States of Matter (CIE AS Chemistry)

Carbon and silicon are elements in Group 14.
 

[2]

C₆₀ (s) → C₆₀ (g)

Diamond also sublimes but only above 3800 K.

C_diamond (s) → C (g)

Explain why C₆₀ and diamond sublime at such different temperatures.

[4]

C₆₀ forms hydrocarbons with similar chemical properties to those of alkenes. One such hydrocarbon is C₆₀H₁₈.

[1]

[1]

0.144 g of C₆₀ is placed in a 100 cm³ container of hydrogen gas at a temperature of 20 °C and a pressure of 1.00 × 10⁵ Pa.

The container is heated to make the C₆₀ and hydrogen gas react. The reaction occurs as shown in the equation.

After the reaction, the container is allowed to cool to 20 °C. The pressure decreases to 2.21 × 10⁴ Pa. All of the C₆₀ has reacted.

[1]

amount of C₆₀ = .................................................... mol [1]

amount of hydrogen gas = .................................................... mol [3]

molecular formula = ........................................................... [2]

Silicon shows the same type of bonding and structure as diamond.

Silicon reacts with magnesium to form Mg₂Si.

Solid Mg₂Si reacts with dilute hydrochloric acid to form gaseous SiH₄ and a solution of magnesium chloride.

[2]

 [1]

Copper and iodine are both solids which have different physical and chemical properties.

Each element has the same face-centred crystal structure which is shown below.

The particles present in such a crystal may be atoms, molecules, anions or cations. In the diagram above, the particles present are represented by the black balls. 

Which type of particles are present in the iodine crystal? Give their formula.

particle ....................................
formula ...................................

When separate samples of copper or iodine are heated to 50 °C, the copper remains as a solid while the iodine turns into a vapour.

Explain, in terms of the forces present in the solid structure, why copper remains a solid at 50 °C.

Explain, in terms of the forces present in the solid structure, why iodine turns into a vapour when heated to 50°C.

Calculate the volume, in cm³, that 5.00 g of iodine vapour occupies at 185 °C and 100 kPa.

The gas constant R = 8.31 J K^–1 mol^–1

Give your answer to 3 significant figures.

Although copper is a relatively unreactive metal, when it is heated to a high temperature in an excess of chlorine, copper(II) chloride is formed.

This question is about ideal gas theory. 

State the basic assumptions of the kinetic theory as applied to an ideal gas.

Carbon dioxide does not behave as an ideal gas. 

Suggest one reason why not. 

Explain why CO₂ is a gas at room temperature.

Carbon dioxide can be used to inflate life jackets. 

Explain the effect of decreasing the temperature of carbon dioxide on the pressure inside a life jacket.

Until 1985, carbon was thought to exist in only two structural forms or allotropes. In 1985 another form, buckminsterfullerene, was discovered, in which the carbon exists as spherical molecules.

The other two forms of carbon have very different structures.

The diagram shows the structure of buckminsterfullerene.

The molecule of buckminsterfullerene contains 60 carbon atoms.

Suggest a reason why buckminsterfullerene reacts with hydrogen under suitable conditions and give a formula for the product.

In 2010, two scientists from the University of Manchester were awarded the Nobel Prize for Physics for their work on graphene, a 'nano-material' and new structural form of carbon. 

Explain whether you would expect samples of graphene and buckminsterfullerene to be electrical conductors.

The kinetic theory of gases is used to explain the large scale (macroscopic) properties of gases by considering how individual molecules behave.

State two basic assumptions of the kinetic theory as applied to an ideal gas.

State two conditions under which the behaviour of a real gas approaches that of an ideal gas.

Place the following gases in decreasing order of ideal behaviour.

ammonia, neon, nitrogen

most ideal .......................................................................................... least ideal

Explain your answer.

Explain why a liquid eventually becomes a gas as the temperature is increased.

Phosphine, PH₃, is a gas formed by heating phosphorous acid, H₃PO₃, in the absence of air.

4H₃PO₃ (s) → PH₃ (g) + 3H₃PO₄ (s)

State the shape and bond angle in PH₃ (g).

3.45 × 10⁻² mol of H₃PO₃ is completely decomposed at 100 kPa pressure and 210 °C.

Calculate the volume occupied, in cm³, by the phosphine gas produced.

1.85 g of white phosphorus was reacted with 75.00 cm³ of 1.25 mol dm^-3 sodium hydroxide solution to make phosphine.

P₄ (s) + 3OH⁻ (aq) + 3H₂O (l) → PH₃ (g) + 3H₂PO₂⁻ (aq)

Deduce which chemical is the limiting reagent.  

Use the information in part (c) to calculate the volume, in cm³, of phosphine that was produced at room temperature and pressure.  Give your answer to three significant figures.

Oxygen exists as a diatomic gas, O₂ (g). A sample of O₂ (g) was made during a chemical reaction. When measured at 303 kPa and 28 °C the sample occupied a volume of 95.0 cm³.

Calculate the mass of oxygen formed.

For this calculation, assume that oxygen behaves as an ideal gas under these conditions.

Calculate the number of electrons involved in the bonding of this sample of oxygen. You may find it helpful to use your answer to (a).

O₂ (g) does not behave as an ideal gas under these conditions. 

Explain why O₂ (g) behaves even less ideally at:

• very high pressures
• very low temperatures

The homologous series of alkanes undergo combustion with oxygen.

A 2.0 dm³ flask contains 10.84 g of a gaseous alkane, X. The pressure in the flask is 300 kPa and the temperature is 20 ^oC.

Write an equation for the complete combustion of X.

Airbags are safety devices fitted to modern cars. They are designed to rapidly inflate in the event of a collision, in order to protect the occupants of the car from the effects of the impact, and then quickly deflate.

The inflation of an airbag depends on the chemical decomposition of sodium azide, NaN₃.

The azide ion, N₃^–, contains one triple bond. Draw a ‘dot-and-cross’ diagram to show the arrangement of outer electrons present in an azide ion.

Suggest three properties of sodium azide. Explain your answer.

550 g of sodium azide, sodium hydroxide and ammonia were produced during the chemical reaction of sodium amide, NaNH₂, and dinitrogen monoxide. The yield of sodium azide in this reaction was 95.0%.

Calculate the mass, in grams, of sodium amide required for this reaction.

In a serious collision, the airbag deploys and rapidly fills with nitrogen as sodium azide decomposes.

2NaN₃ (s) → 2Na (s) + 3N₂ (g)

Calculate the mass of sodium azide that must decompose in order to inflate an airbag to a volume of 7.50 × 10⁻² m³ at a pressure of 150 kPa and temperature of 35 °C.

Sodium azide is toxic. It can be destroyed by reacting it with acidified nitrous acid, HNO₂. 

This question is about the melting points of different chemicals.

The melting and boiling points of calcium and chlorine are given in Table 4.1.

Sulfur dioxide and magnesium oxide are both oxides. The melting point of sulfur dioxide is –72 ^oC and the melting point of magnesium oxide is 2852 ^oC

Silver chloride is used in photography films as well as having antiseptic properties. 

Diamond and ice are types of crystals.

Describe the structure and bonding present in both diamond and ice. Explain why the melting point of these two substances is very different. You should refer to the type of bonding present in both diamond and ice in your answer.

Mercury is a naturally occurring element that is a liquid at room temperature and pressure. Some of its physical properties are shown in Table 5.1.

Mercury can react with bromine to form mercury(II) bromide, HgBr₂. 

Compare and explain the electrical conductivity of mercury and mercury(II) bromide.

The strength of ionic bonding in different compounds can be compared by using the amount of energy required to separate the ions, as shown in Table 5.2.

Using the data from Table 5.2, explain how changes in the cation affect the bond strength in an ionic compound.

Sodium chloride and iodine are both solids. Sodium chloride does not melt until it reaches a temperature of 1074 K yet iodine sublimes when heated gently, giving off purple vapours. Sodium chloride will conduct electricity when molten and iodine is a very poor conductor of electricity.

Graphene, graphite and diamond are all forms of solid carbon.

Explain, in terms of structure and bonding, why graphene and graphite are good electrical conductors but diamond is a poor electrical conductor.