Covalent bonding

Hydrazine (N₂H₄) is a compound of nitrogen and hydrogen.

Scientists are researching the use of hydrazine in fuel cells.

Table 2 gives some information about the use of hydrogen and hydrazine in fuel cells.

Evaluate the use of hydrazine instead of hydrogen in a fuel cell.

Figure 6 shows a model of the hydrazine molecule.

Complete the dot and cross diagram for hydrazine in Figure 7.

Show the outer shell electrons only.

Give one advantage of the ball and stick model in Figure 6 compared to the dot and cross diagram.

Figure 8 shows the displayed formula equation for the reaction of hydrazine with oxygen.

The reaction is exothermic.

The energy released forming new bonds is 581 kJ/mol greater than the energy needed to break existing bonds.

Table 3 shows some bond energies.

Calculate the bond energy (X) of the bond.

This question is about hydrogen and compounds of hydrogen. Figure 3 shows the displayed formulae for the reaction between hydrogen and chlorine.

Figure 3

Table 4 shows the bond energies.

Which expression shows how to calculate the overall energy change for the reaction in Figure 3 ? Use Table 4. Tick (✓) one box.

The reaction between hydrogen and chlorine is exothermic.

Explain why this reaction releases energy to the surroundings.

Figure 4 shows part of a reaction profile for the reaction between hydrogen and chlorine. Complete the reaction profile in Figure 4. You should:

• label the activation energy

• label the overall energy change.

Draw a dot and cross diagram for a molecule of hydrogen chloride (HC l). Show the outer shell electrons only.

Figure 5 represents molecules of methane and of poly(ethene).

Methane is a gas at room temperature but poly(ethene) is a solid at room temperature.

Explain why methane and poly(ethene) exist in different states at room temperature.

This question is about carbon and compounds of carbon.

Figure 9 shows diagrams that represent different structures.

Use Figure 9 to answer questions 06.1 and 06.2.

Which diagram represents graphite?

Tick (✓) one box.

Which diagram represents poly(ethene)?

Tick (✓) one box.

Figure 10 represents the structure of diamond.

How many covalent bonds does each carbon atom form in diamond?

Which is a property of diamond?

Tick (✓) one box.

Figure 11 shows a model of a molecule.

Complete the molecular formula of the molecule.

Molecular formula = C__ H__

Carbonic acid is a compound of carbon.

The formula of carbonic acid is H₂CO₃

Which ion is produced by carbonic acid in aqueous solution?

Tick (✓) one box.

Calculate the relative formula mass (M_r) of carbonic acid (H₂CO₃).

Relative atomic masses (A_r): H = 1 C = 12 O = 16

This question is about silicon and compounds of silicon.

The reactivity series sometimes includes non-metals such as carbon, hydrogen and silicon. Silicon can be extracted by reducing silicon dioxide with different substances. The equation for one possible reaction is:

Explain what this reaction shows about the position of silicon in the reactivity series.

Aluminium also reduces silicon dioxide. Carbon is used rather than aluminium to reduce silicon dioxide because carbon is cheaper than aluminium. Carbon can be obtained by heating coal. Aluminium is obtained from aluminium oxide. Explain why aluminium is more expensive than carbon.

Magnesium also reduces silicon dioxide. The equation for the reaction is:

Give one reason why the products are difficult to separate if magnesium is used to reduce silicon dioxide.

Calculate the minimum mass in grams of magnesium needed to completely reduce 1.2 kg of silicon dioxide. Relative atomic masses (A_r): O = 16 Mg = 24 Si = 28

Si₂H₆ is a covalent compound of silicon and hydrogen.

Complete Figure 9 to show the outer shell electrons in a molecule of Si₂H₆

Si₂H₆ reacts with oxygen. The equation for the reaction is:

30 cm³ of Si₂H₆ is reacted with 150 cm³ (an excess) of oxygen.

Calculate the total volume of gases present after the reaction. All volumes of gases are measured at the same temperature and pressure.

This question is about carbon and its compounds.

Fullerenes are molecules of carbon atoms.

The first fullerene to be discovered was Buckminsterfullerene (C₆₀).

What shape is a Buckminsterfullerene molecule?

Give one use of a fullerene.

Propanone is a compound of carbon, hydrogen and oxygen.

Figure 13 shows the dot and cross diagram for a propanone molecule.

Complete Figure 14 to show a propanone molecule.

Use a line to represent each single bond.

Use Figure 13.

Figure 14

Determine the molecular formula of propanone.

Use Figure 13.

Propanone is a liquid with a low boiling point.

Why does propanone have a low boiling point?

Tick (✓) one box.

Figure 15 represents the structure of graphite.

Explain why graphite is:

• a good electrical conductor

• soft and slippery.

You should answer in terms of structure and bonding.

This question is about carbon and its compounds.

Fullerenes are molecules of carbon atoms. The first fullerene to be discovered was Buckminsterfullerene (C₆₀).

What shape is a Buckminsterfullerene molecule?

Give one use of a fullerene.

Propanone is a compound of carbon, hydrogen and oxygen. Figure 1 shows the dot and cross diagram for a propanone molecule.

Complete Figure 2 to show a propanone molecule. Use a line to represent each single bond. Use Figure 1.

Figure 2

Determine the molecular formula of propanone. Use Figure 1.

Propanone is a liquid with a low boiling point. Why does propanone have a low boiling point? Tick (✓) one box.

Figure 3 represents the structure of graphite.

Explain why graphite is:

• a good electrical conductor

• soft and slippery.

You should answer in terms of structure and bonding.

This question is about citric acid. Figure 7 represents one molecule of citric acid.

Complete the molecular formula of citric acid. Use Figure 7. C 6 H __ O __

What type of bonding is shown in Figure 7 ? Tick (✓) one box.

Figure 8 shows two representations of one molecule of citric acid, A and B.

Figure 8

Give two advantages of representation A compared with representation B. Advantages of A:

A student investigated the temperature change during the reaction between citric acid and sodium hydrogencarbonate solution. Citric acid is a solid. This is the method used.

1. Pour 25 cm³ of sodium hydrogencarbonate solution into a polystyrene cup.

2. Measure the temperature of the sodium hydrogencarbonate solution.

3. Add 0.25 g of citric acid to the cup.

4. Stir the solution.

5. Measure the temperature of the solution.

6. Repeat steps 3 to 5 until a total of 2.00 g of citric acid has been added.

Table 4 shows some of the student’s results.

How do the results in Table 4 show that the reaction is endothermic?

Three of the student’s results are plotted on Figure 9. A line of best fit for these points is drawn. Complete Figure 9. You should:

• plot the data from Table 4 on Figure 9

• draw a line of best fit through the points you have plotted

• extend your line of best fit to meet the line of best fit already drawn on Figure 9.

Determine the overall temperature change for the reaction. Use Figure 9.

What is the dependent variable in this investigation? Tick (✓) one box.

This question is about ammonia, NH₃

Complete the dot and cross diagram for the ammonia molecule shown in Figure 6. Show only the electrons in the outer shell of each atom.

Give one limitation of using a dot and cross diagram to represent an ammonia molecule.

Explain why ammonia has a low boiling point. You should refer to structure and bonding in your answer.

Ammonia reacts with oxygen in the presence of a metal oxide catalyst to produce nitrogen and water.

Which metal oxide is most likely to be a catalyst for this reaction? Tick (✓) one box.

Figure 7 shows the displayed formula equation for the reaction.

Table 3 shows some bond energies.

Calculate the overall energy change for the reaction. Use Figure 7 and Table 3.

Explain why the reaction between ammonia and oxygen is exothermic. Use values from your calculation in Question 05.5

Figure 8 shows the reaction profile for the reaction between ammonia and oxygen. Complete Figure 8 by labelling the:

• activation energy

• overall energy change.

The halogens are elements in Group 7.

Bromine is in Group 7.

Give the number of electrons in the outer shell of a bromine atom.

Bromine reacts with hydrogen. The gas hydrogen bromide is produced.

What is the structure of hydrogen bromide?

Tick one box.

What is the formula for fluorine gas?

Tick one box.

A student mixes solutions of halogens with solutions of their salts.

Table 1 shows the student’s observations.

Explain how the reactivity of the halogens changes going down Group 7.

Use the results in Table 1.

A company uses chlorine to produce titanium chloride from titanium dioxide.

What is the relative formula mass (M_r) of titanium dioxide, TiO₂ ?

Relative atomic masses (A_r): O = 16 Ti = 48

Tick one box.

The company calculates that 500 g of titanium dioxide should produce 1.2 kg of titanium chloride.

However, the company finds that 500 g of titanium dioxide only produces 900 g of titanium chloride.

Calculate the percentage yield.