A transparent glass of water can contain living and nonliving substances invisible to the human eye. Watch this video to learn more about substances in water.
Lesson E2: Substances in Water
Figure E.1.2.1 – Electronic meters test for water oxygen levels.
Figure E.1.2.2 – Fish die in bodies of water with low dissolved oxygen.
Figure E.1.2.3 – Algae growth in water decreases dissolved oxygen.
Most living things, including aquatic creatures, need oxygen for cellular respiration. Bodies of water without dissolved oxygen cannot support a wide variety of life.
Some water bodies contain low oxygen levels. Low oxygen water zones can exist for natural reasons. Sometimes deep, dense parts of the ocean don’t mix with upper, less dense layers. Without water mixing, these deep water zones are not replenished with
oxygen.
Low oxygen in water also exists for human-caused reasons. Sometimes extra fertilizer washes off farm fields into waterways, causing excess green algae to grow. Bacteria decompose dead green algae. In the process, the bacteria use up oxygen in the
water, leaving none available for larger organisms like fish.
Watch More
Ocean Dead Zones
Watch these two videos to learn more about how low oxygen levels affect ocean habitats.
Figure E.1.2.4 – Water filter jugs remove most of the chlorine from drinking water.
Figure E.1.2.5 – Chlorine in swimming pools kills disease-causing microorganisms.
Figure E.1.2.6 – Fluoride is a mineral that prevents cavities and tooth disease.
Water Additives
In water treatment plants, workers add substances to water before it is pumped to homes. Drinking water usually contains very small amounts of chlorine, to kill disease-causing microorganisms. Chlorine is not harmful to humans when consumed in low
concentrations. People who don’t like the taste of chlorinated water can buy water filters to remove the chlorine. However, people should not drink the chlorinated water in swimming pools. Swimming pools contain larger amounts of chlorine, to kill
microorganisms transferred by people into the water.
Another water additive in many communities is fluoride, which prevents tooth decay. Fluoride is also found in most toothpastes, and dentists give fluoride treatments. Scientific studies show that consuming small amounts of fluoride doesn’t hurt
people. Regardless, the addition of fluoride to drinking water is controversial. Supporters of water fluoridation appreciate that it prevents tooth decay, especially for people who can’t afford to see a dentist regularly. Opponents of water fluoridation
don’t like additional chemicals added to tap water that they have no choice over and cannot easily remove.
Watch More
Water Fluoridation
Watch this video to learn more about drinking water fluoridation.
Figure E.1.2.7 – Ocean water contains invisible dissolved salts.
Figure E.1.2.8 – Most of the salt dissolved in the ocean is the same substance as table salt.
Figure E.1.2.9 – The salty shoreline of the Dead Sea.
Salty Seas
Sodium chloride salt is the main salt dissolved in ocean water. Sodium chloride is the chemical name for the table salt we put on our food. Seawater also contains smaller amounts of magnesium, calcium, and potassium salts. Magnesium salts are also
known as Epsom salts, which some people put in their bathwater.
The salt minerals dissolved in the ocean originally came from rocks. Some salt enters the ocean from minerals released by underground volcanoes. Other salt minerals from rocks on the land are dissolved by flowing river water. Rivers carry the salt
minerals to the ocean.
Watch More
Sea Salt
Watch these two videos to learn more about why the ocean is salty.
Lesson Activity
Frozen Water
Problem:
How does salinity affect the rate at which water freezes? Your task is to design and carry out an experiment testing the rate of freezing for fresh water compared to a saltwater solution.
Hypothesis:
A hypothesis is a testable answer to a scientific question. In other words, what do you think the result of this activity will be?
Hint: In this case, think about how you would state a prediction of what would freeze faster; fresh water or a saltwater solution.
Download:
DOWNLOAD this document. It
provides a space for you to write your own hypothesis, and also space to answer questions about variables in this experiment. You will also find space to write your procedure, and analysis questions that come later in this activity. A table is also
provided for you to record your observations.
Use the document you downloaded to write or type your answers to the following questions about variables. When you have written your answers, click on the questions to check your answers.
We keep controlled variables the same to be sure the experiment is fair. This experiment has several controlled variables including the size of container used, the amount of water in each container, the initial temperature of the water, and
the temperature of the freezer.
Materials:
Water
Salt
2 plastic bottles
Timer
Thermometer
Measuring spoons
Any other materials you think are useful
Instructions:
Design and write a procedure for this experiment. Remember, you are trying to compare the freezing rate of fresh water to freezing rate of salt water. Write your procedure as numbered steps with enough detail so someone else could easily do the
experiment.
Before you start writing your procedure, consider these questions:
How are you going to measure the responding variable?
What are all the specific things you need to keep the same in order to make it a fair test?
Test your procedure by doing the experiment, and record your results in a table like this:
Observations Table
Solution
Time to Freeze
Fresh water
Salt Water
Analysis Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
The freshwater solution froze faster than the saltwater solution. This is because salt particles interfered with water particles coming closer together to form a solid.
Salty seawater takes longer to freeze compared to freshwater bodies like lakes. This is why oceans often don’t freeze completely, even in cold winter temperatures.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit E Lesson 2 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum,
or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
Clear fresh water isn’t always safe to drink. Fresh water directly from a stream can contain invisible dissolved pollutants that harm humans. Fresh water can also contain invisible harmful microorganisms such as bacteria. For example, wild animal
feces containing harmful E coli bacteria could wash into a stream.
When many people live in a small area, water can easily become contaminated with unsafe substances. Having a large water treatment system is cost-efficient for a large population and ensures that everyone in the area has safe drinking water.
The well water is likely hard water that contains lots of dissolved calcium and magnesium. Scale from these minerals in the water are collecting around the tap as water evaporates.
Decomposing vegetation on the land is broken down by bacteria. Decomposing vegetation and bacteria are in contact with melting snow on the land. Melted snow running into rivers contains additional bacteria from the decomposing vegetation. As
a result, water treatment plants need to add more chlorine to drinking water, to kill this additional bacteria.
Reading
and Materials for This Lesson
