Dissolving Experiments with Solids and Liquids
Day 1
Materials
Two large clear plastic bottles
Gallon of water
Powdered sports drink , with label instructions
Funnel to pour the powder
Spoon to stir
Cups for students
Alka Seltzer tablets, for follow-up lesson the next day
Ice
Stopwatch (if choosing to do the alka seltzer experiment)
Preparation
Check the instructions for how much powder to add for the amount you will make. Plan ahead to match ounces to scoops. Error on the side of adding a little too much. Modeling how you use measurement and proportion shows young people how math is something we all need.
Ask the students if they can see that the two bottles are identical. Announce that you will use the same powder and water for both bottles. The difference will be that bottle B will be more than half full of ice. Fill bottle A with water. Fill bottle B almost to the same level with ice and then enough water to reach the same level as bottle A.
Everyone knows it must be dissolved so we can drink it. Put the same amount of powder in each bottle.
What’s the only difference between the two bottles?
A question to put to a vote:
Would you put ice in the bottle and then stir it up?
Would you stir it up first, and add the ice later?
Half of the class makes a circle, take turns and tries to shake bottle ‘A’ so that the sugar dissolves. The other half forms a circle and takes turns trying dissolve the sugar in ‘B’. Students take turns multiple times until it’s clear that the bottle with ice isn’t dissolving all the sugar. Hold the bottles upside-down for a minute. You can still see crystals falling inside. Any undissolved crystals will pile up. Turn the bottle right-side up and it will be obvious if crystals have not been dissolved.
The bottle at room temperature will dissolve quickly. The group with case ‘B’ will find that the crystals are persistent. Since students will be using energy to shake the bottle, the heat will raise the temperature as they take turns trying to dissolve the sugar. The sugar will dissolve when the bottle is warm enough for the ice to melt.
Students answer the question; Would you stir it up first, and put in the ice later?
Did the cold water slow down the dissolving? Did anyone get the cold bottle ‘B’ to dissolve completely like case ‘A’ ?
After students write in their journals, test to see if they can tell the difference in taste between the 2 bottles. Bottle A might have a stronger taste and bottle B might be sweeter.
Day 2
Materials
Lots of clear cups
Water
Ice
Alka Seltzer tablets
Thermometers
Stopwatch
Show the class two cups marked clearly as A and the other as B. Case A will have ordinary tap water and we use a thermometer to write down the temperature in the journals. Case B has the same level of water in the cup, but is more than half full of ice. The second thermometer goes in B and students write this in their journals.
While the temperatures adjust, ask the students if they remember yesterday, the cold water didn’t let the Gatorade powder dissolve as fast. If I drop a seltzer tablet in each cup, will one dissolve faster than the other?
Students show YES/NO cards, vote by standing or otherwise show a prediction. Assessment is apparent when the example yesterday should predict the result today.
3,2,1 drop the seltzer tablets in both cups at the same time. and use a stopwatch to time the bubbling of case A, and continue timing to record bubbling for Case B. Students talk about what we did and what we saw. We use that discussion to write what we did and what we learned. Students enter in their journals as best they can and read their entry to three other students.
