Key ConceptsDifferent substances space made from different atoms, ions, or molecules, which interact with water in different ways. Since dissolving depends on the interaction in between water and the substance being dissolved, each substance has actually a properties solubility.
Students will certainly observe a solubility test between salt and sugar. They will certainly then be gift with 4 known crystals and also an unknown. Based on the solubility demonstration, the course will design a solubility check to uncover the identification of the unknown.
Students will have the ability to identify and control variables when making a solubility test. College student will be able to explain why different substances dissolve to various extents in water.
Download the student task sheet, and distribute one every student as soon as specified in the activity. The task sheet will serve as the “Evaluate” ingredient of every 5-E lesson plan.
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Be sure you and also the college student wear correctly fitting goggles.
Materials because that the DemonstrationsGram balanceSimple balanceGraduated cylinderWater4 clean plastic cups2 small plastic cupsSalt Sugar cereal balls (Kix work well)Zip-closing plastic bag (quart-size, storage-grade)
Materials because that Each GroupSalt (sodium chloride)Epsom salt (magnesium sulfate)MSG (monosodium glutamate)Sugar (sucrose)Coarse kosher salt (sodium chloride) WaterBlack construction document Masking tapePen or long-term markerMagnifierGram balance5 tiny plastic cups 5 clear plastic cupsGraduated cylinderPaper towel
About this Lesson
This lesson will certainly take 2 or three class periods.
Do a demonstration to display that different substances have various solubilities.
Tell students that in this demonstration, you will certainly pour salt and sugar right into water to uncover out which dissolves better. In bespeak to do this check fair, you will use the very same amount (mass) of salt and also sugar, the same amount of water in ~ the exact same temperature, and also you will certainly swirl every in the same method for the same size of time.
Question to Investigate
Which disappear in water better, salt or sugar?
Materials because that the DemonstrationBalance that measures in gramsGraduated cylinderWater2 clean plastic cups2 little plastic cupsSalt Sugar
Teacher PreparationLabel 1 clear plastic cup and 1 little cup Salt.Label the various other clear plastic cup and also another little cup Sugar.Measure 5 grams of salt and 5 grams that sugar and also place castle in the pair of small labeled cups. Pour 5 mL that room-temperature water right into the pair of larger empty cups.
ProcedureAt the same time, pour the salt and sugar into the water in the matching cups. Swirl every cup at the exact same time and also in the same method for around 20 seconds. Walk approximately the room to display students the amount of salt and sugar left in the bottom of every cup. If you have an overhead projector, location the cup on the projector so that the entire class can compare what is left undissolved in each cup. Ask students whether one substance appears to dissolve better than the other. Swirl again for 20 seconds and observe. Climate swirl because that 20 an ext seconds and have students make their last observations. Slowly and also carefully to water the solution from every cup back into its empty labeled cup. Shot not come let any type of undissolved crystal enter these cups. Show students the cup so the they deserve to compare the lot of undissolved crystal remaining.
Much an ext sugar will dissolve 보다 salt. There will be more undissolved salt 보다 sugar left in the cups.
Note: Solubility is generally measured through the number of grams the a substance that dissolves in a particular volume the water in ~ a given temperature. The vault demonstration supplies this conventional way to measure solubility. One more approach can be to to compare the number of molecules or ions of each substance the dissolves in water. This would need a way to “count” the molecules or ion in each substance.Explore
Have students try to determine the unknown based on appearance.
Let students understand that prior to doing a solubility test, they will look carefully at the crystals to see if castle might have the ability to get part clues about the identity of the unknown by illustration alone. Have actually students follow the procedure below and record your observations about the crystals on the task sheet. Allow students know that they deserve to look in ~ the crystals and also touch them however they must not taste them.
Question to Investigate
Can you determine the unknown crystal by the means it looks?
Materials for Each GroupBlack construction paperMasking tapePen or permanent marker5 tiny plastic cupsSaltEpsom saltMSGSugarUnknown (Coarse kosher salt)Magnifier
Teacher PreparationLabel the 5 tiny plastic cup Salt, Epsom salt, MSG, Sugar, and also Unknown. Add at least two teaspoons the each decision to its labeled cup.
ProcedureUse masking tape and a pen come label 4 corners the a piece of black color construction record Sugar, Salt, Epsom salt, and also MSG. Label the facility Unknown.Place little samples of Epsom salt, table salt, sugar, MSG, and also the unknown top top the labeled locations of the building and construction paper.
Use a magnifier to look closely at each type of crystal.
All of the crystals space white, yet some are more transparent or opaque 보다 others. Each type of decision is likewise a different size and also shape.
Have student teams share their concepts for a solubility test and consider exactly how each setup controls variables.
As each group presents your plans, have the course identify exactly how each solubility check controls variables. All groups will likely indicate that they usage the exact same volume that water in ~ the same temperature in the same form of containers, and also the exact same amount of every crystal. Yet there might be part disagreement in just how to measure up the very same amount of every crystal. Some students may imply they use the very same volume the each crystal while others may indicate the same mass of every crystal. If no one suggests using mass, define that in the demonstration, you offered an equal mass the salt and also sugar—5 g of each.
Ask students:Is it better to usage the very same volume (like a teaspoon or 5 mL) or the exact same mass (like 5 g) of each crystal? Why? phone call students that you will execute a demonstration that will help them view whether they have to use a volume or mass measure so that they deserve to dissolve the exact same amount of each crystal in water.
Do a demonstrate to display that fixed is better than volume in measure up equal amounts for a solubility test.
Question to Investigate
Is it better to measure up the same volume or very same mass of every crystal as soon as conducting a solubility test to recognize an unknown?
Materials for the Demonstration2 clean plastic cupsCereal balls (Kix occupational well)Zip-closing plastic bag (quart-size storage-grade)Balance
Fill 2 clear plastic cups totally with grain balls. Both cups must be identical and also contain the very same amount of grain balls. Test these cup on a balance come make sure that these cups have the very same mass.
ProcedureHold the cups filled with grain up so the students deserve to see that both have around the very same amount of grain in them. Ar the cups in the facility of each end of a simple balance come prove to her students the both save on computer the same amount the cereal.
Ask college student to do a prediction:I to be going to crush the cereal balls in one cup. Execute you suppose the elevation of cereal in this cup to be higher, lower, or the exact same as in the various other cup? student will most likely say the the crushed grain will no take up as much room in the cup.Pour the grain from one of the cups into a storage-grade, zip-closing plastic bag. Obtain as much air the end as possible and seal the bag. Place the bag on the ground, and crush the cereal thoroughly v your foot. Once the grain is pulverized, open up the bag, and pour the crushed cereal ago into the cup.
Ask students:Which cup contains more cereal?Students will realize that both cup contain the exact same amount the cereal, but some may have actually an urge to say the the cup through the cereal balls contains an ext cereal.Was any kind of cereal included or gotten rid of from one of two people cup?Point the end that even though the crushed cereal takes up less space, the is still the exact same amount of matter (cereal) as remained in the cup before it was crushed.How could you prove that these 2 cups save on computer the exact same amount of matter? college student should indicate placing the cup on a balance together you go before.
Place the cups on opposite end of a balance to prove that the mass of cereal in each cup is the same.
Even though the volume of grain balls is better than the volume that crushed grain balls, the cups will balance on the scale.
Relate student observations in the demonstration to the five crystals they will certainly dissolve in water.
Tell students to imagine the the large cereal balls represent large crystals and also the crushed grain represents tiny crystals. Define that the size and also shape that the crystals may be different, however the balance shows that their mass is the same. Repeat students that mass is a measure of the quantity of matter. Because the big and little crystals (cereal) have actually the same mass, both cup contain the exact same amount that matter. Break up that, in order come measure equal amounts, that is far better to measure up the fixed of substances 보다 the volume.
Ask students:In the solubility test you will certainly do, you will have to measure equal quantities of the five crystals. How will friend measure equal amounts? after ~ this demonstration, students have to realize that measuring mass because that a solubility check is far better than measure by volume.
Based on what student observed once they looked very closely at the various crystals in addition to evidence native the demonstration, they should realize that various crystals have a slightly different size or shape. This will reason them to pack differently in the spoon for this reason that more granules that one will certainly be in the spoon 보다 the other.
Note: The following explanation may be too difficult for students however is consisted of here because that you come think around and discuss with student if friend think the is appropriate. Even if salt and also sugar granules were specifically the same size and shape and also packed specifically the same method in a spoon, that still would certainly not it is in a an excellent idea to usage a teaspoon to measure equal amounts for a solubility test. Here’s why: Salt is around 25% an ext dense than sugar. As such a teaspoon of salt weighs much more than a teaspoon of sugar by virtually 25%. Your dissolving test would certainly not be accurate due to the fact that you would be starting out v a bigger mass the salt than sugar.
Have students weigh five grams of every of the crystals because that the solubility test.
Materials because that Each GroupGram balance5 little plastic cups 5 clear plastic cupsMasking tape and pen or irreversible markerSaltEpsom saltMSGSugarUnknown (coarse kosher salt)Water
ProcedureUse masking tape and a pen to label the 5 small plastic cups Salt, Epsom salt, MSG, Sugar, and Unknown. Label the 5 bigger clear plastic cups the very same way. Sweet 5 g of each crystal and also place every in its tiny labeled cup.
If you do not have enough time, you can stop here and also have students store the crystals and conduct the test one more day. If girlfriend do have time to conduct the test, the procedure follows.
Have college student dissolve the four known crystals and the unknown in room-temperature water.
The amount of water used in the procedure is specific and should be used due to the fact that it gives clear results. Swirling the crystals in water is a great way of mix them to aid them dissolve. Lead the class so the all groups pour their crystal samples right into the water at the very same time. Also tell students when to swirl the water and crystals and also when to stop and also observe. There will certainly be 3 20-second intervals.
Question to Investigate
Can you recognize an unknown making use of a solubility test?
Materials for Each GroupGraduated cylinder5 g every of salt, Epsom salt, MSG, sugar, and also unknown (coarse kosher salt)5 clear plastic cupsWater
ProcedureUse a graduated cylinder to add 5 mL of room temperature water to every empty clear plastic cup. Match up every pair that labeled cups so the each cup of decision is close to its corresponding cup of water.
When her teacher speak you to, work-related with your lab partner to pour the weighed amount of each crystal into its cup of water in ~ the same time.
Slowly and carefully pour the solution from every cup earlier into its small empty cup. Shot not to let any type of undissolved crystal go into the tiny cup. Compare the amount of crystal remaining in each clear plastic cup.
Results might vary. However, sugar should dissolve the most, complied with by Epsom salt. MSG should show up to dissolve a bit much more than salt and the unknown. The salt and also the unknown should appear to dissolve come a comparable degree.
Discuss college student observations and also the possible identity of the unknown.
Ask students:Are there any crystals that you can rule out as most likely not the unknown? based upon their observations, students room most most likely to remove sugar and Epsom salt as the unknown.Which cup or cup seem to have around the very same amount of crystal left undissolved as the unknown?The unknown, salt, and MSG show up to have similar amounts of decision that did not dissolve. What do you think is the identification of the unknown? Students might conclude that the unknown is salt, however in some cases might think the could additionally be MSG.What proof do you have to support your conclusion?Students should cite the amount of decision left behind in each cup as proof that the unknown is either salt or MSG. If who in the course had a very different conclusion and had really different observations, what execute you think may have led to these differences? Students have to mention feasible errors in weighing the crystals, in measuring the quantity of water used, stirring in a various way, or accidentally putting the crystals right into the wrong cups.
Tell students the their test confirmed that various substances have various solubilities. In fact, solubility is a characteristic residential or commercial property of a substance. Describe to students the this kind of solubility test can assist eliminate few of the crystals, but may not be accurate enough to identify the unknown. Since they may have some doubt about the identity of the unknown, student will do a recrystallization test through the crystal services made throughout the solubility test.
Have student conduct an additional test to confirm the identity of the unknown.
Explain come students the they might be able to get an ext clues around the identification of the unknown if they enable the remedies of the dissolved crystals come recrystallize. Enabling the substances to recrystallize from their solutions can show similarities and also differences that were no as quickly seen in the original crystals.
Materials notes: The recrystallization test have to be done automatically after the solubility test through the remedies made throughout the solubility test. Students will certainly reuse the large clear plastic cups and also solutions native the dissolving component of the activity, follow to the procedure.
Question to Investigate
Will the crystals that kind when the options evaporate help identify the unknown?
Materials for Each GroupFive solutions made in the activity, every in a small plastic cup5 clean plastic cup from the activityMagnifierWaterPaper towel
ProcedureRinse every large, clean plastic cup v water to remove any type of remaining crystal. Dried each with a document towel. Closely pour the solution from each small cup right into its corresponding large, clean plastic cup. Allow the solutions to sit overnight. The following day, usage a magnifier to very closely observe the crystals from both the top and also bottom of the cup.
Salt and also the unknown look an extremely similar. Epsom salt, MSG, and sugar look different from each other and different indigenous salt and also the unknown. The sugar may not have actually recrystallized yet, however given an ext time the will type crystals.
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Ask students:Describe the crystals in every cup. What execute you think is the identification of the unknown? students should comment on the shape and also size of the different crystals and notification that both salt and the unknown look very similar.
Tell students that the unknown is outlet kosher salt. That is chemically the very same as continual salt, but the procedure for making plain table salt and also kosher salt is different and also this is why lock look different.