Bburette[1]
A burette measures to the nearest 0.05 cm3, so it can measure 25.15 cm3.
D273 K[1]
Pure water freezes at 0 °C and temperature in K = temperature in °C + 273.
Water displacement or upward delivery. [1]
Calcium oxide (quicklime). [1]
Gas Y reacts with acids, so it cannot be dried with concentrated sulfuric acid.
Remove the insoluble solid Z from the three other substances by filtration. [1]
From the two immiscible layers, use a separating funnel to run off liquid X, the lower layer. [1]
Separate solid Y from its solution in W by evaporation or crystallisation. [1]
DA yellow solid that melts at 60 °C.[1]
A pure substance has a fixed, sharp melting point.
B104 °C[1]
Dissolved salt raises the boiling point of water a little, so the boiling point is just above 100 °C.
Amelting point −39 °C and boiling point 357 °C[1]
BAdd methylbenzene and stir, then filter, then add the residue to water and stir, and then filter this mixture.[1]
Methylbenzene dissolves R only, so the residue is P and Q. Water then dissolves Q only, so the final residue is pure P.
Bto act as a drying agent[1]
Concentrated sulfuric acid absorbs water, so it dries the gases.
Cmeasuring cylinder[1]
Cless dense than air[1]
The apparatus is upward delivery, so gas X must be less dense than air. There is not enough information to deduce its solubility in water.
Aset-up A[1]
Solid Y is insoluble in ethanol, so filtration separates them easily: Y is the residue and ethanol is the filtrate. The boiling points are distractors.
D0.538[1]
Rf of B = 713 = 0.538
A100 °C and a colourless distillate[1]
Only water boils off, so the thermometer at the side arm reads its boiling point, 100 °C, and the distillate is pure, colourless water.
The black dye is impure because there is more than one spot on the chromatogram. [1]
Determine the boiling point or freezing point of the black dye. [1]
If it boils or freezes at a fixed temperature, it is pure. or If it boils or freezes over a range of temperatures, it is not pure. [1]
Dye B is insoluble in the solvent (ethanol). [1]
Dye A [1]
Distance moved by A = 4.0 − 1.5 = 2.5 cm and distance moved by the solvent front = 7.0 − 1.5 = 5.5 cm. Rf = 2.5 ÷ 5.5 = 0.45 [1]
Fractional distillation [1]
Distillation alone is not accepted.
The components have different boiling points. [1]
No. The components are miscible (they mix). [1]
All the dyes must have different solubilities in the same solvent (the mixture of water and ethanol). [1]
The Rf value of the yellow dye in pure water (0% ethanol) is zero, so the yellow dye is insoluble in pure water. [1]
The Rf value of the red dye in pure ethanol (100% ethanol) is zero, so the red dye is insoluble in pure ethanol. [1]
The black dye would not be completely separated into its components if either pure water or pure ethanol were used. [1]
Percentage of ethanol = 32200 × 100% = 16% [1]
So the Rf value of the blue dye is 0.72. [1]
No, the student cannot conclude that the black dye is pure. [1]
The Rf values of the blue, red and yellow dyes are all 0.4 when the solvent is 80% ethanol, so the three dyes give only one spot. [1]
The start line must be drawn in pencil. [1]
The level of the solvent must be below the start line. [1]