Chemical Changes Flashcards
1
Q
What is the general reaction between metals and oxygen?
A
Metal + oxygen → metal oxide
2
Q
Why are reactions of metals with oxygen called oxidation reactions?
A
Because the metal gains oxygen.
3
Q
What is reduction in terms of oxygen?
A
Reduction = loss of oxygen.
4
Q
What is oxidation in terms of oxygen?
A
Oxidation = gain of oxygen.
5
Q
What happens when metals react with other substances?
A
Metal atoms form positive ions.
6
Q
How is the reactivity of a metal determined?
A
It is related to its tendency to form positive ions.
7
Q
What is the reactivity series?
A
A list of metals arranged in order of their reactivity.
8
Q
What two non-metals are often included in the reactivity series?
A
Carbon and hydrogen.
9
Q
Which metals are most reactive in the reactivity series?
A
Potassium, sodium, lithium, calcium.
10
Q
Which metals are least reactive in the reactivity series?
A
Iron, hydrogen, copper.
11
Q
What is the full order of the reactivity series from most to least reactive?
A
Potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper.
12
Q
How does potassium react with water?
A
Violently.
13
Q
How does sodium react with water?
A
Very quickly.
14
Q
How does lithium react with water?
A
Quickly.
15
Q
How does calcium react with water?
A
More slowly than lithium.
16
Q
Which metals react with water?
A
Potassium, sodium, lithium, calcium.
17
Q
How does calcium react with dilute acid?
A
Very quickly.
18
Q
How does magnesium react with dilute acid?
A
Quickly.
19
Q
How does zinc react with dilute acid?
A
Fairly slowly.
20
Q
How does iron react with dilute acid?
A
More slowly than zinc.
21
Q
How does copper react with dilute acid?
A
Very slowly.
22
Q
Which metals react with dilute acid?
A
Potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron (copper reacts very slowly).
23
Q
What happens in a displacement reaction?
A
A more reactive metal can displace a less reactive metal from a compound.
24
Q
How is displacement in metals similar to halogens?
A
A more reactive element replaces a less reactive one in a compound.
25
Why is gold found in the Earth as a pure metal?
Because it is very unreactive.
26
How are most metals found in nature?
As compounds that require chemical reactions to extract them.
27
How are metals less reactive than carbon extracted?
By reduction with carbon.
28
What does reduction involve in terms of oxygen?
Loss of oxygen.
29
What does OIL RIG stand for?
Oxidation Is Loss, Reduction Is Gain (of electrons).
30
What happens when sodium is oxidised?
It loses an electron, forming a +1 charge.
31
What is the ionic equation for sodium oxidation?
Na → Na⁺ + e⁻
32
What happens when a sodium ion (Na⁺) is reduced?
It gains an electron and becomes neutral sodium again.
33
What is the ionic equation for sodium reduction?
Na⁺ + e⁻ → Na
34
What must be true about charges in ionic equations?
The total charge must be the same on both sides.
35
In the reaction 2Na + 2HCl → 2NaCl + H₂, which element is oxidised?
Sodium (Na) is oxidised.
36
What is the ionic equation for sodium oxidation in this reaction?
2Na → 2Na⁺ + 2e⁻
37
In a reaction where 2Na + 2HCl → 2NaCl + H₂, what happens to hydrogen ions (H⁺)?
Hydrogen ions (H⁺) gain electrons and are reduced to form hydrogen gas (H₂).
38
What is the ionic equation for hydrogen reduction?
2H⁺ + 2e⁻ → H₂
39
What do acids and metals react to produce?
A salt and hydrogen
40
What type of reaction is the reaction between an acid and a metal?
A redox reaction
41
What happens to the metal in an acid-metal reaction?
The metal is oxidized (loses electrons)
42
What happens to the hydrogen ions in an acid-metal reaction?
They are reduced (gain electrons)
43
Write the general word equation for an acid-metal reaction.
Acid + Metal → Salt + Hydrogen
44
Write the ionic equation for the oxidation of magnesium in an acid-metal reaction.
Mg → Mg²⁺ + 2e⁻
45
Write the ionic equation for the reduction of hydrogen in an acid-metal reaction.
2H⁺ + 2e⁻ → H₂
46
What happens when an acid reacts with an alkali?
A salt and water are produced
47
What happens when an acid reacts with a base?
A salt and water are produced
48
What happens when an acid reacts with a metal carbonate?
A salt, water, and carbon dioxide are produced
49
Write the general word equation for acid + alkali.
Acid + Alkali → Salt + Water
50
Write the general word equation for acid + base.
Acid + Base → Salt + Water
51
Write the general word equation for acid + metal carbonate.
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
52
What type of salt does hydrochloric acid produce?
Chlorides (XCl)
53
What type of salt does nitric acid produce?
Nitrates (XNO₃)
54
What type of salt does sulfuric acid produce?
Sulfates (XSO₄)
55
What determines the salt produced in an acid reaction?
The acid used and the positive ion in the base, alkali, or carbonate
56
What must the charges of ions in a salt add up to?
Zero (neutral charge)
57
How are soluble salts made?
By reacting acids with solid insoluble substances (metals, metal oxides, hydroxides, carbonates)
58
How do you know when the acid has been neutralised in salt production?
Excess solid sinks to the bottom
59
What is the final process in making soluble salts?
Filtering out excess solid and then crystallising the salt
60
What ions do acids produce in aqueous solutions?
H⁺ ions
61
What ions do alkalis produce in aqueous solutions?
OH⁻ ions
62
What is the pH scale range?
0 to 14
63
What pH is neutral?
pH 7
64
What pH range is acidic?
Less than 7
65
What pH range is alkaline?
Greater than 7
66
What is the ionic equation for any neutralisation reaction?
H⁺(aq) + OH⁻(aq) → H₂O(l)
67
What is titration used for?
Measuring the volumes of acid and alkali that react exactly with each other
68
What is the first step in a titration?
Wash the burette with dilute hydrochloric acid and then water
69
What volume of acid should the burette be filled to?
100 cm³, aligning the meniscus with the 100 cm³ mark
70
For titrations what is used to transfer the alkali into the conical flask?
A 25 cm³ pipette with a pipette filler
71
What indicator is used in titrations?
Phenolphthalein (pink in alkali, colourless in acid)
72
How is the endpoint of the titration determined?
When the indicator changes colour
73
What is the ‘titre’ in a titration?
The volume of acid required to exactly neutralise the alkali
74
Describe the whole method of titration.
1. Wash burette using dilute hydrochloric acid and then water
2. Fill burette to 100cm3 with acid with the meniscus’ base on the 100cm3
line
3. Use 25cm3 pipette to add 25cm3
of alkali into a conical flask, drawing alkali into the
pipette using a pipette filler
4. Add a few drops of a suitable indicator to the conical flask (eg: phenolphthalein
which is pink when alkaline and colourless when acidic)
5. Add acid from burette to alkali until end-point is reached (as shown by indicator)
6. The titre (volume of acid needed to exactly neutralise the acid) is the difference
between the first (100cm3
) and second readings on the burette
7. Repeat the experiment to gain more precise results
75
Convert 1 dm³ to cm³.
1000 cm³
76
What is the formula for moles?
Moles = Volume × Concentration
77
What is the formula for concentration?
Concentration = Moles / Volume
78
If 25 cm³ of HCl is neutralised by 20 cm³ of 0.5 mol/dm³ NaOH, what is the concentration of HCl?
0.4 mol/dm³
79
What is a strong acid?
An acid that is completely ionised in aqueous solution
80
Give examples of strong acids.
Hydrochloric acid, nitric acid, sulfuric acid
81
What is a weak acid?
An acid that is only partially ionised in aqueous solution
82
Give examples of weak acids.
Ethanoic acid, citric acid, carbonic acid
83
How does pH relate to acid strength?
The lower the pH, the stronger the acid (for a given concentration)
84
If pH decreases by one unit, what happens to the H⁺ ion concentration?
It increases by a factor of 10
85
What is the difference between ‘strong/weak’ and ‘concentrated/dilute’?
Strong/weak refers to ionisation; concentrated/dilute refers to the amount of substance in a given volume
86
What happens when an ionic substance is melted or dissolved?
The ions are free to move within the liquid or solution
87
What is electrolysis?
The process of breaking down a substance using electricity
88
What is the substance being broken down in electrolysis called?
The electrolyte
89
Which ions move to the negative electrode (cathode)?
Positively charged ions
90
Which ions move to the positive electrode (anode)?
Negatively charged ions
91
What happens to ions at the electrodes?
They are discharged, producing elements
92
What happens when a simple ionic compound (e.g., lead bromide) is electrolysed in its molten state?
The metal (lead) forms at the cathode, and the non-metal (bromine) forms at the anode
93
Why does the metal form at the cathode in molten electrolysis?
Because metal ions are positively charged and attracted to the negative electrode
94
Why does the non-metal form at the anode in molten electrolysis?
Because non-metal ions are negatively charged and attracted to the positive electrode
95
Why are some metals extracted using electrolysis instead of carbon reduction?
They are more reactive than carbon
96
Give an example of a metal extracted by electrolysis.
Aluminium
97
Why is electrolysis expensive for metal extraction?
Large amounts of energy are needed to melt the compounds and produce the electrical current
98
How is aluminium extracted?
By electrolysis of a molten mixture of aluminium oxide and cryolite
99
Why is aluminium oxide mixed with cryolite in the extraction process?
To lower its melting point and reduce energy costs
100
Why do the positive carbon electrodes need to be replaced during aluminium extraction?
Oxygen reacts with the carbon electrodes, forming carbon dioxide, and they burn away
101
Can metals that react with carbon also be extracted by electrolysis?
Yes
102
What determines which ions are discharged when an aqueous solution is electrolysed?
The relative reactivity of the elements involved
103
What is usually produced at the cathode in an aqueous solution?
Hydrogen, unless the metal is less reactive than hydrogen
104
Why does hydrogen often form instead of a metal at the cathode?
More reactive metal ions prefer to stay in the solution
105
What is produced at the anode in an aqueous solution if halide ions (Cl⁻, Br⁻, I⁻) are present?
A halogen (chlorine, bromine, or iodine)
106
What is produced at the anode in an aqueous solution if no halide ions are present?
Oxygen
107
Why does oxygen form at the anode if no halide ions are present?
Water molecules break down, producing OH⁻ ions, which are discharged
108
What does a half-equation represent?
The reaction at one of the electrodes
109
How are electrons represented in half-equations?
By the symbol ‘e⁻’
110
Write the half-equation for a positive ion (X⁺) at the cathode.
X⁺ + e⁻ → X (Reduction)
111
What happens to positive ions at the cathode?
They gain electrons (reduction)
112
Write the half-equation for a negative ion (X⁻) at the anode.
X⁻ → X + e⁻ (Oxidation)
113
What happens to negative ions at the anode?
They lose electrons (oxidation)
