States of Matter: Chemistry 9701 (Cambridge International AS & A Level)

Which of these four gases would be expected to show the greatest deviation from ideal gas behaviour, at the same temperature and pressure?

A technician is finding the molar mass of a volatile organic liquid, X, using a heated gas syringe. A few drops of liquid X, of mass 0.145 g, are injected into the syringe and allowed to vaporise completely. The resulting gas occupies 42.5 cm³, measured at a pressure of 101 kPa and a temperature of 100 °C.

(a) Convert the volume, pressure and temperature of the gas produced into the SI units required to use the ideal gas equation. [3]

(b) Use the ideal gas equation $pV = nRT$, where $R = 8.31\ \text{J K}^{-1}\text{mol}^{-1}$, to calculate the amount, in mol, of gas produced. [3]

(c) Hence calculate the molar mass of X, giving your answer to 3 significant figures. [2]

A technician is given four unlabelled solids, P, Q, R and S, and measures the following properties.

(a) Identify the type of lattice structure present in each of P, Q, R and S. [4]

(b) Suggest, in terms of the particles present and the forces or bonds between them, why solid P remains solid up to such an extremely high temperature. [2]

(c) Suggest why solid Q only becomes able to conduct electricity once it has melted, and does not conduct as a solid. [2]

(d) Suggest why solid R does not dissolve in water but dissolves readily in a non-polar organic solvent. [2]

A sealed rigid canister of volume 2.00 dm³ contains a sample of an ideal gas at a pressure of 250 kPa and a temperature of 500 K.

What amount, in mol, of gas is present in the canister? (R = 8.31 J K⁻¹ mol⁻¹)

A steel cylinder used for industrial welding contains argon gas compressed to a very high pressure.

(a) State two assumptions of the kinetic theory model that define an ideal gas. [2]

(b) State the conditions of pressure and temperature under which a real gas is expected to show the greatest deviation from ideal gas behaviour. [2]

(c) Using your assumptions from (a), explain why a real gas deviates from ideal behaviour under the conditions you gave in (b). [3]

A steel cylinder contains 2.50 mol of compressed carbon dioxide gas, CO₂, at a temperature of 350 K and a pressure of $6.00\times10^{6}\ \text{Pa}$.

(a) Use the ideal gas equation $pV = nRT$, where $R = 8.31\ \text{J K}^{-1}\text{mol}^{-1}$, to calculate the volume, in dm³, that this amount of CO₂ would occupy at this pressure and temperature if it behaved as an ideal gas. Give your answer to 3 significant figures. [4]

(b) The actual volume occupied by the CO₂ is measured experimentally under these same conditions and found to be 1.34 dm³, noticeably larger than the ideal volume calculated in (a). Calculate the percentage by which this actual measured volume exceeds the ideal volume from (a). [2]

(c) Using the assumptions of the kinetic theory model of an ideal gas, explain why real CO₂ at this high pressure occupies a larger volume than the ideal gas equation predicts. [2]

A rigid steel cylinder of fixed volume 8.00 dm³ contains carbon dioxide gas, CO₂ ($M_r = 44.0$), at a pressure of $3.50\times10^{5}\ \text{Pa}$ and a temperature of 291 K. Assume that the CO₂ behaves as an ideal gas throughout.

(a) Convert the volume into the SI unit required for the ideal gas equation, and use $pV = nRT$, where $R = 8.31\ \text{J K}^{-1}\text{mol}^{-1}$, to calculate the amount, in mol, of CO₂ present in the cylinder. [3]

(b) Calculate the mass, in g, of CO₂ present in the cylinder. [2]

(c) The sealed cylinder is left in direct sunlight and warms up, so that the pressure rises to $4.20\times10^{5}\ \text{Pa}$ while the volume of the cylinder and the amount of gas inside it remain unchanged. Use the ideal gas equation to calculate the new temperature of the gas, in K. [3]

Two identical rigid flasks, 1 and 2, each of volume 500 cm³, are filled with different gases at the same temperature of 298 K and the same pressure of $1.00\times10^{5}\ \text{Pa}$. Flask 1 contains oxygen, O₂ ($M_r = 32.0$); flask 2 contains carbon dioxide, CO₂ ($M_r = 44.0$). Assume both gases behave ideally.

(a) Using the ideal gas equation $pV = nRT$, explain why the two flasks must contain equal amounts, in mol, of gas. [2]

(b) Calculate the amount, in mol, of gas present in each flask, giving your answer to 3 significant figures. [3]

(c) Calculate the mass of gas present in each flask, and use your answers to explain why the two flasks contain different masses of gas even though they contain equal amounts (and hence equal numbers of molecules) of gas. [3]

Diamond and graphite are both crystalline forms (allotropes) of carbon, and both are giant covalent (macromolecular) lattices with very high melting points. However, the two solids have very different physical properties, summarised below.

(a) Describe the arrangement of carbon atoms and the covalent bonding present in diamond. [3]

(b) Describe the arrangement of carbon atoms and the covalent bonding present in graphite. [3]

(c) Explain, in terms of structure and bonding, why graphite conducts electricity but diamond does not. [2]

(d) Explain, in terms of structure and bonding, why graphite is much softer than diamond even though both contain strong covalent bonds. [2]

A student measures the properties of an unknown solid, Z. It has a high melting point, it conducts electricity both as a solid and when molten, and it can be hammered into different shapes without shattering (it is malleable).

Which type of lattice structure does Z most likely have?