Principles of Chemistry

State whether iron, sulfur, iron sulfide, and a mixture of iron and sulfur are elements, compounds or mixtures.

Describe a physical method you could use to separate the iron filings from the sulfur powder in the mixture.

Explain why you cannot separate iron sulfide into iron and sulfur by a physical method.

Explain how you could use melting point to decide if the sample is pure or a mixture.

The student finds the melting point is between 127°C to 134°C. What does this suggest about the sample? Give a reason.

Suggest a separation technique the student could use to obtain pure aspirin from this sample, and briefly describe how it works.

State whether the resulting solution is a pure substance, a compound, or a mixture. Give a reason.

The boiling point of pure water is 100°C. Adding the salt changes the boiling point to 100.2°C. Calculate the increase in boiling point.

Suggest a separation technique you could use to obtain pure water from this solution. State the process and what happens during it.

State what is meant by a pure substance in terms of melting and boiling points.

Water is mixed with some sugar. Describe what happens to its melting point and boiling point, compared to pure water.

Name one method that could be used to separate the sugar from the water and briefly describe how it works.

Sample A consists only of nitrogen gas. Sample B contains sodium chloride crystals. Sample C is a solution made by dissolving food dye in water. Classify each sample as an element, compound, or mixture.

The chemist uses paper chromatography to separate the dyes in Sample C. After running the experiment, she observes three coloured spots at different distances from the pencil line. What does this result tell you about the composition of Sample C?

Explain how you could use the chromatogram to identify if Sample C contains the same dyes as a reference mixture of known dyes.

Describe how the scientist can use the appearance of the chromatogram to decide if each sample is a pure substance or a mixture.

The scientist measures the distances on the chromatogram for one spot as follows: Distance from pencil line to spot centre: 2.4 cm Distance from pencil line to solvent front: 4.0 cm Calculate the Rf value for this spot. Show your working.

Give the definitions for (i) element, (ii) compound, and (iii) mixture.

Describe how the student could use melting point measurements to determine whether Sample X is pure or a mixture.

The student performs a paper chromatography experiment with a spot of Sample X and three reference dyes A, B and C on the same chromatography paper. The chromatogram is developed using a suitable solvent.

The diagram below shows the results.

The solvent front has moved 6.0 cm from the pencil line. The spots are found at the following distances above the pencil line: Sample X: 2.0 cm, 4.5 cm Dye A: 2.0 cm Dye B: 4.5 cm Dye C: 3.7 cm

Calculate the R_f value for the spot at 3.7 cm. Show your working.

Explain what the melting point results show about whether sample X is a pure substance or a mixture.

Describe how paper chromatography was carried out in this investigation. Include the key steps.

Use the chromatogram to identify which dyes are present in sample X. State your reasoning.

Calculate the R_f value for the dye in sample X that matches Dye B. Give your answer to two decimal places.

State two differences between a mixture and a compound, using the chemist’s powder as an example.

The chemist dissolves a small amount of the powder in water and runs a paper chromatography experiment alongside three known food dyes (dye A, dye B and dye C). The chromatogram below was produced: