STATES OF MATTER
State the name given to the following changes of state:
(a) Solid to gas directly [1 mark]
(b) Gas to liquid [1 mark]
Describe the arrangement and movement of particles in a solid. [2 marks]
(a) Sublimation [1]
(b) Condensation [1]
Arrangement: Regular lattice pattern / packed tightly together [1].
Movement: Vibrate about fixed positions [1].
State the relative mass, relative charge, and location of a proton, neutron, and electron. [5 marks]
Proton: Relative mass 1 [1 mark], relative charge +1 [1 mark], located in the nucleus. Neutron: Relative mass 1, relative charge 0 (neutral) [1 mark], located in the nucleus. Electron: Relative mass 1/1840, relative charge -1 [1 mark], located in electron shells or energy levels. [1 mark]
State the type of bonding present in: a) Sodium chloride [1 mark] b) Methane [1 mark]
Define an ionic bond. [1 mark]
a) Ionic bonding [1 mark] b) Covalent bonding [1 mark]
The strong electrostatic attraction between oppositely charged ions. [1 mark]
State the most appropriate piece of laboratory apparatus used to accurately measure: a) Exactly 25.0 cm3 of a liquid solution. [1 mark] b) 32 cm3 of a gas produced during a reaction. [1 mark]
State the separation technique used to obtain pure water from a sodium chloride solution. [1 mark]
a) Volumetric pipette or burette [1 mark] b) Gas syringe [1 mark]
Simple distillation [1 mark]
State the characteristic flame color produced by each of the following metal cations:
Lithium ion [1 mark]
Sodium ion [1 mark]
Potassium ion [1 mark]
Copper(II) ion [1 mark]
Red or Crimson [1 mark]
Yellow or Orange-yellow [1 mark]
Lilac [1 mark]
Blue-green [1 mark]
A pure solid substance is heated steadily until it boils.
State what happens to the temperature of a pure substance while it is melting. Explain why. [2 marks]
Explain how a cooling curve can be used to distinguish between a pure substance and an impure mixture. [2 marks]
Temperature remains constant [1] because heat energy is used to overcome / break intermolecular forces rather than increasing kinetic energy [1].
A pure substance melts/freezes at a sharp, fixed temperature (flat horizontal region) [1], whereas an impure mixture melts/freezes over a range of temperatures [1].
An atom of sodium has an atomic number of 11 and a mass number of 23.
State the number of protons, neutrons, and electrons in this neutral atom. [3 marks]
Write the electronic configuration for this sodium atom and state its group number in the Periodic Table. [2 marks]
Protons: 11 [1 mark]; Neutrons: 12 [1 mark]; Electrons: 11 [1 mark]
Electronic configuration: 2,8,1 [1 mark]; Group number: Group 1 because it has 1 valence electron. [1 mark]
Compare the melting points and electrical conductivity of sodium chloride and water.
State which substance has the higher melting point and explain why in terms of structure and bonding. [2 marks]
Explain why solid sodium chloride does not conduct electricity, but molten sodium chloride does. [2 marks]
Sodium chloride [1 mark]. It has a giant ionic lattice with strong electrostatic forces of attraction between ions that require a large amount of energy to break. [1 mark]
In solid sodium chloride, the ions are fixed in a lattice and cannot move. [1 mark] In molten sodium chloride, the lattice breaks down and ions are free to move to carry electric charge. [1 mark]
A student is given a solid mixture of insoluble sand and soluble copper(II) sulfate crystals. Describe the steps required to obtain pure, dry samples of both sand and copper(II) sulfate crystals from the mixture. [4 marks]
Add distilled water to the mixture and stir to dissolve the copper(II) sulfate. [1 mark]
Filter the mixture using filter paper and funnel to collect the sand as the residue. [1 mark]
Wash the sand residue with distilled water and dry it in an oven or warm area. [1 mark]
Heat the filtrate (copper sulfate solution) to evaporate water to the point of crystallization, then allow it to cool and form crystals. [1 mark]
Describe the practical test and positive result used to identify each anion:
Carbonate ion [2 marks]
Chloride ion [2 marks]
Test: Add dilute acid (such as hydrochloric acid) and pass the gas produced into limewater. [1 mark] Result: Effervescence occurs and limewater turns cloudy or milky. [1 mark]
Test: Add dilute nitric acid, then add aqueous silver nitrate. [1 mark] Result: A white precipitate forms. [1 mark]
Concentrated ammonia solution NH3 and concentrated hydrochloric acid HCl are placed at opposite ends of a long, sealed glass tube at the same time.
State the chemical name and formula of the white ring that forms inside the tube. [2 marks]
Explain why the white ring forms closer to the hydrochloric acid end of the tube. [2 marks]
Name: Ammonium chloride [1]; Formula: NH4Cl [1].
Ammonia molecules (Mr = 17) have a lower relative molecular mass than hydrogen chloride molecules (Mr = 36.5) [1]. Lighter gas particles move/diffuse faster than heavier particles [1].
Chlorine exists as two naturally occurring isotopes: Chlorine-35 and Chlorine-37.
Define the term isotopes. [2 marks]
Explain why isotopes of the same element have identical chemical properties. [2 marks]
Atoms of the same element with the same number of protons but different numbers of neutrons. [2 marks]
They have the exact same electronic configuration and number of valence electrons [1 mark], which determines how an atom reacts chemically. [1 mark]
Describe the covalent bonding in a molecule of carbon dioxide (CO2) in terms of electron sharing. [3 marks]
The central carbon atom shares a total of 4 pair of electrons (two double bonds) with two oxygen atoms. [1 mark]
Each oxygen atom shares 2 pairs of electrons with the central carbon atom and retains 2 lone pairs of non-bonding electrons. [1 mark]
All atoms achieve a stable octet (8 outer shell electrons). [1 mark]
A food dye sample containing three colored substances is analyzed using paper chromatography.
Explain why the baseline must be drawn in pencil rather than ink. [1 mark]
Explain how an Rf value is determined for a spot on a chromatogram. [2 marks]
State why a locating agent is used when performing chromatography on colorless samples. [1 mark]
Pencil is insoluble in the solvent and will not dissolve or run to contaminate the chromatogram. [1 mark]
Measure the distance moved by the spot from the baseline [1 mark], then divide it by the distance moved by the solvent front from the baseline. [1 mark]
It reacts with colorless spots to produce visible colored spots on the paper. [1 mark]
An unknown aqueous solution X is tested:
Adding aqueous sodium hydroxide produces a light blue precipitate.
Upon adding excess sodium hydroxide, the light blue precipitate remains insoluble.
Adding aqueous ammonia produces a light blue precipitate which dissolves in excess to form a dark blue solution.
Identify the cation present in solution X. [1 mark]
Describe the word equation for the initial precipitate formed when sodium hydroxide is added. [2 marks]
Copper(II) ion [1 mark]
Copper(II) sulfate + Sodium hydroxide -> Copper(II) hydroxide + Sodium sulfate [2 marks]
A sealed syringe contains a fixed mass of gas at room temperature.
Describe and explain, in terms of kinetic theory, what happens to the volume of the gas when the pressure on the plunger is increased at constant temperature. [3 marks]
Describe and explain what happens to the pressure exerted by the gas inside the syringe if the temperature is increased while the volume is kept constant. [3 marks]
Volume decreases [1]. Gas particles are pushed closer together because there are large spaces between gas molecules [1]. The frequency of collisions with the walls increases [1].
Pressure increases [1]. Particles gain kinetic energy and move faster [1], colliding with the container walls more frequently and with greater force [1].
Consider the magnesium ion (Mg2+) with atomic number 12, and the oxide ion (O2-) with atomic number 8.
State the electronic configuration of the Mg2+ ion and the O2- ion. [2 marks]
Explain why both ions are described as being isoelectronic, yet remain different chemical elements. [2 marks]
Mg 2+ ion: 2,8 [1 mark]; O 2- ion: 2,8 [1 mark]
Both ions have the exact same total number of electrons (10 electrons). [1 mark] They are different elements because they have different numbers of protons in their nuclei (Magnesium has 12 protons, Oxygen has 8 protons). [1 mark]
Diamond and graphite are two allotropes of carbon.
Describe the structure and bonding in diamond and explain why it is extremely hard. [2 marks]
Describe the structure and bonding in graphite and explain why it can conduct electricity and act as a lubricant. [3 marks]
Diamond has a giant covalent lattice where each carbon atom is bonded to 4 other carbon atoms tetrahedrally by strong covalent bonds. [1 mark] High energy is required to break this rigid 3D network. [1 mark]
Graphite consists of layers of carbon atoms arranged in hexagonal rings, where each carbon is bonded to 3 other carbons. [1 mark] Conductivity: Each carbon atom has one delocalized electron free to move along the layers to carry charge. [1 mark] Lubricant: Weak intermolecular forces between layers allow them to slide over each other easily. [1 mark]
Crude oil is separated into useful fractions using fractional distillation in a fractionating column.
Explain the principle upon which fractional distillation separates liquids. [2 marks]
Describe how temperature varies along the fractionating column and explain where fractions with lower boiling points are collected. [2 marks]
Liquids in the mixture have different boiling points. [1 mark]
The column is hotter at the bottom and cooler at the top. [1 mark] Components with lower boiling points evaporate first and condense near the top of the column where it is cooler. [1 mark]
Describe tests and positive observations to distinguish between:
Sulfur dioxide gas and Carbon dioxide gas. [3 marks]
Iron(II) and Iron(III) ions in aqueous solution. [2 marks]
Pass both gases into acidified aqueous potassium manganate(VII). [1 mark] Sulfur dioxide turns potassium manganate(VII) from purple to colorless. [1 mark] Carbon dioxide causes no color change in potassium manganate(VII). [1 mark]
Add aqueous sodium hydroxide or aqueous ammonia. [1 mark] Iron(II) forms a green precipitate, whereas Iron(III) forms a red-brown precipitate. [1 mark]
Liquid air at minus 200 degrees Celsius is allowed to warm up slowly in a fractional distillation column. Nitrogen boils at minus 196 degrees Celsius and oxygen boils at minus 183 degrees Celsius. State which gas boils off first and explain why in terms of structure and intermolecular forces. [2 marks]
Nitrogen boils off first. [1 mark] Nitrogen has a lower boiling point because it requires less thermal energy to overcome its weaker intermolecular forces. [1 mark]
Carbon-14 is a radioactive isotope of carbon used in radiocarbon dating.
State the composition of the nucleus of a Carbon-14 atom (atomic number 6). [2 marks]
Explain why isotopes of the same element have slightly different physical properties such as density and rate of diffusion. [2 marks]
6 protons [1 mark] and 8 neutrons [1 mark] in the nucleus.
Physical properties depend on mass. [1 mark] Isotopes have different numbers of neutrons, resulting in different atomic masses. [1 mark]
Describe metallic bonding. [3 marks]
Explain, in terms of structure and bonding: a) Why metals are malleable and ductile. [2 marks] b) Why brass (an alloy of copper and zinc) is harder and less malleable than pure copper. [2 marks]
A lattice of positive metal ions [1 mark] surrounded by a sea of delocalized electrons. [1 mark] Held together by electrostatic attraction between positive ions and delocalized electrons. [1 mark]
a) Layers of positive metal ions can slide over each other [1 mark] without breaking the continuous metallic bond. [1 mark] b) Zinc atoms are a different size compared to copper atoms. [1 mark] This distorts the regular lattice structure, making it harder for layers of ions to slide over one another. [1 mark]
A student investigates the effect of concentration on the rate of reaction between marble chips (calcium carbonate) and dilute hydrochloric acid.
Describe a complete experimental method to measure the rate of this reaction. Include the apparatus used, measurements taken, and variables controlled. [5 marks]
Explain how you would process the collected data to compare rates of reaction for different concentrations. [2 marks]
Apparatus: Conical flask connected to a gas syringe. [1 mark] Procedure: Place a fixed mass of marble chips into the flask, add a set volume of hydrochloric acid. [1 mark] Measurements: Measure the volume of carbon dioxide gas produced at regular time intervals using a timer. [1 mark] Control variables: Keep temperature constant [1 mark] and keep the surface area or size of marble chips identical. [1 mark]
Plot a graph of volume of gas versus time. [1 mark] Compare the steepness or gradient of the initial slope; a steeper slope indicates a faster rate of reaction. [1 mark]
A solid compound Y was analyzed in the laboratory:
Test 1: Heating solid Y produced a colorless gas that relit a glowing splint.
Test 2: Solid Y was dissolved in distilled water. Adding aqueous sodium hydroxide produced a white precipitate that dissolved in excess to form a colorless solution.
Test 3: Adding aqueous ammonia to solution Y produced a white precipitate that also dissolved in excess to form a colorless solution.
Test 4: Adding dilute hydrochloric acid followed by aqueous barium nitrate produced a thick white precipitate.
Identify the systematic chemical name of compound Y and explain the reasoning for each test result. [5 marks]
Test 1: Gas relighting a glowing splint confirms Oxygen gas. [1 mark]
Tests 2 and 3: A white precipitate soluble in excess sodium hydroxide AND soluble in excess ammonia confirms the cation is Zinc. [2 marks]
Test 4: Forming a white precipitate with barium nitrate insoluble in acid confirms the anion is Sulfate. [1 mark]
Identity: Compound Y is Zinc sulfate. [1 mark]