Water Science

Educator's Notes

Water covers almost three-quarters (about 379 million square kilometres) of the Earth's total surface. Water makes the Earth the "blue" planet: the water which covers our planet make it visually unique from all others in the solar system. Plants, animals and people all need clean water to live a healthy life.

What Is Water?

Science defines water as a pure, colourless, transparent, tasteless and odourless compound of oxygen and hydrogen. Its chemical symbol is H₂O. This means that the water molecule has two atoms of hydrogen (symbol H) and one atom of oxygen (symbol O). The water molecule is V-shaped and triangular. While water molecules are electrically neutral, the oxygen atom holds a small negative charge and the two hydrogen atoms hold small positive charges. Scientists believe this unusual electrical balancing, called polarity, gives water some of its remarkable properties.

Water molecules are attracted to each other, creating hydrogen bonds. These strong bonds determine almost every physical property of water and many of its chemical properties, too.

Water as a Chemical

Everyone knows a good deal about water – what it feels like, looks like, how plentiful (or scarce) it is, and why it is important to life. But fewer people think of water as a chemical – something that reacts with other substances, producing new materials.

Water reacts with many different substances:

• when some metals (such as sodium) are added to water, the reaction produces hydrogen gas as one of the products;
• when some non-metallic oxides are added to water they form compounds called acids (a major ingredient of acid rain – carbonic acid – is formed when carbon dioxide reacts with water);
• when a metallic oxide reacts with water, compounds called bases are formed;
• many compounds, when mixed together in a dry state, do not react. If some water is added to the mixture, however, a reaction often begins. Baking powder is a mixture of dry chemicals which releases bubbles of gas only after water is added.

The Universal Solvent

Scientists often call water the universal solvent because water can dissolve more substances than any other liquid. In fact, water, in a "pure" state, is not found in nature. As the universal solvent, water dissolves almost any substance to form solutions. The reasons why water combines easily with other substances are threefold:

1. water molecules are very small and move easily around other atoms and molecules;
   
   
2. the negative charge on the oxygen atom and the positive charges on the hydrogen atoms allow water molecules to interact with other molecules;
   
   
3. Water is very stable – at 2000°C only about 2% of water molecules break into parts. These parts are hydrogen ions with a positive charge (H+) and hydroxide ions with a negative charge (OH-).

Some substances dissolve more easily in water than do others. Common table salt (sodium chloride) dissolves in water very easily. When placed in water, the sodium chloride molecule falls apart. The positively charged sodium ion (Na+) binds to the oxygen, while the negatively charged chloride ion (CI-) attaches to the hydrogen. This makes a very stable "salty" water molecule.

There is hardly a substance known which has not been identified in solution in the Earth's waters. Were it not for the solvent property of water, life could not exist, because water transfers nutrients vital to life in animals and plants.

A drop of rain water falling through the air dissolves atmospheric gases. When rain reaches the Earth, it affects the quality of the land, lakes and rivers by delivering those dissolved gases.

Water is a dynamic and mobile substance which is constantly going through chemical and physical transformations. It has been called "nature's magician", since it can appear in many forms and perform some incredible tricks. Water is found naturally in all three states of matter; solid, liquid and gaseous; a rare occurrence among other natural substances.

Density

Density is defined as the mass of an object per unit volume of the object. Density is determined by calculating the ratio of the mass of the object and its volume. For example, one cubic centimetre has a mass of one gram at 4°C. The density of water is 1.00 g/cm³.

The density of water is an important physical constant. It is used as a standard of reference to which the densities of other substances are compared.

Unlike most substances, which are most dense in their solid form, ice (solid water) is actually lighter (less dense) than liquid water. As a result, ice floats on water. The strong hydrogen bonds formed when water freezes lock water molecules together in a fixed crystal pattern.¹ When ice melts, the structure collapses and molecules move closer together. Liquid water at 4°C is about 9% more dense than ice. If ice was more dense than water, rivers, lakes and seas would freeze from the bottom up rather than from the top down, and they would never completely thaw in summer. This property plays an important role in lake and ocean ecosystems. Floating ice often insulates and protects animals and plants living in the water below.

Buoyancy

Buoyancy is an important property that applies to all fluids, including water. If you weigh an object in air and then weigh the same object suspended in water, you will find that the object weighs less when suspended in water. This is because the water exerts and upward force on a submerged object. This upward force is referred to as buoyancy.

For some people it is easier to learn to swim in salt water than in fresh water because salt water has more buoyant force than does fresh water. Our bodies float better in the salty water.

Specific Gravity

Specific Gravity refers to the weight of a substance as compared to an equal volume of water. Water is the standard for calculating the specific gravity of solids and liquids. If we find that one cubic foot of iron is 7.6 times as heavy as one cubic foot of water, we say that the specific gravity of iron is 7.6.

Specific gravity can be used to identify certain types of matter. Every specific type of matter has its own characteristic value for specific gravity.

Boiling and Freezing

Pure water at sea level boils at 100°C and freezes at 0°C. At higher elevations (lower atmospheric pressures) water's boiling temperature decreases. This is why it takes longer to boil an egg at higher altitudes. The temperature does not get high enough to cook the egg properly.

If a substance is dissolved in water, then the freezing point of the water is lowered. Thus, when salt is sprinkled on ice, the ice appears to melt. In fact, salt; a hydroscopic substance; readily bonds with the water molecules in the ice. This bonding effectively breaks down the ice structure, releasing molecules which return to their liquid form. The salt dissolves in the liquid water, which now has a lower freezing point (since it has salt dissolved in it). Simple, right?

Thermal Properties

Scientists have found that one gram of water requires 2 500 joules of heat to change into a gas at its boiling temperature (100°C). Pure water boils at 100°C, but extra energy is needed to push water molecules into the air. This is called latent heat – heat required to change water from one phase to another. The specific heat of water is the amount of heat required to raise the temperature of one gram of liquid water one degree Celsius. One gram of water requires 4.18 joules to raise its temperature 1°C. This is a relatively high ratio – in fact, water absorbs or releases more heat than many substances for each degree of temperature increase or decrease. Because of this, water is used for cooling and for transferring heat in thermal and chemical processes.

Since a great deal of heat is required to raise the temperature of water, large bodies of water have a moderating effect on our climate. Large bodies of water, like the Atlantic Ocean or the Great Lakes, are the world's great heat reservoirs and heat exchangers. They are also the source of much of the moisture that falls as rain and snow over adjacent land masses.

On hot days, water slowly absorbs heat slowly, which has a cooling effect on the surrounding air. When the air cools to below water temperature, the effect is reversed, and water gives off heat. In Atlantic Canada, the ocean affects our climate by curbing the extreme temperatures of both winter and summer. Another example of this effect is found at the beach: have you ever found the sand hot to the point of burning, while the temperature of the water at the shore was temperate or even cool?

When water is colder than the air, precipitation is curbed, winds are reduced, and fog banks are formed. Local fog or mist is likely to occur if a lake cools the surrounding air enough to cause saturation (small water droplets are suspended in the air).

Energy is also lost when water freezes. Water molecules release 334 joules of energy for every gram when moving from the high energy phase of liquid water to the low energy phase of ice. That is why nights when ice is freezing often feel warmer than nights when ice melts.

Surface Tension

At first glance, water seems to be without strength – it flows and drips and condenses seemingly effortlessly. However, molecules of water stick to each other very well, creating a very powerful surface tension.

Water molecules on the edge of a water drop hold closely together, forming a very tight layer. You can see this surface tension in action when you watch a water droplet form on the tip of a leaf. The drop "sticks" to the leaf as it slowly swells to form the drop. The surface of the water acts as its own sack, holding itself together, slowly stretching and expanding until the weight of the droplet finally becomes too great for the surface tension and the droplet falls. Surface tension also permits water to hold up substances heavier and more dense than water itself. For example, a needle or paper clip will float on the surface of a full water glass, if placed very carefully.

Surface tension allows many aquatic insects, like water spiders and pod skaters, to "walk" across rivers and streams. Next to mercury, water has the highest surface tension of all commonly occurring liquids.

Surface tension is essential to the transfer of energy from wind to water that creates waves. Waves are necessary for rapid oxygen diffusion in lakes and seas.

Adhesion and Cohesion

Water molecules bind not only to other water molecules, but also to other types of molecules. Attraction between two unlike substances such as water and glass is called adhesion. When water sticks to a surface, it is because of the forces of attraction between the two different substances involved.

The adhesion of water to soil particles is an important factor in agriculture. The forces of adhesion can pull water to the surface, where it can be used by plants.

Cohesion is a force which holds a solid or liquid together, owing the attractions between molecules. Whereas adhesive forces attract different types of molecules, cohesive forces attract molecules within a substance. Cohesive forces decrease with temperature increases.

Capillary Action

Capillary action helps explain the ability of water to "climb". Water molecules spread a thin film by leapfrogging over one another and then clinging to the surface of the substance over which they are moving. Moving through the roots of a tree up into its long trunk, water can climb up to 50 metres above ground level. Water will also move long distances through the soil by spreading its moist film from particle to particle. This is how water readily wets many materials. Capillary action allows a paper towel or a sponge to be used to soak up spilled water.

Another example of capillary action can be observed by looking at water in a thin glass tube (a test tube or tall, thin drinking glass will do). The molecules at the edge reach for and adhere to the molecules of the glass just above them. At the same time they tow other water molecules along with them. The water surface, in turn, pulls the entire body of water to a new level until the downward force of gravity is too great to overcome.

Meniscus

In the case described, the free surface of the water curves, so that water is seen to rise up along the sides of the cylinder slightly. The curved surface of the liquid is referred to as the meniscus. The curved surface of water is unique: if another liquid, such as mercury was placed in the cylinder, the curved surface would be opposite to that of water. This difference is due to the difference in the degree of attraction between the molecules in the liquids. Mercury has strong attractive forces between the mercury molecules (good cohesive force), but does not have strong attractive forces with the molecules of the glass container (weaker adhesive force).

Did you know? Raindrops are not tear-shaped. Scientists, using high-speed cameras, have discovered that raindrops actually resemble the shape of a small hamburger bun. The average human body is composed of about 55% water. Life on earth probably originated in water. The human body needs 2 litres of water a day in our climate; we can last only a few days without water. Most of our food is water: tomatoes are about 95% water, spinach is about 91% water, milk is about 90% water, apples contain about 85% water, potatoes are about 80% water, beef is about 61% water and hot dogs contain about 56% water.

Activities

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Water Tricks – #1

Grades 4, 5, 6 – Science

Purpose

Students will be able to identify and discuss cohesion.

Water molecules are attracted to each other due to their molecular structure. This is known as cohesion. A familiar example of a cohesive device is glue (the students suggest other cohesive devices and look up the word "cohesion" in a dictionary). Water molecules stick together unless their cohesive bonds are weakened. Adding soap to a body of water is one way to weaken the bonds between water molecules.

Materials

• Roll of waxed paper
• copies of the Water Race Maze
• tape
• eyedropper
• toothpicks
• watch with a second hand
• liquid soap
• ruler

Procedure

Hand out the Water Tricks Score Card.

Pose the question, "how can your water drop be guided through the maze?". Ask the student to hypothesize (predict) how the drop will be moved. Once they have determined a method of moving the drop (guiding it by using the toothpick), ask them to predict how long it will take to move the drop through the maze (Water Race).

Tape a piece of waxed paper over top of the maze to protect it. Place a water drop inside the circle on the maze. Ask the students to move the water drop through the maze with a toothpick. If the drop separates, instruct them to go back, collect it, then continue (you may ask the students to imagine that the drop is a dog, and the toothpick is a leash). Time how long it takes to move the drop through the maze and record the actual time. Calculate the difference.

Ask the students to predict how long the water drop may be stretched. Record the predictions, then, in three to five trials, stretch the water drop. Record the longest stretch and calculate the difference between the predicted length of stretch and the actual.

Show the students the effect of soap on cohesion by dipping the toothpick in soap before beginning the second trial of the water maze activity. The water drop disperses and will not be pulled along by the toothpick. Be sure to tape fresh waxed paper over the maze after introducing the soap, and to use fresh toothpicks and water. Soap residue (no matter how diluted) will spoil the results of this activity.

Extension

Ask the students to imagine the implications of this activity in their everyday lives.

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Water Tricks – #2

Grades 4, 5, 6 – Science

Purpose

Students will be able to identify and discuss surface tension.

Aluminum should sink when placed in water because its density is greater than that of water. However, when a piece of foil is place flat on the surface of water, it can float. This is because the surface tension of water is strong enough to hold up the foil (much as a heavy ship floats in the ocean). Surface tension is caused by the cohesion of the water molecule. The molecules below the surface of the water are attracted equally in all directions. While those on the surface are only attracted to the sides and down. This causes the surface of the water to "contract" and act like it is covered with a film. The surface tension of water is strong enough to hold up some objects more dense than water. This is also why insects, such as the water strider, are able to walk on the water.

Materials

• Aluminum foil cut in 5 inch squares
• water
• plastic bowls

Procedure

Ask the students to predict whether the aluminum foil will float or sink when it is placed on the water. Demonstrate that the 5 inch by 5 inch square will float. Ask the students to predict how many times they can fold the square of aluminum foil before it sinks in the bowl. Have the students record the answers on the Water Tricks Score Card.

Fold, or have the students fold, the aluminium in half once, and attempt to float the aluminum. Continue folding the aluminum and placing it carefully (parallel) on the surface of the water until the aluminum sinks. Ask the groups to record the actual number of times they were able to fold the aluminum, and calculate and record the difference between their prediction and the actual result.

Extension

This activity may be extended to include fractions and exponents. Each time the foil is folded in half, the students decrease the area of the aluminum by a power of two. After three folds, you have only one eighth of the original surface area; after four folds, one sixteenth.

Try floating other materials – wood chips, pieces of plastic, etc..

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Water Tricks – #3

Grades 4, 5, 6 – Science, English Language Arts extension

Purpose

Students will be able to identify and discuss the principle of adhesion.

Water is able to travel through the narrow spaces between the fibres of paper towels by capillary action (much as groundwater moves through an aquifer). The attractive force that exists between water molecules and paper fibres is greater than the cohesive force between water molecules. Attraction between unlike molecules is called adhesion.

Materials

• 3 different brands of paper towels (use the towelling found in the school washrooms for one brand!)
• rulers
• pencils
• tape
• bowls or cups for water
• water

Procedure

You may wish to include an English Language Arts component by asking the students to design and write a television commercial based on the results of their experiments.

Ask the students to predict which paper towel will absorb water the quickest and why they chose that particular towel. Record the responses on the Water Tricks Score Card.

Mark each strip of paper towel at 18 cm. The students tape the strips to a pencil at equal distances and dip all three brands into the bowl or cup of water simultaneously. The paper towels may take either a very quick dip, or the towels may be held underwater (evenly) while the students watch the water being absorbed up the towel. In which strip does the water reach the 18 cm mark first?

Students record which paper towel absorbs quickest. Students calculate the difference between their predication and the actual result.

Extension

Use other absorbent materials in the experiment and construct a comparative graph with the results. Ask the students to interpret, from the graph, which material(s) would act as a more environmentally-responsible alternative to using paper towelling in their homes (Reduce, Reuse, Recycle).

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Hard Water, Soft Water

Grades 4, 5, 6 – Science, Mathematics

Purpose

Students will observe, classify and order water samples according to their degree of hardness or softness. Students should be able to describe the difference between hard and soft water and determine which type of water is better for cleaning by the end of this activity.

Pure water does not exist, except in the lab. When water is considered pure, it is made up of two hydrogen atoms and one oxygen atom – H₂0. But water mixes with many things – as a raindrop, it mixes with minerals in the soil and carries those minerals with it to the groundwater or as it flows toward a stream or river. When water is full of minerals, it is known as hard water. When water has a few quantities of calcium and magnesium in it, it is generally called soft water. Distilled water is water that has been softened.

Hard water can cause problems in plumbing because it deposits minerals in the pipes, causing a build up. You can tell if you have hard water at home if it is difficult to get a lather when shampooing or if there isn't much sudsing when you are washing dishes by hand. Soft water produces more suds and, therefore, it is better for cleaning. Many people install water softeners in their homes for that reason. Water softeners use salts to remove most of the calcium and magnesium from tap water.

Materials

• distilled water
• tap water
• bottled water
• salt water
• food colouring
• liquid soap
• 4 baby food jar with lids for each group
• 1 eye dropper per group
• paper, pen/pencil

Procedure

Divide the students into small groups. Mix a salt water solution of one tablespoon of salt per litre of tap water (or use sea water). Provide each group with 60 ml of each type of water, coloured with food colouring (red for tap water, blue for distilled water, yellow for salt water, green for bottled water).

Ask the students to predict which of the samples will "suds up" the most. Have them determine what might affect the amount of suds. Explain the concepts of hard and soft water to the class, and indicate that this experiment will determine the softness or hardness of each water sample.

Have one student per group record the results of the experiment on a sheet of paper, along with each groups' predictions.

Add 2 drops of liquid soap to each water sample and tighten the lid. Shake all jars for either the same amount of time (1 minute) or for the same number of shakes. Encourage the students to use equal force while shaking the samples. Gather the results for further discussion.

Extension

Test different types of water – try rain water, melted snow, lake, stream or pond water. Ask the students to guess what types of materials are present in these waters and imagine how they came to be there. Have the students bring water samples from home.

Survey the different types of water and graph the results (including the results of the original experiment).

Which is cheaper, bottled water or softened water? Make a graph of the costs of each. Ask the students to survey bottled water users.

Try using water softening salts to soften a hard water sample and note the results.

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Water Mixer

Grades 4, 5, 6 – Science

Purpose

Students review the physical properties of water and discover how water reacts when mixed with different substances. Students investigate similarities and differences existing between water, cooking oil, food colouring, vinegar and salt. They observe water mixing with these substances and use their five senses to classify the outcome of each mixing experiment.

During this activity, students will review the physical properties of water, hypothesize the outcome of each experiment and discover how water reacts differently with various substances.

Materials

(for each student/group of students):

• 5 clear glasses
• water
• 5 clear containers (clear plastic glasses work well)
• 3 Tbsp cooking oil
• 3 Tbsp vinegar
• 2 Tbsp food colouring
• 2 Tbsp salt
• 2 Tbsp baking soda

Procedure

1. Fill each glass with water
2. Display vinegar, oil, food colouring, salt and baking soda in separate containers.
3. Ask students to complete Activity Chart #1.
4. Add 3 Tbsp of vinegar to glass #1.
5. Add 3 Tbsp of oil to glass #2.
6. Add 2 Tbsp of food colouring to glass #3.
7. Add 2 Tbsp of salt to glass #4.
8. Add 2 Tbsp of baking soda to glass #5.
9. Observe and compare how water has mixed with each of the materials.
10. Have students complete Activity Chart #2.

Discussion

Teacher's Notes

Water Mixer Activity
Chart #1 – Describe each of these substances

	Water	Vinegar	Oil	Salt	Baking Soda	Food Colouring
Colour	clear	clear yellow brown red (depending on the type of vinegar used)	yellow	white grains	white powder very small white grains	red, green, blue, yellow, etc. (depending on the colour being used)
Smell	no smell	very strong smell	no smell or very light smell	no smell (some students may say they "smell" salt)	no smell	no smell
Taste	no particular taste	sour, strong, acidic	thick, oily taste	very salty	salty	no taste
Feel	wet, not sticky	wet, not sticky, similar to water	oily, maybe sticky, much thicker than water	dry, small grains	dry, powdery grains	liquid, thicker than water

Water Mixer Activity
Chart #2 – What happened whan you added ______ to the water?

Vinegar	Oil	Salt	Baking Soda	Food Colouring
Water diluted the vinegar	Oil floats to the top - bubbles up to the top in large, flat circles	Water seems to melt some of the salt	Water begins to bubble (you can hear it bubble)	Food colouring disperses through the glass of water
Vinegar changed the colour of the water (if coloured vinegar was used)	Oil and water did not really mix - separated out after a short period had elapsed	Salt grains float to the bottom of the glass and slowly disolve if not mixed	Water colour may blur (become clouded), but eventually returns to clear state	Colour slowly travels through the water
Water tastes sour after the vinegar was added	Oily film sits on top of the water	Water remains the same colour, but smells and tastes salty	Water smells faintly salty and tastes salty	Water changes colours - becomes the same/almost the same as the food colouring
The water smelled like vinegar		Salt seems to disappear after mixing	Baking soda sinks to the bottom of the glass and slowly dissolves. If mixed, baking soda dissolves more quickly and bubbles are renewed	Water tastes the same

Extension

Students can draw connections between this activity and their daily lives by identifying where they have seen similar reactions occur in different environments.

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Good Water

Grade 6 – Science, Mathematics

Purpose

Students will measure pH, nitrates, and phosphates as indicators of water quality.

Nitrate and phosphate levels increase when excess amounts of fertilizers or sewage water enter waterways. Nitrate levels above 1 part per million (ppm) indicate contamination. Phosphate levels above 0.1 ppm may cause explosive algae growth. When these algal mats die, the decay process depletes the water of dissolved oxygen and so endangers the aquatic habitat.

In 1909, S.P. Sorensen introduced the pH scale to measure the "potential of Hydrogen". pH refers to the concentration of hydrogen ions (H+) on a scale of 1 to 14. On this scale, pH values of less than 7 indicate an acid, while those greater than 7 indicate a base (alkaline substance). Pure water is neither an acid nor a base – it is a neutral with a pH value of 7. Vinegar has a pH of 3. Rainwater is slightly acidic with a pH of 6.5. Ammonia has a pH of 11 or 12. Most fish tolerate a pH range of between 6 and 8.5.

Materials

• water samples from various sources (school water fountain, home, etc.)
• plastic vials with tops (cleaned, emptied pill bottles will do)
• neutral litmus paper (available from Boreal: 1-800-387-9393; perhaps from local pharmacies; your local high school may be able to provide small amounts)
• nitrate and phosphate testing kit (Boreal; local hospital or pharmacy; call the Department of Natural Resources to borrow; local museum; local high school)

Procedure

1. Collect water samples from various sources. Label each sample, contained in a clean plastic vial, with the location of the sample, date and time of day the sample was taken.
2. Test samples with litmus paper in the classroom. Estimate the pH values. Which samples are acidic?
3. Test the samples using the phosphate and nitrate testing kits. Are all water samples equal?
4. Have the students record their observations in a report or on a chart or bar graph.

Extensions

Watch the weather. Collect samples again after a rainstorm or an extended dry period. Do pH values change? Do phosphate or nitrate values change? Can the students imagine why the values may or may not change?

Use the local or school library to research acid rain. What types of compounds cause acid rain. What types of industries contribute the most to acid rain production? Has your area been affected by acid rain?

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One Drop at a Time

Grades 4, 5, 6 – Science, Mathematics

Purpose

Students will estimate and measure how much water is used during everyday activities

See the Section Water Facts for statistics relating to national water consumption.

Materials

• empty 2 litre milk or juice jug
• empty 2 litre plastic bottle

Procedure

1. Discuss water usage around the home. Have students estimate how many litres some household appliances use and how much the students would use showering or brushing their teeth. Write these estimates down for students and/or the class to keep as a record.
2. Discuss and explore methods of measuring water usage at home. Suggest considering a timing an activity and repeating the activity while catching the water in a jug or bottle. For example, students could record the time they spend brushing their teeth with the water running, then after the activity is completed, run the water from the faucet for the same period of time while catching the faucet water in a container. Students would measure the amount of water they actually used during each activity and report back to the class.
3. Check with manufacturers or local furniture/appliance/plumbing stores for average washing machine, toilet, and dishwasher water usage (or refer to other activities contained in this Kit).
4. Compare the data received with data received during students' home measuring experiments.
5. Discuss ways to save water at home.

Extensions

Have students groups develop a plan to save 25% of the water they are currently using at home. Can their plans be implemented easily? If they can be, the students may develop and commit to a conservation contract aimed at actual reduction of their water consumption. Solicit parental support for this project.

(English Language Arts, Social Studies)
Contact your local water utility for an estimate of your area's total average water needs. Can the students apply conservation principles to formulate a water stewardship or resource management programme for the area? Conduct a mock parliament to debate the merits of the programme with students representing members of environmental agencies, government, the local citizenry, and representatives of industry. Discuss the points of view which might exist between the various parties.

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Water Weight

Grades 5, 6 – Science, Mathematics

Purpose

Students will investigate water pressure and compare the results of differing pressures on a flow of water.

Scientists measure pressure in atmospheres. One atmosphere of pressure equals 1 kg/cm². As divers descend in water, each 10 metres adds another atmosphere of pressure. In the deep sea, pressure ranges from 300 to 500 atmospheres.

Humans have SCUBA dived as deep as 66.5 m (what is the water pressure in atmospheres at this point?). At such pressures, our blood absorbs gases (like nitrogen) from the compressed air we breathe. If we return to the surface too quickly, the gas expands in our bloodstream, causing painful bubbles in tissues and around joints.

Materials

• copy of Water Weight Table
• two 2 litre bottles
• funnel
• grease pencil (available at stationery and art-supply stores)
• clean overhead transparency
• nail
• large tub or sink

Procedure

1. Starting at the bottom of one bottle, have student groups measure and mark in a straight line the following four spots: 4 cm, 8 cm, 12 cm, 16 cm.
2. Push the nail through these marks to make four holes in the bottle. Make sure that the holes line up in a straight vertical line.
3. Place the bottle in a sink or tub (water will be spilling!) on the edge of the clean overhead transparency.
4. Mark the bottle's position on the transparency sheet with the grease pencil.
5. Use the other bottle and the funnel to pour water into the bottle with the holes.
6. Small streams of water will flow out of the holes. Using a grease pencil, mark the spot where each stream of water lands.

Which stream shoots farthest? Why? What happens as the water level decreases?

How far above the hole must the water level be for it to create a stream away from the bottle, rather than just trickling down the side of the bottle.

Extensions

(English Language Arts, science)
Use the library to research how hydroelectric power is generated. How do dams create extra weight for more pressure (and power) to turn the turbines.

Grades 4, 5, 6
(English Language Arts, Social Studies)
Research how water power was used traditionally to power Nova Scotian industries. Research current small-scale hydroelectric operations in Nova Scotia. Visit the Nova Scotia Museum of Industry to see water power in action. Visit Sherbrooke Village or Balmoral Grist Mill to see actual examples of water powered mills.

Grades 4, 5, 6
(English Language Arts, Science)
Research how scientists cope with deep-sea dives. Investigate and report on famous deep-sea expeditions (Titanic, for example), and how scientists prevented exploratory vessels from collapsing.

Research species of deep-sea fish and report on how they have adapted to their environments.

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Aquatic Notes

Grades 4, 5, 6 – Science

Purpose

Students will explore how the mass of water can affect sound vibrations.

Sound is a form of energy (a vibration) that travels through the air in waves. Sound vibrations have different frequencies. Scientists measure frequency in vibrations per second, or Hertz (Hz). Our sense of hearing interprets the changes in frequencies as a change in pitch. A low-pitched sound has a low frequency. A high-pitched sound has a high frequency. You can change the frequency of a vibrating object by changing its structure. A more secure object may vibrate faster than a loose object when struck.

An easy way to change the structure of a cup it to add weight – fill it with water. As the glass I filled, it becomes more stable and vibrates slower when struck. Sound travels 1 450 metres per second in seawater that has a density of 1.025 grams per cm³ and 334 metres per second through air at 20°C that has a density of 0.001293 grams per cm³.

Materials

• variously shaped and sized drinking glasses (all of the same material – glass works best – and of the same relative thickness)
• pencil or other instrument with which to strike the glasses
• pitcher of water

Procedure

1. Divide students into groups and assign each group to one shape of cup. Fill cups with water to different levels.
2. Students gently tap the rim of each cup with their pencil. They should hear different pitches: the cups should vibrate at different frequencies.
3. After they've tapped the rims several times, ask students to note whether there is any difference in the sounds, and why, if there is a difference, is there a difference. Note: more water makes the sides of the cups more stable and the vibration is slower, which results in lower pitch.
4. Student groups may hear different pitches for different shaped cups filled to the same level. Tall, thin glasses may vibrate faster than short, wide glasses.

Extensions

Grade 6
Test the pitch of the cups using a less dense liquid than water (like rubbing alcohol which has a density of 0.791 grams per cm³) or a more dense liquid (like glycerin at 1.26 grams per cm³). Is there a difference in the pitch?

Grades 4, 5, 6
(Music)
Students can compare which musical notes are produced by the glasses by comparing sounds with a known musical instrument, such as a piano or guitar.

(English Language Arts)
Students may research and report on the ability of some sea creatures (like dolphins and whales) to communicate via sound.

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Salty Solutions

Grade 6 – Science, Mathematics

Purpose

Students will learn about and use one method of measuring salt content in water.

Open ocean water has a uniform salinity of about 35 parts per thousand or 35 grams of dissolved solids per 1 000 grams of water. Chlorine and sodium account for the majority (more than 85%) of these dissolved solids. Other solids occurring regularly in sea water include sulfate, magnesium, calcium, and potassium. Tidal marshes, wetlands and estuaries experience varying salinity values, depending on the addition of fresh water.

Materials

• four plastic, litre bottles with the tops cut off
• salt
• water
• scale
• waterproof markers or grease pencils (available at stationery stores)
• hydrometer (available from Boreal catalogue, or one can usually be borrowed from a high school science lab or local museum)

Procedure

1. Divide students into four groups and give each a bottle. Fill the bottles with water (lukewarm). A litre bottle holds about 1 814 grams of water – add water to bring the weight of the bottle to about 1 800 grams (you'll have to test this activity out beforehand to determine approximately to what level on the bottle the students will add water).
2. Students weigh the bottles and record their findings on the Salty Solutions chart provided.
3. Three groups add salt to their bottles to create differing salinities. Students stir in the salt until it is completely dissolved.
   • to one group's bottle add 63.5 grams of salt for a salinity of about 35 ppt
   • to another group's bottle add 31.75 grams of salt for a salinity of about 17 ppt
   • to the third group's bottle add 15.8 grams of salt for a salinity of about 8.7 ppt
   • Leave the fourth group's bottle free of salt (0 ppt). Mark water levels on bottles with waterproof markers or grease pencils.
4. Use the hydrometer to chart the reading for the three solutions and the "salt-free" water.
5. Set all four bottles on a table in the classroom near a window (where sun can reach the bottles) but away from any heat sources. Chart the changes in water levels and salinity (using the hydrometer) over a two or three day period. As water is lost through evaporation, how does salinity change?

Extensions

Do weather patterns affect salinity? Ask the students to predict whether or not weather patterns affect salinity and record their hypothesis. Then, leave the bottles outside on a rainy day. Check with the local weather channel for information about the predicted/received rainfall totals, and compare those totals to the rainfall caught in the students' bottles. Test the salinity of the water in the bottles after the rainfall and record the changes. Try leaving the bottles in the sun for a protracted period of time. Again, test and record the salinity of the samples.

Ask the students to imagine the implications of their findings. Ask the students to research information about the Dead Sea. Can they see the correlation between their findings and that body of water?

Use varying weights of water in the bottles and varying amounts of salt. Have the students calculate the salinity of the water by dividing the weight of salt by the weight of water in the bottle. The resulting number, multiplied by 1 000 equals the salinity of the water in parts per thousand (ppt). Can the students explain, mathematically, what effect weather patterns have on salinity?

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Notes:

1. The crystal pattern formed when water freezes is an open, six sided (hexagonal) structure. Frozen water molecules in ice are farther apart than are liquid water molecules: open spaces exist within the structure of the frozen (ice) mass that do not occur in liquid water masses.

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