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This lesson shows students that matter such as salt seems to have disappeared when dissolved in water, but it is still there.
Materials
For each team:
- clear plastic cup
- weight
- table salt
- plastic spoon for stirring
- measuring spoon
Background for teachers
Dissolving a solid in a liquid, such as table salt in water, is a physical change because only the state of matter has changed. Physical changes are often reversible. If the water is allowed to evaporate, the salt will return to a solid state. While the salt may not recrystallize into the same uniform crystals you started with, it is still salt. When salt is dissolved in water, the water tastes salty because the salt is still in it. It does not combine with the water to cause a chemical reaction.
This activity can take several weeks to complete, so start at the beginning of your study of the subject. Once the water has evaporated, students should have a good understanding of the difference between a chemical reaction and a physical change.
Intended learning outcomes
1-Use scientific process and thinking skills.
2-Manifest scientific attitudes and interests.
3-Understand scientific concepts and principles.
4-Communicate effectively using scientific language and reasoning.
Instructional procedures
Attached files
- salt_journal.pdf
Dissolve salt diary page - team_salt.pdf
Team Procedures for "Dissolving Salt"
Invitation to learn:
Show the class a glass of water and have them list its physical properties. Then show them some salt and have them list its properties. Pour about a tablespoon of table salt into the water and stir until all the salt has dissolved. Ask the class to describe the salt water. Say, "You cannot see the salt; where does the salt come from?" Have someone taste the salt water and describe what it tastes like. Question: "Where did the salt go?" (It's still in the water; you can taste it.) Ask the students how they can get the salt out of the water again. Then have the teams complete the instructional procedures below.
Instruction procedures:
Collaborative teams of 3-5 must go through the following procedures: (See "Team Procedures" in the Appendices)
- Pour about 15 ml (about 1 tablespoon) of salt into a clear plastic cup. Place the cup on a scale and find the weight of the cup and salt. Record the weight.
- Fill the beaker about 1/3 full of hot tap water and stir until all the salt has dissolved.
- Use a permanent marker to draw a line at the water level and place the cup where it can remain undisturbed while the water evaporates.
- Make a prediction (hypothesis): What happens to the salt when the water evaporates?
- Check the cup daily. If you notice changes, record your observations.
- When the water has completely evaporated, record your observations of the cup. Weigh the cup and material in the cup. Record the weight.
- Answer the following questions:
- How does the weight of the cup after the water has evaporated compare to the weight of the cup and salt before the water was added? Explain why.
- What is the material of the cup?
- Was your prediction correct?
- Was it a chemical reaction or a physical change when the salt dissolved in the water? How do you know that? (It was a physical change because all the salt was still there when the water evaporated. No new substances were formed.)
Extensions
You might consider having some of the class do this activity with sugar or baking soda. Then have the teams compare the data at the end of the procedures.
Assessment plan
Use this rubric to rate your students' performance:
Name of the student ____________________________________
| 4 | 3 | 2 | 1 | |
| Magazine side | Descriptions and data clear and accurate. All observations are completed. | Descriptions and data usually clear and accurate. All observations are completed. | Descriptions and data somewhat clear and accurate. All sightings incomplete. | Descriptions and data are unclear and inaccurate. All observations incomplete. |
| Participation in Activity | Used the time well and focused on the activity. | Time quite well spent. Remained focused on the activity most of the time. | Did the activity but didn't seem very interested. The focus fell off on several occasions. | Participation was minimal OR the student appeared negative participant. |
Bibliography
This lesson is part of the Fifth Grade Science Teacher Resource Book (TRB3) http://www.usoe.org/curr/science/core/5th/TRB5/. TRB3 is designed as your textbook for teaching the science curriculum to your students. This book covers all the objectives of each standard and benchmark. If taught effectively, a student should do well on the End-of-Level (CRT) tests. TRB3 is designed for teachers who know very little about science, as well as for teachers with a broad knowledge of science.
made:11/04/2002
Topical:14/09/2022
127455
FAQs
How do you dissolve salt? ›
When salt is mixed with water, the salt dissolves because the covalent bonds of water are stronger than the ionic bonds in the salt molecules.
Is dissolving salt in water a chemical or physical change? ›For example salt dissolving in water is usually considered to be a physical change, however the chemical species in salt solution (hydrated sodium and chlorine ions) are different from the species in solid salt.
How do you get dissolved salt back? ›You can boil or evaporate the water and the salt will be left behind as a solid. If you want to collect the water, you can use distillation. This works because salt has a much higher boiling point than water. One way to separate salt and water at home is to boil the salt water in a pot with a lid.
Is dissolving salt in water a reversible or irreversible change? ›Dissolution of salt in water is a reversible change.
What cleaner dissolves salt? ›To remove salt stains, prepare a solution of 1 cup vinegar and a squirt of dish soap to every gallon of warm water. (Water alone won't work and may just move the salt around and re-deposit it). 3. Apply the vinegar mix to stains and scrub with a stiff brush or broom.
What makes salt dissolve faster? ›Most solids, including sugar and salt, become more soluble with increasing temperature. This is because heat increases molecular movement, causing more collisions between the water molecules and the solid.
What type of change is dissolving common salt in water? ›Dissolving common salt in water - Physical change.
What type of change salt dissolves in water? ›Therefore, dissolving salt in water is an example of a chemical change.
Why is salt dissolving a physical change? ›Dissolving a solid in liquid, such as table salt in water, is a physical change because only the state of the matter has changed.
Can salt dissolve in water without stirring? ›The a parameter represents the time taken for the sodium chloride sample to dissolve at 0 °C with no stirring, so this result indicated that the sodium chloride sample would dissolve at 0 °C without stirring in 2457 s (40 min 57 s).
Can you reverse salt in water? ›
The most common and effective way to remove salt from water is through physical filtration. Specifically, reverse osmosis systems are capable of removing salt and a wide variety of other contaminants from softened water.
Does salt dissolve in cold water? ›Salt water is salt mixed with fresh water. However, salt in cold water does not dissolve as well as if the water is warm. Warm water has more room between the water molecules, allowing more salt to fit. Cool water molecules are tighter together and will not allow much salt to dissolve.
How can salt dissolving in water be reversed? ›Evaporation: Salt can be separated from its solution because the mixing of salt in water is a change that can be reversed by evaporation. Evaporation is the process of changing a liquid into its vapor state by the action of heat.
Why is dissolving salt in water a chemical change? ›When salt dissolves, the ionic bonds between the atoms break. The reactant (sodium chloride or NaCl) differs from the products (sodium and chloride ions), so a chemical change occurs.
What is the reverse change of dissolving? ›Even when salt dissolves, it can still go back to the way it was before. Salt that has dissolved in water can be returned back to salt by evaporating the water. Evaporating - In a bathroom, hot water from the shower can change state into gas. This is called evaporation and it can be reversed.
Does vinegar deactivate salt? ›Add an acid.
You can add lemon juice, lime juice, or apple cider vinegar to salty food to help neutralize the saltiness. A tomato product, such as tomato sauce or tomato paste, will also work since tomatoes are acidic.
The acidic nature of vinegar along with the sweetness of sugar evens out the excess salty flavour.
Does white vinegar break down salt? ›Yes, salt will dissolve in vinegar.
What are 3 ways to dissolve a salt? ›1 Answer. You could crush or grind it into smaller pieces, stir the solution, or increase the temperature of the solution.
How much salt will dissolve in a gallon of water? ›One gallon of water will dissolve 3 pounds of salt. To dissolve 8 pounds of salt, at least 3 gallons of water should be in the brine tank.
What will dissolve the highest amount of salt? ›
Expert-Verified Answer
Hence hot water will easily allow more salt to be dissolved in it.
Answer and Explanation: When you mix salt and water together, you form a mixture, which can also be called a solution. The salt will dissolve into the water, and the mixture will be homogeneous because you can no longer see the salt. Since water dissolves salt, water is the solvent and salt is the solute.
Is baking soda and vinegar a chemical change? ›A chemical reaction is a process in which substances undergo a chemical change to form a different substance. Mixing baking soda and vinegar will create a chemical reaction because one is an acid and the other a base.
Is dissolving a physical change? ›(2) Yes, dissolving is a physical change because, for example, when we dissolve sugar in water, the sugar particles spread out and form a solution with water. This process can be reversed by evaporating water and collecting the sugar.
Why dissolving is not a chemical change? ›The dissolving of a solid in water is a physical change, because no chemical reaction occurs, and there is no new substance produced as a result. The components of the solid separate while in the water, but do not form new chemical bonds with other atoms to make a new product.
What is salt water in chemistry? ›Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride).
Will all salt dissolve in water? ›Most salt is soluble in water. When salt is mixed into water, it breaks down and dissolves. Salts contain both negative and positive ions held together by the force of attraction between opposite charges, or polarity.
Do all types of salt dissolve in water? ›All sodium, potassium, and ammonium salts are soluble in water. 3. The chlorides, bromides, and iodides of all metals except lead, silver, and mercury(I) are soluble in water.
What best explains the fact that salt dissolves in water? ›Table salt dissolves in water because the very polar water molecules attract both the positively charged sodium ions and the negatively charged chloride ions. This interaction is called an ion / dipole interaction.
Can you drink ocean water if you boil it? ›Desalination is the process of removing salt from seawater, making it drinkable. This is done either by boiling the water and collecting the vapor (thermal) or by pushing it through special filters (membrane).
Why can't we drink sea water? ›
Drinking seawater can be deadly to humans.
Seawater contains salt. When humans drink seawater, their cells are thus taking in water and salt. While humans can safely ingest small amounts of salt, the salt content in seawater is much higher than what can be processed by the human body.
There's the cost of building the facility, then there are the ongoing operational costs. The Pacific Institute's research shows that seawater desalination costs nearly four times more than water importation, and five times as much as capturing and processing rainwater.
What does salt not dissolve in? ›Alcohol does not dissolve salt as well as water does.
How long does it take salt to dissolve in tap water? ›Results. Boiling water (70 degrees) - fully dissolved in the 2 minute period.
Does hot or cold water remove salt? ›Rinsing with warm water
Although warm water is capable of removing more salt then cold water, it will not remove all of the salt. And it will still need another process. Seeing the risk warm water brings with it, it is often advised to skip warm water and use more effective processes with less risk.
Use pelletized gypsum soil condition to reverse salt damage on lawns. The gypsum, or calcium sulfate, replaces the salt with calcium and sulfur, which will help to heal the grass and encourage new growth. It is also useful in helping the soil retain water.
What is the reversible reaction of salt? ›If you heat the salt solution, the water will evaporate, leaving the salt behind, the water vapour can be cooled so that it condenses back to liquid form (water). This is a reversible change because we will get the salt and water back in their original forms.
How do you remove soluble salts from water? ›Elevating the temperature of the water to 120-140 F (49 C to 60 C) and using a wetting agent, such as some water blast inhibitors, to reduce the surface tension of the water increase the rate at which the soluble salts will dissolve. Increasing the velocity of the water particles will also be beneficial.
Does dissolving salt in water change temperature? ›When a salt is dissolved in water, the temperature of solution decreases.
What are the 5 reversible changes? ›Processes such as melting, boiling, evaporation, freezing, condensation, dissolution are reversible changes.
Is dissolving always reversible? ›
Reversible changes
If you can get back the substances you started the reaction with, that's a reversible reaction. A reversible change might change how a material looks or feels, but it doesn't create new materials. Examples of reversible reactions include dissolving, evaporation, melting and freezing.
- Thermal decomposition of salts such as hydrates copper-sulphate results in the dehydration of the salt. CuSO4.5H2O→CuSO4(s)+5H2O(g)
- Decomposition of ammonium chloride is also a reversible reaction. ...
- Formation of water by combustion of hydrogen.
1 Answer. You could crush or grind it into smaller pieces, stir the solution, or increase the temperature of the solution.
Can you dissolve salt from water? ›The isolated ions are spread evenly in the solvent to form a homogeneous mixture. This process continues until the salt is completely dissolved. If the amount of salt added to the water is too much, some of the salt will not dissolve and will sink to the bottom. Salt dissolves but does not melt in water.
Does vinegar dissolve salts? ›Yes, salt will dissolve in vinegar.
Does salt dissolve without stirring? ›A common misconception about dissolving is that heating and/or stirring are required for the dissolving process to occur. In this study, quantitative experimental evidence was collected and analyzed to demonstrate that neither heating nor stirring is required for dissolving.
Why isn't my salt dissolving? ›Using too much salt? You could well have reached what they call the saturation point, beyond which more salt won't dissolve. Heating the water will make more dissolve, but this will come out of the solution once it cools.
How long does it take for salt to dissolve? ›Generally it takes salt 2 minutes to dissolve in boiling water.
Does salt dissolve in water without boiling? ›Yes! Salt does dissolve quicker in room temperature water than in cold water.
What temperature does salt dissolve in water? ›At 20 °C (68 °F) one liter of water can dissolve about 357 grams of salt, a concentration of 26.3% w/w. At boiling (100 °C (212 °F)) the amount that can be dissolved in one liter of water increases to about 391 grams, a concentration of 28.1% w/w.
Will salt dissolve in cold water? ›
Salt water is salt mixed with fresh water. However, salt in cold water does not dissolve as well as if the water is warm. Warm water has more room between the water molecules, allowing more salt to fit. Cool water molecules are tighter together and will not allow much salt to dissolve.
What happens if you mix vinegar with salt? ›When an acid reacts with base it forms salt. Vinegar is acetic acid CH 3 COOH and simple salt is sodium chloride . The reaction between acid and the salt takes place as follows: Hence from the above reaction, we can say that when vinegar reacts with salt hydrochloric acid is produced.
Why won't my salt dissolve in vinegar? ›Re: Maintain Salt Granules in Vinegar
Because vinegar is mostly water, and because salt dissolves in water, that is what is happening. There is no "chemical reaction" as such. You can add salt until no more will dissolve to make a supersaturated solution or a paste, if you like.
Vinegar and Epsom salt would not create anything. Vinegar and zinc, though, would create hydrogen.
What is the best liquid to dissolve salt? ›Solvents and the Polarity Index
Chemical-Ecology.net offers a list of solvents which shows water as having a polarity index of nine. That means that it is the most balanced solution with regard to its polarity, and, therefore, is the only solution which will dissolve a salt.
All sodium, potassium and ammonium salts are soluble, except carbonates. If it's a silver or lead salt, chances are it won't be soluble.