Illustrated Guide to Home Chemistry Experiments

Chapter 17 Laboratory: Photochemistry 313

FIGURE 17-2: Iodine/oxalate solutions (from left) before exposure
to light, after extended exposure to a sun lamp, and after extended
exposure to strong sunlight

dISoALp S : dilute all solutions with at least three or

four times their volume of tap water and then flush them

down the drain with plenty of water.

Compare the tint of the test tube to the comparison

samples. Determine the nearest match, interpolating if

necessary. Record your results in Table 17-1.

oALIpToN ACTIvITIES

If you have time and the required materials, consider

performing these optional activities:

• Repeat the experiment using different types of light
  sources (a plant grow-light, UV light, and so on) Do the
  results with different types of light most resemble the
  control test tube, the one exposed to direct sunlight, or
  some intermediate result? Propose an explanation for
  your observations.


• Determine whether increasing the intensity or
  exposure duration for a type of light that in your
  original experiment did not activate the reaction
  changes the results. If not, propose an explanation.


• Repeat the experiment using a different concentration
  of iodine (for example, 5 drops or 20 drops per tube
  instead of 10). Do your results change for the various
  types of light you tested?


• Repeat the experiment using four test tubes wrapped
  completely in red, yellow, green, and blue cellophane
  and exposed to direct sunlight. Does the color of
  the cellophane affect the reaction rate? If so, which
  colors result in the fastest and slowest reaction rates?
  Propose an explanation.


• Graph the colorimetry data that you recorded in Table
  17-1. Is the reaction rate linear, or nearly so? If not,
  propose an explanation.

TABLE 17-1: Photochemical reaction of iodine and oxalate—observed data

15 minutes30 minutes One hour Two hours Four hours

Example Halfway between

#1 & #2

Close match to

#2

Slightly paler than

#6

Colorless N/A

Test tube A

(dark)

Test tube B

(direct sun)

Test tube C

(open shade)

Test tube D

(ambient)

Test tube E

(fluorescent)

Test tube F

(incandescent)