Use a copy of the Periodic Table where you need one.
Which apparatus is most suitable for measuring 22.15 cm3 of sodium hydroxide?
Source: 2023 GESS Sec 3 End-of-Year P1 Q1
Hexane and water are immiscible liquids. Which method could be used to separate a mixture of hexane and water, and how is the purity of the separated hexane checked?
| method of separation | purity check | |
|---|---|---|
| A | filtration | find the boiling point |
| B | filtration | by sublimation |
| C | use a separating funnel | find the boiling point |
| D | use a separating funnel | by sublimation |
Source: BMSS Prelim 2024 P1 Q2, adapted
Butyl ethanoate and water are two immiscible liquids with similar boiling points. Which method is most suitable to separate a mixture of water and butyl ethanoate?
Source: Broadrick Prelim 2024 P1 Q3
A student wants to separate a mixture of iodine and sodium chloride. Which method should she use?
Source: 2025 TKGS Sec 4 Prelim P1 Q2
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 each method?
| first liquid collected by fractional distillation | first liquid collected using a separating funnel | |
|---|---|---|
| A | Y | Y |
| B | Y | Z |
| C | Z | Y |
| D | Z | Z |
Source: BBSS Prelim 2024 P1 Q4
Which apparatus is most suitable to measure 27.8 cm3 of a solution?
Source: BLSS Prelim 2024 P1 Q3
The measurements from a chromatography experiment using substance F are shown. The diagram is not drawn to scale. What is the Rf value of F?
Source: 2024 CHS Sec 3 End-of-Year Section A Q2
A student accidentally mixed 50 cm3 of water with 50 cm3 of oil. Which method would allow him to obtain 25 cm3 of the oil most easily?
Source: 2024 CHS Sec 3 End-of-Year Section A Q3
Which mixture can be separated by using the set-up below?
Source: 2024 CHS Sec 3 End-of-Year Section A Q5
A sample of black ink contains a mixture of red, blue and yellow dyes. A solvent mixture of ethanol and water can be used to separate the dyes in the black ink. The coloured dyes have different Rf values in solvents with different compositions of ethanol, as shown in the graph in Fig. 7.1.
Source: 2024 SMSS Sec 3 End-of-Year P2 Q2
Four amino acids P, Q, R and S were analysed using paper chromatography with two solvents. Table 8.1 shows the Rf values.
| amino acid | P | Q | R | S |
|---|---|---|---|---|
| Rf in solvent 1 | 0.30 | 0.00 | 0.60 | 0.90 |
| Rf in solvent 2 | 0.60 | 0.52 | 0.25 | 0.85 |
Source: 2025 Compassvale Sec 4 Exp Prelim P2 Q4
Ethanol, C2H5OH, and propylene glycol, C3H8O2, can be separated by fractional distillation. Ethanol has a boiling point of 78 °C and propylene glycol has a boiling point of 188 °C. A thermometer is placed at point T, the top of the fractionating column where the vapour leaves for the condenser.
Source: 2023 HYSS Sec 3 End-of-Year P2 Q2, adapted
An ester is a substance formed by the reaction of an alcohol and an organic acid. Propyl ethanoate is formed by the reaction of propanol (boiling point 97 °C) and ethanoic acid (boiling point 120 °C), with a small amount of concentrated sulfuric acid as a catalyst. The glassware in Figure 1.1 and Figure 1.2 can be used to make the ester, both using the same quantities of chemicals from the start.
| plant acid | Rf value |
|---|---|
| tartaric acid | 0.22 |
| citric acid | 0.30 |
| oxalic acid | 0.36 |
| malic acid | 0.46 |
| succinic acid | 0.60 |
Source: SJI 2020 Year 3 End-of-Year P2 A1
Bburette[1]
A burette measures to the nearest 0.05 cm3. A pipette measures one fixed volume and a measuring cylinder is less accurate.
Cuse a separating funnel, then find the boiling point[1]
Duse a separating funnel[1]
Immiscible liquids form layers, so they are separated with a separating funnel. Their boiling points are similar, so distillation does not work well.
Bsublimation[1]
Iodine changes straight from solid to gas on warming, leaving the sodium chloride behind.
BY by fractional distillation and Z using a separating funnel[1]
The liquid with the lower boiling point, Y, is collected first by fractional distillation. In a separating funnel the denser liquid, Z, is at the bottom and runs off first.
Aburette[1]
B0.61[1]
Rf = distance moved by Fdistance moved by the solvent front = 5590 = 0.61
Duse of a separating funnel[1]
Oil and water are immiscible and form two layers, so a separating funnel separates them.
Ciodine and sodium chloride[1]
The set-up is sublimation. Iodine sublimes and forms crystals on the cold funnel, while sodium chloride stays behind.
The blue dye and the yellow dye both have an Rf value of 0 (or almost 0) in pure water. [1]
There is no (or little) separation of the blue and yellow dyes. [1]
64% ethanol and 36% water [1]
All three dyes have the same Rf value (about 0.4) where the lines cross, so they form one spot.
Rf of the blue dye at 80% ethanol = 0.7 [1]
Distance travelled = 0.7 × 10.0 = 7.0 cm [1]
A locating agent is added to react with the amino acids and form coloured spots. [1]
Ultraviolet light can also be used for substances that show up under it.
S is the most soluble, as its Rf value is the highest in both solvents. [1]
Rf is the distance moved by the spot divided by the distance moved by the solvent, so the highest Rf means it travelled the furthest from the start line. [1]
Solvent 2, as all the amino acids are soluble in solvent 2. [1]
The Rf value of Q in solvent 1 is 0.00, which means it is insoluble in that solvent. [1]
Ethanol [1]
To make sure the condenser is fully filled with water, for more efficient cooling of the vapour into liquid. [1]
To measure the temperature of the vapour entering the condenser, which is the boiling point of the liquid being collected. [1]
No. Water and oil are immiscible. [1]
Propanol is a flammable liquid. or It gives more even heating around the flask. [1]
In Figure 1.2, the vapours escape into the surroundings, so less reactant is available for reaction. [1]
In Figure 1.1, the Liebig condenser condenses the vapours back into the flask, so more reactant is able to react to form more product. [1]
To react with the colourless spots and make them visible (coloured). [1]
Sample 2, as it has moved higher up the paper than sample 1. [1]
Rf = distance travelled by the sampledistance travelled by the solvent front [1]
Sample 1: Rf = 0.20 to 0.24 (with working). It is tartaric acid. [1]
Sample 2: Rf = 0.44 to 0.48 (with working). It is malic acid. [1]