This unit deals with how solids dissolve in liquids and what affects their dissolution. By studying the dissolution process and related factors, students develop an interest in and curiosity about solutions. The purpose of this area is to encourage students to understand the properties of solutions and nurture their interest in the everyday phenomenon of matter dissolving into liquids. Through a range of experiments, students should understand the phenomena of dissolution through the perspective of particle theory, identify the factors which affect the volume of solids dissolved in liquids and devise innovative methods to compare the concentrations of solutions. Through these activities, they naturally come to learn the definitions of solute, solvent and solution.

The grade 5 English science unit, Solutions, meets the academic content standards set in the Korean curriculum, which state students should:

a) Compare the weights of a solid before and after dissolving it and understand the phenomenon of dissolution through the perspective of particle theory.

b) Learn that the dissolving volumes of solids differ according to the types and volumes of solute through the activities of dissolving a variety of solids in water.

c) Develop new methods to compare the concentrations of solutions.

d) Confirm via experiment that the temperature of water is a major factor affecting a solute’s volume when dissolved.

What’s my target?

A solution is made when a solute dissolves in a solvent. The solutions we will look at are those where a solid dissolves in a liquid. The solid is the solute and the liquid is the solvent.

Solute + Solvent = Solution When the solute dissolves, it looks like it disappears, but it is still in the solution. The weight of the solvent and the solute is the same as the weight of the solution.

Things I need:

4 small beakers 4 soluble powders Scales Filter paper Spoon Water

What do I need to do?

1. Weigh the values of the solutes and solvents from the table.

2. Add them together in a beaker. Give the beaker a swirl to dissolve the solute.

3. Wait a few minutes and then weigh the solution. Record the results.

What happened?

Number Solute Weight Solvent Weight Expected weight of solution

Actual weight of solution

1 Sugar 5 grams Water 50 grams 2 Salt 4 grams Water 100 grams 3 Baking soda 3 grams Water 150 grams 4 2 grams Water 200 grams

What did I learn?

1. What is made when a solute is dissolved in a solvent?

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2. If 10 grams of solute dissolve in 90 grams of solvent, what will be the weight of the solution?

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Solution Solvent Solute

What’s my target?

Solubility is the ability for the solute to dissolve in a solvent to make a solution. A solute will only dissolve if it is attracted to the solvent particles. A solute that dissolves in a solvent is said to be soluble. A solid that cannot dissolve in a liquid is said to be insoluble. If the solid does not dissolve, no solution is made. It is simply a mixture.

Things I need:

Vegetable oil Water Food coloring Salt Pet bottle Tablespoon Spoon

What do I need to do?

1. Add a few tablespoons of vegetable oil into a pet bottle

2. Slowly add water until the bottle is about three quarters full. Add a few drops of food coloring.

3. Wait until the food coloring colors the water. Then, add salt, about the size of half a peanut. Continue to add this amount each time you add some salt.

What happened?

Draw a picture of your lava lamp in action.

What did I learn?

1. Which solvent appeared to dissolve the salt best; oil or water?

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2. Use the particle theory to explain why a solute is able to dissolve in a solvent.

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The solute (cubes) is not attracted to the solvent (pyramids) so it doesn’t dissolve.

The solute (cubes) is attracted to the solvent (spheres) so it dissolves.

What’s my target?

Different amounts of different solutes will dissolve at a given temperature. For example, 35g of salt will dissolve in 100mL of water, but only 20.8g of copper sulfate pentahydrate will dissolve in 100mL of water if the water is kept at room temperature. When a solute dissolves, it will spread out evenly throughout the solvent.

Things I need:

Copper sulfate Jar with lid Teaspoon Water Steel wool

What do I need to do?

1. Put 2 teaspoons of copper sulfate into the jar.

2. Pour some water into the jar. Put the lid on and swirl it to dissolve the copper sulfate.

3. Extra: Put a marble-sized piece of steel wool into the copper sulfate solution for a few minutes and observe what happens.

What happened?

Draw a pictures to show your solute, solvent and the solution that you made by completing the first two steps.

What did I learn?

1. Did the dissolved copper sulfate stay in one area or did it spread evenly throughout the solution? How do you know this?

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The temperature-solubility graph to the side shows how many grams of the salts dissolve in 100 grams of water.

Step 3 shows a single replacement reaction, where one element replaces a similar element in a compound. In this case, we turned the iron (steel wool) into copper.

What’s my target?

It is possible to identify an unknown powder by looking at both its physical and chemical properties.

A powder’s physical properties include what it looks like and how it feels.

A powder’s chemical properties are how it reacts with other substances, such as water. For example, is it soluble or insoluble?

Things I need:

Salt Sugar Baking Powder Flour Corn starch 15 cups Teaspoon Water Vinegar Iodine

What do I need to do?

1. Put 1 teaspoon of the salt into 3 different cups. Do the same with the other powders. Note what the powders look like and how they feel.

2. Add 3 teaspoons of water to one of the cups that has salt in it. In the second cup that has salt, add 3 teaspoons of vinegar. In the last cup with salt, add 3 teaspoons of iodine. Do the same for the other powders.

3. Complete the chart with all your observations. The teacher will then give your group a mystery powder. Complete the previous steps and see if you can identify it based on your results.

Powder Appearance Texture

Salt

Flour

Baking soda

Corn starch

Mystery powder

What did I learn?

1. What properties of the mystery powder allowed you to identify it? ________________________________________________________________________________________________________________________________________________________________________________________________

Powder + water + vinegar + iodine

Salt

Flour

Baking soda

Corn starch

Mystery powder

What happened?

What’s my target?

When a solvent is stirred, more solvent particles are free to bump into the solute particles and surround them. This means that it is quicker for the solute to dissolve. If the solute is broken into smaller pieces, it is easier for the solvent particles to bump into them. This means that the solute will dissolve quicker.

The saliva in your mouth is a good solvent for dissolving candies made from sugar. Using your tongue and teeth also helps.

Things I need:

3 candies Stopwatch

What do I need to do?

1. Place a candy in your mouth. Do not chew or move your tongue. Time how long it takes to dissolve.

2. Place another candy in your mouth. Do not chew it, but you can move it around with your tongue. Time how long it takes to dissolve.

3. Place the final candy in your mouth. You can chew it and move it around with your tongue. Time how long it takes to dissolve.

What happened?

Method of eating Not crushed or stirred

Not crushed, but stirred

Crushed and stirred

Time What did I learn?

1. How does moving candy around with your tongue help to dissolve it quicker?

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2. How does chewing candy help to dissolve it quicker?

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What’s my target?

Heat causes the particles of a solvent to move faster. When a solute is put into a heated solvent, the solvent particles will quickly hit against the solute. As the solute starts to break, the surface area of the solute increases, which allows the solvent particles to bump into more solute particles more quickly.

If you want something to dissolve as quickly as possible, you should crush the solute and stir it in a heated solvent.

Things I need:

Alka-Seltzer tablets 3 cups Water Stopwatch

What do I need to do?

1. Half-fill a cup with cold water, another with room-temperature water and the last with warm water.

2. Drop an Alka-Seltzer tablet into each cup at the same time.

3. Observe the fizz in each cup and time how long it takes for each tablet to dissolve.

What happened?

Water Type Cold water Room-temperature Warm water Time to Dissolve

What did I learn?

1. Which type of water dissolved the tablet quickest? Why?

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2. What three things should you do to dissolve a solid very quickly?

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What’s my target?

We learned that a solution is made when a solute dissolves in a solvent. A solution can be classified as dilute or concentrated.

A dilute solution is made when only a small amount of solute dissolves in a solvent.

A concentrated solution is when a lot of solute is dissolved in a solvent.

Things I need:

Sports drink powder 2L bottle of water Cups

What do I need to do?

1. Put a small amount of the sports drink powder in the 2L bottle of water.

2. Put the lid on the bottle and give it a shake to dissolve the powder. Pour out about half of the solution into cups for everyone to taste.

3. In the remaining 1L of the water in the bottle, add the remainder of the sports drink powder. Give it a shake to dissolve the powder. Pour the solution into cups for everyone to taste.

What happened?

Solution Dilute Concentrated Taste

What did I learn?

1. Draw an example showing the particles in a dilute solution. Describe it.

2. Draw an example showing the particles in a concentrated solution. Describe it.

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What’s my target?

In all solutions, there is a maximum amount of solute that can be dissolved in a solvent. When no more solute can be dissolved at a given temperature, the solution is said to be saturated. When a solvent is very hot, it can hold more dissolved solute than when it is cold. When the solution cools down, the solute comes out of the water and forms crystals.

Things I need:

2 cups water 4 cups sugar Food coloring Heater Saucepan Square plastic container Wooden spoon

What do I need to do?

1. Pour 2 cups of water and a few drops of food coloring into a saucepan. Add 4 cups of sugar and stir to try and dissolve as much sugar as possible.

2. Put the saucepan on a heater and continue to stir until all the sugar dissolves.

3. Allow the solution to cool and then pour it into a square plastic container. Leave it for about a week and observe what happens.

What happened? Picture after step 1 Picture after step 3

What did I learn?

1. What type of solution did you make after step 1?

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2. Why did crystals form when you left the solution for about 1 week?

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What’s my target?

A dilute solution is when only a little amount of solute has dissolved in a solvent. A concentrated solution is when a large amount of solute has dissolved in a solvent. Objects that don't normally float in dilute solutions start to float in concentrated solutions. For example, an egg won't float in a dilute saltwater solution, but it will in a concentrated saltwater solution.

Things I need:

2 golf balls 2 large beakers Salt Spoon Water

What do I need to do?

1. Watch your teacher put a golf ball in water with only a small amount of salt dissolved in it.

2. Watch your teacher put a golf ball in water with a large amount of salt dissolved in it.

3. Use the information you have learned to try and make a golf ball float in the middle of the beaker.

What happened?

Use the following pictures to help you draw a salt solution with a density that shows how a golf ball would float in the middle of the water.

What did I learn?

1. Why could the golf ball float when the teacher completed step 2?

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= dissolved salt

What’s my target?

A solution that has only a small amount of solute dissolved in it will be lighter than a solution where a lot of the same solute has dissolved. The dissolved particles in the dilute solution are far apart, making it less dense than a solution that has a lot of solute dissolved in it. A lighter solution will float on top of heavier solutions. This can be seen in density columns.

Things I need:

300g sugar Water Balance Graduated cylinder Beakers Stirring rod Food colorings Test tubes Pipettes

What do I need to do?

1. Use the sugar and water amounts from the table to make up sugar solutions. Add one drop of food coloring to each solution.

2. Use a pipette to put a few milliliters of the different solutions into the same test tube. Start with purple and finish with red.

What happened?

Draw a picture of your density rainbow column.

What did I learn?

1. Why was the blue solution heavier than the yellow solution?

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2. Why could the orange solution stay on top of the yellow solution?

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3. If you made a solution using 50g of sugar and make it up to 140mL, between what colors do you expect it to stay?

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Final volume with water is 140mL

Red 0g of sugar

Orange 14g of sugar

Yellow 28g of sugar

Green 42g of sugar

Blue 56g of sugar

Purple 70g of sugar