CHEM 123 LAB FINAL UBC ACTUAL EXAM QUESTIONS AND ANSWERS
PRACTICE QUESTIONS WITH SOLUTIONS NEWEST | ALREADY GRADED
A+/NEWEST UPDATE!!!
1. During a CHEM 123 laboratory investigation, a student is instructed to
determine the concentration of an unknown solution by titrating it with a
standardized solution. The student records the initial and final burette
readings carefully and uses the stoichiometric relationship between the
reactants. Which laboratory skill is most directly demonstrated by this
procedure?
A. Qualitative identification based solely on color
B. Gravimetric separation of an insoluble solid
C. Quantitative volumetric analysis using a titration
D. Spectroscopic identification of an unknown compound
Answer: C
2. A student obtains three burette readings of 18.42 mL, 18.39 mL, and 18.41
mL for repeated titrations of the same sample. Which conclusion is most
appropriate about these results?
A. The measurements demonstrate good precision because they are closely
grouped
B. The measurements demonstrate poor precision because none is exactly
18.40 mL
C. The results are necessarily accurate because they agree closely
D. The data cannot be evaluated because three trials are insufficient
Answer: A
3. While performing a titration, a student reads the bottom of the meniscus
from above the level of the liquid rather than at eye level. What type of
error is most likely introduced?
A. Random error caused by fluctuations in temperature
B. Systematic reading error caused by parallax
C. Chemical error caused by an incorrect stoichiometric coefficient
pg. 1
, D. Instrument calibration error caused by the balance
Answer: B
4. A student needs to transfer exactly 25.00 mL of a solution into an
Erlenmeyer flask for a quantitative analysis. Which piece of glassware is
specifically designed to deliver a highly accurate fixed volume?
A. Beaker
B. Graduated cylinder
C. Erlenmeyer flask
D. Volumetric pipette
Answer: D
5. A student fills a burette with titrant and notices an air bubble trapped in the
burette tip before beginning the titration. If the bubble remains during the
initial reading and disappears during delivery, what is the principal concern?
A. The delivered volume indicated by the burette will not correspond
accurately to the volume entering the sample
B. The titrant concentration will automatically double
C. The endpoint will become independent of the indicator
D. The burette will become calibrated automatically
Answer: A
6. A CHEM 123 student is asked to rinse a burette with a small amount of the
solution that will subsequently be placed into it rather than rinsing it only
with distilled water. What is the main reason for this procedure?
A. To increase the volume capacity of the burette
B. To prevent residual water from diluting the titrant
C. To remove all dissolved oxygen from the titrant
D. To make the titrant more acidic
Answer: B
7. During a titration, a student adds titrant rapidly while approaching the
expected endpoint and accidentally passes the endpoint. What is the most
likely effect on the calculated unknown concentration?
A. The calculation becomes more precise because additional titrant
pg. 2
, improves the signal
B. The excess titrant can cause the measured endpoint volume to be too
large, producing an incorrect calculated concentration
C. The excess titrant has no effect on the calculation
D. The sample concentration becomes chemically standardized by the
overshoot
Answer: B
8. A student is preparing a standard solution from a solid reagent using a
volumetric flask. After dissolving the solid, the student fills the flask to the
calibration mark and mixes thoroughly. Why is the calibration mark
important?
A. It identifies the temperature at which the solution must be stored
B. It establishes a known final solution volume for calculating concentration
C. It determines the molecular mass of the solute
D. It prevents the solute from reacting with water
Answer: B
9. A student accidentally fills a volumetric flask above its calibration line while
preparing a standard solution. What is the most likely consequence?
A. The final solution volume is greater than intended, so the concentration
is lower than calculated from the intended volume
B. The solution concentration is automatically increased
C. The solute becomes completely insoluble
D. The molecular weight of the solute changes
Answer: A
10. In an acid-base titration, an indicator changes color over a limited pH range.
Why must the indicator be selected appropriately?
A. Its color change should occur near the equivalence-point region so the
endpoint approximates the stoichiometric equivalence point
B. Its color change should occur only at pH 7 regardless of the reaction
C. The indicator must chemically consume all of the acid
pg. 3
, D. The indicator must have the same concentration as the titrant
Answer: A
11. A student titrates a weak acid with a strong base and chooses an indicator
whose transition range is substantially below the expected equivalence-
point pH. What problem could result?
A. The endpoint may occur before the stoichiometric equivalence point is
reached
B. The titration will necessarily become more accurate
C. The indicator will increase the acid's Ka
D. The equivalence point will disappear
Answer: A
12. A student performs a titration using phenolphthalein and observes a faint
pink color that persists after swirling. What does this observation generally
indicate in a properly selected titration?
A. The solution has definitely reached pH 14
B. The endpoint has approximately been reached
C. All solvent has evaporated
D. The acid has been completely removed from the laboratory
Answer: B
13. A student is determining the concentration of an acid using a standardized
NaOH solution. If the balanced equation shows a 1:1 molar relationship
between the acid and NaOH, which relationship is appropriate at
equivalence?
A. Moles of acid equal moles of NaOH delivered
B. Mass of acid equals mass of NaOH delivered
C. Volume of acid equals volume of NaOH delivered
D. Concentration of acid equals concentration of NaOH regardless of
volume
Answer: A
14. A 0.1000 M NaOH solution is used to titrate 25.00 mL of a monoprotic acid.
If equivalence occurs after 20.00 mL of NaOH is delivered, what is the acid
pg. 4
PRACTICE QUESTIONS WITH SOLUTIONS NEWEST | ALREADY GRADED
A+/NEWEST UPDATE!!!
1. During a CHEM 123 laboratory investigation, a student is instructed to
determine the concentration of an unknown solution by titrating it with a
standardized solution. The student records the initial and final burette
readings carefully and uses the stoichiometric relationship between the
reactants. Which laboratory skill is most directly demonstrated by this
procedure?
A. Qualitative identification based solely on color
B. Gravimetric separation of an insoluble solid
C. Quantitative volumetric analysis using a titration
D. Spectroscopic identification of an unknown compound
Answer: C
2. A student obtains three burette readings of 18.42 mL, 18.39 mL, and 18.41
mL for repeated titrations of the same sample. Which conclusion is most
appropriate about these results?
A. The measurements demonstrate good precision because they are closely
grouped
B. The measurements demonstrate poor precision because none is exactly
18.40 mL
C. The results are necessarily accurate because they agree closely
D. The data cannot be evaluated because three trials are insufficient
Answer: A
3. While performing a titration, a student reads the bottom of the meniscus
from above the level of the liquid rather than at eye level. What type of
error is most likely introduced?
A. Random error caused by fluctuations in temperature
B. Systematic reading error caused by parallax
C. Chemical error caused by an incorrect stoichiometric coefficient
pg. 1
, D. Instrument calibration error caused by the balance
Answer: B
4. A student needs to transfer exactly 25.00 mL of a solution into an
Erlenmeyer flask for a quantitative analysis. Which piece of glassware is
specifically designed to deliver a highly accurate fixed volume?
A. Beaker
B. Graduated cylinder
C. Erlenmeyer flask
D. Volumetric pipette
Answer: D
5. A student fills a burette with titrant and notices an air bubble trapped in the
burette tip before beginning the titration. If the bubble remains during the
initial reading and disappears during delivery, what is the principal concern?
A. The delivered volume indicated by the burette will not correspond
accurately to the volume entering the sample
B. The titrant concentration will automatically double
C. The endpoint will become independent of the indicator
D. The burette will become calibrated automatically
Answer: A
6. A CHEM 123 student is asked to rinse a burette with a small amount of the
solution that will subsequently be placed into it rather than rinsing it only
with distilled water. What is the main reason for this procedure?
A. To increase the volume capacity of the burette
B. To prevent residual water from diluting the titrant
C. To remove all dissolved oxygen from the titrant
D. To make the titrant more acidic
Answer: B
7. During a titration, a student adds titrant rapidly while approaching the
expected endpoint and accidentally passes the endpoint. What is the most
likely effect on the calculated unknown concentration?
A. The calculation becomes more precise because additional titrant
pg. 2
, improves the signal
B. The excess titrant can cause the measured endpoint volume to be too
large, producing an incorrect calculated concentration
C. The excess titrant has no effect on the calculation
D. The sample concentration becomes chemically standardized by the
overshoot
Answer: B
8. A student is preparing a standard solution from a solid reagent using a
volumetric flask. After dissolving the solid, the student fills the flask to the
calibration mark and mixes thoroughly. Why is the calibration mark
important?
A. It identifies the temperature at which the solution must be stored
B. It establishes a known final solution volume for calculating concentration
C. It determines the molecular mass of the solute
D. It prevents the solute from reacting with water
Answer: B
9. A student accidentally fills a volumetric flask above its calibration line while
preparing a standard solution. What is the most likely consequence?
A. The final solution volume is greater than intended, so the concentration
is lower than calculated from the intended volume
B. The solution concentration is automatically increased
C. The solute becomes completely insoluble
D. The molecular weight of the solute changes
Answer: A
10. In an acid-base titration, an indicator changes color over a limited pH range.
Why must the indicator be selected appropriately?
A. Its color change should occur near the equivalence-point region so the
endpoint approximates the stoichiometric equivalence point
B. Its color change should occur only at pH 7 regardless of the reaction
C. The indicator must chemically consume all of the acid
pg. 3
, D. The indicator must have the same concentration as the titrant
Answer: A
11. A student titrates a weak acid with a strong base and chooses an indicator
whose transition range is substantially below the expected equivalence-
point pH. What problem could result?
A. The endpoint may occur before the stoichiometric equivalence point is
reached
B. The titration will necessarily become more accurate
C. The indicator will increase the acid's Ka
D. The equivalence point will disappear
Answer: A
12. A student performs a titration using phenolphthalein and observes a faint
pink color that persists after swirling. What does this observation generally
indicate in a properly selected titration?
A. The solution has definitely reached pH 14
B. The endpoint has approximately been reached
C. All solvent has evaporated
D. The acid has been completely removed from the laboratory
Answer: B
13. A student is determining the concentration of an acid using a standardized
NaOH solution. If the balanced equation shows a 1:1 molar relationship
between the acid and NaOH, which relationship is appropriate at
equivalence?
A. Moles of acid equal moles of NaOH delivered
B. Mass of acid equals mass of NaOH delivered
C. Volume of acid equals volume of NaOH delivered
D. Concentration of acid equals concentration of NaOH regardless of
volume
Answer: A
14. A 0.1000 M NaOH solution is used to titrate 25.00 mL of a monoprotic acid.
If equivalence occurs after 20.00 mL of NaOH is delivered, what is the acid
pg. 4
