Lab 1 - Spectrophotometry and Dilutions

Question 1

calibrating the spectrophotometer

Answer 1

With the sample compartment empty and the cover closed, set transmittance to 0%. Place the reference solution in the sample compartment, close the cover, and set transmittance to 100%.

Question 2

reference solution

Answer 2

contains everything except the “absorbing species” - in the case of the sports drink this is the food coloring

Question 3

relationship between absorbance and concentration

Answer 3

Absorbance varies linearly with concentration; this is why we use absorbance when interested in concentration.

Question 4

reflectance

Answer 4

In a transparent solution, the light that is not transmitted is absorbed. If a solution is cloudy, then what the spec shows as absorbance is a combination of absorbance and reflectance - you could no longer calculate absorbance from percent transmittance and vice versa.

Question 5

calculating absorbance from percent transmittance

Answer 5

• -convert percentage to a decimal
• -take the log
• -change the sign

Question 6

subtractive coloring

Answer 6

removing a color from one side of the color wheel, creates the color from the opposite side of the wheel… ex. removing orange, creates blue; removing green, creates red

Question 7

Is the color of the sports drink the color of light it absorbs or the color of light it transmits?

Answer 7

The color of the sports drink is the color of light it transmits.

Question 8

calibration

Answer 8

validating the output of a measuring device by setting the output to known standards

Question 9

dilutions

Answer 9

stock concentration/diluted concentration = __ fold dilution

take the inverse
__ part stock/__ total volume solution preparing

EX: we want 10ml of 5mM soln from a 20mM soln
20mM/5mM=4 fold
1 part stock/4 parts total volume
1/4 of 10ml = 2.5 ml 20mM soln
3/4 of 10ml = 7.5 ml 5mM soln