Separation and purification

The apparatus for fractional distillation shown below is being used to separate a mixture of two liquids. The thermometer is absent from the setup. Where should the bulb of the thermometer be positioned?

May/June 2015

The apparatus for fractional distillation shown is being used to separate a mixture of two liquids. One thermometer is not included in the apparatus. At what position should the bulb of the thermometer be placed?

May/June 2015

For questions 3 to 6 inclusive, mark the correct answer by placing a tick (✓) in the box beside it.

May/June 2016

The diagram shows the apparatus for distilling seawater.

May/June 2016

A student uses the apparatus shown to separate hexane, $\text{C}_6\text{H}_{14}$, (b.p. $69^{\circ}\text{C}$) from heptane, $\text{C}_7\text{H}_{16}$, (b.p. $98^{\circ}\text{C}$).

May/June 2016

Since sand does not dissolve in water, whereas sodium chloride does dissolve in water, a beaker containing $10.0\text{ g}$ of a sand and sodium chloride mixture is provided.

May/June 2017

Using the apparatus shown, a student separates propanoic acid (b.p. $141\,^{\circ}\text{C}$) from butanoic acid (b.p. $164\,^{\circ}\text{C}$).

May/June 2017

Which mixture can have its components separated by adding water, stirring, and then filtering?

May/June 2018

Which term correctly names the process of converting seawater into water that is safe to drink?

May/June 2018

By adding water, stirring and then filtering, which mixture can be split into its component substances?

May/June 2018

Mixtures may be separated by different methods, chosen according to the physical properties of the components. A student is given two mixtures.

May/June 2018

A student prepares an aqueous solution of potassium nitrate. She adds dilute nitric acid to an aqueous solution of a salt. State a salt that she could use.

May/June 2018

River water contains numerous impurities. Which process by itself can produce pure water from river water?

May/June 2019

What property of a liquid ester can be used to assess its purity before being used as a food flavouring?

May/June 2021

What series of procedures should be followed to obtain a pure, dry sample of hydrated copper(II) sulfate, $\text{CuSO}_4\cdot5\text{H}_2\text{O}$, from a mixture containing hydrated copper(II) sulfate and calcium carbonate, $\text{CaCO}_3$?

May/June 2021

Which property of a liquid ester can be used to test whether it is pure before being used as a food flavouring?

May/June 2021

Which separation method would produce pure samples of both substances in the mixture?

May/June 2021

The table lists four mixtures, and each mixture contains two substances. The two substances must be separated and collected. Which row is correct?

May/June 2022

A laboratory contains a powdered blend of solid iodine and solid carbon. Iodine is very soluble in hexane and only slightly soluble in water. Carbon is insoluble in both solvents. One portion of the mixture is shaken with hexane. This is $X$. A different portion of the mixture is shaken with water. This is $Y$. Which procedure is used to obtain a pure sample of iodine?

May/June 2023

Which method is used to separate a solid mixture of copper powder and sodium chloride so that pure, solid samples of each compound are obtained?

May/June 2024

A sample of compound $X$ that contains impurities has a melting point of $120\,^{\circ}\text{C}$. $X$ is then purified, and its melting point is measured once more. Which row is correct?

May/June 2025

A student is preparing a sample of aqueous copper(II) sulfate. Excess copper(II) oxide powder is added to warm sulfuric acid, and the mixture is stirred. What apparatus is used to separate aqueous copper(II) sulfate from the extra copper(II) oxide?

May/June 2025

Some power stations rely on the combustion of fossil fuels.

May/June 2025

Q consists of solid magnesium oxide mixed with solid barium sulfate. Magnesium oxide does not dissolve in water. When it reacts with dilute hydrochloric acid, a solution of magnesium chloride is produced. Barium sulfate does not dissolve in water and does not react with dilute hydrochloric acid.

May/June 2025

Q consists of solid copper(II) carbonate mixed with solid lead sulfate. Lead sulfate does not dissolve in water and shows no reaction with dilute sulfuric acid. Copper(II) carbonate is insoluble in water. When it reacts with dilute sulfuric acid, copper(II) sulfate solution is produced.

May/June 2025

Which property of a liquid ester can be used to test whether it is pure before it is used as a food flavouring?

Oct/Nov 2015

The diagram illustrates the fractional distillation of an aqueous solution of ethanol. Which statement accounts for why ethanol is collected as the distillate?

Oct/Nov 2015

Which characteristic of a liquid ester can be measured to test whether it is pure before it is used as a food flavouring?

Oct/Nov 2015

Benzene and cyclohexane are both flammable liquids. They can be blended together without forming separate layers. Their boiling points are very close to one another. Because of this, a mixture of these two liquids is hard to separate by fractional distillation. Why is it hard to separate a mixture of benzene and cyclohexane by fractional distillation?

Oct/Nov 2016

A student produced hydrated copper(II) sulfate crystals by allowing excess insoluble copper(II) oxide to react with dilute sulfuric acid. CuO + H$_2$SO$_4$ + 4H$_2$O $\rightarrow$ CuSO$_4\cdot$5H$_2$O

Oct/Nov 2016

A student uses the apparatus shown to separate a mixture of pentane and hexane. Pentane is collected in the conical flask.

Oct/Nov 2016

Copper(II) oxide and carbon are both black solids, but when Copper(II) oxide is treated with dilute sulfuric acid it forms aqueous copper(II) sulfate, whereas carbon shows no reaction with dilute sulfuric acid.

Oct/Nov 2016

A mixture containing sand and sodium chloride can be separated in three stages. In step 1, water is added to the mixture. The diagram illustrates steps 2 and 3. At which point is pure sodium chloride collected?

Oct/Nov 2017

Fullerenes are solid carbon allotropes. They are present in soot, which also contains other carbon allotropes. Fullerenes dissolve in liquid hydrocarbons such as heptane, whereas the other carbon forms in soot do not dissolve in heptane.

Oct/Nov 2017

Which separation process is used in each of the following? 1 collecting copper(II) sulfate crystals from aqueous copper(II) sulfate 2 collecting ethanol from the fermentation of glucose 3 collecting nitrogen from liquid air

Oct/Nov 2019

Which substance has the property of being soluble in water?

Oct/Nov 2019

Water may be separated from aqueous copper(II) sulfate by using distillation.

Oct/Nov 2019

Carbon and copper(II) oxide are each black solids. Copper(II) oxide reacts with dilute sulfuric acid to give an aqueous solution, whereas carbon neither reacts with nor dissolves in dilute sulfuric acid. In addition, neither carbon nor copper(II) oxide dissolve in water. The mixture contains only carbon and copper(II) oxide.

Oct/Nov 2019

Crude oil (petroleum) is separated into useful fractions by fractional distillation. The places in the fractionating column where fractions X and Y are obtained are shown. Which statement is correct?

Oct/Nov 2020

The sample is a mixture of copper(II) carbonate and carbon. Both substances are solids and are insoluble in water.

Oct/Nov 2020

A student prepares aqueous copper(II) sulfate. The student pours copper(II) oxide powder into warm sulfuric acid in excess and mixes the contents by stirring. Which apparatus should be used to separate aqueous copper(II) sulfate from the extra copper(II) oxide?

Oct/Nov 2021

A mixture containing three liquids is separated using fractional distillation. Which of the following statements are correct?

Oct/Nov 2021

A large number of industries need pure oxygen. How is pure oxygen obtained in large quantities for these purposes?

Oct/Nov 2021

An impure specimen of compound X has a melting point of $120\,^{\circ}\text{C}$. X is then purified, and its melting point is measured once more. Which row is the correct one?

Oct/Nov 2021

A liquid, X, is separated by distillation from a mixture with the apparatus illustrated. While the distillation is taking place, the thermometer shows a temperature between $157\,^{\circ}\text{C}$ and $160\,^{\circ}\text{C}$. Which statement about liquid X is correct?

Oct/Nov 2022

When iron is allowed to react with dilute hydrochloric acid, hydrogen is produced. Because the iron contains impurities, some hydrogen sulfide gas is produced as well. Hydrogen sulfide gas dissolves in water. A mixture of gases can be dried by passing it through concentrated sulfuric acid. Which diagram shows apparatus that is suitable for preparing a pure, dry sample of hydrogen?

Oct/Nov 2022

Petroleum is separated in a fractionating column. Which of the following statements are correct?

Oct/Nov 2024

Sulfur dioxide is produced by warming sodium sulfite with hydrochloric acid. It is an acidic gas and is denser than air. Which arrangement of apparatus is suitable for preparing and collecting a dry sample of sulfur dioxide?

Oct/Nov 2025

A sample consists of two solids, X and Y, with no other substances present. Both X and Y dissolve in water. The student separates X and Y in two stages. Step 1: The student adds the mixture to a beaker of cold water and stirs it. What is step 2?

Oct/Nov 2025