chemistry tys

Question 1

Nitrogen gas and oxygen gas does not react together under normal conditions in the atmosphere. Under the conditions in a car engine, nitrogen gas reacts with oxygen to produce nitrogen monoxide. Use ideas about energy and collision to explain why.

Answer 1

The temperature of the car engine is high, thus the nitrogen and oxygen would gain heat energy and therefore the kinetic energy of the molecules would increase. As a result, the molecules will have energy equal to or greater than the activation energy required for effective collision to take place, allowing them to react to produce carbon monoxide.

Question 2

Form nitric acid from nitrogen monoxide

Answer 2

2NO+O2 -> 2NO2

4NO2 + 2H2O + O2 -> 4HNO3

Question 3

Metals and ionic compounds can both conduct electricity. Describe how the metals and ionic compounds conduct electricity

Answer 3

Metals consists of a ‘sea of electrons’, which are free to move about to conduct electricity. Ionic compounds in molten and aqueous states consists of mobile ions which acts as charge carries to conduct electricity

Question 4

Mild steel has different properties from pure iron. It is stronger and more brittle. Why?

Answer 4

The larger carbon atoms disrupt the orderly arrangement of the iron atoms, making it harder for the atoms to slide past one another when a force is applied, thereby making steel stronger than iron.

Question 5

Describe a set-up that could be used to electroplate a layer of tin onto an iron can.

Answer 5

Connect the tin metal to the positive terminal of the cell, making it an anode. Connect the iron can to the negative terminal of the cell, making it a cathode. Immerse both electrodes into the electrolyte which is tin(ii) nitrate solution.

Question 6

Carbon and silicon are elements in Group IV of the periodic table. Their oxides have very different melting points. Explain how and why?

Answer 6

Carbon dioxide has a simple molecular structure, little energy is needed to overcome the weak intermolecular forces of attractions between the molecules hence a low melting point.
In contrast, silicon dioxide has a giant molecular structure, large amount of energy is needed to overcome the strong covalent bonds between the atoms hence a high melting point.

Question 7

Discuss the differences between the way that bonds are formed in MgO and O2.

Answer 7

In magnesium oxide, magnesium atom loses 2 electrons to oxygen atom to form Mg2+ and O2- ions, forming strong electrostatic forces of attraction between the ions. In oxygen molecules, 2 oxygen atoms share 4 electrons to form strong covalent bonds.

Question 8

When sodium is heated in hydrogen, the metal glows as an exothermic reaction takes place. How would the observations differ when potassium is heated in hydrogen? Explain your answer.

Answer 8

Since potassium is a more reactive metal than sodium metal, potassium will glow brighter and be hotter when heated in hydrogen.

Question 9

What are isotopes?

Answer 9

Isotopes are different forms of the same elements with same number of protons but different number of neutrons.

Question 10

Suggest why isotopes have the same chemical reactions?

Answer 10

All 3 isotopes contain the same number of electrons in the outer shell ( state how many ) thus they have the same chemical reactions.

Question 11

Explain why lead reacts with nitric acid but gold does not?

Answer 11

Lead is positioned about hydrogen in the reactivity series and gold is positioned below hydrogen thus lead can react with hydrogen but not gold.

Question 12

Dilute HCL or H2SO4 cannot be used to remove compounds of lead. Explain why HNO3 can be used but not HCL or H2SO4.

Answer 12

Lead reacts with dilute HNO3 to form soluble lead (ii) nitrate that can further react with more HNO3 and hence HNO3 can be use to remove compounds of lead.
However, lead reacts with dilute HCL or H2SO4 to form a layer of insoluble lead(ii) chloride and lead (ii) sulfate, which prevents a further reaction. Hence dilute HCL or H2SO4 cannot be used to remove compounds of lead.

Question 13

Explain why ammonia can only be used to identify one of the 3 ions, lead, zinc and aluminium.

Answer 13

Zinc reacts with aqueous ammonia forms white precipitate and is soluble in excess aqueous ammonia. However, both lead and aluminium reacts with aqueous ammonia to forms white precipitate that is insoluble in excess aqueous ammonia.

Question 14

Explain how the magnesium protects the pipe from rusting

Answer 14

Magnesium is more reactive than iron, thus Magnesium acts as a sacrificial protection and corrodes in place of iron.

Question 15

Explain how oil and paint prevent rusting

Answer 15

Oil and paint acts as a protective layer that prevents oxygen and water in the air to come into contact with the iron on the steel pipe.

Question 16

Explain why different combinations of metals produce different voltage.

Answer 16

When two different metals with different reactivities are connected in a simple cell, different voltages are produced. The further apart the metals are in the reactivity series, the greater the voltage produced in the cell.

Question 17

Explain, in terms of collisions and energy, why using a catalyst would increase the rate of reaction?

Answer 17

A catalyst provides an alternative pathway that has a lower activation energy. Thus there will be more particles with energy equal to or greater than the activation energy. This will increase the frequency of effective collision and hence the rate of reaction will increase.

Question 18

Describe how metals and solutions of ionic compounds conduct electricity differently.

Answer 18

Metals are able to conduct electricity in solid, liquid and molten state because of the presence of a mobile delocalised electrons in their metallic structure.
In contrast, the dissociation of ionic compounds in water produces ions. The presence of these mobile ions enable solutions of ionic compounds to conduct electricity

Question 19

Conductions of electricity can have a different effect on metals and on solutions of ionic compounds. Describe the difference.

Answer 19

Conduction of electricity increase the temperature of metals, without any chemical changes. However in solutions of ionic compounds, electrolysis will occurs, and the compounds are broken down into its constituents.

Question 20

Explain how and why helium and argon are chemically similar

Answer 20

Both of their atoms have fully filled outermost electron shells, thus both have stable electronic configuration. Hence argon and helium are chemically inert and unreactive.

Question 21

Why is it important that carbon monoxide is collected and burned?

Answer 21

Carbon monoxide is a harmful pollutants that bind with haemoglobin in the blood to reduce the ability of the red blood cells to transport oxygen in the body. Hence carbon monoxide should be collected and burned to prevent its release to the atmosphere.

Question 22

State how a coating on a catalyst affects the reaction.

Answer 22

A coating on a catalyst reduces the surface area of the catalyst available for collisions with reactants and thus decrease the effectiveness of the catalyst. This then results in the a slower rate of reaction.

Question 23

Give 2 similarities of hydrogen and the elements in Group 1.
Give 2 properties of hydrogen that do not fit with the properties of the elements in Group1.

Answer 23

2 similarities :

1. Both only have 1 valence electron.
2. Both form ions with a +1 charge

2 properties :

1. Hydrogen in a non-metals while group 1 elements are metal.
2. Hydrogen exists as a gas while group 1 elements as solids.
3. Hydrogen exists as diatomic covalent molecules while group 1 metals exists as metallic substances.

Question 24

Explain why the help of equations, why coke is essential to the process of making iron from haematite ?

Answer 24

1. Iron is extracted from haematite which contains iron(iii) oxide. Coke is essential as a carbon source and is added to react with oxygen to produce carbon dioxide :
   C+O2 -> CO2
2. Carbon dioxide then reacts further with carbon to produce carbon monoxide
   CO2 + C -> 2CO
3. Carbon monoxide acts as a reducing agent and reacts with the iron (iii) oxides present in haematite to produce iron
   3CO + Fe2O3 -> 2Fe + 3 CO2

Question 25

Iron from the blast furnace contains carbon and silicon as impurities. What is the source of silicon impurities in the blast furnace?

Answer 25

The iron ore used to extract iron typically contains silicon impurities in the form of silicon dioxide.

Question 26

Give reasons why it is important to use scrap steel to make new steel.

Answer 26

Iron is a finite resource, recycling the scrap metals allow for the conversation of the precious natural resources. Recycling is also cheaper than extracting iron from haemetite.

Question 27

An element that shows both metallic and non-metallic character

Answer 27

Aluminium

Question 28

Give 3 characteristics of transition metals

Answer 28

1. Have high density
2. Have variable oxidation states.
3. Formed coloured compounds

Question 29

Suggest why planting more trees is not a long term solution to the increase in the amount of CO2.

Answer 29

There is limited land for tress to be planted and land will ran out after some time. Trees will not be able to absorb all the excess carbon dioxide at night through respiration as well. As such, planting more trees is not a long term solution.

Question 30

Explain why frizzing is observed.

Answer 30

Frizzing occurs because calcium reacts with the water in the salt solutions to produce hydrogen gas

Question 31

Explain, in terms of collisions between the reacting particles, why a higher temperature will affects the rate of reactions.

Answer 31

At higher temperatures, reactant particles have more kinetic energy. They move faster and collide more frequently, thus increasing the frequency of effective collision between the reactant particles. This causes an increase in the rate of reaction.

Question 32

Describe the trend in melting points down group I and group VII

Answer 32

The melting point of Group I elements decreases down the group while the melting point of Group VII increases down the group.

Question 33

Describe the reactivity down group I and group VII

Answer 33

The reactivity of Group 1 increases down the group while the reactivity of Group VII elements decreases down the group.

Question 34

Give 2 reasons why catalyst reduce costs in the long run

Answer 34

Catalyst provide alternative pathway with lowered activation energy which accelerate the rate of reactions. Thus, the desire products are obtained within the shortest amount of time and in less harsh conditions. This reduces the cost required for the operations of facilities

Question 35

Explain how oil, paint and the plastic coating slows down rusting

Answer 35

Rust forms when iron corrodes in the presence of water and oxygen. The oil, paint and the plastic coating provides a physical barrier which minimises the contact of iron with oxygen and water. Thus, it slows down the process of rusting.

Question 36

What is precipitation for?

Answer 36

Insoluble salts. The salts are insoluble in water. An insoluble salt can be obtained from the reaction between water-soluble salts where it is collected as a solid residue by filtration.

Question 37

Explain, in terms of collisions between reacting particles, how a lower pressure affects the rate of reaction in the reactor.

Answer 37

When the pressure in the reactor is reduced, the number of reacting gaseous particles per unit volume is reduced. This leads to a lower frequency of collision, subsequently resulting in a lower frequency of effective collision. Thus, the rate of reaction is likely to decrease.

Question 38

Suggest an advantage of making products from blast furnace slag rather than other substances

Answer 38

The waste products can be recycled for other uses, instead of discarded.

Question 39

Explain why Group V and Group IV oxides are less effective at neutralising acidity

Answer 39

Group IV and Group V elements are non-metals, which tend to form acidic or amphoteric oxides

Question 40

Describe what happens to the arrangement and movement of the particles in potassium chloride when it dissolves in water

Answer 40

When potassium chloride is dissolved in water, it no longer exists in a lattice structure. Instead, it exist as K+ and CI- ions moving freely in solution and each ion is surrounded by water molecules.

Question 41

How to calculate the enthalpy change?

Answer 41

△H of combustion ( kJ/mol) ÷ mass ( Mr ) = △H of reaction ( kJ/g )

Question 42

Use ideas about breaking and forming bonds to explain why all the values of △H is negative.

Answer 42

The total energy taken in to break the bonds ( in ____ ) is less than the total energy to form the bonds ( in _____). Hence, energy is given out to the surroundings and the enthalpy change is negative.

Question 43

What is the difference between strong and weak acid?

Answer 43

A strong acid completely ionises in water while a weak acid partially ionise in water

Question 44

Both diamond and graphite have some similarities and differences between their bonding and structures. Describe the similarities and differences.

Answer 44

In both diamond and graphite, carbon atoms are covalently bonded and are held together in a giant molecular structure. However, the carbon atoms in diamond and graphite are arranged differently. In diamond, each carbon atom is covalently bonded to 4 other carbon atoms while in graphite, each carbon atom is bonded to 3 other carbon atoms. Carbon atoms in diamond are arranged in a rigid structure while in graphite, carbon atoms are arranged in continuous layers of hexagons that can slide past each other easily.

Question 45

How can he check from his test results to find out whether his sample contains impurities?

Answer 45

He can check if his sample contain impurities based on whether it melts at a fixed temperature or over a range of temperatures. The sample contain impurities if it melts over a range of temperature.

Question 46

Explain the term weak acid

Answer 46

Weak acid partially dissociates in water to give out H+ ions.

Question 47

What are compound and mixture

Answer 47

A compound consists of two or more atoms of different elements that are chemically combined in fixed ratios.
A mixture consists of two or more different substances which are either elements or compounds. These substances can be present in any ratio.

Question 48

Why blue litmus paper must be moist when testing for the presence of an acidic gas ie hydrogen chloride

Answer 48

Hydrogen chloride molecules ionise completely in water to produce hydrogen ions. Hydrogen ions are responsible for the acidic property which turn blue litmus red.

Question 49

Explain why acid can conduct electricity when dissolved in water but not when in solid.

Answer 49

In the presence of water, acid molecules dissociate to form ions. These ions are free moving to carry electric current. When in solid, the acids exist as neutral molecules with no free moving charged particles to conduct electricity.

Question 50

Soil can become too acidic from acid rain and excessive use or fertilisers. The excess acid in the soil can be treated by adding calcium oxide, hydroxide. Why is it not advisable to add ammonium fertilisers together with calcium oxides/ hydroxides?

Answer 50

They react with ammonium slats to form ammonia gas which escapes into the atmosphere. Thus, the plants cannot absorb the ammonium ion which provides the nitrogen it needs. Calcium oxides/ hydroxides which is required to neutralise the soil acidity is also lost/

Question 51

What is a salt?

Answer 51

A salt is a substance formed when a metal ion or ammonium ion replaces one or more hydrogen ions of an acid

Question 52

Trend across the period from left to right. Why?

Answer 52

There is a decrease in metallic properties and an increase in non-metallic properties. ie changes from metals to non-metals. Across the period, the number of valence electrons increases. The ability of the atom to lose electrons decreases but the ability of the atom to gain electrons increases.

Question 53

Why does the reactivity of Group I elements increase down the group?

Answer 53

Down the group, the atomic radius of the atom increases as the number of electrons shells increases. The valence electrons becomes further away from the nucleus and the electrostatic forces of attraction between the valence electron and the nucleus becomes weaker. as a result, it is easier for the atom to lose electron and so the reactivity increases down the group.

Question 54

Explain why caesium has a lower melting point than sodium.

Answer 54

Caesium has a larger atomic radius than sodium as it has more electrons shell. The valence electron becomes further away from the nucleus and the electrostatic forces of attractions between the valence electron and nucleus becomes weaker. Lesser energy is needed to overcome these forces of attractions.

Question 55

Why do the melting and boiling points of Group VII elements increase down the group?

Answer 55

Down the group, the size of the molecules increases. The intermolecular forces of attraction becomes stronger. More energy is need to overcome these forces and hence, down the group, the elements has a higher melting and boiling points.

Question 56

Why does the reactivity of Group VII elements decreases down the group?

Answer 56

Down the group, the atomic radius increases as the number of electron shells increases. The valence electrons becomes further away from the nucleus and the electrostatic forces of attraction between valence electron and nucleus becomes weaker. As a results, it is harder for the atom to gain an additional electron and so the reactivity decreases down the group.

Question 57

Explain why ionic compounds have high melting point/n boiling points and exists as a solid at room temperature.

Answer 57

Ionic compounds have a giant ionic crystals lattice structure with strong electrostatic forces of attraction between the oppositely charged ions, which requires a lot of energy to overcome. Hence, ionic compounds have high melting point and boiling points, and exist as solids at room temperature.

Question 58

Explain why simple covalent compounds have low melting/ boiling points and exists ad a liquid or gas at room temperature.

Answer 58

Simple covalent compounds have simple molecular structure with weak intermolecular forces of attraction which requires littler energy to overcome. Hence, simple covalent compounds have low melting/ boiling point and exists as liquid or gas at rom temperature.

Question 59

Explain why diamond and graphite has a high melting and boiling point.

Answer 59

Both diamond and graphite have a giant molecular structure. A lot of energy is needed to break the network of strong covalent bonds between the carbon atoms, hence both diamonds and graphite has a high melting / boiling point.

Question 60

Explain why metals ( except group 1 and mercury ) have a high melting point.

Answer 60

Metals have a giant metallic structure with strong electrostatic forces of attraction between the fixed metal cations and sea of delocalised mobile electrons, which requires a lot of energy to overcome.

Question 61

Define the term allotropes

Answer 61

Allotropes are different forms of the same elements with different arrangement of atoms.

Question 62

Define the terms ‘monobasic acid’ and ‘dibasic acid’

Answer 62

A monobasic acid is one whereby one more of acid dissociates to produce one mole of H+ ions. a dibasic acid is one whereby one mole of acid dissociates to produce 2 moles of H+ ions.

Question 63

Explain why one mole of hydrochloric acid reacts faster with Mg metal as compared to one mole of ethanoic acid.

Answer 63

Ethanoic acid is a weak acid that dissociate partially in water to produce a lower concentration of H+ ions, while hydrochloric acid is a strong acid that dissociate completely in water to produce a higher concentration of H+ ions.

Question 64

Define the term ‘alkali’

Answer 64

An alkali is a soluble base that dissociates in water to produce OH- ions

Question 65

What is the purpose of adding lime (CaO) or limewater (Ca(OH)2) to acidic soil?

Answer 65

To neutralise the excess acidity of the soil, thus increasing the pH of the soil.

Question 66

Explain fully how galvanising the steel pipes helps to prolong the work life of the pipes

Answer 66

The layer of the zinc coating prevents the iron in steel pipe from coming into contact with oxygen and water in the air, thus prevents rusting. Even if the layer of zinc coating is scratched/ dented, zinc, being more reactive than iron in the steel, loses electrons more readily and corrodes in place of iron in steel, offering sacrificial protection.

Question 67

Explain how higher concentration of solution affects the speed of a reaction

Answer 67

A higher concentration means that there is more reacting particles per unit volume, thus the particles are closer together, resulting in more frequent effective collisions and hence, a faster speed of reactions

Question 68

Explain why powdered CaCO3 reacts more quickly with Hcl than CaCO3 lumps?

Answer 68

CaCO3 powder provides a larger surface area for the reacting particles to collide as compared to CaCO3 lumps, resulting in more frequent effective collisions and hence, a faster speed of reaction.

Question 69

Define ‘catalyst’

Answer 69

A catalyst is a substance that is being added to a chemical reaction in small amounts to speed up the rate of reaction without itself being chemically changed,

Question 70

State the source of carbon monoxide gas

Answer 70

Carbon monoxide gas is produced from the incomplete combustion of carbon-containing fuels due to insufficient oxygen.

Question 71

Describe how nitrogen dioxide is formed in the car engine/ blast furnace

Answer 71

At high temperature in the car engine/blast furnace, nitrogen and oxygen from air reacts to form nitrogen monoxide, which reacts with more oxygen to form nitrogen dioxide.

Question 72

State one harmful effect of nitrogen dioxide.

Answer 72

Nitrogen dioxide can react with water vapour and oxygen in the air to form dilute nitric acid , which dissolves in rain water to from acid rain, which corrodes marble building/ make soil acidic for growth of crops.

Question 73

State the environmental problems that can be caused by CO2/ methane gas

Answer 73

CO2 and methane are both greenhouse gases that traps heat, leading to global warming. This results in the melting of polar ice caps and expansion of sea water, leading to flooding of low-lying areas and possible famines due to destruction of crops.