Key Concepts

The polarity the water molecules permits water to dissolve numerous ionically external inspection substances.Salt (sodium chloride) is make from positive sodium ion bonded to an unfavorable chloride ions. Water can dissolve salt because the positive component of water molecules attractive the negative chloride ions and the negative part that water molecules attracts the hopeful sodium ions.The amount of a problem that deserve to dissolve in a fluid (at a specific temperature) is called the solubility of the substance. The substance being liquified is called the solute, and the problem doing the dissolving is referred to as the solvent.

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Summary

Students will certainly make a 2-D design of a salt crystal and use water molecule cut-outs to show how water disappear salt. After see an computer animation of water dissolving salt, students will certainly compare exactly how well water and also alcohol dissolve salt. They will relate their monitorings to the structure of salt, water, and alcohol on the molecule level.

Objective

Students will be able to explain, top top the molecule level, why water deserve to dissolve salt. College student will have the ability to identify the variables in their experiment. College student will also be may be to explain why a much less polar liquid, such together alcohol, is not an excellent at dissolving salt.

Evaluation

Download the student task sheet, and also distribute one per student as soon as specified in the activity. The task sheet will certainly serve as the “Evaluate” component of each 5-E lesson plan.

Safety

Be sure you and also the college student wear correctly fitting goggles. Isopropil alcohol is flammable. Save it away from flames or spark sources. Read and also follow every warnings ~ above the label. Alcohol need to be disposed of according to neighborhood regulations.

Materials for Each Group

Construction paper, any colorScissorsTape or glueWaterIsopropyl alcohol (70% or higher)SaltBalance2 clean plastic cups2 tiny plastic cupsGraduated cylinder

About the products

You may select to laminate the water molecules, sodium ions, and also chloride ions situated on the last page of the task sheet so the you can reuse them through your students next year.


Engage

Make a model of a salt crystal.

Project the photo Sodium Chloride Crystal.

Remind students the the eco-friendly balls represent an unfavorable chloride ions and also the gray balls represent confident sodium ions.

Ask students:

What is it around water molecules and also the ions in salt that might make water able to dissolve salt? The optimistic and an unfavorable polar ends of a water molecule room attracted to the negative chloride ions and positive sodium ions in the salt.

Give each college student an activity sheet.

Students will document their observations and also answer questions around the activity on the activity sheet. The define It through Atoms & Molecules and Take It more sections of the activity sheet will certainly either it is in completed together a class, in groups, or individually, depending upon your instructions. Look at the teacher version of the activity sheet to find the questions and also answers.

Question to Investigate

How walk salt dissolve in water?

Materials

Activity sheet with sodium and also chloride ions and also water moleculesConstruction paper, any type of colorScissorsTape or glue

Procedure

Make a version of a salt crystalCut the end the ions and also water molecules. Arrange the ions on a item of construction record to stand for a 2-D salt crystal. Do not tape this pieces down yet.

Project picture and have students version what happens as soon as salt disappear in water.

Show students a collection of four pictures to help explain the procedure of water dissolve salt.

Project the picture Sodium Chloride dissolve in Water.

Point out that numerous water molecules deserve to arrange themselves near an ion and help remove the from the crystal. Display students that the positive area of a water molecule will certainly be attracted to the an adverse chloride ion and that the an adverse area that a water molecule will be attracted to the positive sodium ion.

Model exactly how water disappear salt

Look at the images showing how water molecules dissolve salt. Climate arrange the water molecules around the sodium and also chloride ion in the exactly orientation. The positive component of the water molecules should be close to the an unfavorable chloride ion. The an adverse part that the water molecules must be near the positive sodium ion.

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Move the water molecules and also sodium and chloride ions to model exactly how water dissolves salt. Explore

Have students command an experiment to uncover out whether water or isopropyl alcohol would certainly be much better at dissolve salt.

Ask college student to do a prediction:

Think around the polarity that water molecules and alcohol molecules. Perform you think alcohol would be just as good, better, or worse 보다 water at dissolving salt?

Discuss exactly how to set up a test to compare exactly how water and also alcohol dissolve salt. Be sure students recognize variables together as:

Amount the water and also alcohol usedAmount of salt added to each liquidTemperature of every liquidAmount the stirring

Question to Investigate

Is alcohol simply as good, better, or worse than water at dissolving salt?

Materials because that Each Group

WaterIsopropyl alcohol (70% or higher)SaltBalance2 clear plastic cups2 little plastic cupsGraduated cylinder

Procedure

In different cups, measure two samples that salt that sweet 5 g each.Place 15 mL that water and alcohol right into separate cups.

At the very same time, include the water and alcohol come the samples the salt.

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Swirl both cup the same means for about 20 seconds and also check for the quantity of salt dissolved.Swirl for another 20 seconds and check. Swirl because that the critical 20 seconds and check. Closely pour turn off the water and also alcohol native the cups and also compare the amount of undissolved salt left in each cup.

Expected Results

There will be much less undissolved salt in the cup with the water 보다 the alcohol. This way that much more salt dissolved in the water 보다 in the alcohol.

Extend

Have students compare the solubility of two various ionic substances in water.

Compare the solubility the the ionic building materials calcium carbonate (CaCO3) and also sodium carbonate (Na2CO3) in water.

Ask students:

How could you compare the solubility of calcium chloride and also calcium carbonate? student should suggest measuring equal quantities of each substance and adding equal quantities of water in ~ the exact same temperature.

Question to Investigate

Do every ionic building material dissolve in water?

Materials because that Each Group

Sodium carbonateCalcium carbonateWater2 clear plastic cups2 tiny plastic cupsBalance

Procedure

Label two clear plastic cups Sodium Carbonate and also Calcium Carbonate.Measure 2 g every of salt carbonate and calcium carbonate and also put castle in their labeled cups.Measure 15 mL the water into each of 2 empty cups.

At the same time, to water the water right into the salt carbonate and also calcium carbonate cups.

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Gently swirl both cups.

Expected Results

The salt carbonate will dissolve, however the calcium carbonate will certainly not. Define that no all ionically external inspection solids dissolve in water.

Discuss student observations.

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Ask students:

Do every ionic substances dissolve in water? exactly how do girlfriend know?Because calcium carbonate does not dissolve in water, students must realize that not all ionic building materials dissolve in water.

Explain that on the molecule level, the ion that make up calcium carbonate are attracted so strongly to each various other that the attraction by water molecule cannot traction them apart. The is a an excellent thing since calcium carbonate is the product that sea shells and also bird eggs space made of. Calcium phosphate is one more ionic solid that does no dissolve in water. This is also good because that is the material that bones and also teeth space made of.

Sodium carbonate division apart totally into ions that are incorporated throughout the water, developing a solution. The sodium and carbonate ions will certainly not settle to the bottom and cannot it is in filtered out of the water.

But calcium lead carbonate does no break up into its ions. Rather it is simply mixed in through the water. If given enough time, the calcium carbonate will clear up to the bottom or deserve to be filtered out of the water. Salt carbonate liquified in water is a great example of a solution, and undissolved calcium lead carbonate is a mixture, not a solution.

Note: The lead carbonate ion is various from the single-atom ion such as salt (Na+) and also chloride (Cl−) that students have actually seen for this reason far. The lead carbonate ion (CO32−) is created of much more than one atom. These varieties of ions, referred to as polyatomic ions, are consisted of of a group of covalently bonded atoms that act together a unit. They generally gain or lose one or much more electrons and also act as an ion. Another common polyatomic ion is the sulfate ion (SO42−). This ion is component of Epsom salt together magnesium sulfate (MgSO4) and many fertilizers as potassium sulfate (K2SO4). You can decide if friend would like to introduce students to this two common polyatomic ions.