Solubility Lab Packet

Transcription

1 Solubility Lab Packet **This packet was created using information gathered from the American Chemical Society s Investigation #4: Dissolving Solids, Liquids, and Gases (2007). It is intended to be used by 6 th Grade Students at Riverwood Middle School.**

2 Table of Contents 2 Activity 4.1: Defining Dissolving A. Does sugar dissolve in water? B. Does food coloring dissolve in water? C. Does sugar dissolve in oil? D. Does food coloring dissolve in oil? Activity 4.2: Dissolving a Substance in Different Liquids E. Does colored sugar dissolve equally well in water, vegetable oil, and alcohol? Activity 4.3: Dissolving Different Liquids in Water F. Do all liquids dissolve in water? Activity 4.4: Gases can Dissolve in Liquids G. Can a gas dissolve in a liquid? Activity 4.5: Temperature affects Dissolving H. Does cocoa mix dissolve better in hot water or cold water? I. Do salt and sugar dissolve better in hot water than in cold water? Activity 4.6: Let s Review

3 Activity 4.1: Defining Dissolving We keep lots of different drinks in our refrigerator. There s milk, juice, soda, and water. My parents even have carbonated water, which I never drink. The other day I was thirsty and took a look in the fridge. For some reason, nothing really interested me. I decided to mix some drink mix in water to make something different. The mix dissolved really quickly and made this purplish drink. It was pretty good. I thought that the mix might improve the carbonated water so I tried dissolving some in there. There was a lot of bubbling, and it didn t taste too bad. The mix dissolved well in water and in carbonated water so I was curious about whether it would dissolve in something else. I wasn t going to drink it, but I tried dissolving some of the mix in a little vegetable oil. I got a pretty interesting result. I wondered why things dissolve the way they do. I also wondered if I could use dissolving to make my own flavored soda. How can you tell when a substance has dissolved? Take a closer look: Two of the main ingredients in most drink mixes are sugar and coloring. You can do an activity to find out how well those ingredients dissolve in water. A. Does sugar dissolve in water? Materials Water 2 teaspoons of sugar 2 tablespoons of vegetable oil Food coloring 4 clear plastic cups 1 tablespoon 1 teaspoon 1. Place about 1 tablespoon of room-temperature water in each of 2 clear plastic cups. 2. Add 1 teaspoon of sugar to one cup and swirl for about 10 seconds. Observe. 3. Swirl for another 10 seconds and observe. Swirl for a final 10 seconds and observe. 3

4 4 4. What did you observe when you swirled the sugar and water together? 5. What do you think happened to the sugar crystals? B. Does food coloring dissolve in water? 1. Gently place 1 drop of food coloring in the other cup of water. Observe. 2. Gently swirl for a few seconds. Swirl again for a few more seconds. 3. What do you observe? 4. Do you think there is more food coloring in one part of the water than in another? What makes you think that? 5. Do you think there is more sugar in one part of the water than in another? 6. Based on your observations so far, how do you know when a substance has dissolved? C. Does sugar dissolve in oil? 1. Place 1 tablespoon of vegetable oil in each of 2 clear plastic cups.

5 2. Add 1 teaspoon of sugar to one cup and swirl for about 10 seconds. Observe. 3. Swirl for another 10 seconds and observe. Swirl for a final 10 seconds and observe. 4. What do you observe? 5. Would you say that sugar dissolved in the oil? Why? D. Does food coloring dissolve in oil? 6. Gently place 1 drop of food coloring in the other cup of oil. Observe. 7. Gently swirl for a few seconds. Swirl again for a few seconds. 8. What do you observe? 9. Would you say that the food coloring dissolved in the oil? Why? 10. Even though a substance dissolved in one liquid, will it necessarily dissolve in another? Explain your answer based on your observations in this activity. 11. How can you tell when a substance has dissolved? 5

6 In the previous experiments, you saw that sugar and food coloring dissolve in water, but do not dissolve in oil. So we can safely say that just because one substance dissolves in one liquid, it will not necessarily dissolve in another. When a substance dissolves, it is broken all the way down to its molecules or ions. These are so small and so well-mixed that you cannot see them and they do not settle to the bottom. In the activity, you also saw that solids (like sugar) and liquids (like food coloring) can dissolve. A substance that dissolves in a solution is called a solute. A solvent is the substance that dissolves a solute. So, sugar and food coloring were solutes that dissolved in the water. Water was the solvent. Solubility, the amount of substance that can dissolve in a liquid, is a physical property. In the coming activities, you will learn more about dissolving solids and liquids and see that gases can dissolve too. Activity 4.2: Dissolving a Substance in Different Liquids E. Does colored sugar dissolve equally well in water, vegetable oil, and alcohol? Materials Water 3 clear plastic cups Vegetable oil Food coloring Isopropyl rubbing alcohol 3 popsicle sticks Sugar in Ziploc bag (sandwich size) 1 teaspoon 1. Your teacher will give you a plastic bag with 1 tablespoon of sugar in it. Add 1 drop of food coloring to the sugar. 2. Leaving air in the bag, seal the bag securely. 3. Shake the bag vigorously until the sugar is thoroughly colored. 4. Once you have the colored sugar, add 1 teaspoon of colored sugar to 1 tablespoon of water, alcohol, and vegetable oil. 5. Stir each with a clean Popsicle stick. 6. Record you observations in the table below. What do you observe? Describe what happens to both the color and the sugar when you stir colored sugar in each liquid. Water Alcohol Oil 6

7 7 7. In the experiment, you compared how well colored sugar dissolves in water, alcohol, and oil. What did you do to make sure it was a fair comparison? 8. If a substance dissolves in one liquid, will it necessarily dissolve equally well in another? Explain your answer using evidence from your experiment. 9. Let s say your teacher gave you a sample of water and a sample of isopropyl rubbing alcohol, but did not tell you which one was which. Assuming you had no colored sugar, do you think dissolving salt or some other solute might help you identify the liquids? Why or why not? Activity 4.3: Dissolving Different Liquids in Water F. Do all liquids dissolve in water? You know that some solids, like sugar, can dissolve in water. In this experiment, you will find out if liquids can dissolve in water. Materials Water Corn syrup Vegetable oil 3 clear plastic cups Isopropyl rubbing alcohol 3 popsicle sticks 1. Half-fill three clear plastic cups with room-temperature water. 2. While looking at the water from the side, slowly pour the alcohol into the first cup of water.

8 8 3. Observe first to see if the alcohol dissolves in the water. 4. Stir to see if the alcohol dissolves. 5. Record your observations in the chart below. 6. Repeat Steps 2-5 for vegetable oil and corn syrup. What do you observe? Describe what happens when you mix the following liquids (isopropyl alcohol, vegetable oil, and corn syrup) with water. Use the table to organize your observations. Isopropyl Alcohol Vegetable Oil Corn Syrup Does it dissolve in water? Does it dissolve in water? Does it dissolve in water? How do you know? How do you know? How do you know? 7. Do all liquids dissolve equally well in water? Use evidence from your experiment to justify your answer. 8. The USGS Website states that Water is called the universal solvent, because it is capable of dissolving more substances than any other liquid, which is important to every living thing on Earth. It means that wherever water goes, either through the air, the ground, or through our bodies, it takes along valuable chemicals, minerals, and nutrients.

9 9 How did our labs prove that water is the universal solvent? Activity 4.4: Gases can Dissolve in Liquids G. Can a gas dissolve in a liquid? Carbonated water is made by dissolving carbon dioxide gas in water. Materials Unopened bottle of club soda 1. Very slowly unscrew the bottle cap. 2. Wait a few seconds. Observe the bubbles. 3. Tighten the cap on the bottle. 4. What did you see when your teacher slowly opened a bottle of carbonated water? 5. What gas are the bubbles made of? 6. Where was this gas before the bottle was opened? 7. Based on this demonstration, what can you conclude about gases dissolving in liquids? Activity 4.5: Temperature affects Dissolving H. Does cocoa mix dissolve better in hot water or cold water? In this experiment, you are going to compare how well cocoa mix dissolves in cold and hot water.

10 Materials Hot and cold water 2 clear plastic cups Powdered cocoa mix 2 popsicle sticks 1. Place ¼ cup of cold and hot water in each of 2 cups. 2. At the same time, add 1 teaspoon of cocoa mix to each cup. 3. Stir each for 10 seconds and observe. 4. Stir for another 10 seconds and observe again. 5. What do you observe? Describe what happens when you place cocoa mix in cold and hot water. Cold Water Hot Water Based on what you saw in your experiment, does increasing the temperature of a liquid affect how much cocoa will dissolve in it? I. Do salt and sugar dissolve better in hot water than in cold water? Materials Hot and cold water 4 graduated cylinders Sugar 4 straws Salt 4 small cups for Salt in Cold and Hot Water 1. Pour 50 ml of hot water into a cup and 50 ml of cold water into another cup. 2. Pour 20 grams of salt into each cup at the same time. 3. Stir the contents of each graduated cylinder with a straw for about 1 minute.

11 4. Allow the contents to settle as you do the same solubility test for sugar. for Sugar in Cold and Hot Water 5. Pour 50 ml of hot water into a cup and 50 ml of cold water into another cup. 6. Pour 20 grams of sugar into each cup at the same time. 7. Stir the contents of each graduated cylinder with a straw for about 1 minute. 8. Allow the contents to settle. 9. Solubility is the capability of a solute to dissolve in a solvent. In the experiment, what substance(s) is the solute? What substance(s) is the solvent? 10. Does salt dissolve better in hot water than in cold water? Explain your answer, based on your observations from the demonstration. 11. Does sugar dissolve better in hot water than in cold water? Explain your answer, based on your observations from the demonstration. 12. Which is affected most by increasing temperature of water the solubility of salt or the solubility of sugar? Explain your answer. 11

12 The curves on the graph below show the amount of salt and sugar that can be dissolved in water at different temperatures. You may use a ruler or straight edge to help you read the graph and fill out the cart beside it. 12 How much salt and sugar will dissolve in water at different temperatures? Salt (g) Sugar (g) Freezing water (0 C) Room temp water (20 C) Warm water (50 C) Very hot water (80 C) Boiling water (100 C)

13 13. Which is affected most by increasing the temperature of water the solubility of salt or the solubility of sugar? Use the graph and chart to explain your answer. Activity 4.6: Let s Review Based on the information gathered throughout the lab, answer the following questions about the many aspects of dissolving. 1. If someone said to you, Since a solid dissolves in water, it will dissolve just as well in other liquids. Would you agree or disagree? What kind of test could you do to show whether or not you are right? 2. If someone said to you, If one liquid dissolves in water, that means that other liquids will dissolve just as well in water too. Would you agree or disagree? What kind of test could you do to show whether or not you are right? 3. The chart on the next page shows approximately how much potassium chloride can dissolve in 100 milliliters of water at different temperatures. Potassium chloride is used as a salt substitute for people who should not eat regular salt (sodium chloride). 13

14 14 Solubility of Sodium Chloride and Potassium Chloride Temperature C Sodium Chloride Potassium Chloride The graph shows how much salt (sodium chloride) and sugar (sucrose) can dissolve in 100 milliliters of water at different temperatures. Use the information about the solubility of potassium chloride in the chart above to mark new points on the graph. Then draw a smooth line that comes as close as possible to all the points. This new line will show the solubility of potassium chloride at different temperatures.

15 4. According to the graph, which substance s solubility is most affected by increasing the temperature of the water? Use evidence from the graph to explain your answer. 5. At what temperature would you say the solubility of sodium chloride and potassium chloride are about the same? 6. Look at the lines showing the solubility of sodium chloride and potassium chloride. Which is more soluble at low, medium, and high temperatures? 15