Which of these is a mixture?
Learners' Alley, Matter, Mixtures and Separation slides
What happens to the temperature of a pure liquid while it boils?
Learners' Alley, Matter, Mixtures and Separation slides
Which gas diffuses fastest at the same temperature? Relative molecular masses: chlorine 71, carbon dioxide 44, helium 4, oxygen 32.
Learners' Alley, Matter, Mixtures and Separation slides
Which separation method gives a pure solid from a solution of a substance that decomposes on heating?
Learners' Alley, Matter, Mixtures and Separation slides
A spot has an Rf of 0.40. The solvent front moved 10.0 cm. How far did the spot move?
Learners' Alley, Matter, Mixtures and Separation slides
Salt dissolves in water.
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Learners' Alley, Matter, Mixtures and Separation slides
Substances can be classified as elements, compounds or mixtures. Which underlined substance best represents a mixture?
2024 NASS O Prelim P1-P2 Q8
A student made four statements about elements, compounds and mixtures.
statement 1: Elements are made up of only one type of atom.
statement 2: Compounds have similar properties to the elements they are made of.
statement 3: Little or no energy change is involved when a compound is formed.
statement 4: Mixtures have a fixed ratio of components.
How many of the above statements are correct?
2024 AES O Prelim P1 Q10
A new substance was discovered, and a series of experiments were conducted on it. Which observation suggests that the substance cannot be an element?
2024 Serangoon O Prelim P1 Q4
The conical flask contains compound X which is present in liquid and gaseous states. Which statement is correct?
Source: 2024 Compassvale O Prelim P1 Q4
The rate of diffusion of gas P (Mr = 32) and gas Q (Mr = 64) was compared at 30 °C and 60 °C. Which would have the slowest rate of diffusion?
Source: 2022 CHIJ St Nicholas O EOY P1 Q2
What happens to the molecules when steam condenses to form water?
Source: 2024 Temasek O Prelim P1 Q5
Dry ice sublimes at −78 °C. Which statement describes what happens to dry ice at 0
Source: 2024 SMSS O Sec3 P1 Q3
A mixture is made up of two liquids whose boiling points differ by 52.5 °C. What other information about the liquids is necessary to identify the appropriate method to separate them?
Source: 2024 Bukit View O Prelim P1 Q2
Which statement is correct?
Source: 2024 SKSS O Prelim P1 Q1
The table shows some mixtures and their constituents obtained using suitable separation techniques.
| mixture | constituent obtained | |
|---|---|---|
| 1 | aqueous sodium chloride | water |
| 2 | solid iodine and solid nickel | solid iodine |
| 3 | aqueous sodium chloride | solid sodium chloride |
Which row gives the correct separation techniques to obtain the constituents from the mixture? Each option gives the technique for 1, 2 and 3 in that order.
Source: 2024 Bukit View O Prelim P1 Q4
The boiling points of four substances found in air are given in the table.
| substance | boiling point / °C |
|---|---|
| argon | −186 |
| carbon dioxide | −78 (sublimes) |
| nitrogen | −196 |
| oxygen | −183 |
Air is cooled to −190 °C such that some substances condense into liquid. When the temperature is then raised, which liquid would turn into a gas first?
Source: 2024 BMSS O Prelim P1 Q4
Which statement about chromatography is correct?
Source: 2026 Dunman O Prelim P1 Q1
The table gives the results of chromatography experiments that were carried out on some known food colours, using the same solvent.
| food colour | distance from start line to solvent front / mm | distance moved by food colour spot / mm |
|---|---|---|
| Ponceau 4R | 60 | 42 |
| Carmoisine | 74 | 45 |
| Fast red | 67 | 27 |
| Erythrosine | 58 | 17 |
Which food colour is the most soluble in the solvent used?
Source: 2024 SCGS O Prelim P1 Q3
A chemist is given an unknown white powder. What should the chemist do to determine the purity of the unknown substance?
Source: 2024 Jurongville O Prelim P1 Q5
A liquid is suspected to be pure ethanol. What is the best way to test its purity?
Source: 2025 CCHY O Prelim P1 Q5
Which substance should be pure for the intended use?
Source: 2023 Catholic High School O Prelim P1 Q4
An impure sample of compound X has a melting point of around 120 °C. X is purified and its melting point is measured again. Which row is correct? Each option gives the method of purification, then the melting point of pure X.
Source: 2026 KSS O Prelim P1 Q3
Cair[1]
Air is nitrogen, oxygen, carbon dioxide and other gases that are not chemically combined, and its make-up varies.
Water and carbon dioxide are compounds. Oxygen is an element.
Cit stays constant[1]
The energy goes into overcoming the forces of attraction between the particles, not into raising the temperature.
The temperature rises again only after all the liquid has boiled.
Chelium[1]
Helium has the smallest mass, so its particles move fastest and diffuse fastest.
Chlorine, carbon dioxide and oxygen are all heavier, so they diffuse more slowly.
Bcrystallisation[1]
Crystallisation is gentler. It heats only to a saturated solution, cools it, and gives a pure solid.
Evaporation to dryness would heat the solute until it decomposes. Simple distillation collects the solvent, not the solid. Sieving separates solids by particle size.
B4.0 cm[1]
Rf = distance moved by the spotdistance moved by the solvent front
Distance moved by the spot = 0.40 × 10.0 cm = 4.0 cm
Salt is the solute and water is the solvent.[1]
Its solvent is water.[1]
A mixture: the water and carbon dioxide are not chemically combined, and the amount of carbon dioxide can vary.[1]
Argon (single atoms), nitrogen, N2 (molecules), carbon dioxide, CO2 (compound).[1]
The particles gain energy and overcome the forces of attraction between them, so they move far apart, quickly and randomly.
In the gas the particles are far apart, so it takes up much more space than the closely packed solid.[2]
In a warmer kitchen the particles have more kinetic energy, so they move faster and diffuse faster.[1]
Any two of evaporation, crystallisation, simple distillation, fractional distillation and sublimation.[1]
By the physical property in which the components differ, such as particle size, solubility, or melting and boiling points.[1]
Graphite does not dissolve in the solvent, so the line stays put. Ink would dissolve, run up the paper and its colours would confuse the result.[1]
No. The spot and the solvent front both move further in the longer run, in the same proportion, so the ratio stays the same.[1]
The Rf value of a substance changes with the solvent.[1]
P is a mixture: a pure substance boils at one fixed temperature.[1]
Chromatography (a pure substance gives one spot) and measuring its melting point (a pure substance melts at a fixed temperature).[1]
Dwhite solid that melts from 56 °C to 58 °C[1]
A mixture melts over a range of temperatures. A pure substance, element or compound, melts at one temperature.
The white solid melts from 56 °C to 58 °C, so it is a mixture. The green powder breaks down into simpler substances on heating, so it is a compound. Nothing in A or C shows a mixture.
Aone[1]
Only statement 1 is correct: an element holds one type of atom.
A compound has properties different from those of its elements (2), its formation usually involves a large energy change (3), and a mixture has no fixed ratio (4).
CWhen heated strongly, a brown solid and a yellow gas are produced.[1]
Strong heating breaks the substance down into two simpler substances. An element cannot be broken down into simpler substances by chemical methods, so the substance is a compound.
A fixed boiling point only shows that it is pure. Dissolving does not break it down. Forming oxides means it reacts with oxygen, which an element can do.
AEnergy is gained when X changes from liquid to gas.[1]
Energy is absorbed to overcome the forces of attraction between the particles when a liquid changes to a gas.
A molecule has the same mass in every state. Sublimation is solid to gas, not liquid to gas. Particles in a liquid slide past one another, while vibrating about fixed positions describes a solid.
Cgas Q at 30 °C[1]
A heavier gas diffuses more slowly, and a lower temperature gives slower particles. Gas Q is the heavier gas and 30 °C is the lower temperature.
So the slowest rate is gas Q at 30 °C.
CThe molecules lose energy and move closer together.[1]
When steam condenses, the molecules lose energy, move more slowly and come closer together to form a liquid.
The molecules do not change size, and they do not break up into atoms in a change of state.
BThe carbon dioxide particles become far apart.[1]
0 °C is above the sublimation temperature of −78 °C, so the solid carbon dioxide turns straight into a gas, in which the particles are far apart. The particles do not change size, and they take in energy from the surroundings as the solid sublimes.
Dtheir miscibility[1]
Immiscible liquids form layers and are separated with a separating funnel. Miscible liquids with different boiling points are separated by distillation.
So the method depends on whether the liquids mix. Colour, density and melting point do not decide it.
DA substance that remains in the heated flask after distillation is called a residue.[1]
In distillation the solvent is vaporised and collected, and the solid left in the flask is the residue.
The filtrate is the liquid that passes through the filter paper, not the solid. A saturated solution is one in which no more solute can dissolve. A solution is a mixture, not a compound.
Adistillation, sublimation, evaporation[1]
Water is obtained from sodium chloride solution by distillation, because the solvent has a lower boiling point than the solute.
Iodine sublimes on heating and nickel does not, so sublimation gives solid iodine. Solid sodium chloride is obtained from its solution by evaporating the water.
Filtration separates an insoluble solid from a liquid, so it cannot separate dissolved sodium chloride. Crystallisation does not give iodine from nickel.
Aargon[1]
At −190 °C only the substances that boil above −190 °C are liquids: argon and oxygen. Nitrogen is still a gas and carbon dioxide is a solid.
As the temperature rises, the liquid with the lower boiling point boils first, so argon (−186 °C) turns into a gas before oxygen (−183 °C).
DThe Rf value is a ratio of the distance travelled by a component to the solvent front.[1]
Rf is the distance moved by the substance divided by the distance moved by the solvent front.
The first statement is wrong because Rf depends on the solvent, so a value is only fixed for one substance in one solvent. Locating agents are for colourless substances, not coloured inks. The start line must be above the solvent level, or it would dissolve into the solvent.
APonceau 4R[1]
Rf = distance moved by the spot ÷ distance moved by the solvent front. Ponceau 4R gives 42 ÷ 60 = 0.70, carmoisine 45 ÷ 74 = 0.61, fast red 27 ÷ 67 = 0.40 and erythrosine 17 ÷ 58 = 0.29.
The more soluble a colour is in the solvent, the further it travels with the solvent, so the most soluble colour has the largest Rf value: Ponceau 4R.
Cmeasure its melting point[1]
A pure substance has a specific melting point. A mixture melts over a range of temperatures, so the melting point shows whether the powder is pure.
Burning it, a solubility test and testing conductivity do not show how many substances are present.
Bmeasure its boiling point[1]
A pure liquid boils at one specific temperature under fixed conditions. A mixture boils over a range, so the boiling point shows whether the liquid is pure ethanol.
Burning, reacting with ethanoic acid and testing with litmus paper do not show whether other substances are present.
Aa drug for curing diseases[1]
Impurities in a drug can harm the patient, so a drug must be pure.
Airplane bodies are made from aluminium alloys, petrol is a mixture of hydrocarbons, and tap water contains dissolved substances that are safe to drink.
Bcrystallisation, 125 °C[1]
X melts at about 120 °C, so it is a solid at room temperature. A solid is purified by crystallisation.
Impurities lower the melting point, so pure X melts above 120 °C, at 125 °C.