Question to Investigate Is it better to measure the same volume or same mass of each crystal when conducting a solubility test to identify an unknown? Materials for the Demonstration 2 clear plastic cups Cereal balls Kix work well Zip-closing plastic bag quart-size storage-grade Balance Teacher Preparation Fill two clear plastic cups completely with cereal balls. Procedure Hold the cups filled with cereal up so that students can see that both have about the same amount of cereal in them.
Place the cups in the center of each end of a simple balance to prove to your students that both contain the same amount of cereal. Ask students to make a prediction: I am going to crush the cereal balls in one cup. Do you expect the height of cereal in this cup to be higher, lower, or the same as in the other cup?
Students will probably say that the crushed cereal will not take up as much room in the cup. Pour the cereal from one of the cups into a storage-grade, zip-closing plastic bag. Get as much air out as possible and seal the bag. Place the bag on the ground, and crush the cereal thoroughly with your foot. Once the cereal is pulverized, open the bag, and pour the crushed cereal back into the cup.
Ask students: Which cup contains more cereal? Students will realize that both cups contain the same amount of cereal, but some may have an urge to say that the cup with the cereal balls contains more cereal. Was any cereal added or removed from either cup? Point out that even though the crushed cereal takes up less space, it is still the same amount of matter cereal as was in the cup before it was crushed.
How could you prove that these two cups contain the same amount of matter? Students should suggest placing the cups on a balance as you did before. Expected Results Even though the volume of cereal balls is greater than the volume of crushed cereal balls, the cups will balance on the scale. Relate student observations in the demonstration to the five crystals they will dissolve in water. Ask students: In the solubility test you will do, you will need to measure equal amounts of the five crystals.
How will you measure equal amounts? After this demonstration, students should realize that measuring mass for a solubility test is better than measuring by volume. Have students weigh five grams of each of the crystals for the solubility test. Label the 5 larger clear plastic cups the same way.
Weigh 5 g of each crystal and place each in its small labeled cup. Have students dissolve the four known crystals and the unknown in room-temperature water. Question to Investigate Can you identify an unknown using a solubility test? Materials for Each Group Graduated cylinder 5 g each of salt, Epsom salt, MSG, sugar, and unknown coarse kosher salt 5 clear plastic cups Water Procedure Use a graduated cylinder to add 5 mL of room temperature water to each empty clear plastic cup.
Match up each pair of labeled cups so that each cup of crystal is near its corresponding cup of water. With the help of your lab partners, swirl each cup at the same time and in the same way for about 20 seconds and observe.
Swirl again for another 20 seconds and observe. Swirl again for the last 20 seconds and make your final observations. Expected Results Results may vary. Discuss student observations and the possible identity of the unknown. Ask students: Are there any crystals that you could rule out as probably not the unknown? Based on their observations, students are most likely to eliminate sugar and Epsom salt as the unknown.
Which cup or cups seem to have about the same amount of crystal left undissolved as the unknown? The unknown, salt, and MSG appear to have similar amounts of crystal that did not dissolve. What do you think is the identity of the unknown? Students might conclude that the unknown is salt, but in some cases might think it could also be MSG. What evidence do you have to support your conclusion? Students should cite the amount of crystal left behind in each cup as evidence that the unknown is either salt or MSG.
If someone in the class had a very different conclusion and had very different observations, what do you think may have led to these differences? Students should mention possible errors in weighing the crystals, in measuring the amount of water used, stirring in a different way, or accidentally pouring the crystals into the wrong cups.
Have students conduct another test to confirm the identity of the unknown. Question to Investigate Will the crystals that form when the solutions evaporate help identify the unknown? Materials for Each Group Five solutions made in the activity, each in a small plastic cup 5 clear plastic cups from the activity Magnifier Water Paper towel Procedure Rinse each large, clear plastic cup with water to remove any remaining crystal.
Dry each with a paper towel. Carefully pour the solution from each small cup into its corresponding large, clear plastic cup. Allow the solutions to sit overnight. The next day, use a magnifier to carefully observe the crystals from both the top and bottom of the cup. Expected Results Salt and the unknown look very similar.
Ask students: Describe the crystals in each cup. Students should discuss the shape and size of the different crystals and notice that both salt and the unknown look very similar. Salt Remind students that sodium chloride is an ionic compound. Polar water interacts with these oppositely charged ions to dissolve the salt. Epsom salt Tell students that Epsom salt is an ionic compound. Polar water interacts with these oppositely charged ions to dissolve the Epsom salt. Polar water interacts with these oppositely charged ions to dissolve the MSG.
Sugar Sucrose is not an ionic compound. Sucrose has many O—H bonds, which give it positive and negative polar areas. These areas attract other sucrose molecules and hold them together in a crystal. These polar areas interact with water and cause entire sucrose molecules to separate from one another and dissolve. Extend Help students review the similarities and differences in the way salt and sugar dissolve in water. Ask students: When salt dissolves, why are water molecules attracted to the sodium and chloride ions?
Polar water interacts with these oppositely charged ions to get it to dissolve. Ask students: When sugar dissolves, why are water molecules attracted to sucrose molecules? What are the similarities and differences between water dissolving salt and water dissolving sugar? The sodium and chloride ions separate from one another and become surrounded by water molecules as they dissolve.
Entire sucrose molecules separate from other sucrose molecules. The covalent bonds holding the atoms in the sucrose molecule do not come apart.
Downloads Lesson 5. Students would record these observations for each teaspoon of the chemical added. The experiment was done in two separate glasses: one glass of water had the sugar added and the other glass of water had the salt added. Students would answer questions before starting the activity to make predictions, they would perform the experiment or look through pictures to make their observations , and then answer follow up questions that specifically targeted their chemical thinking with regards to this activity.
Prior to this activity was a lesson regarding the vocabulary saturation, solution, solute, solvent, etc… and a lesson regarding how to calculate the concentration of a solution or the amount of solute dissolved. The school this formative assessment was given in is a high school in a small urban city. The grade level of students this formative assessment was given to were grades 10 and The specific class that this formative assessment was administered to was a standard level, full year high school chemistry class.
Because of the asynchronous flow of the remote learning period, this was challenging to be able to fully communicate with my students during this activity to fully understand their chemical thinking as they were working.
I think this activity could have worked better in a synchronous remote learning environment, however, because some students may not have access to the materials needed for this activity at home, materials could have been prepared in a way in advance to get them to the students so they could perform this activity at home. Doing it in a synchronous environment could have also led to interesting suggestions, ideas, or follow ups that students might have thought about on the fly as they were doing the activity.
Often times, these ideas and thoughts might be missed in an asynchronous environment where students have time to consider their answer in what they deliberately share at the end, and it might be refined and missing elements of their chemical thought process.
Outside of the asynchronous vs synchronous challenge of the formative assessment, I found this formative assessment rather successful in giving students an opportunity to explore aspects they know about molecules and how they interact with each other specifically, polar intermolecular forces and see if they can make a model or conclusion about why these chemicals dissolve differently.
During the Remote Learning session, Google Classroom was the primary tool for instruction and organization of learning materials. For this specific Formative Assessment, two documents were provided to students: one was a Google Doc with the questions and instructions for the activity, the other was a Google Slides presentation containing several pictures that were taken during a demo of the activity in case some students did not have access to the materials at home for this activity, they could work with the image slides to make their observations.
Do you think salt and sugar will dissolve the same way in water? Saturated — Holding as much water or moisture as can be absorbed; thoroughly soaked. Unsaturated — of organic molecules having carbon-carbon double or triple bonds and therefore not containing the greatest possible number of hydrogen for the number of carbon atoms.
Because dissolve can be said to become broken up or absorbed by something or to disappear into something else. When sugar becomes absorbed into water, this is an example of when sugar dissolves into water. When a substance dissolves in water, and each water molecule is like a tiny magnet.
For a substance to dissolve in water, it must also be a polar molecule, or it must be capable of breaking into polar molecules. For example, when you add some salt in water it can be dissolved into water and become salt water. No, dissolve differently. I think they dissolve differently because some of the salt did not dissolve and sugar is much more soluble in water than is salt. For example, when you add 8 spoons of salt into water the salt already starts to stay in the bottom of the cup.
Sugar molecules, on the other hand, maintain the bonds between their constituent atoms when dissolved, and thus remain as whole molecules in the solution.
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