Dissolved Oxygen Lab
Equipment and Materials
o Dissolved Oxygen Sensor
o Clean, opaque containers with lids, 2
o Labels and labeling pens
o Beaker, 250 mL
o Pipet with bulb
o Balance
o Hot plate
o Wash bottle and waste container
o Water, 5.0 L
o Elodea or similar plant, 1 sprig
o Table salt (NaCl), 3.5 g
o Liquid fertilizer, 3 drops
o Soluble solid fertilizer, 3.5 g
o Soil sample, 5.0 g
o 1.0 M sodium sulfite (Na2SO3), 12 drops
o Protective gear
Safety Precautions
Wear safety glasses and follow standard laboratory safety procedures.
Background
Dissolved oxygen (DO) is perhaps the most critical parameter in the ability of a
body of water to support life. The absence of DO can be an indicator of severe
pollution and limits the types of organisms that can survive.
In this lab you will use a dissolved oxygen sensor to examine the effect of three
common types of water pollution on dissolved oxygen levels.
Predict
Will pollutants affect the concentration of dissolved oxygen in water? How?
Procedures
1. Fill a clean container with enough water to be able to immerse the dissolved
oxygen probe without touching the bottom of the container. The metal ring on
the probe must be at least 1.0 cm below the surface. Measure and record in the
data table the dissolved oxygen (DO) concentration of the water under the
following conditions:
a. After heating to boiling, tightly sealing in a closed container, and
allowing it to cool without being exposed to air;
b. Right out of the tap;
c. After heating it to 40˚C;
d. After stirring a small amount of soil into it to make it turbid;
e. After dissolving 3.5g of soluble solid fertilizer per 100.0 mL of water;
f. After adding 3 drops of liquid fertilizer per 250.0 mL of water;
g. After dissolving 3.5g of table salt (NaCI) in 100.0 mL of water;
h. After five days in a sealed opaque container;
i. After adding organic matter (e.g., elodea or grass clippings), sealing it
from air, and letting it sit in the dark for five days.
2. Aerate some water by shaking it in a closed container; mix it with air for about
ten seconds. Then pour 200.0 mL of the aerated tap water into a clean beaker.
Measure the DO concentration and record it in the data table.
a. Add 2 drops of 1.0 M sodium sulfite (Na2SO3). Measure the DO
concentration and record it in the data table.
Note: Be sure to slowly stir the solution with the probe as it
equilibrates.
b. Repeat step a.
c. Repeat step a.
Data
Condition of Water
Tap water right out of the faucet
Tap water heated to 40˚C
Tap water, boiled, sealed, and cooled to room temp.
Turbid tap water (soil added)
Tap water, with 3 drops/200 mL liquid fertilizer added
Tap water, with 3.5 g/100 mL solid fertilizer added
Tap water, with 3.5 g/100 mL salt added
Tap water after 5 days in sealed opaque container
Tap water with organic material added, after 5 days in
sealed opaque container
200 mL aerated tap water
Aerated tap water after 2 drops/200 mL 1M H2SO3
Aerated tap water after 4 drops/200 mL 1M H2SO3
Aerated tap water after 6 drops/200 mL 1M H2SO3
Tap water right out of the faucet
Dissolved Oxygen
Post lab questions:
1. Find the definitions of the following terms:
Aerobic
Anaerobic
Anoxia
Biodegradable
Biological oxygen demand (BOD)
Dissolved oxygen
Eutrophication
Pollution
Salinity
Water quality
2. Was your prediction correct? Which of your water samples had the greatest
effect on the concentration of dissolved oxygen (DO)? Which had the least
effect?
3. Which had the greater effect on DO concentrations: man-made or natural
factors? Explain your answer.
4. Which type of pollution is more likely to occur in the water bodies in your
community? Explain.
5. What are some consequences of reduced DO concentrations in natural
bodies of water?
This project is funded by a grant awarded under the President’s Community Based Job Training Grant as
implemented by the U.S. Department of Labor’s Employment and Training Administration (CB-15-162-06-60).
NCC is an equal opportunity employer and does not discriminate on the following basis:

against any individual in the United States, on the basis of race, color, religion, sex, national origin,
age disability, political affiliation or belief; and

against any beneficiary of programs financially assisted under Title I of the Workforce Investment Act
of 1998 (WIA), on the basis of the beneficiary’s citizenship/status as a lawfully admitted immigrant
authorized to work in the United States, or his or her participation in any WIA Title I-financially
assisted program or activity.
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