Matter, Mixtures and Separation

Which diagram represents a mixture of compounds?

The following diagrams can be used to illustrate

1 a mixture of elements and compounds
2 a mixture of elements
3 molecules of an element
4 molecules of a compound

What is the correct order of the diagrams? Each option gives the diagrams for 1, 2, 3 and 4 in that order.

The melting and boiling points of five substances are tabulated.

At which temperature would two liquids exist?

In a change of state at constant temperature and pressure:

• energy is released as stronger forces of attraction form between the particles
• the average distance between the particles changes very little.

Which change of state is being described?

The melting points and boiling points of four elements are shown.

In which elements are the particles far apart at 0 °C?

Hydrogen sulfide, H₂S, is a colourless and poisonous gas. The melting point of hydrogen sulfide is −82 °C and the boiling point is −60 °C. Which statement correctly describes the particles of hydrogen sulfide at −75 °C?

The melting points and the boiling points of four substances are listed in the table.

Which substance exists as a liquid at −90 °C?

A sample of clean, dry air is cooled to −190 °C. The carbon dioxide forms a solid at −79 °C.

What is the state of argon, oxygen and nitrogen at −190 °C? Each option gives the state of argon, oxygen and nitrogen in that order.

A mixture of propane, butane, hydrogen sulfide and carbon dioxide at –30 °C is allowed to cool down gradually to –200 °C.

Which compound can be solidified first?

Small crystals of purple KMnO₄ (M_r = 158) and orange K₂Cr₂O₇ (M_r = 294) were placed at the centres of separate petri dishes filled with agar jelly. They were left to stand under the same physical conditions. After some time, the colour of each substance had spread out as shown.

The lengths of the arrows indicate the relative distances travelled by particles of each substance. Which statement is correct?

The table gives the densities and boiling points of five solvents.

What is the best method to separate liquids II and V?

Three separations are listed.

1 obtaining ethanol from a mixture of water and ethanol
2 obtaining water from a mixture of oil and water
3 obtaining water from calcium chloride solution

Which techniques would be involved in these separations? Each option gives the technique for 1, 2 and 3 in that order.

A liquid mixture of Y and Z is separated. Liquids Y and Z are immiscible. Y has a lower boiling point than Z. Y has a lower density than Z. Y and Z can be separated from each other both by fractional distillation and by using a separating funnel.

Which row correctly gives the first liquid to be collected by fractional distillation and by using a separating funnel? Each option gives the first liquid by fractional distillation, then the first liquid using the separating funnel.

Aqueous iron(II) sulfate, a pale green solution, is distilled using the set-up shown.

What is the temperature shown by the thermometer and the colour of the distillate in the conical flask?

A student carried out an experiment using the set-up shown to separate a mixture containing four alcohols.

The boiling points of the four alcohols used are: butanol 117 °C, ethanol 79 °C, pentanol 138 °C and propanol 97 °C.

Despite repeated attempts, the student only managed to obtain two alcohols from the mixture. Which alcohols did he fail to obtain?

Four statements about a mixture containing X, Y and Z are given.

1 X and Y are miscible liquids.
2 Z is soluble in X but not in Y.
3 Y has a lower boiling point than X or Z.
4 Z will decompose upon heating.

Which row correctly lists the steps required to separate all three substances?

Salicylic acid is a substance used in skin ointments and a sample of it is found to contain impurities like iron and sodium iodide. Salicylic acid sublimes at 76 °C and is soluble in water.

What is the best method to obtain pure salicylic acid from the sample?

A laboratory assistant has a mixture of solid sulfur and solid carbon. Sulfur is very soluble in carbon disulfide (boiling point 46 °C) and slightly soluble in water. Carbon is insoluble in both solvents.

A sample of the mixture is shaken with water. This is P. Another sample of the mixture is shaken with carbon disulfide. This is Q. Which procedure is used to prepare a pure sample of sulfur?

Thin layer chromatography (TLC) separates molecules in a mixture by their affinity for the stationary phase (the plate) and the mobile phase (the solvent). The less polar molecules move further up the plate than more polar molecules. Distances are in mm.

R_f = distance moved by molecule ÷ distance moved by solvent front, in a particular solvent. The mixture contains W, X, Y and Z, shown beside the plate.

What is the R_f of molecule Y?

The R_f values for the colours E, F, G and H in four different solvents are shown in the table.

Which solvent could be used to separate a mixture of all four colours E, F, G and H?

The R_f values of some substances are shown below. The solvent used is ethanol.

Which of the following cannot be concluded from the R_f value of X?

The chromatogram obtained from a chromatography experiment on substance S is shown.

What is the R_f value of S?

A food colouring is analysed by paper chromatography.

From its chromatogram, what is the R_f value of the least soluble dye?

The diagram shows the chromatogram of four substances, W, X, Y and Z.

Which statement is correct?

A chromatography experiment was done on a brand of food colouring to determine the number of coloured dyes present. Chromatogram A shows the separation of the dyes using water as a solvent. It is then rotated clockwise 90° and placed in ethanol as a solvent, as shown in chromatogram B.