Experimental Chemistry：练习题

Which piece of apparatus is most suitable for measuring exactly \(25.0\text{ cm}^3\) of an aqueous solution during a titration?

Four samples of food dyes, W, X, Y, and Z, were analysed using paper chromatography alongside an illegal dye, D. The resulting chromatogram is shown in the diagram.

Which food sample contains the illegal dye D?

A student needs to separate a solid mixture of ammonium chloride and sodium chloride to obtain pure dry samples of each. Knowing that ammonium chloride sublimes upon heating while sodium chloride does not, which sequence of experimental steps is most effective?

Which method is most suitable for separating an insoluble solid, such as sand, from a liquid?

Which separation method is most suitable for separating a mixture of ethanol and water?

State the separation technique used to obtain pure water from a solution of sodium chloride.

A liquid mixture containing two miscible liquids, \(X\) (boiling point \(78^{\circ}\text{C}\)) and \(Y\) (boiling point \(118^{\circ}\text{C}\)), is contaminated with a soluble solid impurity \(Z\). A student attempts to purify the mixture using fractional distillation followed by purity verification.

Which of the following procedural steps and observations is scientifically correct?

A) During fractional distillation, liquid \(Y\) with the higher boiling point will be collected first at the top of the fractionating column because its vapour condenses more readily.

B) The presence of solid impurity \(Z\) will cause the melting point of the extracted solid component to be sharp and occur at a higher temperature than the pure substance.

C) Fractional distillation separates \(X\) and \(Y\) based on differences in their boiling points, where glass beads in the fractionating column provide a large surface area for repeated condensation and vapourisation.

D) Paper chromatography of the collected distillate using water as a solvent will show multiple spots for pure liquid \(X\), confirming its identity through comparison with \(R_f\) values.

A student is provided with a solid mixture containing sodium chloride (table salt) and sand. The student plans to obtain pure, dry samples of both solid sand and sodium chloride crystals from this mixture.

(a) Name the solvent that should be added to dissolve one component of the mixture.
(b) Name the separation technique used to separate the sand from the resulting mixture.
(c) Describe how pure, dry crystals of sodium chloride can be obtained from the filtrate.