CHEM 123 - Lab final - UBC
what is the importance of having a control group when performing an experiment? -
Correct Answer-it gives you something to compare your test groups to
what additional chemicals must be added to the liquid sample of vitamin C prior to
titrating? - Correct Answer-starch, excess KI, and HCl
what is the purpose of adding starch to the liquid sample of vitamin C ? - Correct
Answer-it forms an intensely blue-coloured complex with iodine (serves as the indicator)
what is the purpose of adding excess KI to the liquid sample of vitamin C? - Correct
Answer-it forms an intensely blue-coloured complex with iodine (serves as the indicator)
what is the purpose of adding HCl to the liquid sample of vitamin C? - Correct Answer-to
supply H+ ions to the reaction
How much KIO3 should be used in the titration to maintain 4 significant figures in the
measurements? - Correct Answer-at least 10 mL of KIO3 (usually recommended to use
25 mL)
What reaction takes place during an iodometric titration? - Correct Answer-oxidation-
reduction reaction
what is used as the oxidizing agent in an iodometric titration? - Correct Answer-
potassium iodate
top-loading balance - Correct Answer-- used for prepwork and obtains a mass to the
nearest +/-0.1g (uncertainty of +/- 0.05g)
- used prior to analytical balance
analytical balance - Correct 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? - Correct Answer-analytical balance
when is a reading considered stable? - Correct Answer-if it persists for 2 seconds
what temperature should objects be weighed? - Correct Answer-at room temperature
, should objects be dry or wet when weighed? - Correct Answer-Dry
should you use the same balance for all measurements? - Correct Answer-yes
Describe the steps for weighing by difference - Correct 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? - Correct 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) -
Correct 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
why do we perform iodometric titrations - Correct Answer-to find the concentration of an
unknown by mixing it with a solution of known concentration
What are the 4 (general) steps of an iodometric titration? - Correct Answer-combine
solutions, reach endpoint, calculate, determine the concentration of the unknown
what is a parallax error? - Correct 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? - Correct Answer-clean with deionized water
and then rinse with solution that will be pipetted (the sample)
how to clean a pipette - Correct Answer-- pour at least 25ml of deionized water into a
clean beaker
what is the importance of having a control group when performing an experiment? -
Correct Answer-it gives you something to compare your test groups to
what additional chemicals must be added to the liquid sample of vitamin C prior to
titrating? - Correct Answer-starch, excess KI, and HCl
what is the purpose of adding starch to the liquid sample of vitamin C ? - Correct
Answer-it forms an intensely blue-coloured complex with iodine (serves as the indicator)
what is the purpose of adding excess KI to the liquid sample of vitamin C? - Correct
Answer-it forms an intensely blue-coloured complex with iodine (serves as the indicator)
what is the purpose of adding HCl to the liquid sample of vitamin C? - Correct Answer-to
supply H+ ions to the reaction
How much KIO3 should be used in the titration to maintain 4 significant figures in the
measurements? - Correct Answer-at least 10 mL of KIO3 (usually recommended to use
25 mL)
What reaction takes place during an iodometric titration? - Correct Answer-oxidation-
reduction reaction
what is used as the oxidizing agent in an iodometric titration? - Correct Answer-
potassium iodate
top-loading balance - Correct Answer-- used for prepwork and obtains a mass to the
nearest +/-0.1g (uncertainty of +/- 0.05g)
- used prior to analytical balance
analytical balance - Correct 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? - Correct Answer-analytical balance
when is a reading considered stable? - Correct Answer-if it persists for 2 seconds
what temperature should objects be weighed? - Correct Answer-at room temperature
, should objects be dry or wet when weighed? - Correct Answer-Dry
should you use the same balance for all measurements? - Correct Answer-yes
Describe the steps for weighing by difference - Correct 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? - Correct 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) -
Correct 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
why do we perform iodometric titrations - Correct Answer-to find the concentration of an
unknown by mixing it with a solution of known concentration
What are the 4 (general) steps of an iodometric titration? - Correct Answer-combine
solutions, reach endpoint, calculate, determine the concentration of the unknown
what is a parallax error? - Correct 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? - Correct Answer-clean with deionized water
and then rinse with solution that will be pipetted (the sample)
how to clean a pipette - Correct Answer-- pour at least 25ml of deionized water into a
clean beaker
