Chemical Bonding and StructureIB MYP Chemistry: Topic test

1. 1
   At a building site in Lima, workers use calcium oxide, CaO, known as quicklime, to prepare mortar. Calcium oxide forms when calcium reacts with oxygen. A calcium atom has two electrons in its outer shell and an oxygen atom has six.

   (a)

   What happens to the electrons when calcium atoms react with oxygen atoms to form calcium oxide?

   [1 mark]

   • AEach calcium atom gains two electrons from an oxygen atom
   • BEach calcium atom transfers two electrons to an oxygen atom
   • CCalcium atoms and oxygen atoms share two pairs of electrons
   • DEach oxygen atom transfers six electrons to a calcium atom

   (b)

   What is the formula of calcium oxide, which contains Ca²⁺ and O²⁻ ions?

   [1 mark]

   • ACa₂O
   • BCaO₂
   • CCa₂O₂
   • DCaO

   (c)

   Describe how the ions are held together in solid calcium oxide.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemistry teacher in Bogotá builds models of oxygen gas, O₂, and hydrogen chloride gas, HCl. Both gases are made of molecules. An oxygen atom has six electrons in its outer shell, a hydrogen atom has one and a chlorine atom has seven. Hydrogen chloride boils at −85 °C.

   (a)

   How many pairs of electrons are shared between the two atoms in an oxygen molecule, O₂?

   [1 mark]

   • ATwo
   • BOne
   • CThree
   • DFour

   (b)

   Why does hydrogen chloride have such a low boiling point?

   [1 mark]

   • AThe covalent bond in each molecule is very weak
   • BThe ions in solid hydrogen chloride are only weakly attracted to each other
   • CThe forces between the molecules are weak, so little energy is needed to separate them
   • DDelocalised electrons can move freely between the molecules

   (c)

   Describe the dot-and-cross diagram of a hydrogen chloride molecule, HCl. State how many electrons are in the shared region between the atoms and how many outer electrons on the chlorine atom are not involved in the bond.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students in Jakarta test the hypothesis that an ionic compound conducts electricity only when its ions are free to move. They connect each of four samples in turn into a circuit with a lamp, a 6 V supply and two carbon electrodes: solid potassium iodide, potassium iodide solution, solid sugar and sugar solution. They record whether the lamp lights. Safety glasses are worn.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   Only the potassium iodide solution made the lamp light. Explain these results using ideas about particles and charge, and suggest one improvement to the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A glassworks in Murano, Italy, makes glass by melting sand, which is silicon dioxide, SiO₂. Sand melts at about 1700 °C, so the furnaces burn natural gas all day. Sodium chloride melts at 801 °C. The glassworks employs 400 people, but its sand is dredged from the local coast and local fishers say this is damaging the shoreline.

   (a)

   Compare the structure and bonding of silicon dioxide and sodium chloride. Use them to explain why both have high melting points but only molten sodium chloride conducts electricity.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of the glassworks continuing to dredge sand from the coast, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A foundry in Taipei makes bicycle frames from an aluminium alloy instead of pure aluminium. Pure aluminium is soft and bends easily. Aluminium is also used for overhead power cables because it conducts electricity well.

   (a)

   Why is the alloy harder than pure aluminium?

   [1 mark]

   • AAll the atoms are the same size, so the layers slide over each other easily
   • BThe alloy has no delocalised electrons to hold the atoms together
   • CAtoms of different sizes disrupt the regular layers, so the layers cannot slide easily
   • DThe atoms in the alloy are held together by ionic bonds

   (b)

   Which statement describes the bonding in aluminium?

   [1 mark]

   • APositive aluminium ions are attracted to a sea of delocalised electrons
   • BAluminium atoms share pairs of electrons with their neighbours
   • CPositive aluminium ions are attracted to negative ions
   • DAluminium atoms are held together by weak forces between molecules

   (c)

   Explain why aluminium can conduct electricity in the overhead cables.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A technician in Dublin is preparing reagents for the school stock room. The ions available are Mg²⁺, Al³⁺ and K⁺, together with NO₃⁻, SO₄²⁻, CO₃²⁻ and OH⁻.

   (a)

   What is the formula of potassium carbonate?

   [1 mark]

   • AKCO₃
   • BK(CO₃)₂
   • CK₂(CO₃)₂
   • DK₂CO₃

   (b)

   What is the name of the compound with the formula Mg(NO₃)₂?

   [1 mark]

   • AMagnesium nitride
   • BMagnesium nitrate
   • CMagnesium dinitrate
   • DMagnesium nitrogen oxide

   (c)

   Explain, using ion charges, why the formula of aluminium sulfate is Al₂(SO₄)₃.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A mining company in Sri Lanka extracts sapphires, which are crystals of aluminium oxide, Al₂O₃. It also sells crushed aluminium oxide as an abrasive for sandpaper. An aluminium atom has three electrons in its outer shell and an oxygen atom has six.

   (a)

   Describe, in terms of electrons, how aluminium atoms and oxygen atoms form aluminium oxide. State the charge on each ion formed.

   [3 marks]

   (b)

   Aluminium oxide has a melting point of 2072 °C. Explain this melting point using its structure and bonding. State whether aluminium oxide conducts electricity as a solid and when molten, giving a reason for each.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A materials class in Kigali studies potassium chloride, which is used in fertilisers, copper, which is used in electrical wiring, and hydrogen, which is proposed as a fuel. A national programme plans to bring electricity to remote villages using copper cables, which will mean opening new copper mines.

   (a)

   Explain why potassium chloride, copper and hydrogen differ in their melting points and electrical conductivity.

   [6 marks]

   (b)

   Discuss the social, economic and environmental effects of opening new copper mines to supply the programme, and reach a justified conclusion.

   [6 marks]

   Total for question 8: 12 marks

End of questions