topic 4 - chemical changes Flashcards
1
Q
What is the definition of oxidation in the context of metal reactions?
A
Oxidation is a reaction where a metal gains oxygen.
2
Q
What is the definition of reduction in the context of metal reactions?
A
Reduction is a reaction where a metal loses oxygen.
3
Q
How do metals form positive ions?
A
When metals react with other substances metal atoms lose electrons to form positive ions.
4
Q
What is the reactivity series?
A
The reactivity series is a list that arranges metals in order of their reactivity based on their reactions with water and dilute acids.
5
Q
List the metals in the reactivity series from most reactive to least reactive. HINT: Include potassium sodium lithium calcium magnesium zinc iron and copper.
A
The order of reactivity from most reactive to least reactive is: potassium sodium lithium calcium magnesium zinc iron copper.
6
Q
Describe the reaction of potassium with water.
A
Potassium reacts violently with water producing potassium hydroxide and hydrogen gas.
7
Q
Describe the reaction of sodium with water.
A
Sodium reacts very quickly with water producing sodium hydroxide and hydrogen gas.
8
Q
Describe the reaction of lithium with water.
A
Lithium reacts quickly with water producing lithium hydroxide and hydrogen gas.
9
Q
Describe the reaction of calcium with water.
A
Calcium reacts more slowly with water compared to potassium sodium and lithium producing calcium hydroxide and hydrogen gas.
10
Q
What is the reaction of calcium with dilute acid like?
A
Calcium reacts very quickly with dilute acid producing calcium salt and hydrogen gas.
11
Q
What is the reaction of magnesium with dilute acid like?
A
Magnesium reacts quickly with dilute acid producing magnesium salt and hydrogen gas.
12
Q
What is the reaction of zinc with dilute acid?
A
Zinc reacts fairly slowly with dilute acid producing zinc salt and hydrogen gas.
13
Q
How does iron react with dilute acid?
A
Iron reacts slowly with dilute acid producing iron salt and hydrogen gas.
14
Q
What is the reaction of copper with dilute acid?
A
Copper reacts very slowly with dilute acid and is often considered unreactive in this context.
15
Q
What non-metals are often included in the reactivity series?
A
Non-metals hydrogen and carbon are often included in the reactivity series.
16
Q
How does the reactivity of a metal relate to its tendency to form positive ions?
A
The more reactive a metal is the greater its tendency to lose electrons and form positive ions.
17
Q
What is the principle behind the displacement of metals from compounds?
A
A more reactive metal can displace a less reactive metal from its compound.
18
Q
How does the reactivity series relate to metal extraction?
A
Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon during the extraction process.
19
Q
Why is gold found in the Earth as the metal itself?
A
Gold is very unreactive which means it does not readily form compounds with other elements allowing it to exist in its native metallic state.
20
Q
What does reduction involve in the context of metal extraction?
A
Reduction involves the loss of oxygen from a metal oxide or the gain of electrons by a metal ion.
21
Q
What is the mnemonic ‘OIL RIG’ used to remember in chemistry?
A
The mnemonic stands for ‘Oxidation Is Loss and Reduction Is Gain’ of electrons.
22
Q
What happens to sodium when it is oxidised? Write the ionic equation.
A
When sodium is oxidised it loses one electron resulting in a sodium ion with a +1 charge. The ionic equation is Na → Na⁺ + e⁻.
23
Q
What happens to a sodium ion when it is reduced? Write the ionic equation.
A
When a sodium ion is reduced it gains an electron returning to a neutral sodium atom. The ionic equation is Na⁺ + e⁻ → Na.
24
Q
Why is it important for charges to balance in ionic equations?
A
Charges on each side of the ionic equation must add up to the same number to maintain charge conservation and the integrity of the reaction.
25
List the steps typically involved in the extraction of metals from their ores.
1. Crushing and grinding the ore 2. Concentration of the ore 3. Reduction of ore to metal 4. Purification of metal.
26
What is a reduction reaction in simple terms?
A reduction reaction is a chemical process where a substance gains electrons or loses oxygen.
27
What characterizes metals that are found in their elemental form naturally?
These metals are often unreactive or noble metals meaning they do not easily combine with other elements or exist in compound forms.
28
Explain the role of carbon in the extraction of metals less reactive than it.
Carbon can be used to reduce the metal oxides to their elemental form by displacing the metal from its oxide often in the form of carbon monoxide.
29
Provide an example of a less reactive metal that can be extracted using carbon.
Iron can be extracted from iron oxide (Fe2O3) using carbon in a blast furnace.
30
Briefly describe what occurs during the oxidation of a metal.
During oxidation a metal loses electrons resulting in an increase in oxidation state and often forms positive ions.
31
What is the significance of oxidation and reduction in metal extraction?
Oxidation and reduction are crucial processes in metal extraction as they enable the transformation of metal ores into usable metal by transferring electrons.
32
What does the term 'oxidised' mean in the context of chemical reactions?
To be oxidised means that a substance loses electrons during a chemical reaction which increases its oxidation state.
33
What does the term 'reduced' mean in the context of chemical reactions?
To be reduced means that a substance gains electrons during a chemical reaction which decreases its oxidation state.
34
Consider the reaction: 2Na + 2HCl -> 2NaCl + H2. Which element is oxidised?
Sodium (Na) is the element that is oxidised as it loses electrons. The half-reaction is: 2Na -> 2Na + 2e-.
35
In the same reaction (2Na + 2HCl -> 2NaCl + H2) which element is reduced?
Hydrogen (H) is the element that is reduced as it gains electrons. The half-reaction is: 2H+ + 2e- -> H2.
36
How can you determine which elements are oxidised and reduced in a chemical equation?
To determine oxidation and reduction analyze the changes in oxidation states of the elements involved. Identify which elements lose electrons (oxidised) and which gain electrons (reduced).
37
What is the general reaction format for a reaction of acids with metals?
The general reaction format is: Acid + Metal -> Salt + Hydrogen. This reaction produces a salt and hydrogen gas.
38
Give an example of a redox reaction involving an acid and a metal.
An example is the reaction of hydrochloric acid (HCl) with zinc (Zn): Zn + 2HCl -> ZnCl2 + H2. Here zinc is oxidised and hydrogen ions are reduced.
39
What is the significance of redox reactions in chemistry?
Redox reactions are significant because they involve the transfer of electrons which is fundamental to many chemical processes including energy transfer battery functions and metabolic pathways.
40
In the equation 2Na + 2HCl -> 2NaCl + H2 what is the oxidation state of sodium before and after the reaction?
Before the reaction the oxidation state of sodium is 0 (elemental state). After forming NaCl the oxidation state of sodium is +1.
41
In the equation 2Na + 2HCl -> 2NaCl + H2 what is the oxidation state of hydrogen before and after the reaction?
Before the reaction hydrogen in HCl has an oxidation state of +1. After forming H2 the oxidation state of hydrogen is 0 (elemental state).
42
What ions make up hydrochloric acid (HCl)?
Hydrochloric acid (HCl) is made up of hydrogen ions (H+) and chloride ions (Cl-).
43
What ions make up sodium chloride (NaCl)?
Sodium chloride (NaCl) is made up of sodium ions (Na+) and chloride ions (Cl-).
44
What type of reaction is sulfide oxidation and provide an example.
Sulfide oxidation is a redox reaction where sulfide ions (S^2-) are oxidised to elemental sulfur (S) or sulfate (SO4^2-). An example is: 2S^2- + O2 -> 2S + 2O^2-.
45
What role does acid play in the reaction between metals and acids?
In the reaction between metals and acids the acid provides hydrogen ions (H+) which are reduced to form hydrogen gas (H2) while the metal is oxidised.
46
Name two acids commonly used in reactions with metals.
Two commonly used acids are hydrochloric acid (HCl) and sulfuric acid (H2SO4).
47
What does OIL RIG stand for in chemistry?
OIL RIG stands for 'Oxidation Is Loss' and 'Reduction Is Gain' which refers to the electron transfer process in redox reactions.
48
In the reaction involving magnesium and hydrochloric acid (2HCl + Mg -> MgCl2 + H2) how many electrons does magnesium lose?
Magnesium loses 2 electrons in the reaction represented by the ionic equation Mg -> Mg^2+ + 2e^-.
49
What does it mean for magnesium to be oxidized in the context of redox reactions?
Magnesium being oxidized means that it loses electrons which increases its oxidation state from 0 in elemental magnesium to +2 in magnesium ions.
50
In the reaction 2H + 2e^- -> H2 what happens to hydrogen?
Hydrogen gains electrons which is termed reduction. The oxidation state of hydrogen decreases from +1 in the ionic form to 0 in diatomic hydrogen (H2).
51
What is a redox reaction?
A redox reaction is a chemical reaction where there is a transfer of electrons between two species; one species is oxidized (loses electrons) and the other is reduced (gains electrons).
52
Can you explain what happens during the neutralization of an acid by an alkali?
During the neutralization of an acid by an alkali the acid reacts with the base (or alkali) to produce a salt and water.
53
What are the products of the reaction between an acid and a metal carbonate?
The products of the reaction between an acid and a metal carbonate are a salt water and carbon dioxide.
54
What salts are produced from the following acids? 1. Hydrochloric acid (HCl) 2. Nitric acid (HNO3) 3. Sulfuric acid (H2SO4).
1. Hydrochloric acid (HCl) produces chlorides (XCl). 2. Nitric acid (HNO3) produces nitrates (XNO3). 3. Sulfuric acid (H2SO4) produces sulfates (XSO4).
55
What is produced when hydrochloric acid reacts with sodium hydroxide (an alkali)?
When hydrochloric acid reacts with sodium hydroxide it produces sodium chloride (a salt) and water.
56
What role does the metal carbonate play in the acid-base reaction?
The metal carbonate acts as a base that neutralizes the acid resulting in the formation of a salt carbon dioxide and water.
57
Give an example of a neutralization reaction between an acid and an alkali. What are the products?
An example is the reaction between sulfuric acid (H2SO4) and sodium hydroxide (NaOH): H2SO4 + 2NaOH -> Na2SO4 + 2H2O. The products are sodium sulfate (a salt) and water.
58
What is the significance of the positive ions in salts derived from bases alkalis or carbonates?
The positive ions (cations) in salts derived from bases alkalis or carbonates represent the metal element designated as X in various salts. These cations are crucial for determining the formula and balancing the charge with the associated negative ion (anion) from the acid.
59
How do you determine the correct ratio of positive ions to negative ions in a salt?
The charges on the positive ion from the base alkali or carbonate must balance the charges of the negative ion from the acid so that the total charge equals zero. For example if the positive ion has a +1 charge (like Na+) and the negative ion has a -2 charge (like SO4^2-) you need 2 positive ions (2 Na+) to balance the overall charge.
60
Given sodium hydroxide and sulfuric acid what salt forms and what is its formula?
When sodium hydroxide (NaOH) reacts with sulfuric acid (H2SO4) the resulting salt is sodium sulfate and its formula is Na2SO4. This is because Na+ is a +1 cation and SO4^2- is a -2 anion requiring two Na+ ions to balance the charge.
61
What are common anions that can be obtained from acids?
Common anions that can be derived from acids include chloride (Cl-) nitrate (NO3-) and sulfate (SO4^2-). These anions are frequently involved in the formation of soluble salts.
62
What is the general process for making soluble salts from acids?
To make soluble salts from acids you typically react them with a solid insoluble substance such as metals metal oxides hydroxides or carbonates. The general process involves: 1. Adding the solid insoluble substance to the acid until it dissolves. 2. Noticing that the acid has been neutralized when excess solid remains and settles at the bottom. 3. Filtering out the excess solid thus leaving a salt solution followed by evaporating some water and allowing the rest to evaporate slowly to crystallize the salt.
63
What is the definition of neutralization in the context of acids and bases?
Neutralization is the chemical reaction between an acid and a base resulting in the formation of a salt and water. During this process the pH of the solution moves closer to 7 indicating a neutral solution.
64
Explain the concept of crystallization in the salt production process.
Crystallization is the method used to obtain solid salt from a salt solution by allowing water to evaporate slowly. This results in the formation of crystals which can be collected and purified. It typically follows the filtration of the neutralized solution and involves letting the remaining solution evaporate over time to allow salt crystals to grow.
65
What role does pH play in the context of acids and bases during neutralization reactions?
The pH scale is a measure of the acidity or basicity of a solution. In neutralization reactions strong acids have low pH values (below 7) while bases have high pH values (above 7). When an acid reacts with a base the resulting salt solution ideally has a pH close to 7 indicating that the acid's effects have been neutralized.
66
What ions do acids produce in aqueous solutions?
Acids produce H⁺ ions in aqueous solutions.
67
What ions do alkalis produce in aqueous solutions?
Alkalis produce OH⁻ ions in aqueous solutions.
68
What is the pH scale and what does it measure?
The pH scale ranges from 0 to 14 and measures the acidity or alkalinity of a solution.
69
How can pH be measured?
pH can be measured using a universal indicator or a pH probe.
70
What is the pH value of a neutral solution?
A neutral solution has a pH of 7.
71
What is the pH value of an acidic solution?
An acidic solution has a pH less than 7.
72
What is the pH value of an alkaline solution?
An alkaline solution has a pH greater than 7.
73
What is the ionic equation for any neutralization reaction?
The ionic equation for any neutralization reaction is H⁺(aq) + OH⁻(aq) → H₂O(l).
74
What is a titration used for in chemistry?
Titrations are used to measure the volumes of acid and alkali solutions that react with each other.
75
What is the first step in carrying out a titration?
Wash the burette using dilute hydrochloric acid and then water.
76
How do you fill the burette for a titration?
Fill the burette to 100 cm³ with acid ensuring the meniscus is on the 100 cm³ line.
77
How much alkali do you add to the conical flask in a titration?
Use a 25 cm³ pipette to add 25 cm³ of alkali into the conical flask.
78
What tool do you use to draw alkali into the pipette?
A pipette filler is used to draw alkali into the pipette.
79
What indicator is commonly used in a titration with alkalis?
Phenolphthalein is a common indicator used which is pink when alkaline and colorless when acidic.
80
What is indicated by the end-point of a titration?
The end-point of a titration is reached when the acid is added to the alkali until the desired color change occurs indicating neutralization.
81
What is the indicator in a titration experiment?
An indicator is a substance that changes color at a certain pH level signaling the endpoint of the titration process.
82
How is the titre volume of acid determined in titration?
The titre volume of acid needed to exactly neutralise the base is calculated by taking the difference between the initial and final readings on the burette.
83
Why should the titration experiment be repeated?
Repeating the experiment allows for more precise results by minimizing errors and increasing the reliability of the data collected.
84
What is the relationship between cubic centimeters and decimeters cubed?
1 dm³ is equal to 1000 cm³.
85
What is the significance of the phrase 'one mole of a substance in grams is the same as its relative atomic mass in grams'?
This means that if you have a relative atomic mass of a substance (e.g. Sodium has a relative atomic mass of 23) then one mole of that substance will weigh 23 grams.
86
How much dilute hydrochloric acid (HCl) is neutralised by sodium hydroxide (NaOH) in the example given?
25 cm³ of dilute hydrochloric acid is neutralized by 20 cm³ of 0.5 mol/dm³ sodium hydroxide.
87
How do you convert volume from cm³ to dm³?
To convert from cm³ to dm³ you divide the volume in cm³ by 1000. For example 25 cm³ = 25/1000 = 0.025 dm³.
88
What is the formula for calculating moles?
Moles can be calculated using the formula: Moles = Volume (in dm³) x Concentration (in mol/dm³).
89
What is the mole calculation for NaOH in the hydrochloric acid neutralization example?
The moles of NaOH are calculated as Moles = 0.02 dm³ x 0.5 mol/dm³ which equals 0.01 moles.
90
What is the mole ratio for the neutralization reaction between HCl and NaOH?
The balanced equation for the reaction is HCl + NaOH → NaCl + H₂O which indicates a 1:1 mole ratio between HCl and NaOH.
91
How do you calculate the concentration of hydrochloric acid after the neutralization?
Concentration is calculated using the formula: Concentration = Moles/Volume. Thus for HCl: Concentration = 0.01 moles / 0.025 dm³ = 0.4 mol/dm³.
92
What are strong acids and how do they behave in solution?
Strong acids are those that completely ionize in aqueous solution such as hydrochloric acid (HCl) nitric acid (HNO₃) and sulfuric acid (H₂SO₄).
93
What differentiates strong acids from weak acids?
Weak acids only partially ionize in solution resulting in a lower concentration of hydrogen ions compared to strong acids.
94
Give an example of a weak acid.
An example of a weak acid is acetic acid (CH₃COOH) which does not fully dissociate in water.
95
What is the neutralization reaction between HCl and NaOH in terms of products formed?
The products of the neutralization reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) are sodium chloride (NaCl) and water (H₂O).
96
What are the three types of acids discussed in the solution?
Ethanoic acid citric acid and carbonic acid.
97
What is the relationship between the strength of an acid and pH?
The stronger the acid the lower the pH for a given concentration of aqueous solutions.
98
How does a decrease in pH by one unit affect hydrogen ion concentration?
As the pH decreases by one unit the concentration of hydrogen ions (H+) in the solution increases by a factor of 10.
99
What is the difference between strong and weak acids versus concentrated and dilute solutions?
Strong and weak refer to the degree of ionization of the acid in solution (H+ ion concentration) while concentrated and dilute refer to the amount of substance in a given volume.
100
What happens to an ionic substance during electrolysis when it is melted or dissolved?
The ions become free to move about within the liquid or solution.
101
What is the process of electrolysis?
Electrolysis is the process of passing an electric current through a molten or dissolved ionic substance breaking the substance down into its constituent elements.
102
What is the electrolyte in the context of electrolysis?
The electrolyte is the substance that is broken down during the electrolysis process.
103
What occurs to positively and negatively charged ions during electrolysis?
Positively charged ions move to the negative electrode (cathode) while negatively charged ions move to the positive electrode (anode).
104
What is the definition of pH?
pH is a measure of the acidity or basicity of an aqueous solution specifically the concentration of hydrogen ions (H+) present.
105
What is the significance of the pH scale?
The pH scale ranges from 0 to 14 where values below 7 indicate acidity 7 indicates neutrality and values above 7 indicate basicity.
106
How does the concentration of hydrogen ions relate to the strength of an acid?
A stronger acid will dissociate more completely in water producing a higher concentration of hydrogen ions compared to a weaker acid at the same concentration.
107
What are the key differences in the behavior of strong acids versus weak acids in aqueous solutions?
Strong acids dissociate completely in solution resulting in a high concentration of hydrogen ions whereas weak acids partially dissociate producing a lower concentration of hydrogen ions.
108
What role does the cathode play during electrolysis?
The cathode is the electrode where reduction occurs and positively charged ions are attracted to it.
109
What future implications can arise from understanding electrolysis?
Understanding electrolysis is crucial for applications in electroplating metal extraction and the production of chemicals through electrolytic processes.
110
What is the positive electrode in an electrolysis process called?
The positive electrode is called the anode.
111
What happens to ions at the electrodes during electrolysis?
Ions are discharged at the electrodes resulting in the production of elements.
112
What is produced at the anode when a simple ionic compound like lead bromide is electrolyzed in molten state?
Bromine the non-metal is produced at the anode.
113
What is produced at the cathode when lead bromide is electrolyzed in molten state?
Lead the metal is produced at the cathode.
114
Why do metals get produced at the cathode during electrolysis?
Metals are positive ions which are attracted to the negative electrode (cathode) where they are discharged.
115
Why are non-metals produced at the anode during electrolysis?
Non-metals are negative ions which are attracted to the positive electrode (anode) where they are discharged.
116
What process is used to extract metals that are more reactive than carbon?
Electrolysis of molten compounds is used to extract metals that are more reactive than carbon.
117
Why can't metals that are more reactive than carbon be extracted by reduction with carbon?
Because these metals are too reactive reduction with carbon cannot effectively free them from their compounds.
118
What major drawbacks are associated with the electrolysis extraction process?
Large amounts of energy are required to melt the compounds and to produce the electrical current necessary for electrolysis.
119
What substance is used to lower the melting point of aluminium oxide during electrolysis?
Cryolite is mixed with aluminium oxide to lower its melting point for the electrolysis process.
120
Why is aluminium oxide mixed with cryolite in the electrolysis process?
Aluminium oxide has a very high melting point and mixing it with cryolite makes it cheaper to melt and process.
121
What is the chemical formula for aluminium oxide?
The chemical formula for aluminium oxide is Al2O3.
122
What is the significance of using inert electrodes during electrolysis?
Inert electrodes do not participate in the chemical reaction; they serve merely as a site for the discharge of ions.
123
What is the general equation for the electrolysis of molten lead bromide?
At the cathode (reduction): Pb^2+ + 2e- → Pb (lead). At the anode (oxidation): 2Br^- → Br2 + 2e- (bromine gas).
124
What phenomenon occurs at the positive electrodes in the electrolysis of cryolite?
At the positive electrodes in the electrolysis of cryolite oxygen is formed which reacts with the carbon of the positive electrodes to produce carbon dioxide leading to the gradual burning away of the electrodes.
125
What types of metals can be extracted using electrolysis?
Metals that react with carbon can be extracted by electrolysis particularly when electrolyzing cryolite.
126
What factors determine the ions discharged during the electrolysis of aqueous solutions?
The ions discharged during the electrolysis of aqueous solutions depend on the relative reactivity of the elements involved and the nature of the ions present in the solution.
127
What is produced at the cathode during the electrolysis of an aqueous solution?
At the cathode (negative electrode) during the electrolysis of an aqueous solution hydrogen gas is produced unless the metal being electrolyzed is less reactive than hydrogen.
128
What happens when a halide ion is present at the positive electrode during electrolysis?
If halide ions (Cl- Br- I-) are present at the positive electrode during electrolysis one of the halide ions will be discharged. This occurs in preference to producing oxygen.
129
What is produced at the positive electrode when no halide ions are present in an aqueous solution?
When no halide ions are present in an aqueous solution during electrolysis oxygen is produced at the positive electrode.
130
What ions are generated when water molecules break down in an aqueous solution?
When water molecules break down in an aqueous solution they produce hydrogen ions (H+) and hydroxide ions (OH-).
131
What is the role of inert electrodes in the electrolysis of aqueous solutions?
Inert electrodes provide a surface for the electrochemical reactions to occur without participating in the reaction themselves.
132
What can be inferred about the reactivity of halides compared to OH- in aqueous electrolysis?
Halide ions are typically more easily discharged at the positive electrode than hydroxide ions (OH-) which is why they are discharged preferentially in their presence.
133
Explain the half-equation representation of reactions at electrodes during electrolysis.
The half-equation representation of reactions at electrodes shows the individual half-reactions occurring at the cathode and anode detailing the reactants products and electron transfer involved in the process.
134
What is a common product of the reactions involving the oxidation of hydroxide ions during electrolysis?
A common product during the oxidation of hydroxide ions (OH-) at the anode is oxygen gas (O2).
135
What is a half equation in electrochemistry?
A half equation represents the reduction or oxidation reaction of a species at an electrode. It shows the species involved the electrons gained or lost and ensures charge and mass balance.
136
In a half equation how are the small numbers related to the larger numbers?
In a half equation the small number (coefficient for electrons) is always the same as the total charge represented by the two larger numbers (the coefficients for the species involved in the reaction) to maintain charge balance.
137
What symbol is used to represent electrons in half equations?
Electrons are represented by the symbol e- in half equations.
138
What does the half equation for the negative electrode (cathode) look like?
For the negative electrode (cathode) the half equation is represented as: X + ne- → X- indicating that positive ions (X) are reduced by gaining electrons (e-).
139
What is the process occurring at the negative electrode?
At the negative electrode positive ions are reduced as they gain electrons from the electrode.
140
What does the half equation for the positive electrode (anode) look like?
For the positive electrode (anode) the half equation is represented as: X- → X + ne- indicating that negative ions (X-) are oxidized by losing electrons (e-).
141
What is the process occurring at the positive electrode?
At the positive electrode negative ions are oxidized as they lose electrons to the electrode.
142
What is the importance of charge balance in half equations?
Charge balance is crucial in half equations to ensure that the total charge is conserved during the oxidation or reduction process adhering to the law of conservation of charge.
143
What roles do the negative and positive electrodes play in a galvanic cell?
In a galvanic cell the negative electrode is the site of reduction (cathode) while the positive electrode is the site of oxidation (anode). This creates a flow of electrons from the anode to the cathode.
144
How do half equations contribute to the overall redox reaction?
Half equations provide a clear representation of the individual oxidation and reduction processes that occur during a redox reaction allowing for the overall reaction to be constructed by combining the two half equations.
