Chemistry 9202 | Paper 1 Mock 01 | Written Paper 1

A roadside worker uses solid sodium chloride to help melt ice on a footpath. Fig. 1 shows salt crystals spread over the icy surface.

(a) Name the state of sodium chloride before it dissolves. [1]
(b) Give the name of the mixture formed when sodium chloride dissolves in melted water. [1]
(c) Suggest why salt can make ice melt at a temperature below 0 degrees C. [2]
(d) Give one reason why workers should use only the amount of salt needed. [1]
(e) What happens to the arrangement of water particles when ice becomes liquid water? [1]

At a coastal chemical works, gases from an air-separation unit and a hydrogen plant are fed into a high-pressure vessel. Fig. 1 shows the route used to make ammonia for a solution fertiliser. The reaction mixture is cooled after leaving the reactor. Ammonia becomes a liquid and is removed, while nitrogen and hydrogen that have not reacted are returned to the compressor. Iron is used in the reactor.

In one pass through the reactor, 18% of the nitrogen reacts. Table 1 gives the amount of each gas entering the reactor.

(a) Complete the balanced symbol equation for the reversible reaction.
N₂(g) + H₂(g) ⇌ NH₃(g) [2]
(b) Give one reason why the gases are compressed before entering the reactor. [1]
(c) Suggest two advantages of recycling the unreacted nitrogen and hydrogen shown in Fig. 1. [2]
(d) Use Table 1 and the equation to calculate the number of moles of ammonia made and the number of moles of nitrogen left after one pass. [3]
(e) What does the iron catalyst do to the energy needed for the reaction? [2]

Fig. 1 shows a model of sodium metal before it reacts with water in a demonstration. The dots between the sodium ions represent outer electrons that are not held by one atom.

(a) Name the type of bonding in sodium metal. [1]
(b) What is the name given to the electrons shown as dots? [1]
(c) Use Fig. 1 to suggest why sodium conducts when it is solid. [1]
(d) Give the charge on a sodium ion. [1]
(e) Complete the sentence. Metallic bonding is the attraction between positive ions and ______ electrons. [1]

This cross-section is from a high-temperature ceramic crucible. Fig. 1 compares a giant ionic lattice with separate water molecules that can enter cracks in the ceramic.

(a) Name the particles in the left-hand structure. [1]
(b) Give one reason why the ionic ceramic can withstand high temperature. [1]
(c) What type of bond joins oxygen to hydrogen in a water molecule? [1]
(d) Suggest why liquid water can conduct a little when impurities are present. [1]

A horticulture supplier prepares potassium nitrate crystals for a vertical farm. The compound is used in a nutrient solution because it provides potassium and nitrogen. A technician dissolves a weighed sample in hot water, then cools the solution to check how many crystals can be recovered. Fig. 1 shows the filtration stage after the crystals have formed. The funnel paper holds the crystals, while the liquid that passes into the flask is the filtrate.

The sample contains 18.0 g of potassium nitrate, KNO₃, dissolved in 50.0 g of water at 70 °C. At 70 °C, 31.0 g of potassium nitrate dissolves in 100 g of water. At 20 °C, only 13.0 g dissolves in 100 g of water.

(a) Use the solubility data to calculate the maximum mass of potassium nitrate that remains dissolved at 20 °C and the mass of crystals that can be collected. [3]
(b) Describe how the technician should obtain dry crystals after cooling the solution. [3]
(c) Complete the ionic equation, including state symbols, for potassium nitrate dissolving in water.
KNO₃(s) → ______ + ______ [2]
(d) Suggest why distilled water, rather than nutrient solution containing other compounds, is used for this check. [1]

The table below shows an investigation into four solids used in a school collection. The student puts each solid into a circuit, then heats a small sample. Fig. 1 shows an ionic lattice model for magnesium oxide, MgO. Magnesium loses electrons and oxygen gains electrons.

Table 1

(a) Complete the formula for magnesium oxide: Mg__O__. [1]
(b) What is the charge on an oxide ion? [1]
(c) Use Table 1 to name one solid that has metallic bonding. [1]
(d) Suggest why magnesium oxide has a high melting point. [2]

This diagram is a cross-section of a rechargeable battery electrode. The manufacturer uses thin sheets of aluminium because the sheets must conduct electricity and be rolled into a compact cell. Fig. 1 shows metal ions in layers with a sea of electrons between them. The battery is not filled with pure water because water can react during charging.

(a) Name the bonding in aluminium. [1]
(b) Give one property that allows aluminium sheet to be rolled. [1]
(c) Use Fig. 1 to explain why aluminium conducts. [2]
(d) Suggest why aluminium has a higher melting point than a simple molecular substance. [1]

A gas company investigates a small leak from a methane pipe. Fig. 1 shows the dot-and-cross arrangement for methane. Dots and crosses represent outer-shell electrons from different atoms.

(a) Complete the formula for methane: C__H4. [1]
(b) What is the number of covalent bonds in one methane molecule? [1]
(c) Give two safety actions the engineer should take if a methane leak is suspected. [2]
(d) Suggest why methane does not conduct electricity. [2]

Fig. 1 shows a dot-and-cross diagram made by a student for magnesium oxide, used as a lining material in a small furnace.

(a) Complete the formula of magnesium oxide: Mg___ [1]
(b) What type of chemical bond joins the magnesium and oxygen atoms? [1]
(c) Use the diagram to give the number of electrons transferred from each magnesium atom. [1]
(d) Suggest why solid magnesium oxide does not conduct electricity. [1]

A sports company compares materials for the sole of a climbing shoe. Fig. 1 shows a simple molecular model of a rubber-like polymer before and after sulfur links are added between chains. This process is called vulcanising. The links make the material less likely to stretch too far on hot rock.

(a) Name the substance type made from long chains of repeating units. [1]
(b) Suggest why sulfur links make the sole less stretchy. [2]
(c) Give one property, other than being less stretchy, needed for a climbing-shoe sole. [1]

This figure is a dot-and-cross diagram for one molecule of ammonia, NH3, made during the manufacture of fertiliser. Nitrogen and hydrogen are non-metals. The dots are electrons from nitrogen and the crosses are electrons from hydrogen. A technician compares ammonia with an ionic fertiliser before deciding how it should be stored.

(a) Complete the sentence. Each N-H bond is formed by a shared pair of electrons. This is a ______ bond. [1]
(b) What is the total number of hydrogen atoms in two molecules of ammonia? [1]
(c) Suggest why ammonia has a much lower melting point than sodium chloride. [2]

Fig. 1 shows a quality-control flow chart for a company making sodium chloride for saline solution. Rock salt is crushed and mixed with water. Insoluble sand is removed, then water is evaporated from the salt solution to obtain crystals. Samples from the final batch are checked by measuring melting range and by testing whether a solution of the crystals leaves a residue after evaporation. The company needs a pure compound because impurities could affect the medical use of the saline solution.

(a) Name the substance that passes through the filter in Fig. 1. [2]
(b) Give the reason why sand can be separated from sodium chloride solution by filtration. [2]
(c) Use particle ideas to describe what happens to water particles when the salt solution is evaporated. [4]
(d) Suggest two tests or observations that would show the final sodium chloride crystals are pure. [4]

Fig. 1 shows electron-shell diagrams prepared for a lesson on noble gases. Table 1 lists the number of electrons in atoms of helium, neon and argon. The teacher asks the class to use the diagrams to predict their chemical behaviour.

(a) Name the group containing neon. [1]
(b) What does the period number tell you about an atom? [1]
(c) Give one reason why argon is unreactive. [1]
(d) Complete the name of the element with 2 electrons: ______. [1]

The table below shows results from a student who added equal-sized pieces of magnesium, calcium and iron to separate samples of dilute acid. Fig. 1 shows the order of these metals in the student’s reactivity series. The volume of hydrogen was measured after 60 s.

(a) What gas is collected in this reaction? [1]
(b) Use Table 1 to name the metal with the fastest reaction. [1]
(c) Complete the word equation: magnesium + acid → magnesium ______ + hydrogen. [1]
(d) Suggest why the pieces of metal were made the same size. [1]

Fig. 1 shows a food scientist using a burette to measure lactic acid in yoghurt. A 10.0 cm3 yoghurt extract requires 18.60 cm3 of 0.100 mol/dm3 sodium hydroxide solution. The reaction between lactic acid and sodium hydroxide is 1:1.

(a) Give the number of moles of sodium hydroxide used. [2]
(b) What is the number of moles of lactic acid in the extract? [1]
(c) Use the sample volume to calculate the concentration of lactic acid. [2]
(d) Name the piece of apparatus used to deliver the sodium hydroxide accurately. [1]

A student tests a new alloy coin. Fig. 1 shows the coin placed in a measuring cylinder containing water. The water level rises from 42.0 cm3 to 45.5 cm3. The mass of the coin is 28.0 g.

(a) Complete the calculation of the volume of the coin.
volume = ............ cm3 [1]
(b) Use the equation density = mass ÷ volume to calculate the density of the coin. Give your answer to one decimal place. [2]
(c) Suggest why a coin should be made from a hard alloy. [1]
(d) Give one reason why the coin is not made from pure gold. [1]

A recycling centre separates aluminium drinks cans from steel food cans. Fig. 1 shows cans moving on a conveyor belt beneath an electromagnet. The electromagnet is switched on for part of the belt. Table 1 gives the mass of metal collected in one hour.

(a) Name the metal that is attracted to the electromagnet. [1]
(b) Use Table 1 to calculate the total mass of cans collected. [1]
(c) Give one environmental benefit of recycling aluminium. [1]
(d) Suggest why an electromagnet is more useful than a permanent magnet in this machine. [1]