Elements Compounds And Mixtures
Pure iron, sea water, and carbon dioxide are classified respectively as:
A student heats a sample of an unknown substance and records its temperature over time. The heating curve shows a sloped section where the substance changes from solid to liquid. What does this indicate about the substance?
Which separation technique would be most appropriate to obtain pure water from a solution of sodium chloride in water?
During fractional distillation of a mixture of ethanol and water, ethanol is collected first. Which statement correctly explains why?
State the purpose of the fractionating column in fractional distillation.
During filtration, a student separates a mixture of sand and water. Which row correctly identifies the filtrate and the residue?
A student is obtaining copper sulfate crystals from copper sulfate solution by crystallisation. Explain why the solution should not be heated to dryness.
In paper chromatography, why must the baseline be drawn in pencil rather than pen?
A food colouring produces four distinct spots on a chromatogram, while a reference dye produces one spot. What can be concluded?
A spot on a chromatogram has moved 5.4 cm from the baseline. The solvent front has moved 9.0 cm from the baseline. Calculate the Rꜰ value.
A chemist analyses a liquid sample and finds it boils at exactly 100 °C throughout the entire change of state. Which conclusion is correct?
Sodium is a reactive metal and chlorine is a toxic gas. However, sodium chloride is safe to eat. Which statement best explains this observation?
A student sets up a simple distillation apparatus but connects the cold water so it enters at the top of the condenser and exits at the bottom. Suggest why this reduces the efficiency of condensation.
A compound can only be separated into its elements by a chemical reaction. Which statement correctly explains why?
During a crystallisation experiment, a student tests for saturation by dipping a glass rod into the hot solution. Small crystals form on the rod. What should the student do next?
A student performs paper chromatography and notices that one of the spots has remained on the baseline and has not moved at all. Which explanation is correct?
A student calculates the Rꜰ value of substance X in solvent A and obtains 0.65. Another student calculates the Rꜰ value of substance Y in solvent B and obtains 0.65. Can the students conclude that X and Y are the same substance?
A spot on a chromatogram has moved 2.8 cm from the baseline. The solvent front has moved 8.0 cm from the baseline. Calculate the Rꜰ value.
In the paper chromatography practical, a student places the chromatography paper into the beaker but the solvent level is above the pencil baseline. Suggest what will happen and why.
A mountain climber at high altitude boils water and finds it boils at 85 °C instead of 100 °C. A student claims this proves the water is impure. Evaluate this claim.