CHEM 123 LAB FINAL UBC ACTUAL SCRIPT
2026 COMPLETE QUESTIONS AND CORRECT
ANSWERS GRADED A+
◉ What are the 4 (general) steps of an iodometric titration?
Answer: combine solutions, reach endpoint, calculate, determine the
concentration of the unknown
◉ What reaction takes place during an iodometric titration?
Answer: oxidation-reduction reaction
◉ what is used as the oxidizing agent in an iodometric titration?
Answer: potassium iodate
◉ top-loading balance
Answer: - used for prepwork and obtains a mass to the nearest +/-
0.1g (uncertainty of +/- 0.05g)
- used prior to analytical balance
◉ analytical balance
Answer: - used to determine a precise mass to the nearest +/-
0.0001 g
,- masses are always reported to 4 decimal places
◉ does an analytical balance or top-loading balance need to be
recorded to 4 decimal places?
Answer: analytical balance
◉ when is a reading considered stable?
Answer: if it persists for 2 seconds
◉ what temperature should objects be weighed?
Answer: at room temperature
◉ should objects be dry or wet when weighed?
Answer: Dry
◉ should you use the same balance for all measurements?
Answer: yes
◉ Describe the steps for weighing by difference
Answer: - place clean empty weigh boat on top loading balance
- tare top loading balance & weigh boat to 0.00g
- add approximate mass (+/- 20%) of chemical to weigh boat
,- close all doors on analytical balance and tare it to 0.0000g
- weigh the sample & weigh boat and record the value (1)
- transfer weighed sample into beaker (from weigh boat)
- weigh the emptied weigh boat and record the value (2)
Subtract value 2 from value 1 to get the mass of the chemical
◉ how do we know if something is a standard solution?
Answer: if it has a known concentration to at least 4 significant
figures)
◉ describe the steps to take when preparing a standard solution (in
a volumetric flask)
Answer: - weigh & dissolve the solid compound (using weigh by
difference)
- clean the volumetric flask, funnel, and stopper 3x with deionized
water
- quantitatively transfer the dissolved sample into the volumetric
flask (using and funnel and rinsing beaker/stir rod with deionized
water)
- fill volumetric flask to a few centimetres below the calibration
mark (do not go above this line)
, - use a dropper to add water dropwise to volumetric flask until the
bottom of the meniscus is resting on the calibration line (if you go
past calibration mark, you must start over)
- stopper the flask and invert the flask 20x
◉ what is a parallax error?
Answer: when your eye level is higher or lower than the bottom of
the meniscus where you must record a volume
◉ how do you prepare a volumetric pipette?
Answer: clean with deionized water and then rinse with solution
that will be pipetted (the sample)
◉ how to clean a pipette
Answer: - pour at least 25ml of deionized water into a clean beaker
- use pipet bulb to half-fill the pipette with deionized water
- hold pipette horizontally and role around to coat the inside with
water
- discharge the water through the tip into the sink or waste beaker
- repeat the wash 2 times with deionized water
- transfer 25 mL of the solution to be pipetted into a clean & dry
beaker
- draw approximately 5 mL of solution into the pipet and hold in
horizontal position and coat inside with solution
2026 COMPLETE QUESTIONS AND CORRECT
ANSWERS GRADED A+
◉ What are the 4 (general) steps of an iodometric titration?
Answer: combine solutions, reach endpoint, calculate, determine the
concentration of the unknown
◉ What reaction takes place during an iodometric titration?
Answer: oxidation-reduction reaction
◉ what is used as the oxidizing agent in an iodometric titration?
Answer: potassium iodate
◉ top-loading balance
Answer: - used for prepwork and obtains a mass to the nearest +/-
0.1g (uncertainty of +/- 0.05g)
- used prior to analytical balance
◉ analytical balance
Answer: - used to determine a precise mass to the nearest +/-
0.0001 g
,- masses are always reported to 4 decimal places
◉ does an analytical balance or top-loading balance need to be
recorded to 4 decimal places?
Answer: analytical balance
◉ when is a reading considered stable?
Answer: if it persists for 2 seconds
◉ what temperature should objects be weighed?
Answer: at room temperature
◉ should objects be dry or wet when weighed?
Answer: Dry
◉ should you use the same balance for all measurements?
Answer: yes
◉ Describe the steps for weighing by difference
Answer: - place clean empty weigh boat on top loading balance
- tare top loading balance & weigh boat to 0.00g
- add approximate mass (+/- 20%) of chemical to weigh boat
,- close all doors on analytical balance and tare it to 0.0000g
- weigh the sample & weigh boat and record the value (1)
- transfer weighed sample into beaker (from weigh boat)
- weigh the emptied weigh boat and record the value (2)
Subtract value 2 from value 1 to get the mass of the chemical
◉ how do we know if something is a standard solution?
Answer: if it has a known concentration to at least 4 significant
figures)
◉ describe the steps to take when preparing a standard solution (in
a volumetric flask)
Answer: - weigh & dissolve the solid compound (using weigh by
difference)
- clean the volumetric flask, funnel, and stopper 3x with deionized
water
- quantitatively transfer the dissolved sample into the volumetric
flask (using and funnel and rinsing beaker/stir rod with deionized
water)
- fill volumetric flask to a few centimetres below the calibration
mark (do not go above this line)
, - use a dropper to add water dropwise to volumetric flask until the
bottom of the meniscus is resting on the calibration line (if you go
past calibration mark, you must start over)
- stopper the flask and invert the flask 20x
◉ what is a parallax error?
Answer: when your eye level is higher or lower than the bottom of
the meniscus where you must record a volume
◉ how do you prepare a volumetric pipette?
Answer: clean with deionized water and then rinse with solution
that will be pipetted (the sample)
◉ how to clean a pipette
Answer: - pour at least 25ml of deionized water into a clean beaker
- use pipet bulb to half-fill the pipette with deionized water
- hold pipette horizontally and role around to coat the inside with
water
- discharge the water through the tip into the sink or waste beaker
- repeat the wash 2 times with deionized water
- transfer 25 mL of the solution to be pipetted into a clean & dry
beaker
- draw approximately 5 mL of solution into the pipet and hold in
horizontal position and coat inside with solution
