be extracted from
= gain of oxygen

39
Q

explain reduction

A

a reaction that separates a metal from its oxide is called a reduction reaction
loss of oxygen

40
Q

how can metals be extracted from ores

A

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
Q

redox reactions
oxidation
reduction

A

oxidation is loss of electrons
gain of electrons is reduction
OILRIG

42
Q

Give an example of a redox reaction

A

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
Q

explain displacement reactions

A

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
Q

what happens during electrolysis

A

elecric current passsed through electrolyte (molten or dissolved ionic compound) ion moves towards electrodes , where they react and compound decomposes

45
Q

what happens in ions in electrolysis

A

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
Q

why should electrodes be inert

why do ionic compounds have to be molten

A

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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