Chemical Changes C4 Flashcards
(111 cards)
1
Q
What does testing the pH of a solution involve?
A
Using an indicator.
2
Q
What is the pH scale range?
A
The pH scale goes from 0 to 14.
3
Q
What pH value indicates a neutral substance?
A
A neutral substance has a pH of 7.
4
Q
What does the pH scale measure?
A
It measures how acidic or alkaline a solution is.
5
Q
What happens to the acidity as pH decreases?
A
The lower the pH of a solution, the more acidic it is.
6
Q
What happens to the alkalinity as pH increases?
A
The higher the pH of a solution, the more alkaline it is.
7
Q
What is an acid?
A
An acid is a substance that forms aqueous solutions with a pH of less than 7.
8
Q
What ions do acids form in water?
A
Acids form H ions in water.
9
Q
What is a base?
A
A base is a substance with a pH greater than 7.
10
Q
What is an alkali?
A
An alkali is a base that dissolves in water to form a solution with a pH greater than 7.
11
Q
What ions do alkalis form in water?
A
Alkalis form OH ions in water.
12
Q
What is the reaction between acids and bases called?
A
Neutralisation.
13
Q
What are the products of an acid-base neutralisation?
A
The products are salt and water.
14
Q
How can pH be measured electronically?
A
Using a pH probe attached to a pH meter.
15
Q
What does a pH meter display?
A
The pH is given on a digital display as a numerical value.
16
Q
What are wide range indicators?
A
Indicators that gradually change colour over a broad range of pH.
17
Q
What does universal indicator do?
A
It gives different colours depending on the pH level.
18
Q
What happens when an acid neutralises a base?
A
The products are neutral, i.e., they have a pH of 7.
19
Q
What can an indicator show during a neutralisation reaction?
A
It can show that the neutralisation reaction is over.
20
Q
If the pH of an unknown solution is found to be 8, is it acidic or alkaline?
A
The solution is alkaline.
21
Q
What is the significance of pH in the human body?
A
Skin is slightly acidic with a pH of 5.5.
22
Q
What colour would you expect universal indicator to turn in lemon juice?
A
It would turn a colour indicating acidity.
23
Q
What do acids produce in water?
A
Acids produce protons (H+ ions) in water.
24
Q
What is the difference between strong and weak acids?
A
Strong acids ionise completely in water, while weak acids do not fully ionise.
25
Give examples of strong acids.
Examples of strong acids include sulfuric acid, hydrochloric acid, and nitric acid.
26
Give examples of weak acids.
Examples of weak acids include ethanoic acid, citric acid, and carbonic acid.
27
What happens to the equilibrium position in weak acids?
The position of equilibrium lies well to the left because only a few acid particles release H+ ions.
28
What is pH a measure of?
pH is a measure of the concentration of H+ ions in a solution.
29
How does the pH of strong acids compare to weak acids?
The pH of a strong acid is always less than that of a weaker acid if they have the same concentration.
30
What happens to H+ ion concentration with a decrease of 1 on the pH scale?
The concentration of H+ ions increases by a factor of 10.
31
What is the difference between strong acids and concentrated acids?
Acid strength refers to the proportion of acid molecules that ionise, while concentration measures how much acid is in a certain volume of water.
32
Can you have a dilute strong acid?
Yes, you can have a dilute strong acid or a concentrated weak acid.
33
What happens to pH with increasing acid concentration?
pH will decrease with increasing acid concentration regardless of whether it's a strong or weak acid.
34
If a student added strong acid to a weakly acidic solution of pH 6, and the new solution was pH 3, how many times did the concentration of H+ increase?
The concentration of H+ increased by a factor of 1000.
35
What are Metal Oxides and Metal Hydroxides?
They are bases. Some dissolve in water and are called alkalis.
36
What happens in neutralisation reactions?
All metal oxides and metal hydroxides react with acids to form a salt and water.
37
What is the general reaction for an acid reacting with a metal oxide?
Acid + Metal Oxide → Salt + Water
38
What do acids and metal carbonates produce?
They produce a salt, water, and carbon dioxide.
39
What is the reaction between calcium carbonate and hydrochloric acid?
Calcium carbonate + Hydrochloric acid → Salt + Water + Carbon Dioxide
40
How do you make soluble salts using an insoluble base?
Mix the right acid with an insoluble base until no more reacts.
41
What is the process to obtain pure solid crystals of salt from a solution?
Gently heat the solution, then allow it to cool for crystallisation.
42
What is crystallisation?
The process of forming solid crystals from a solution.
43
What should you do if asked to describe how to make a pure, dry sample of a soluble salt?
Understand the method and the reactants to use.
44
What does the reactivity series list?
The reactivity series lists metals in order of their reactivity towards other substances.
45
How is a metal's reactivity determined?
A metal's reactivity is determined by how easily it loses electrons, forming positive ions.
46
What happens when metals react with water or acid?
When metals react with water or acid, they lose electrons and form positive ions.
47
What does a higher position in the reactivity series indicate?
The higher a metal is in the reactivity series, the more easily it reacts with water or acid.
48
What do metals produce when they react with acids?
Metals react with acids to produce a salt and hydrogen gas.
49
Which metals react vigorously with cold dilute acids?
Magnesium reacts vigorously with cold dilute acids such as HCl and H2SO4.
50
What is the general reaction of metals with dilute acids?
Acid + Metal → Salt + Hydrogen
51
Which metals react explosively with water?
Potassium, sodium, lithium, and calcium react explosively with water.
52
How can the speed of a metal's reaction with water be indicated?
The speed of reaction is indicated by the rate at which bubbles of hydrogen are given off.
53
What is the reaction of calcium with water?
Ca + 2H2O → Ca(OH)2 + H2
54
What is the general reaction of metals with water?
Metal + Water → Metal Hydroxide + Hydrogen
55
How can you investigate the reactivity of metals?
You can investigate the reactivity of metals by measuring the temperature change of the reaction with an acid or water over a set time period.
56
What do carbon and hydrogen represent in the reactivity series?
Carbon and hydrogen are non-metals but are often included in the reactivity series.
57
What happens to less reactive metals like zinc, iron, and copper with water?
Less reactive metals like zinc, iron, and copper won't react with water.
58
What do you observe in the reactions of metals with dilute acids?
Zinc and iron react slowly with dilute acids but more strongly if heated.
59
How are most metals found in the earth?
Most metals are not found as pure lumps; they are found in compounds, requiring extraction.
60
What is oxidation?
Oxidation is the gain of oxygen.
## Footnote
Example: Magnesium is oxidised to make magnesium oxide (2Mg + O₂ → 2MgO).
61
What is a reduction reaction?
A reduction reaction is a process that separates a metal from its oxide by removing oxygen.
62
How can some metals be extracted from their ores?
Some metals can be extracted chemically by reduction using carbon.
63
What happens in the reduction process?
In reduction, the ore loses oxygen, and carbon gains oxygen, thus being oxidised.
## Footnote
Example: 2CuO + C → 2Cu + CO₂.
64
What determines the extraction method of a metal?
The position of the metal in the reactivity series determines whether it can be extracted by reduction with carbon.
65
Which metals require electrolysis for extraction?
Metals higher than carbon in the reactivity series must be extracted using electrolysis.
66
Which metals can be extracted by reduction using carbon?
Metals below carbon in the reactivity series can be extracted by reduction using carbon.
67
What is an ore?
An ore is a type of rock that contains metal compounds.
68
What is the reactivity series?
The reactivity series lists metals in order of reactivity, from potassium to copper.
69
What is the significance of carbon in metal extraction?
Carbon can only take oxygen away from metals that are less reactive than itself.
70
What does oxidation mean in chemistry?
Oxidation can mean the addition of oxygen or a reaction with it, but it primarily refers to the loss of electrons.
71
What is the mnemonic to remember oxidation and reduction?
OIL RIG: Oxidation Is Loss, Reduction Is Gain.
72
What happens during a redox reaction?
Oxidation and reduction occur simultaneously.
73
What happens to iron atoms when they react with dilute acid?
Iron atoms are oxidised to Fe2+ ions, losing electrons to hydrogen ions, which are reduced.
74
What are displacement reactions?
Displacement reactions involve one metal replacing another in a compound.
75
What is the rule for displacement reactions?
A more reactive metal will displace a less reactive metal from its compound.
76
What is the outcome when iron is placed in copper sulfate solution?
Iron will replace copper, resulting in iron sulfate solution and copper metal.
77
In displacement reactions, what happens to the metal ion and metal atom?
The metal ion gains electrons and is reduced, while the metal atom loses electrons and is oxidised.
78
What do ionic equations show?
Ionic equations show only the particles that react in a chemical reaction.
79
What does a more reactive metal do in a displacement reaction?
It displaces a less reactive metal from its compound.
80
What are spectator ions?
Spectator ions do not change in the reaction and can be crossed out in ionic equations.
81
Why are ionic equations important in chemistry?
Ionic equations focus on the substances that are oxidised or reduced.
82
What is electrolysis?
Electrolysis is the process of using an electrical current to cause a chemical reaction.
83
What happens during electrolysis?
An electric current is passed through an electrolyte, causing ions to move towards electrodes where they react.
84
What do positive ions do in electrolysis?
Positive ions move towards the cathode (negative electrode) and gain electrons, resulting in reduction.
85
What do negative ions do in electrolysis?
Negative ions move towards the anode (positive electrode) and lose electrons, resulting in oxidation.
86
Why can't ionic solids be electrolysed?
Ionic solids cannot be electrolysed because their ions are in fixed positions and cannot move.
87
What is produced at the cathode during electrolysis?
Positive metal ions are reduced to the element at the cathode.
88
What is produced at the anode during electrolysis?
Negative non-metal ions are oxidised to the element at the anode.
89
Why can molten ionic compounds be electrolysed?
Molten ionic compounds can be electrolysed because their ions can move freely and conduct electricity.
90
What is an electrolyte?
An electrolyte is a liquid or solution that can conduct electricity.
91
What is an electrode?
An electrode is a solid that conducts electricity and is submerged in the electrolyte.
92
How is aluminium extracted from bauxite?
Aluminium is extracted from bauxite by electrolysis, where aluminium oxide is reduced at the cathode.
93
What happens at the negative electrode during aluminium extraction?
At the negative electrode, Al³⁺ ions gain electrons to form neutral aluminium atoms.
94
What happens at the positive electrode during aluminium extraction?
At the positive electrode, O²⁻ ions lose electrons to form oxygen molecules.
95
What is cryolite?
Cryolite is an aluminium-based compound with a lower melting point than aluminium oxide.
96
What is the role of the anode in electrolysis?
The anode is made of carbon and needs to be replaced regularly as it reacts with oxygen to produce carbon dioxide.
97
What ions are present in an aqueous solution during electrolysis?
In addition to the ions from the ionic compound, there are hydrogen ions (H⁺) and hydroxide ions (OH⁻) from the water.
98
What happens at the cathode if hydrogen ions and metal ions are present?
Hydrogen gas will be produced if the metal ions form an elemental metal that is more reactive than hydrogen (e.g., sodium ions). If the metal ions form an elemental metal that is less reactive than hydrogen (e.g., copper ions), a solid layer of the pure metal will be produced instead.
99
What is produced at the anode if OH⁻ and halide ions are present?
Molecules of chlorine, bromine, or iodine will be formed. If no halide ions are present, then the OH⁻ ions are discharged and oxygen will be formed.
100
What ions are present in a solution of copper(II) sulfate (CuSO₄)?
The solution contains Cu²⁺, SO₄²⁻, H⁺, and OH⁻.
101
What is produced at the cathode when electrolyzing copper(II) sulfate?
Copper metal is produced and coats the electrode because copper metal is less reactive than hydrogen.
102
What is produced at the anode when electrolyzing copper(II) sulfate?
Oxygen and water are produced, and the oxygen can be seen as bubbles.
103
What ions are present in a solution of sodium chloride (NaCl)?
The solution contains Na⁺, Cl⁻, OH⁻, and H⁺.
104
What is produced at the cathode when electrolyzing sodium chloride?
Hydrogen gas is produced because sodium metal is more reactive than hydrogen.
105
What is produced at the anode when electrolyzing sodium chloride?
Chlorine gas is produced because chloride ions are present in the solution.
106
What is the test for hydrogen gas?
Hydrogen makes a 'squeaky pop' with a lighted splint.
107
What is the test for oxygen gas?
Oxygen will relight a glowing splint.
108
What is important to remember when combining half equations?
The number of electrons needs to be the same for each half equation.
109
What happens when a halide isn't present in the aqueous solution at the anode?
The half equation for the anode will involve the discharge of OH⁻ ions.
110
What is produced at the anode when electrolyzing an aqueous solution of copper bromide (CuBr)?
Bromine gas is produced using inert electrodes.
111
What should be included when drawing the apparatus for an electrolysis experiment?
Include a DC power supply, wires, and labels for the anode and the cathode.
