Free Experimental Techniques in Chemistry MCQs with Answers

61. In this laboratory setup for distillation, where does the vaporization take place?

• A. Around the thermometer
• B. In the condenser
• C. In the circulating water
• D. In the heated flask

Explanation: Distillation is described as a two-step process: Vaporization → Condensation. For vaporization to happen, you need a heat source. In a laboratory, this heat is applied directly to the round-bottom flask containing your mixture. As the liquid reaches its boiling point, it turns into vapor and rises. The rest of the equipment is simply there to guide that vapor (distillation head), measure it (thermometer), and cool it back down (condenser) so you can collect it as a pure liquid in the receiving flask.

62. If the liquid being distilled contains dissolved magnesium chloride, where will it be found after distillation is completed?

• A. Around the thermometer
• B. In the condenser
• C. In the circulating water
• D. In the heated flask

Explanation: Distillation is used to separate a volatile liquid (like water) from a non-volatile solid (like magnesium chloride). Think of it as a "purification" step. Because the salt is held together by very strong ionic bonds, it requires thousands of degrees to turn into a gas. Since we only heat the flask to the boiling point of water, the water "escapes" as steam while the salt is "trapped" in the boiling flask. By the end of the experiment, all the water will be in the receiving beaker, and all the magnesium chloride will be left behind as a dry residue in the original flask.

63. If the flame used to heat a flask is an orange color and blackens the bottom of the flask, what correction should you make to solve this problem?

• A. Move the flask farther from the flame.
• B. Move the flask closer to the flame.
• C. Allow less air into the collar of the burner.
• D. Allow more air into the collar of the burner.

Explanation: An orange, sooty flame indicates incomplete combustion due to insufficient oxygen. Opening the collar of the Bunsen burner allows more air to mix with the gas, resulting in a hotter, cleaner, blue flame.

64. If an HCl solution has a concentration of 0.1 M and it requires 30 mL to reach the end point, and during the titration, 15 mL of NaOH solution is used, what is the molarity of the NaOH solution?

• A. 0.1 M
• B. 0.2 M
• C. 0.3 M
• D. 1 M

Explanation: Using the titration formula M1V1=M2V2 for the acid and base. Plugging in the values gives (0.1 M) (30 mL)= Mbase(15 mL). Solving for the molarity of the base yields Mbase= (0.1×30)/15=0.2 M.

65. Which of these choices is the proper way to dilute a concentrated acid?

• A. Add concentrated acid to water slowly, following the appropriate safety protocols.
• B. Add water to the concentrated acid slowly.
• C. Carefully return unused or excess chemicals to their original containers.
• D. Flush eyes with water at the eyewash fountain for at least 15 minutes, then report the accident for further help.

Explanation: Add concentrated acid to water slowly, following the appropriate safety protocols. Adding acid to water ensures controlled heat release, preventing splattering. Adding water to concentrated acid can cause violent exothermic reactions. Always follow proper safety protocols when diluting acids.

66. How do you properly dispose of chemicals not needed in the experiment?

• A. The rule is to add concentrated acid to water slowly.
• B. The rule is to add water to the concentrated acid slowly.
• C. Carefully replace unused or excess chemicals into their properly labeled containers from which they came.
• D. Flush eyes with water at the eyewash fountain for at least 15 minutes, and then report the accident for further help.
• E. Dispose of chemicals in the proper places and following posted procedures. Do not return them to their original containers.

Explanation: You never return chemicals or solutions to their original containers for fear of contaminating the original source.

67. The separation of components of liquid on the basis of their boiling points is called as?

• A. Destructive distillation
• B. Fractional distillation
• C. Vacuum distillation
• D. Partial distillation

Explanation: Destructive distillation is a process that involves heating organic material in the absence of air or oxygen to break it down into simpler chemical compounds. Fractional distillation is a process used to separate a mixture of two or more liquids with different boiling points. This process relies on the fact that each liquid in the mixture has its own unique boiling point. Vacuum distillation is a type of distillation used to separate materials with high boiling points or those that are sensitive to heat. In vacuum distillation, the pressure inside the distillation apparatus is lowered, which reduces the boiling point of the material being distilled. There is no such term as partial distillation.

68. What are the products of destructive distillation of coal?

• A. Coal tar
• B. Coke
• C. Coal gas
• D. All of above

Explanation: Destructive distillation is a chemical process in which decomposition is achieved by heating to a high temperature; the term generally applies to the processing of organic material in the absence of air or in the presence of limited amounts of oxygen. The process breaks up large molecules. 'Coke, coal gas, gaseous carbon, coal tar, ammonia liquor ,and coal oil' are examples of commercial products historically produced by the destructive distillation of coal.

69. Rectified spirit is converted into the absolute alcohol by _.

• A. Crystallization
• B. Distillation
• C. Re-distillation
• D. Fractional distillation

Explanation: c) Re-distillation: Re-distillation is essentially the same as distillation. It is the process of distilling a liquid multiple times to achieve higher purity. In the case of converting rectified spirit into absolute alcohol, the process would involve re-distillation.

70. In a vacuum distillation the boiling point of glycerin is reduced to _?

• A. 290°C
• B. 110°C
• C. 156°C
• D. 210°C

Explanation: Correct option is D. Under vacuum, the boiling temperature of glycerin decreases to 210°C at 50 torr. It is distilled at this temperature without decomposition for purification. Vacuum distillation is the distillation carried on under reduced pressure so that the liquid being distilled boils at a lower temperature than under atmospheric pressure and consequently with less chance of decomposition compared to molecular distillation.