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gcse science > Science - Chemistry - Chemical Changes - C4 > Flashcards

Science - Chemistry - Chemical Changes - C4 Flashcards

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1
Q

what is the PH scale ?

A

a scale that measures how acidic or alkaline a solution is

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2
Q

what numbers - do the PH scale go between ?

A

0 -14

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3
Q

what kind of solution has a PH of less than 7 ?

A

acid

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4
Q

the lower the PH, the what ?

A

the more acidic the solution

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5
Q

what kind of solution has a PH greater than 7 ?

A

alkali

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6
Q

the higher the PH, the what ?

A

the more alkaline the substance is

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7
Q

what is a neutral substance ?

A

a substance that isn’t acidic or alkaline

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8
Q

what is the PH of a neutral substance ?

A

7

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9
Q

give an example of a neutral substance ?

A

pure water

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10
Q

how do you test the PH of a solution ?

A

by using an indicator

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11
Q

what is an indicator ?

A

a dye that changes color depending on whether it’s above or below a certain PH

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12
Q

what is a universal indicator ?

A

an indicator which contains a mixture of dyes so it can gradually change color over a broad range of PH’s

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13
Q

what are universal indicators useful for ?

A

estimating the PH of a solution

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14
Q

give an example of a solution with the PH of 1, red/orange PH ?

A
  • car battery acid
  • stomach acid
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15
Q

give an example of a solution with the PH of 3, orange PH

A
  • vinegar
  • lemon juice
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16
Q

give an example of a solution with a PH 4 / orange

A
  • normal rain
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17
Q

give an example of a solution with a PH 5 / orange, yellow

A

normal rain

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18
Q

what solution has a PH of 7 ?

A

pure rain

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19
Q

what solution has a PH 8 / blue

A

washing up liquid

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20
Q

what solution has a PH 11 / purple ?

A

soap powder

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20
Q

how does a PH probe work ?

A

the probe is placed in the solution you are measuring and the PH is given on digital display as a numerical value

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21
Q

what solution has a PH 9 / dark blue

A

pancreatic juice

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22
Q

what solution has a PH of 12 / purple ?

A

bleach

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22
Q

what solution has a PH of 14 / dark purple ?

A

caustic soda ( drain cleaner )

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22
Q

what is a PH probe ?

A

a probe which can measure PH electronically

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23
Q

which is more reliable :
- an indicator
- a PH probe

A
  • PH probe
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23
Q

what type of ions do acids form when dissolved in water ?

A

hydrogen ions (H+)

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23
Q

show the neutralization reaction equation

A

acid + alkali - salt + water

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23
Q

what happens in a neutralization reaction ?

A

hydrogen ions from the acid react with hydroxide ions from the alkali to produce water

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23
Q

show the neutralization reaction in terms of ions ?

A

H+ + OH-1 - H20

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23
Q

what determines whether a substance is an acid or an alkali ?

A

the type of ions are released when the substance is dissolved in water

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24
Q

what type of ions do alkalis form when dissolved in water ?

A

hydroxide ions (OH-1)

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25
Q

what is a neutralization reaction ?

A

when an acid reacts with an alkali to form a salt and water

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25
Q

what is the PH of the product formed from a neutralization equation ?

A

7

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26
Q

what is titration ?

A

an experiment that lets you see what volume of a reactant is needed to react completely with a certain volume of another reactant

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26
Q

give an example of when you’d use titration

A

to find out exactly how much acid is needed to neutralize a certain quantity of alkali

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26
Q

what can the results of a titration experiment show you ?

A

the concentration of one of the reactants

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27
Q

what does the strength of the acid tell you ?

A

about the proportion of acid particles that will dissociate to produce H+ ions in solution

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27
Q

what happens when acids are added to an aqueous solution ?

A

they ionise to produce H+ ions

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27
Q

what do weak acids do in water ?

A

partially ionise in water, only some of the acid molecules will ionise and release H+ ions

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27
Q

what do strong acids do in water ?

A

ionise completely, all the acid particles dissociate to release H+ ions

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28
Q

give examples of a strong acids

A
  • sulfuric acid
  • hydrochloric acid
  • nitric acid
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29
Q

give examples of weak acids

A
  • carboxylic acid
  • carbonic acid
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30
Q

why can’t you use universal indicator in a titration experiment ?

A

the colour change is too gradual

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31
Q

what type of indicators are good for titrations ?

A
  • phenolphthalein
  • methyl orange
  • litmus

they only have one colour changing compound so will have one distinct colour change at a particular PH

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32
Q

give a hazard when doing the titration experiment

A

acids and alkalis are often corrosive so you need to wear safety goggles to protect your eyes whilst using them

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33
Q

what is the dissociation of acids ?

A

when acids are added to an aqueous solution they ionise to produce H+ ions

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34
Q

give an example of a disassociation of acids ?

A

hydrogen chloride dissolves in water to form hydrogen chloride ions - HCl - H+ + Cl-

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35
Q

if the concentration of H+ ions are higher, the rate of reaction will be ?

A

faster

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36
Q

why will strong acids be more reactive than a weak acid of the same concentration ?

A

strong acids dissaociate more than weak acids so a strong acid will be more reactive than a weak acid of the same concentration

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37
Q

what does the PH measure with H+ ions in a solution ?

A

the concentration

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38
Q

the lower the PH, the what the concentration of H+ ions ?

A

higher

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39
Q

why will the concentration of H+ ions be higher with a lower PH ?

A

it is more acidic

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40
Q

why will the PH of a strong acid be lower than the PH of a weak acid with the same concentration ?

A

strong acids dissociate more than weak acids resulting in a larger concentration of H+ ions

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41
Q

for every decrease of 1 on the PH scale, the concentration of H+ ions increases by a factor of what ?

A

10

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42
Q

how do you calculate the change in H+ concentration ?

A

factor H+ ion concentration changes by = 10 - x

x = difference in PH

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43
Q

what does acid strength tell you ?

A

what proportion of the acid molecules ionise in water

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44
Q

what does the concentration of an acid measure?

A

the number of dissolved acid molecules there are in a certain volume of water, how watered down your acid is

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45
Q

the larger the amount of acid in a certain volume the what ?

A

more concentrated the acid is

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46
Q

the PH will decrease with —– what acid concentration ?

A

increasing

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47
Q

what are bases ?

A

substances that react with acids in neutralisation reactions

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48
Q

why are soluble metal hydroxides alkalis ?

A

they dissolve in water to form OH- ions

49
Q

what are the products of a neutralisation reaction ?

A

a salt and water

50
Q

what is the word equation for metal oxides or metal hydroxides ?

A

acid + metal oxide/ metal hydroxide - salt + water

51
Q

give an example of a neutralisation reaction ?

A

hyrdochloric acid + copper oxide - copper chloride + water

52
Q

reactions with hydrochloric acids give what ?

A

chlorides

53
Q

reactions with sulfuric acid gives what ?

A

sulfates

54
Q

reactions with nitric acid gives what ?

A

nitrates

55
Q

metal carbonates react with acids to make what?

A

a salt, carbon dioxide, and water

56
Q

what is the general equation for the reaction of metal carbonates and acids ?

A

metal carbonate + acid - metal salt + carbon dioxide + water

57
Q

how can soluble salts be made ?

A

by reacting an acid with a metal or an insoluble base

58
Q

what is the reactivity series ?

A

a list of metals that are arranged in order of how reactive they are

59
Q

what is the reactivity of a metal ?

A

how easily it forms positive ions

60
Q

a metal which easily forms positive ions are what ?

A

more reactive

61
Q

which element is at the top of the reactivity series ?

A

potassium

62
Q

which element is at the bottom of the reactivity series ?

A

copper

63
Q

which 2 non - metals are in the reactivity series ?

A

carbon and hydrogen

64
Q

why are carbon and hydrogen in the reactivity series ?

A

so you can compare where metals are in relation to them

65
Q

how do you get a reactivity series ( investigation) ?

A

compare the relative reactivity of different metals with an acid or water and put them in order from most to least reactive

66
Q

the higher a metal is in a reactivity series, the what ?

A

the more easily the metal is reacted with the water or the acid

67
Q

how else can you determine a metals reactivity ( other than reacting them with water/ an acid) ?

A
  • measure the temperature change of the reaction with an acid or water over a set time period
68
Q

if you use the same mass and surface area of metal each time, the more reactive the metal, the greater what ?

A

temperature change

69
Q

what is the reaction between metals and acids ?

A

metals and acids react to form a salt and a hydrogen

70
Q

what is the equation for metals reacting with acids ?

A

acid + metal - salt + hydrogen

71
Q

how can you tell how reactive different metals are when reacting with an acid ?

A

monitoring the rate of hydrogen production

72
Q

when reacting an acid and a metal, how is the speed of reaction shown ?

A
  • ## the rate of bubbles of hydrogen that are given off
73
Q

give examples of metals that react explosively with acids

A
  • potassium
  • sodium
  • lithium
  • calcium
74
Q

give examples of metals which react slowly with acids ?

A

-iron
-magnesium
-zinc

75
Q

what test can be used to show the production of hydrogen?

A

the burning splint test

76
Q

what is the burning splint test ?

A

where you put a lit splint in the mouth of the tube containing the metal and the acid, if the hydrogen is present you will hear a squeaky pop

76
Q

the more reactive the metal, and the more hydrogen produced, the louder the what ?

A

squeaky pop

76
Q

give an example of an element which reacts vigorously with cold dilute acids ?

A

magnesium

77
Q

give an example of a cold dilute acid

A

hydrochloric acid

78
Q

what does the name of the salt formed when mixing metals and acids depend on ?

A

the salt part depends on the name of the metal, and the second part comes from the acid which is used

79
Q

give an example of a salt formed when reacting metals and acids ?

A

hydrochloric acid + magnesium - magnesium chloride + hydrogen

80
Q

what type of salts does hydrochloric acid always produce ?

A

chloride salts

81
Q

what type of salt does sulfuric acid always produce ?

A

sulfate salts

82
Q

give the equation a metal reacting with water

A

metal + water - metal hydroxide + hydrogen

83
Q

will metals that aren’t reactive such as zinc react with water ?

A

no

84
Q

what is a displacement reaction ?

A

where a more reactive metal pushes the less reactive metal out of its compound

85
Q

which metal is unreactive, and found in the earth itself, rather than in a compound ?

A

gold

86
Q

how do you extract metals from the ground that are part of a compound ?

A

extract the metal from metal ores which are mined from the ground

87
Q

what is a metal ore ?

A

a rock which contains metal inside of it to make it profitable to extract the metal from it

88
Q

what are most metal ores ?

A

an oxide of the metal

89
Q

what is a reaction that forms a metal oxide from its metal known as ?

A

oxidation

90
Q

what is oxidation ?

A

the gain of oxygen by an element or compound

91
Q

what is a reaction that separates a metal from its oxide called ?

A

reduction

92
Q

what is reduction ?

A

the loss of oxygen from a compound

93
Q

a metal below carbon in the reactivity series can be what ?

A

extracted from its ore by reducing it in a reaction with carbon

94
Q

how can carbon be used to extract metals ?

A

the ore is reduced as oxygen is removed from it and carbon gains oxygen so is oxidized - displacement reaction

95
Q

why can only metals below carbon use it to extract them from their ores ?

A

as carbon can only tale the oxygen away from metals that are less reactive than itself

96
Q

what do metals that are more reactive than carbon use to extract them from their ores ?

A

electrolysis

97
Q

what is the disadvantage of electrolysis ?

A
  • expensive
98
Q

what is a redox reaction ?

A

where electrons are transferred between substances

99
Q

give an example of a redox reaction ?

A
  • oxidation is a loss of electrons
  • reduction is a gain of electrons
100
Q

why are oxidation and reduction redox reactions ?

A

they happen at the same time

101
Q

how is a displacement reaction a redox reaction ?

A

the metal ion gains electrons and is reduced, the metal atom loses electrons and is oxidized

102
Q

what do ionic equations show ?

A

the particles that react and the products they form

103
Q

what do ionic equations for redox reactions only focus on ?

A

the substances which are oxidized or reduced

104
Q

what are redox reactions in acids and metals like ?

A

metal atoms lose electrons, hydrogen ions gain them

105
Q

what is electrolysis ?

A

the process of breaking down a substance using electricity

106
Q

what is an electrolyte ?

A

a liquid required during electrolysis, needed to conduct electricity

107
Q

what do electrolytes contain ?

A

free ions

108
Q

what do free ions in the electrolyte do to help with electrolysis ?

A

conduct electricity

109
Q

what is an electrode ?

A

a solid that conducts electricity and is submerged into an electrolyte

110
Q

how does electrolysis work ?

A

the electrodes are placed into the electrolyte and ions move from one electrode to the other, which conducts electricity through the circuit. The positive electrolyte goes towards the cathode and gains electrons and the negative ions in the electrolyte goes towards the anode and loses electrons. As ions lose or gain electrons they become atoms or molecules and are released

111
Q

what is a cathode ?

A

a negative electrode

112
Q

which type of ions go to the cathode ?

A

positive ions

113
Q

what is an anode ?

A

a positive electrode

114
Q

which type of ions go to the anode ?

A

negative ions

115
Q

where does reduction occur in electrolysis ?

A

at the negative electrode as the positive ions are gaining electrons

116
Q

where does oxidation occur in electrolysis ?

A

at the positive electrode as negative ions are losing electrodes

117
Q

what are binary compounds ?

A

ionic compounds containing 2 elements which are ions- a positive metal and a negative metal ions

118
Q

what happens during electrolysis of the molten binary compounds ?

A

gives the neutral metal and the non-metal elements, the metal ions will move to the cathode and gain electrons to become neutral and the non-metal ions will move to the anode to lose electrons and become neutral

119
Q

what are half equations ?

A

an equation showing the reactions at electrodes

120
Q

what is used to extract metals from their ores if it is more reactive than carbon ?

A

electrolysis

121
Q

what is the disadvantage of electrolysis ?

A

it is expensive, requires lots of energy to melt the ore and produce the current

122
Q

what is the main ore of aluminium ?

A

bauxite

123
Q

because aluminium has a very high melting point of over 2000 degrees c, melting it would be very expensive, what is done instead ?

A

aluminium oxide is dissolved in a molten cryolite, which brings the melting point to 900 degrees c, saving energy

124
Q

what can electrodes be made out of ?

A

carbon

125
Q

in electrolysis with aluminium, what ions attract to the negative electrode ( cathode ) ?

A

positive aluminium ions

126
Q

what happens between the cathode and aluminium 3 ions in electrolysis ?

A

the a3+ ions pick up 3 electrons and become neutral aluminium atoms, and sink to the bottom of the tank

127
Q

what happens to the oxygen atoms 02- during electrolysis in aluminium?

A

they attract to the anode

128
Q

when attracted to the anode, what happens to the negative o2- ions during electrolysis with aluminium ?

A

they lose 2 electrons and the neutral oxygen atoms combine to form 02 molecules

129
Q

why does the positive carbon electrode sometimes have to be replaced when oxygen attracts to it ?

A

the oxygen and carbon react, forming carbon dioxide, which eats away at the electrode

130
Q

at a negative electrode, if metal ions and H+ ions are present, what will happen to the metal ions ?

A

they will stay in the solution if the metal is more reactive than hydrogen because the more reactive an element, the more likely it is to stay as ions - so hydrogen will be produced unless metal is less reactive than it

131
Q

what will happen at the positive electrode if OH- and halide ions are present ?

A

molecules of chlorine, bromine or iodine will be formed

132
Q

what would happen if no halide ions are present with OH- ions and a positive electrode ?

A

OH- ions are discharged and oxygen and water will be formed

133
Q

what is the experiment carried out when investigating electrolysis of an aqueous solution ?

A
  • get 2 inert electrons, clean their surfaces using emery paper
  • place both electrodes into a beaker filled with your electrolyte and position them so they are inside inverted test tubes containing the aqueous solution
  • connect electrodes to power supply
  • collect gases formed during experiment in test tubes
134
Q

what gases may be produced when doing electrolysis in an aqueous solution ?

A
  • chlorine
  • hydrogen
  • oxygen
135
Q

how do you test to see if chlorine was formed when doing electrolysis in an aqueous solution ?

A
  • it bleaches damp litmus paper turning it white
136
Q

how do you test to see if hydrogen was formed when doing electrolysis in an aqueous solution ?

A
  • it makes a squeaky pop with a lit splint
137
Q

how do you test to see if oxygen was formed when doing electrolysis in an aqueous solution ?

A
  • will relight a glowing splint

gcse science (27 decks)

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