7. A student conducts a chromatography experiment and needs to prepare 100.0 mL of 0.340 M NaCl(aq) — Solution Preparation, Chromatography Chemistry Question
Problem Context
- A student conducts a chromatography experiment and needs to prepare 100.0 mL of 0.340 M NaCl(aq) to use as the solvent.
(a) Calculate the mass of solid NaCl (molar mass 58.44 g/ mol) needed to prepare the 100.0 mL of 0.340 M NaCl(aq).
Model Answer
0.1000 L × (0.340 mol / 1 L) × (58.44 g / 1 mol) = 1.99 g NaCl [1].
(b) In the following table, briefly list the additional steps necessary to prepare the 100.0 mL of 0.340 M NaCl(aq) solution using only materials selected from the choices given. Assume that all appropriate safety measures are already in place. Not all materials in the list may be needed.
• Solid NaCl
• Balance
• Pipet
• Distilled water
• 100.0 mL volumetric flask
• 150 mL beakers
• Weighing paper and scoop
• 50.0 mL graduated cylinder
• Chromatography paper
Model Answer
For step 2: Combine the solid NaCl and some distilled water in a 100.0
mL volumetric flask [1]. For step 4: Fill the volumetric flask with distilled
water to the calibration (100.0 mL) mark [1].
The student uses the NaCl(aq) solvent to separate a mixture of compounds X and Y in a chromatography experiment. After 30 minutes, the student removes the chromatography paper from the chamber. The results of the experiment are shown.
(c) A second student conducts the same chromatography experiment but removes the chromatography paper from the chamber after 15 minutes instead of 30 minutes. Predict the effect, if any, this would have on the separation distance between compounds X and Y in the new experiment. Explain your reasoning.
Model Answer
It would decrease. The solvent front will not travel as far in the
second experiment, so the separation will be smaller [2].
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