CIE iGCSE Co-Ordinated Science C2.2 Atomic structure and the Periodic Table Exam Style Questions Paper 3
Question
(a) The proton numbers and nucleon numbers of carbon and hydrogen are shown in Table 11.1
i) State the number of neutrons in a carbon atom and the number of neutrons in a hydrogen atom.
(ii) State the number of electrons in a carbon atom.
(b) (i) State the difference between a saturated hydrocarbon and an unsaturated hydrocarbon.
(ii) Aqueous bromine is used to show the difference between a saturated hydrocarbon and an unsaturated hydrocarbon.
Describe the result of the test with a saturated hydrocarbon.
(c) Fig. 11.1 shows the apparatus used for the catalytic cracking of a saturated hydrocarbon.
(i) State the purpose of the catalyst in the cracking of a saturated hydrocarbon.
(ii) Cracking is an endothermic reaction.
State what is meant by an endothermic reaction.
(d) The complete combustion of hydrocarbons produces the greenhouse gas carbon dioxide.
(i) Name one other greenhouse gas.
(ii) Identify the gas in the air that reacts with hydrocarbons during combustion.
(iii) Carbon dioxide is one of the gases found in clean air.
State the name of the two gases found in clean air in the greatest proportions.
▶️Answer/Explanation
Ans : 11(a)(i) carbon = 6 ;
hydrogen = 0 ;
11(a)(ii) 6 ;
11(b)(i) unsaturated has a C=C double bond ;
11(b)(ii) aqueous bromine remains orange ;
11(c)(i) speed up the reaction ;
11(c)(ii) temperature decreases / thermal energy is absorbed (from the surroundings) ;
11(d)(i) methane ;
11(d)(ii) oxygen ;
11(d)(iii) oxygen ;
nitrogen ;
Question
(a) A calcium atom has a proton number of 20 and a nucleon number of 40.
Deduce the number of protons, neutrons and electrons in this atom of calcium.
number of protons ……………..
number of neutrons ……………..
number of electrons ……………..
(b) When calcium atoms react, they change into calcium ions, Ca2+.
Describe how calcium atoms change into calcium ions.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(c) Lime is produced from limestone, calcium carbonate, by thermal decomposition.
(i) State the chemical name for lime.
…………………………………………………………………………………………………………………….
(ii) State the name of the gas formed in this thermal decomposition reaction.
…………………………………………………………………………………………………………………….
(iii) Explain why farmers spread limestone onto soil that is used for growing crops.
……………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………….
(d) The main compound in limestone is calcium carbonate, CaCO$_{3}$.
(i) State the number of different elements in calcium carbonate.
…………………………………………………………………………………………………………………….
(ii) State the total number of atoms shown in the formula CaCO$_{3}$.
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans : 11(a) protons = 20 ;
neutrons = 20 ;
electrons = 20 ;
11(b) loses electrons ;
2 electrons ;
11(c)(i) calcium oxide ;
11(c)(ii) carbon dioxide ;
11(c)(iii) neutralise acidic soil ;
11(d)(i) 3 ;
11(d)(ii) 5 ;
Question
(a) Choose from the following substances to answer the questions.
Each substance may be used once, more than once or not at all.
(i) Used as a chemical test for water.
(ii) Used as a solvent.
(iii) Used in aircraft parts.
(iv) Used in the manufacture of sulfuric acid.
(v) Used in the treatment of the water supply.
(vi) Used in the treatment of acidic soil.
(b) Sulfuric acid has the formula H$_{2}$SO$_{4}$.
(i) State the total number of atoms in one molecule of sulfuric acid.
(ii) State the total number of different elements found in one molecule of sulfuric acid.
(c) A student reacts magnesium with dilute sulfuric acid.
The equation for the reaction is shown.
Mg(s) + H$_{2}$SO$_{4}$(aq) MgSO$_{4}$(aq) + H$_{2}$(g)
(i) State the names of the two products of the reaction.
(ii) State the separation technique used by the student to remove any unreacted solid magnesium from the reaction mixture.
▶️Answer/Explanation
Ans : 2(a)(i) copper sulfate ;
2(a)(ii) ethanol ;
2(a)(iii) aluminium ;
2(a)(iv) sulfur ;
2(a)(v) chlorine ;
2(a)(vi) limestone ;
2(b)(i) 7 ;
2(b)(ii) 3 ;
2(c)(i) magnesium sulfate ;
hydrogen ;
2(c)(ii) filtration ;
Question
(a) (i) An atom of calcium has 20 protons and 20 neutrons.
State the number of electrons in this calcium atom.
(ii) State the number of electrons in one calcium ion, Ca2+.
(b) Limestone (calcium carbonate) and lime (calcium oxide) are both calcium compounds.
Fig. 11.1 shows a limekiln in which calcium carbonate thermally decomposes to make calcium oxide and carbon dioxide.
(i) Write the word equation for the thermal decomposition of calcium carbonate.
(ii) The mass of calcium oxide made in this reaction is always less than the mass of calcium carbonate used.
Suggest why.
(iii) The decomposition of calcium carbonate to calcium oxide is an endothermic reaction.
State the meaning of the term endothermic.
(iv) One use for limestone is in the production of lime.
State one other use of limestone.
(v) Suggest why the calcium carbonate is broken into small pieces before being thermally decomposed.
(c) Calcium carbonate has the formula CaCO3.
(i) State the number of different elements shown in this formula.
(ii) State the total number of atoms shown in this formula.
▶️Answer/Explanation
Ans : 11(a)(i) 20 (electrons) ;
11(a)(ii) 18 (electrons) ;
11(b)(i) calcium carbonate → calcium oxide + carbon dioxide ;
11(b)(ii) carbon dioxide released ;
11(b)(iii) (thermal) energy taken in ;
11(b)(iv) neutralising acidified soil ;
11(b)(v) to increase surface area ;
so that reaction is faster ;
11(c)(i) three ;
11(c)(ii) five ;
Question
(a) The list gives the names of seven elements.
aluminium carbon copper chlorine
helium phosphorus sulfur
State which of the elements in the list:
(i) forms diamond and graphite ……………………………………………………………………………
(ii) is a halogen …………………………………………………………………………………………………..
(iii) is electroplated onto another metal …………………………………………………………………..
(iv) is extracted from bauxite …………………………………………………………………………………
(v) is used in the manufacture of sulfuric acid …………………………………………………………
(vi) is used to sterilise drinking water ……………………………………………………………………..
(b) The formula of phosphorus oxide is P4O10.
State the number of atoms of phosphorus and of oxygen contained in one molecule of phosphorus oxide.
phosphorus ………………………………………………………………..
oxygen ………………………………………………………………………..
(c) Explain why phosphorus oxide makes an acidic solution when it dissolves in water.
(d) Phosphorus is contained in fertilisers.
State the two other elements commonly found in fertilisers.
1 …………………………………………………………………………
2 …………………………………………………………………………
▶️Answer/Explanation
Ans : 2(a)(i) carbon ;
2(a)(ii) chlorine ;
2(a)(iii) copper ;
2(a)(iv) aluminium ;
2(a)(v) sulfur ;
2(a)(vi) chlorine ;
2(b) phosphorus 4 oxygen 10 ;
2(c) non-metal oxides are acidic or non-metal oxides form acidic solutions ;
2(d) nitrogen ;
potassium ;
Question
(a) Fig. 5.1 is a chart showing the composition of clean air.
Use your knowledge of the composition of clean air to determine the percentage of other gases in clean air.
Show your working.
percentage = …………………………………………….. %
(b) (i) Argon is one of the other gases in clean air.
Use the Periodic Table on page 24 to determine the electronic structure of an argon atom.
(ii) Use your answer to (b)(i) to explain why argon is very unreactive.
(iii) State one use for argon gas that depends on it being unreactive.
(c) (i) Small quantities of carbon dioxide are found in the air.
State one source of the carbon dioxide found in the air.
(ii) Carbon dioxide is a compound formed from the elements carbon and oxygen.
Describe the difference between an element and a compound.
(iii) Carbon dioxide is a greenhouse gas.
State the name of one other greenhouse gas.
(d) (i) Water is neutral.
State the pH value of pure water.
pH = …………………………………………………
(ii) Carbon dioxide in the air dissolves in rainwater. This causes the rainwater to become slightly acidic.
Suggest a pH value for this rainwater.
pH = …………………………………………………
▶️Answer/Explanation
Ans : 5(a) 78% and/or 21% seen ;
other gases = 1% ;
5(b)(i) 2,8,8 ;
5(b)(ii) full outer shell ;
5(b)(iii) lamps;
5(c)(i) combustion of fossil fuels ;
5(c)(ii) any one from (molecule of an) element contains only one type of atom ;
compound consists of atoms of two or more elements (bound together) ;
5(c)(iii) methane ;
5(d)(i) 7 ;
5(d)(ii) 4–6 ;
Question
Ethanol has the formula C2H5OH.
(a) State the number of different elements in one molecule of ethanol.
(b) Complete Fig. 8.1 to show the structure of ethanol.
(c) State two ways of producing ethanol.
1 …………………………………………………………………………
2 …………………………………………………………………………
(d) Complete the word equation for the complete combustion of ethanol.
ethanol + ………………………….. →………………………….. + …………………………..
(e) Explain why ethanol is not a hydrocarbon.
(f) Ethanol is used in alcoholic drinks.
State one other use for ethanol.
▶️Answer/Explanation
Ans : 8(a) 3 ;
8(b) 
C-O-H ;
all else correct ;
8(c) fermentation ;
reaction of ethene with steam / water ;
8(d) oxygen ;
carbon dioxide and water ;
8(e) contains oxygen ; 1
8(f) solvent / fuel ;
Question
(a) An isotope of magnesium has a proton number (atomic number) of 12 and a nucleon number (mass number) of 26.
Complete Table 5.1 to show the numbers of neutrons and electrons in an atom of this isotope.
(b) Fig. 5.1 shows part of the reactivity series of metals.
Magnesium reacts slowly with cold water.
Use the reactivity series to predict the result when calcium reacts with cold water.
Explain your answer.
prediction ………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
explanation ……………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
(c) Magnesium reacts with carbon dioxide. Magnesium oxide and carbon are made.
(i) Write the word equation for this reaction.
(ii) The reaction between magnesium and carbon dioxide is exothermic.
State what is meant by the term exothermic.
……………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………
(d) Platinum is a transition metal. Magnesium is not a transition metal.
State two properties of platinum that are not properties of magnesium.
1 …………………………………………………………………………………………………………………..
2 ………………………………………………………………………………………………………………….
(e) Table 5.2 shows the composition of an alloy of magnesium.
Complete the table with the % by mass of magnesium.
Calculate the mass of magnesium in 1.0kg of the alloy.
mass = ……………………………………………. kg
▶️Answer/Explanation
Ans: 5(a)
5(b) calcium reacts quickly/quicker ;
calcium is higher in reactivity series than magnesium ;
5(c)(i) magnesium + carbon dioxide → magnesium oxide + carbon ;
5(c)(ii) releases (thermal) energy ;
5(d) any two from:
forms coloured compounds ;
acts as catalyst ;
variable valency ;
5(e) 91.5 (%) ;
0.915 (kg) ;
Question
(a) The list below shows the formulae of six molecules.
CH4 Cl2 CO N2 NH3 O2
Identify which of the molecules from the list is:
(i) an ammonia molecule (Topic – C2.2)
▶️Answer/Explanation
NH3
Explanation: Ammonia is a compound with the chemical formula NH3, consisting of one nitrogen atom and three hydrogen atoms.
(ii) a molecule used in the treatment of water (Topic – C10.1)
▶️Answer/Explanation
Cl2
Explanation: Chlorine (Cl2) is commonly used in water treatment to kill bacteria and other pathogens.
(iii) a molecule formed during the incomplete combustion of carbon-containing substances (Topic – C6.2)
▶️Answer/Explanation
CO
Explanation: Carbon monoxide (CO) is formed during the incomplete combustion of carbon-containing substances when there is insufficient oxygen.
(iv) the molecule of the gas that is 78% of clean dry air (Topic – C10.2)
▶️Answer/Explanation
N2
Explanation: Nitrogen (N2) makes up approximately 78% of the Earth’s atmosphere by volume.
(v) a molecule that contains four covalent bonds. (Topic – C2.5)
▶️Answer/Explanation
CH4
Explanation: Methane (CH4) contains four covalent bonds, one between the carbon atom and each of the four hydrogen atoms.
(b) Lime (calcium oxide) is made from limestone (calcium carbonate) by thermal decomposition.
(i) State the name of the other product of this reaction. (Topic – C6.1)
▶️Answer/Explanation
Carbon dioxide
Explanation: The thermal decomposition of calcium carbonate (CaCO3) produces calcium oxide (CaO) and carbon dioxide (CO2).
(ii) Calcium carbonate is not a fertiliser but is often added to soil. Explain why calcium carbonate is often added to soil. (Topic – C10.1)
▶️Answer/Explanation
To neutralize acidic soil
Explanation: Calcium carbonate is added to soil to neutralize acidity, improving soil pH and making it more suitable for plant growth.
(iii) List the three essential elements needed in a fertiliser. (Topic – C10.1)
▶️Answer/Explanation
1. Nitrogen
2. Phosphorus
3. Potassium
Explanation: These three elements are essential for plant growth and are commonly found in fertilizers to promote healthy development.
Question
(a) An atom of copper has a proton number of 29 and a nucleon number of 63.
(i) State the number of electrons in this copper atom. …………………………….
(ii) State the number of neutrons in this copper atom. …………………………….
(b) Copper oxide is heated with carbon. Copper and carbon dioxide are made.
(i) Write the word equation for this reaction.
(ii) In this reaction, reduction of copper in the copper oxide occurs.
Describe what is meant by the term reduction.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(iii) Explain why copper oxide is described as a basic oxide.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(c) Copper is a transition element.
Transition elements have high densities, high melting points and high boiling points. They are all metals.
State one other property of a transition element.
……………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………..
(d) (i) Brass is a mixture of copper and zinc.
State the term used to describe a mixture of metals.
…………………………………………………………………………………………………………………….
(ii) Brass is more malleable than either copper or zinc.
State the meaning of the term malleable.
…………………………………………………………………………………………………………………….
(iii) State the symbols of both copper and zinc.
copper symbol ……………………
zinc symbol ……………………
(e) A metal key is covered with a layer of copper by electroplating.
(i) The key is an electrode.
State which electrode is the key.
…………………………………………………………………………………………………………………….
(ii) Suggest a suitable electrolyte for electroplating the key.
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 8(a)(i) 29 ;
8(a)(ii) 34 ;
8(b)(i) copper oxide + carbon → copper + carbon dioxide ;
8(b)(ii) loss of oxygen ;
8(b)(iii) metal oxide / reacts with an acid to make a salt / neutralises an acid ;
8(c) any one from:
forms coloured compounds ;
acts as catalyst ; variable valency ;
8(d)(i) alloy ;
8(d)(ii) can be beaten into shape;
8(d)(iii) Cu and Zn ;
8(e)(i) cathode / negative ;
8(e)(ii) copper (II) sulfate ;
Question
(a) An atom of copper has a proton number of 29 and a nucleon number of 63.
(i) State the number of electrons in this copper atom. …………………………….
(ii) State the number of neutrons in this copper atom. …………………………….
(b) Copper oxide is heated with carbon. Copper and carbon dioxide are made.
(i) Write the word equation for this reaction.
(ii) In this reaction, reduction of copper in the copper oxide occurs.
Describe what is meant by the term reduction.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(iii) Explain why copper oxide is described as a basic oxide.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(c) Copper is a transition element.
Transition elements have high densities, high melting points and high boiling points. They are all metals.
State one other property of a transition element.
……………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………..
(d) (i) Brass is a mixture of copper and zinc.
State the term used to describe a mixture of metals.
…………………………………………………………………………………………………………………….
(ii) Brass is more malleable than either copper or zinc.
State the meaning of the term malleable.
…………………………………………………………………………………………………………………….
(iii) State the symbols of both copper and zinc.
copper symbol ……………………
zinc symbol ……………………
(e) A metal key is covered with a layer of copper by electroplating.
(i) The key is an electrode.
State which electrode is the key.
…………………………………………………………………………………………………………………….
(ii) Suggest a suitable electrolyte for electroplating the key.
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 8(a)(i) 29 ;
8(a)(ii) 34 ;
8(b)(i) copper oxide + carbon → copper + carbon dioxide ;
8(b)(ii) loss of oxygen ;
8(b)(iii) metal oxide / reacts with an acid to make a salt / neutralises an acid ;
8(c) any one from:
forms coloured compounds ;
acts as catalyst ; variable valency ;
8(d)(i) alloy ;
8(d)(ii) can be beaten into shape;
8(d)(iii) Cu and Zn ;
8(e)(i) cathode / negative ;
8(e)(ii) copper (II) sulfate ;
Question
5. (a) (i) State the number of electrons in an atom of iron with a proton number of 26 and a nucleon number of 56.
▶️Answer/Explanation
Answer: 26
Sub-topic Code: C16.1 (Atomic Structure)
Detailed Solution: In a neutral atom, the number of electrons is equal to the number of protons. Since the proton number is 26, the number of electrons is also 26.
5. (a) (ii) State the number of neutrons in this atom of iron.
▶️Answer/Explanation
Answer: 30
Sub-topic Code: C16.1 (Atomic Structure)
Detailed Solution: The number of neutrons is calculated as nucleon number minus proton number. For this atom of iron, neutrons = 56 – 26 = 30.
5. (a) (iii) Another atom of iron has a nucleon number of 54. State the proton number of this atom of iron.
▶️Answer/Explanation
Answer: 26
Sub-topic Code: C16.1 (Atomic Structure)
Detailed Solution: The proton number of an element is constant. For iron, the proton number is always 26, regardless of the nucleon number.
5. (b) State the test for aqueous iron(III) ions (Fe³⁺) and give the observation for a positive result.
▶️Answer/Explanation
Answer: sodium hydroxide solution; orange / brown ppt
Sub-topic Code: C9.1 (Chemical Tests)
Detailed Solution: The test for iron(III) ions involves adding sodium hydroxide solution. A positive result is indicated by the formation of an orange or brown precipitate of iron(III) hydroxide.
5. (c) (i) Define the term alloy.
▶️Answer/Explanation
Answer: mixture of metals / mixture of a metal and another element
Sub-topic Code: C25.1 (Alloys)
Detailed Solution: An alloy is a mixture of metals or a mixture of a metal with another element, designed to improve the properties of the base metal.
5. (c) (ii) State one use for stainless steel.
▶️Answer/Explanation
Answer: cutlery / chemical plant
Sub-topic Code: C25.1 (Alloys)
Detailed Solution: Stainless steel is commonly used in cutlery and chemical plants due to its resistance to corrosion and durability.
5. (c) (iii) State the two conditions needed for the rusting of iron.
▶️Answer/Explanation
Answer: (presence of) oxygen; (presence of) water
Sub-topic Code: C21.1 (Redox Reactions)
Detailed Solution: Rusting of iron requires the presence of both oxygen and water. These two conditions facilitate the oxidation of iron to form iron oxide (rust).
5. (c) (iv) Describe and explain one method of rust prevention.
▶️Answer/Explanation
Answer: painting / galvanising / plating / greasing; relevant explanation for method chosen (e.g. stops water / oxygen)
Sub-topic Code: C21.1 (Redox Reactions)
Detailed Solution: One method of rust prevention is painting, which creates a barrier that prevents oxygen and water from reaching the iron surface. Galvanising, plating, and greasing are other methods that achieve the same goal.
Question(a)(i)
An atom of aluminium has a proton number of 13 and a nucleon number of 27.
State what is meant by the term nucleon number.
▶️Answer/Explanation
Answer: The nucleon number is the total number of protons and neutrons in the nucleus of an atom.
Explanation: The nucleon number (also known as the mass number) is the sum of the number of protons and neutrons in the nucleus of an atom. For aluminium, the nucleon number is 27, which means there are 13 protons and 14 neutrons in its nucleus.
Question(a)(ii)
Describe the electronic structure of an atom of aluminium.
You may wish to draw a diagram to help your answer.
▶️Answer/Explanation
Answer: The electronic structure of aluminium is 2.8.3.
Explanation: The electronic structure of an atom describes how electrons are arranged in energy levels (shells) around the nucleus. For aluminium (atomic number 13), the electrons are distributed as follows:
- First shell: 2 electrons
- Second shell: 8 electrons
- Third shell: 3 electrons
This can be represented as 2.8.3.
Question(b)(i)
Aluminium is extracted from its ore by electrolysis.
Name one ore from which aluminium is extracted.
▶️Answer/Explanation
Answer: Bauxite
Explanation: Bauxite is the primary ore from which aluminium is extracted. It contains aluminium oxide (Al2O3), which is processed to obtain pure aluminium through electrolysis.
Question(b)(ii)
Electrolysis results in a chemical change.
Explain what is meant by a chemical change.
▶️Answer/Explanation
Answer: A chemical change involves the formation of new substances with different chemical properties.
Explanation: A chemical change occurs when substances react to form new products with different chemical compositions and properties. In electrolysis, aluminium oxide is broken down into aluminium and oxygen, which are new substances with different properties from the original compound.
Question(c)(i)
Aluminium alloys are used in aircraft parts.
State what is meant by the term alloy.
▶️Answer/Explanation
Answer: An alloy is a mixture of a metal with one or more other elements, usually metals.
Explanation: Alloys are created by mixing a metal with other elements to improve its properties, such as strength, hardness, or resistance to corrosion. For example, aluminium alloys are used in aircraft because they are lightweight and strong.
Question(c)(ii)
State why aluminium alloys are used in aircraft parts.
▶️Answer/Explanation
Answer: Aluminium alloys are used in aircraft parts because they have a low density and are strong.
Explanation: Aluminium alloys are lightweight (low density) and have high strength, making them ideal for aircraft construction. These properties help reduce the overall weight of the aircraft, improving fuel efficiency and performance.
Question(c)(iii)
State why aluminium is used in the form of alloys rather than as pure aluminium.
▶️Answer/Explanation
Answer: Alloys are stronger than pure aluminium.
Explanation: Pure aluminium is relatively soft and not very strong. By forming alloys with other elements, the strength and durability of aluminium are significantly improved, making it more suitable for structural applications like aircraft parts.
Question(c)(iv)
Describe and explain one other use of aluminium.
▶️Answer/Explanation
Answer: Aluminium is used in food containers because it is resistant to corrosion.
Explanation: Aluminium forms a protective oxide layer on its surface, which prevents further corrosion. This makes it ideal for use in food containers, as it does not react with food or degrade over time, ensuring the safety and longevity of the containers.
Question
(a) The formula of sulfuric acid is \( H_2SO_4 \).
(i) State the number of different elements shown in this formula.
▶️Answer/Explanation
Answer:
3 (Hydrogen, Sulfur, Oxygen)
(ii) State the total number of atoms shown in this formula.
▶️Answer/Explanation
Answer:
7 (2 Hydrogen, 1 Sulfur, 4 Oxygen)
(b) Fig. 2.1 shows the electrolysis of dilute sulfuric acid using carbon electrodes.
(i) Name gas P and gas Q. (Sub-topic – C4.1)
▶️Answer/Explanation
Answer:
Gas P: Oxygen
Gas Q: Hydrogen
(ii) State the name of the positive electrode.
▶️Answer/Explanation
Answer:
Anode
(c) Dilute sulfuric acid reacts with some metals.
(i) Suggest a pH for dilute sulfuric acid.
▶️Answer/Explanation
Answer:
Any number less than 7 (e.g., pH 1 or 2)
(ii) State a metal element that does not react with dilute sulfuric acid.
▶️Answer/Explanation
Answer:
Copper
(iii) Name the gas made when dilute sulfuric acid reacts with zinc.
▶️Answer/Explanation
Answer:
Hydrogen
(iv) When dilute sulfuric acid reacts with zinc, an aqueous solution of zinc sulfate is made.
State a method used to separate zinc sulfate from water.
▶️Answer/Explanation
Answer:
Evaporation or crystallisation
Question
(a) Magnesium is in Period 3 of the Periodic Table.
(i) Use the Periodic Table to name the noble gas in Period 3 of the Periodic Table.
▶️Answer/Explanation
Answer: Argon
Explanation: The noble gases are found in Group 18 of the Periodic Table. In Period 3, the noble gas is Argon (Ar).
(ii) Describe the change in metallic character across Period 3.
▶️Answer/Explanation
Answer: The metallic character decreases across Period 3.
Explanation: As you move from left to right across Period 3, the elements become less metallic and more non-metallic. This is because the tendency to lose electrons decreases, and the tendency to gain electrons increases.
(b) Magnesium reacts with carbon dioxide. Magnesium oxide and carbon are made.
(i) Write the word equation for this reaction.
▶️Answer/Explanation
Answer: Magnesium + Carbon dioxide → Magnesium oxide + Carbon
Explanation: The reaction between magnesium and carbon dioxide produces magnesium oxide and carbon. The word equation represents the reactants and products involved in the reaction.
(ii) The reaction between magnesium and carbon dioxide is exothermic. Explain what is meant by an exothermic reaction.
▶️Answer/Explanation
Answer: An exothermic reaction is a reaction that releases thermal energy to the surroundings.
Explanation: In an exothermic reaction, energy is released in the form of heat, causing the temperature of the surroundings to increase.
(c) An atom of magnesium has a proton number (atomic number) of 12 and a nucleon number (mass number) of 24.
Complete Table 2.1 to show the names and numbers of the two particles contained in the nucleus of this magnesium atom.
| Name of particle | Number of particles |
|---|---|
▶️Answer/Explanation
Answer: Protons: 12, Neutrons: 12
Explanation: The proton number (atomic number) is 12, which means there are 12 protons in the nucleus. The nucleon number (mass number) is 24, which is the sum of protons and neutrons. Therefore, the number of neutrons is 24 – 12 = 12.
(d) Magnesium carbonate reacts with dilute hydrochloric acid to make aqueous magnesium chloride.
(i) Magnesium carbonate is insoluble in water. State the separation technique used to remove magnesium carbonate from a mixture of magnesium carbonate and water.
▶️Answer/Explanation
Answer: Filtration
Explanation: Filtration is used to separate an insoluble solid (magnesium carbonate) from a liquid (water). The solid remains on the filter paper, while the liquid passes through.
(ii) Magnesium chloride dissolves in water. State the separation technique used to obtain solid magnesium chloride from a solution of magnesium chloride.
▶️Answer/Explanation
Answer: Crystallization
Explanation: Crystallization is used to obtain a solid (magnesium chloride) from a solution by evaporating the water, leaving behind the solid crystals.
(iii) Magnesium carbonate reacts with dilute hydrochloric acid. Complete the balanced symbol equation for this reaction.
MgCO3 + …..HCl → MgCl2 + CO2 + H2O
▶️Answer/Explanation
Answer: MgCO3 + 2HCl → MgCl2 + CO2 + H2O
Explanation: The balanced equation shows that one mole of magnesium carbonate reacts with two moles of hydrochloric acid to produce one mole of magnesium chloride, one mole of carbon dioxide, and one mole of water.
(iv) Dilute hydrochloric acid contains aqueous chloride ions. State the test for aqueous chloride ions and give the observation for a positive result.
▶️Answer/Explanation
Answer: Test: Add acidified silver nitrate solution. Observation: A white precipitate forms.
Explanation: Chloride ions react with silver nitrate in the presence of nitric acid to form a white precipitate of silver chloride.
(e) Table 2.2 shows the composition of a magnesium alloy.
| Element | % by mass |
|---|---|
| Magnesium | 94 |
| Neodymium | 2 |
| Yttrium | 4 |
(i) Calculate the mass of magnesium in 500 kg of the alloy.
▶️Answer/Explanation
Answer: 470 kg
Explanation: The mass of magnesium in the alloy is 94% of 500 kg. Therefore, 0.94 × 500 kg = 470 kg.
(ii) The alloy is used in aircraft bodies. Suggest why the alloy of magnesium is used rather than pure magnesium for aircraft bodies.
▶️Answer/Explanation
Answer: The alloy is stronger and less dense than pure magnesium.
Explanation: Alloys are generally stronger and more durable than pure metals. In the case of magnesium alloys, they are also lighter, making them ideal for use in aircraft bodies where strength and low weight are crucial.