CHEM 123 - Lab final - UBC Actual Exam Questions
And 100% Verified Answers Graded A+
what is the general rule for volumetric analysis and sig figs? - <<ANSWER>>measurements
need to be precise to at least 4 sig figs (make sure to maintain this precision level when
transferring from container to container)
rule for sig figs in titration results - <<ANSWER>>when adding or subtracting measurements,
result is expressed to the 1st uncertain decimal place (determines the number of sig
numbers in the answer)
rule for sig figs multiplication - <<ANSWER>>product will have the same number of sig figs as
the multipler or divisor w/the smallest number of sig figs
how to use serological pipette - <<ANSWER>>- not as precise as volumetric pipette
- to determine what line to fill the pipette to, subtract the desired volume from 10 mL
- i.e., want 2ml : 10mL - 2mL = 8mL line
- use pipette bulb to draw liquid into the pipette and let liquid drain by gravity
how to prepare diluted solutions - <<ANSWER>>- take stock solution of known concentration
, - create 5 vials (100%, 80%, 60%, 40%, 20%) by adding the correct ratio of dye to deionized
water that adds to a total volume of 10 mL
what does Beer's law describe? - <<ANSWER>>relates the colour intensity of a solution to its
concentration, where absorbance is directly proportional to concentration
what is the analytical wavelength and why is it important? - <<ANSWER>>- the wavelength
of maximal absorbance chosen from the substance's absorbance spectrum
- the analytical wavelength will give us the maximum response for a given concentration of a
sample
how to calibrate pH probe - <<ANSWER>>- place probe in buffer solution with pH of 7 &
record the voltage produced
- Microlab related voltage to measured pH value & calculates the corresponding pH value to
each measured voltage & displays it on the monitor
what is a pH probe - <<ANSWER>>sensor that has 2 combined electrodes
- 1 electrode (calomel electrode) with a fixed potential (voltage) that allows it to act as a
reference for the second electrode
- voltage measured by the second electrode responds linearly to pH (very fragile/expensive)
what is a pH titration curve - <<ANSWER>>it is a curve that plots the volume of titrant added
on the x-axis & pH data on the y-axis based on the measured change in pH of the solution
being titrated
How to calibrate the drop counter - <<ANSWER>>- immerse the pH probe in the solution &
set computer to take pH reading whenever a drop is added
- we calibrate microlab by measuring the volume of approximately 100 drops of solution
delivered from a drop dispenser
- drop counter is selected from microlab's sensor menu & the formula tool is used to convert
drops to volume in mL (so graph reads directly in volume)
- volume = (counter reading in drops)(mL of solution measured by difference)/100 drops
And 100% Verified Answers Graded A+
what is the general rule for volumetric analysis and sig figs? - <<ANSWER>>measurements
need to be precise to at least 4 sig figs (make sure to maintain this precision level when
transferring from container to container)
rule for sig figs in titration results - <<ANSWER>>when adding or subtracting measurements,
result is expressed to the 1st uncertain decimal place (determines the number of sig
numbers in the answer)
rule for sig figs multiplication - <<ANSWER>>product will have the same number of sig figs as
the multipler or divisor w/the smallest number of sig figs
how to use serological pipette - <<ANSWER>>- not as precise as volumetric pipette
- to determine what line to fill the pipette to, subtract the desired volume from 10 mL
- i.e., want 2ml : 10mL - 2mL = 8mL line
- use pipette bulb to draw liquid into the pipette and let liquid drain by gravity
how to prepare diluted solutions - <<ANSWER>>- take stock solution of known concentration
, - create 5 vials (100%, 80%, 60%, 40%, 20%) by adding the correct ratio of dye to deionized
water that adds to a total volume of 10 mL
what does Beer's law describe? - <<ANSWER>>relates the colour intensity of a solution to its
concentration, where absorbance is directly proportional to concentration
what is the analytical wavelength and why is it important? - <<ANSWER>>- the wavelength
of maximal absorbance chosen from the substance's absorbance spectrum
- the analytical wavelength will give us the maximum response for a given concentration of a
sample
how to calibrate pH probe - <<ANSWER>>- place probe in buffer solution with pH of 7 &
record the voltage produced
- Microlab related voltage to measured pH value & calculates the corresponding pH value to
each measured voltage & displays it on the monitor
what is a pH probe - <<ANSWER>>sensor that has 2 combined electrodes
- 1 electrode (calomel electrode) with a fixed potential (voltage) that allows it to act as a
reference for the second electrode
- voltage measured by the second electrode responds linearly to pH (very fragile/expensive)
what is a pH titration curve - <<ANSWER>>it is a curve that plots the volume of titrant added
on the x-axis & pH data on the y-axis based on the measured change in pH of the solution
being titrated
How to calibrate the drop counter - <<ANSWER>>- immerse the pH probe in the solution &
set computer to take pH reading whenever a drop is added
- we calibrate microlab by measuring the volume of approximately 100 drops of solution
delivered from a drop dispenser
- drop counter is selected from microlab's sensor menu & the formula tool is used to convert
drops to volume in mL (so graph reads directly in volume)
- volume = (counter reading in drops)(mL of solution measured by difference)/100 drops
