CMLA Chemistry Basics 4 — Questions and Answers
Question 1: Which separation technique uses differences in solubility and partitioning between a stationary and mobile phase to separate analytes?
- Electrophoresis
- Centrifugation
- Chromatography (Correct answer)
- Spectrophotometry
Correct answer: Chromatography
Chromatography separates analytes based on their differential affinities for a stationary phase versus a mobile phase.
Question 2: When a chemical reaction reaches equilibrium, which of the following is true?
- The reaction stops completely
- The forward and reverse reaction rates are equal (Correct answer)
- All reactants are consumed
- Only products are present
Correct answer: The forward and reverse reaction rates are equal
At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, so the concentrations of reactants and products remain constant.
Question 3: A spectrophotometer measures absorbance. According to Beer-Lambert Law, absorbance is directly proportional to:
- Temperature and pressure
- Wavelength of light used
- Concentration of the absorbing substance (Correct answer)
- Size of the cuvette
Correct answer: Concentration of the absorbing substance
Beer-Lambert Law states A = εlc, meaning absorbance is directly proportional to the concentration of the analyte.
Question 4: Which of the following is true about a saturated solution?
- It can dissolve more solute without any change
- It contains the maximum amount of dissolved solute at a given temperature (Correct answer)
- It is always a concentrated solution
- It cannot be diluted
Correct answer: It contains the maximum amount of dissolved solute at a given temperature
A saturated solution contains the maximum amount of solute that can dissolve in a solvent at a given temperature and pressure.
Question 5: In the context of laboratory reagents, what does 'hygroscopic' mean?
- The substance is flammable
- The substance absorbs moisture from the air (Correct answer)
- The substance evaporates quickly
- The substance is toxic when inhaled
Correct answer: The substance absorbs moisture from the air
Hygroscopic substances readily absorb and retain water from the surrounding air, which can affect the accuracy of mass-based reagent preparation.
Question 6: What is the purpose of a blank in spectrophotometric analysis?
- To calibrate the instrument to 100% absorbance
- To zero the instrument using a solution containing everything except the analyte (Correct answer)
- To measure the absorbance of the standard
- To dilute the sample before reading
Correct answer: To zero the instrument using a solution containing everything except the analyte
The blank contains all reagents except the analyte and is used to set the baseline absorbance to zero, correcting for reagent and solvent absorbance.
Question 7: Which of the following best describes an exothermic chemical reaction?
- It absorbs heat from the surroundings
- It releases heat into the surroundings (Correct answer)
- It occurs only at low temperatures
- It requires a catalyst to proceed
Correct answer: It releases heat into the surroundings
Exothermic reactions release energy (heat) into the surroundings, resulting in a negative enthalpy change (ΔH < 0).
CMLA Chemistry Basics 4
Which separation technique uses differences in solubility and partitioning between a stationary and mobile phase to separate analytes?