Free Experimental Techniques in Chemistry MCQs with Answers

21. What is the correction to the atmospheric pressure due to the 40.8 mm height of the solution in the tube and above the level in the beaker?

• A. 3.0 mm Hg
• B. 6.0 mm Hg
• C. 13.6 mm Hg
• D. 27.2 mm Hg
• E. 40.8 mm Hg

Explanation: The 40.8 mm of water being held up in the tube by atmospheric pressure can be changed to its equivalent height of mercury by dividing it by 13.6, since 1 mm of Hg = 13.6 mm of water. By correcting the atmospheric pressure, we get: 730 mm Hg - 3 mm Hg = 727 mm Hg.

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

• 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: Option b, "The rule is to add water to the concentrated acid slowly," is correct because when diluting a concentrated acid, it's crucial to add water to the acid slowly. This helps prevent the solution from becoming too hot, potentially causing splattering or even a violent reaction. It also ensures that the acid is evenly distributed and diluted.

23. What instrument is used in chemistry labs to measure the molarity of a coloured solution by measuring the light transmitted through it?

• A. Electronic gravimetric balance
• B. pH meter
• C. Spectrophotometer
• D. Computer assisted probes
• E. Galvanometer

Explanation: Option c, "Spectrophotometer," is correct because it is the instrument used in chemistry labs to measure the molarity of a colored solution by quantifying the amount of light transmitted through it. Spectrophotometers work on the principle that different substances absorb light at specific wavelengths, which allows for the determination of concentration based on the amount of light absorbed. One of the new technological additions to chemistry labs is the spectron 20 (a spectrophotometer) that uses the absorption of light waves to do qualitative and quantitative investigations in the lab.

24. Which instrument is used to measure the mass of a substance accurately in the laboratory?

• A. Measuring cylinder
• B. Thermometer
• C. Electronic balance
• D. Burette

Explanation: An electronic balance is used to measure mass accurately. It gives readings in grams or milligrams. Other instruments measure volume or temperature, not mass.

25. What is the main purpose of a burette in titration?

• A. To heat solutions
• B. To measure temperature
• C. To deliver accurate volumes of solution
• D. To measure mass

Explanation: A burette is used to add solution drop by drop. It helps in measuring precise volumes during titration. This ensures accurate calculation of concentration.

26. Solvent extraction is an equilibrium process and it is controlled by:

• A. Law of mass action
• B. The amount of solvent used
• C. Distribution law
• D. The amount of solute

Explanation: Solvent extraction is governed by the Distribution Law. This law states that a solute will distribute itself between two immiscible solvents in a constant ratio of concentrations at equilibrium, based on its relative solubility in each.

27. Which technique is used to separate a solid dissolved in a liquid?

• A. Filtration
• B. Distillation
• C. Evaporation
• D. Decantation

Explanation: Evaporation removes the liquid by heating. The solid remains. as residue, It is commonly used to obtain salt from salt solution.

28. Which of the following is true about filtration?

• A. It separates soluble substances from insoluble ones
• B. It separates insoluble solids from liquids
• C. It separates gases from liquids
• D. It separates mixtures based on boiling points

Explanation: Filtration is used to remove solid particles from a liquid by passing the mixture through filter paper. The solid is retained on the filter while the liquid passes through as filtrate.

29. If the liquid being distilled contains dissolved ammonia gas, 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: The behavior of a substance during distillation depends on its volatility. Ammonia is a gas at room temperature and only stays in water because it is "dissolved." When you heat the mixture in the flask, the ammonia molecules gain energy and escape the liquid almost immediately. They travel as a gas into the condenser, where the cold temperature turns the water vapor back into liquid. Because ammonia loves water (high solubility), it dissolves right back into those fresh water drops and ends up in the collection beaker.

30. In the titration setup, if you introduce 15 mL of the NaOH with an unknown molarity into the flask and then add 5 drops of phenolphthalein indicator, what will you observe?

• A. A pinkish color will appear throughout the solution.
• B. A blue color will appear throughout the solution.
• C. There will be a temporary pinkish color that will dissipate.
• D. There will be a temporary blue color that will dissipate.

Explanation: Sodium hydroxide (NaOH) is a strong base. Phenolphthalein. indicator is colorless in acidic/neutral solutions but turns a distinct pink color in basic solutions (pH > 8.2). Therefore, adding it to NaOH will result in a pink solution.