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Chem 123 Lab Final UBC Actual Exam 2026-2027 BANK
QUESTIONS WITH DETAILED VERIFIED ANSWERS EXAM
QUESTIONS WILL COME FROM HERE (100% CORRECT
ANSWERS A+ GRADED
1. In spectrophotometric analysis, what does the term "absorbance"
refer to?
A. The ratio of transmitted light intensity to incident light intensity
B. The negative logarithm of the transmittance
C. The wavelength of maximum absorption
D. The molar absorptivity coefficient
Answer: B
Explanation: Absorbance (A) is defined as A = -log(T), where T is
transmittance (I/I₀). This logarithmic relationship is fundamental to the
Beer-Lambert Law. Option A describes transmittance, C describes
lambda max, and D is a constant in the Beer-Lambert equation.
2. According to the Beer-Lambert Law, absorbance is directly
proportional to which of the following?
A. Transmittance and path length
B. Concentration and path length
C. Wavelength and molar absorptivity
D. Incident light intensity and concentration
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Answer: B
Explanation: The Beer-Lambert Law is A = εbc, where ε is molar
absorptivity, b is path length, and c is concentration. Absorbance is
directly proportional to both concentration and path length.
Transmittance has a negative logarithmic relationship with absorbance.
3. A student measures the absorbance of a solution three times and
obtains values of 0.452, 0.449, and 0.451. These measurements
demonstrate good:
A. Accuracy
B. Precision
C. Sensitivity
D. Specificity
Answer: B
Explanation: Precision refers to the reproducibility of replicate
measurements, indicating random error. The values are close to each
other, showing high precision. Accuracy refers to closeness to the true
value, which is not known from this data alone.
4. What is the primary purpose of using a blank solution in
spectrophotometry?
A. To calibrate the wavelength selector
B. To zero the instrument by accounting for absorbance from solvents
and reagents other than the analyte
C. To increase the molar absorptivity of the analyte
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D. To dilute the sample to a measurable concentration
Answer: B
Explanation: The blank contains all components except the analyte.
Setting the spectrophotometer to zero absorbance with the blank
corrects for light loss due to the cuvette, solvent, and other matrix
components, ensuring that the measured absorbance is solely due to
the analyte.
5. The molar absorptivity (ε) of a compound represents the absorbance
of a 1.0 M solution in a 1.0 cm path length cuvette. If a solution has a
higher ε value, it indicates:
A. A lower analytical sensitivity
B. A higher analytical sensitivity
C. A larger path length is needed
D. The solution is more concentrated
Answer: B
Explanation: Molar absorptivity is a measure of how strongly a chemical
species absorbs light at a given wavelength. A higher ε means a greater
absorbance for the same concentration, translating to better sensitivity
because a smaller change in concentration yields a larger measurable
change in signal.
6. In a titration experiment to determine the Ksp of potassium
hydrogen tartrate, the titrant used is typically:
A. Hydrochloric acid
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B. Sodium hydroxide
C. Potassium chloride
D. Phenolphthalein
Answer: B
Explanation: Potassium hydrogen tartrate (KHT) is an acidic salt. The
hydrogen tartrate ion (HT⁻) is a weak acid and can be titrated with a
strong base, typically a standardized solution of sodium hydroxide
(NaOH), using phenolphthalein as an indicator.
7. The solubility product constant (Ksp) for KHT is expressed as:
A. [K⁺][HT⁻]
B. [KHT] / [K⁺][HT⁻]
C. [K⁺] + [HT⁻]
D. [K⁺][HT⁻] / [KHT]
Answer: A
Explanation: Ksp is the equilibrium constant for the dissolution of a
sparingly soluble salt. For KHT(s) ⇌ K⁺(aq) + HT⁻(aq), the solid is omitted
from the equilibrium expression, so Ksp = [K⁺][HT⁻].
8. A student adds potassium chloride to a saturated solution of KHT.
According to the common ion effect, what will happen to the solubility
of KHT?
A. The solubility will increase
B. The solubility will decrease
Chem 123 Lab Final UBC Actual Exam 2026-2027 BANK
QUESTIONS WITH DETAILED VERIFIED ANSWERS EXAM
QUESTIONS WILL COME FROM HERE (100% CORRECT
ANSWERS A+ GRADED
1. In spectrophotometric analysis, what does the term "absorbance"
refer to?
A. The ratio of transmitted light intensity to incident light intensity
B. The negative logarithm of the transmittance
C. The wavelength of maximum absorption
D. The molar absorptivity coefficient
Answer: B
Explanation: Absorbance (A) is defined as A = -log(T), where T is
transmittance (I/I₀). This logarithmic relationship is fundamental to the
Beer-Lambert Law. Option A describes transmittance, C describes
lambda max, and D is a constant in the Beer-Lambert equation.
2. According to the Beer-Lambert Law, absorbance is directly
proportional to which of the following?
A. Transmittance and path length
B. Concentration and path length
C. Wavelength and molar absorptivity
D. Incident light intensity and concentration
,2|Page
Answer: B
Explanation: The Beer-Lambert Law is A = εbc, where ε is molar
absorptivity, b is path length, and c is concentration. Absorbance is
directly proportional to both concentration and path length.
Transmittance has a negative logarithmic relationship with absorbance.
3. A student measures the absorbance of a solution three times and
obtains values of 0.452, 0.449, and 0.451. These measurements
demonstrate good:
A. Accuracy
B. Precision
C. Sensitivity
D. Specificity
Answer: B
Explanation: Precision refers to the reproducibility of replicate
measurements, indicating random error. The values are close to each
other, showing high precision. Accuracy refers to closeness to the true
value, which is not known from this data alone.
4. What is the primary purpose of using a blank solution in
spectrophotometry?
A. To calibrate the wavelength selector
B. To zero the instrument by accounting for absorbance from solvents
and reagents other than the analyte
C. To increase the molar absorptivity of the analyte
,3|Page
D. To dilute the sample to a measurable concentration
Answer: B
Explanation: The blank contains all components except the analyte.
Setting the spectrophotometer to zero absorbance with the blank
corrects for light loss due to the cuvette, solvent, and other matrix
components, ensuring that the measured absorbance is solely due to
the analyte.
5. The molar absorptivity (ε) of a compound represents the absorbance
of a 1.0 M solution in a 1.0 cm path length cuvette. If a solution has a
higher ε value, it indicates:
A. A lower analytical sensitivity
B. A higher analytical sensitivity
C. A larger path length is needed
D. The solution is more concentrated
Answer: B
Explanation: Molar absorptivity is a measure of how strongly a chemical
species absorbs light at a given wavelength. A higher ε means a greater
absorbance for the same concentration, translating to better sensitivity
because a smaller change in concentration yields a larger measurable
change in signal.
6. In a titration experiment to determine the Ksp of potassium
hydrogen tartrate, the titrant used is typically:
A. Hydrochloric acid
, 4|Page
B. Sodium hydroxide
C. Potassium chloride
D. Phenolphthalein
Answer: B
Explanation: Potassium hydrogen tartrate (KHT) is an acidic salt. The
hydrogen tartrate ion (HT⁻) is a weak acid and can be titrated with a
strong base, typically a standardized solution of sodium hydroxide
(NaOH), using phenolphthalein as an indicator.
7. The solubility product constant (Ksp) for KHT is expressed as:
A. [K⁺][HT⁻]
B. [KHT] / [K⁺][HT⁻]
C. [K⁺] + [HT⁻]
D. [K⁺][HT⁻] / [KHT]
Answer: A
Explanation: Ksp is the equilibrium constant for the dissolution of a
sparingly soluble salt. For KHT(s) ⇌ K⁺(aq) + HT⁻(aq), the solid is omitted
from the equilibrium expression, so Ksp = [K⁺][HT⁻].
8. A student adds potassium chloride to a saturated solution of KHT.
According to the common ion effect, what will happen to the solubility
of KHT?
A. The solubility will increase
B. The solubility will decrease
