good hypothesis about solubility

Science Experiments on Solubility

Many of the substances people use daily, including shampoo, gasoline and milk, are mixtures. When mixtures are homogenous, meaning the particles of each substance are mixed evenly, they create a solution. Solutions form when the attraction between the solute, a substance that dissolves, and solvent, a substance like water that does the dissolving, is greater than the particles that make up the solute. Solubility measures the amount of a solute that can dissolve in a solvent.

Saturated Solutions

Introduce solubility by testing how much a solute dissolves in water before the solution becomes too saturated. This type of experiment introduces aqueous solutions, or solutions of a substance dissolved in water, to students. The experiment can also spark a discussion about why water is able to dissolve so many substances; the attraction between water and the solute is greater than the particles of the solute. The scientific method dictates you must include a hypothesis; for example, predicting that more of one solute will dissolve than another substance. To test your hypothesis, measure 1 cup each of table salt, Epsom salt and sugar, placing each substance in a separate container. Prepare three plastic cups with 1/2 cup of distilled water each. Add 1 teaspoon of table salt to one plastic cup and stir to dissolve. Continue adding table salt to this cup in small increments until the solute will no longer dissolve. Weigh the remaining salt and subtract from the initial cup to find the amount that remains. Repeat the steps with the Epsom salt as well as sugar. Compare how much of each solute was dissolved to determine if your hypothesis was correct. You should find that some crystals of each substance remain floating in the water because the water is already saturated.

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Science experiments on evaporation for kids in seventh grade, science experiments with purple cabbage, a simple ph experiment to do in a class, effects of acetone on plastic, chemistry experiments with baking soda & hydrochloric acid, testing various solvents.

Water isn't the only liquid that will dissolve solids like salt and sugar. Water is considered the universal solvent because the electrical charge of its molecules attract other substances, but students might wonder if other liquids also attract and dissolve solids. Test water, rubbing alcohol, club soda, cooking oil and nail polish to determine which one is the best solvent. Create your hypothesis; for example, that nail polish will dissolve more solutes and cooking oil will be the most ineffective solvent. Prepare plastic cups with 2 teaspoons of each liquid. Measure and add 1 teaspoon of salt to each liquid and stir for 10 to 30 seconds. Record results, indicating if the salt dissolved completely, partially or not at all. Repeat the experiment with other solutes like baking soda, sugar and sand to determine if multiple substances can dissolve in particular solvents.

Results and Explanations

You will find that water is the best solvent, and heavier liquids like cooking oil are the worst. Some salt will dissolve in alcohol, but since the polarity of alcohol is not as strong as water, it is not as good a solvent. Club soda will likely dissolve more than alcohol because it contains water, but the soda is also somewhat saturated with carbon dioxide. This experiment also shows that "like dissolves like," so while salt dissolves in water because they are both polar compounds, salt will not dissolve in organic compounds like nail polish. Examine your results to see if your hypothesis was correct .

Temperature and Solubility

A common hypothesis states that hot water will dissolve more solute than cold water. Use this experiment to determine if temperature has any effect on solubility. Add a 1/2 cup of lukewarm tap water to a plastic cup. Weigh about 5 tablespoons of salt and gradually add the salt to the tap water, stirring to mix. Stop adding salt when it no longer dissolves. Repeat the mixing steps with 1/2 cup each of ice water and hot water; determine at which temperature more salt dissolves. This experiment proves that the solubility of some substances is dependent on temperature, and you will notice much more salt dissolves in hot water than in cold.

Peeps Solubility

In 1996, scholars James Zimring and Gary Falcon examined the solubility of Peeps, the bird-shaped marshmallow candy. You can duplicate a similar experiment and hypothesize that the candy is not soluble in water but will dissolve in acetone, or nail polish remover. Fill four plastic cups with 1 cup each of water, acetone, vinegar and rubbing alcohol. Submerge one Peeps candy in each liquid and observe every 20 minutes for an hour. Write down your observations. This experiment demonstrates to students the difference between what is expected versus the outcome. Many students think that candy is made from sugar, and since they know sugar will dissolve in liquids like water, they believe the candy will dissolve. The candy doesn't dissolve in any of these liquids. From these results, students can determine that the candy must be made up of other substances resistant to dissolving in liquids.

• Science Buddies: Saturated Solutions: Measuring Solubility
• Education.com: To Test the Solubility of Common Liquid Solvents
• Peep Research: Solubility Testing

Cara Batema is a musician, teacher and writer who specializes in early childhood, special needs and psychology. Since 2010, Batema has been an active writer in the fields of education, parenting, science and health. She holds a bachelor's degree in music therapy and creative writing.

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Solubility and Factors Affecting Solubility

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Learning Objectives

• To understand how Temperature, Pressure, and the presence of other solutes affect the solubility of solutes in solvents.

Solubility is defined as the upper limit of solute that can be dissolved in a given amount of solvent at equilibrium. In such an equilibrium, Le Chatelier's principle can be used to explain most of the main factors that affect solubility. Le Ch â telier's principle dictates that the effect of a stress upon a system in chemical equilibrium can be predicted in that the system tends to shift in such a way as to alleviate that stress.

Solute-Solvent Interactions Affect Solubility

The relation between the solute and solvent is very important in determining solubility . Strong solute-solvent attractions equate to greater solubility while weak solute-solvent attractions equate to lesser solubility . In turn, polar solutes tend to dissolve best in polar solvents while non-polar solutes tend to dissolve best in non-polar solvents. In the case of a polar solute and non-polar solvent (or vice versa), it tends to be insoluble or only soluble to a miniscule degree. A general rule to remember is, "Like dissolves like."

Common-Ion Effect

The common-ion effect is a term that describes the decrease in solubility of an ionic compound when a salt that contains an ion that already exists in the chemical equilibrium is added to the mixture. This effect best be explained by Le Chatelier's principle . Imagine if the slightly soluble ionic compound calcium sulfate, CaSO ​4 , is added to water. The net ionic equation for the resulting chemical equilibrium is the following:

\[ CaSO_{4(s)} \rightleftharpoons Ca^{2+}_{(aq)} + SO^{2-}_{4 (aq)} \]

Calcium sulfate is slightly soluble; at equilibrium, most of the calcium and sulfate exists in the solid form of calcium sulfate.

Suppose the soluble ionic compound copper sulfate (CuSO ​4 ) were added to the solution. Copper sulfate is soluble; therefore, its only important effect on the net ionic equation is the addition of more sulfate (SO 4 2 - ) ions.

\[ CuSO_{4(s)} \rightleftharpoons Cu^{2+}_{(aq)} + SO^{2-}_{4 (aq)} \]

The sulfate ions dissociated from copper sulfate are already present (common to) in the mixture from the slight dissociation of calcium sulfate. Thus, this addition of sulfate ions places stress on the previously established equilibrium. Le Chatelier's principle dictates that the additional stress on this product side of the equilibrium results in the shift of equilibrium towards the reactants side in order to alleviate this new stress. Because of the shift toward the reactant side, the solubility of the slightly soluble calcium sulfate is reduced even further.

Temperature Affects Solubility

Temperature changes affect the solubility of solids, liquids and gases differently. However, those effects are finitely determined only for solids and gases.

The effects of temperature on the solubility of solids differ depending on whether the reaction is endothermic or exothermic. Using Le Chatelier's principle, the effects of temperature in both scenarios can be determined.

• First, consider an endothermic reaction (\(\Delta{H_{solvation}}>0\)): Increasing the temperature results in a stress on the reactants side from the additional heat. Le Chatelier's principle predicts that the system shifts toward the product side in order to alleviate this stress. By shifting towards the product side, more of the solid is dissociated when equilibrium is again established, resulting in increased solubility.
• Second, consider an exothermic reaction ((\(\Delta{H_{solvation}}<0\)): Increasing the temperature results in a stress on the products side from the additional heat. Le Chatelier's principle predicts that the system shifts toward the reactant side in order to alleviate this stress. By shifting towards the reactant's side, less of the solid is dissociated when equilibrium is again established, resulting in decreased solubility.

In the case of liquids, there is no defined trends for the effects of temperature on the solubility of liquids.

In understanding the effects of temperature on the solubility of gases, it is first important to remember that temperature is a measure of the average kinetic energy. As temperature increases, kinetic energy increases. The greater kinetic energy results in greater molecular motion of the gas particles. As a result, the gas particles dissolved in the liquid are more likely to escape to the gas phase and the existing gas particles are less likely to be dissolved. The converse is true as well. The trend is thus as follows: increased temperatures mean lesser solubility and decreased temperatures mean higher solubility.

Le Chatelier's principle allows better conceptualization of these trends. First, note that the process of dissolving gas in liquid is usually exothermic . As such, increasing temperatures result in stress on the product side (because heat is on the product side). In turn, Le Chatelier's principle predicts that the system shifts towards the reactant side in order to alleviate this new stress. Consequently, the equilibrium concentration of the gas particles in gaseous phase increases, resulting in lowered solubility.

Conversely, decreasing temperatures result in stress on the reactant side (because heat is on the product side). In turn, Le Chatelier's principle predicts that the system shifts toward the product side in order to compensate for this new stress. Consequently, the equilibrium concentration of the gas particles in gaseous phase would decrease, resulting in greater solubility.

Pressure Affects Solubility of Gases

The effects of pressure are only significant in affecting the solubility of gases in liquids.

• Solids & Liquids: The effects of pressure changes on the solubility of solids and liquids are negligible.
• Gases : The effects of pressure on the solubility of gases in liquids can best be described through a combination of Henry's law and Le Chatelier principle. Henry's law dictates that when temperature is constant, the solubility of the gas corresponds to it's partial pressure. Consider the following formula of Henry's law:

\[ p = k_h \; c \]

• \(p\) is the partial pressure of the gas above the liquid,
• \(k_h\) is Henry's law constant, and
• \(c\) is the concentrate of the gas in the liquid.

This formula indicates that (at a constant temperature) when the partial pressure decreases, the concentration of gas in the liquid decreases as well, and consequently the solubility also decreases. Conversely, when the partial pressure increases in such a situation, the concentration of gas in the liquid will increase as well; the solubility also increases. Extending the implications from Henry's law , the usefulness of Le Chatelier's principle is enhanced in predicting the effects of pressure on the solubility of gases.

Consider a system consisting of a gas that is partially dissolved in liquid. An increase in pressure would result in greater partial pressure (because the gas is being further compressed). This increased partial pressure means that more gas particles will enter the liquid (there is therefore less gas above the liquid, so the partial pressure decreases) in order to alleviate the stress created by the increase in pressure, resulting in greater solubility.

The converse case in such a system is also true, as a decrease in pressure equates to more gas particles escaping the liquid to compensate.

Consider the following exothermic reaction that is in equilibrium

\[ CO_2 (g) + H_2O (l) \rightleftharpoons H_2CO_3 (aq) \]

What will happen to the solubility of the carbon dioxide if:

• Temperature is increased?
• Pressure and temperature are increased?
• Pressure is increased but temperature is decreased?
• Pressure is increased?
• The reaction is exothermic, so an increase in temperature means that solubility would decrease.
• The change in solubility cannot be determined from the given information. Increasing pressure increased solubility, but increasing temperature decreases solubility
• An increase in pressure and an increase in temperature in this reaction results in greater solubility.
• An increase in pressure results in more gas particles entering the liquid in order to decrease the partial pressure. Therefore, the solubility would increase.

Example 2: The Common Ion Effect

Bob is in the business of purifying silver compounds to extract the actual silver. He is extremely frugal. One day, he finds a barrel containing a saturated solution of silver chloride. Bob has a bottle of water, a jar of table salt (NaCl(s)), and a bottle of vinegar (CH ​3 COOH). Which of the three should Bob add to the solution to maximize the amount of solid silver chloride (minimizing the solubility of the silver chloride)?

Bob should add table salt to the solution. According to the common-ion effect, the additional Cl - ions would reduce the solubility of the silver chloride, which maximizes the amount of solid silver chloride.

Allison has always wanted to start her own carbonated drink company. Recently, she opened a factory to produce her drinks. She wants her drink to "out-fizz" all the competitors. That is, she wants to maximize the solubility of the gas in her drink. What conditions (high/low temperature, high/low pressure) would best allow her to achieve this goal?

She would be able to maximize the solubility of the gas, (\(CO_2\) in this case, in her drink (maximize fizz) when the pressure is high and temperature is low.

Butters is trying to increase the solubility of a solid in some water. He begins to frantically stir the mixture. Should he continue stirring? Why or why not?

He stop stop stirring. Stirring only affects how fast the system will reach equilibrium and does not affect the solubility of the solid at all.

Example 5: Outgassing Soda

With respect to Henry's law, why is it a poor ideal to open a can of soda in a low pressure environment?

The fizziness of soda originates from dissolved \(CO_2\), partially in the form of carbonic acid. The concentration of \(CO_2\) dissolved in the soda depends on the amount of ambient pressure pressing down on the liquid. Hence, the soda can will be under pressure to maintain the desired \(CO_2\) concentration. When the can is opened to a lower pressure environment (e.g., the ambient atmosphere), the soda will quickly "outgas" (\(CO_2\) will come out of solution) at a rate depending on the surrounding atmospheric pressure. If a can of soda were opened under a lower pressure environment, this outgassing will be faster and hence more explosive (and dangerous) than under a high pressure environment.

• The solubility of a solute is the concentration of the saturated solution.
• A saturated solution a solution in which the maximum amount of solute has dissolved in the solvent at a given temperature.
• An unsaturated solution a solution in which the solute has completely dissolved in the solvent.
• A supersaturated solution is a solution in which the amount of solute dissolved under given conditions exceeds it's supposed upper limit.
• Le Ch â telier's principle states that when a system in chemical equilibrium is stressed, the system will shift in a way that alleviates the stress.
• Endothermic reaction : a reaction in which heat is absorbed (ΔH>0)
• Exothermic reaction : a reaction in which heat is released (ΔH < 0)
• Petrucci, Harwood, Herring. General Chemistry: Principles & Modern Applications. 8th ed. Upper Saddle River, New Jersey: Pearson/Prentice Hall, 2002.
• Zumdahl, Steven S. Chemical Principles. 4th ed. Boston: Houghton Mifflin Company, 2002.
• Yalkowsky, Samuel H. Solubility and Solubilzation in Aqueous Media, 1st Edition. Washington D.C.: An American Chemical Society Publication, 1999.
• Letcher, Trevor. Thermodynamics, Solubility and Environmental Issues, 1st Edition. Amsterdam: Elsevier Science, 2007.
• Yalkowsky, Samuel H. Handbook of Aqueous Solubility Data, 1st Edition. Florida: CRC Press, 2003.
• Butler, James N. Ionic Equilibrium: Solubility and pH Calculations, 1st Edition. New Jersey: Wiley-Interscience, 1998.

Experiment: Temperature and Solubility

Introduction.

The "Temperature and Solubility" experiment aims to investigate how the solubility of a substance is influenced by the temperature of the solvent. This experiment is based on the hypothesis that the solubility of a solute increases with the temperature of the solvent, a concept fundamental to understanding solutions in chemistry.

Materials You Need

• Sodium chloride (table salt) or sugar (sucrose)
• Distilled water
• Three beakers or glass jars
• Stirring rods
• Thermometer
• Heating source (like a hot plate or Bunsen burner)
• Balance scale
• Graduated cylinders
• Label the beakers as 'Cold', 'Room Temperature', and 'Hot'. Measure and pour equal volumes of distilled water into each.
• Adjust the temperature of the water in each beaker: add ice for 'Cold' to reach about 5°C, leave 'Room Temperature' as is, and heat 'Hot' to approximately 60°C.
• Weigh out an equal amount of the solute and add it to each beaker.
• Stir each solution continuously and observe the solute's dissolving rate until saturation.

Observations and Results

Record the time each solute takes to dissolve in the different temperature conditions. Note the amount of undissolved solute at the saturation point for each temperature. Compare the solubility in cold, room temperature, and hot water.

Conclusions

Analyze the data to determine if the hypothesis holds true. The conclusion should discuss whether the solubility of the solute was greater in hot water compared to cold, and what this implies about the relationship between temperature and solubility in solutions.

• Solubility Experiment
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Have you ever wondered why some substances dissolve in water while others don’t? This activity visually demonstrates the science behind solubility.

Have you ever wondered why some substances dissolve in water while others don’t? The answer: solubility.

Solubility is the ability of a solid, liquid, or gaseous chemical substance (or solute) to dissolve in a solvent (usually a liquid) and form a homogenous solution. There are three factors that affect solubility:

• Solvent: To determine whether a solute will dissolve in a solvent, remember this saying: “Like dissolves like.”
• Temperature: This factor affects the solubility of both solids and gases, with solubility increasing with the temperature.
• Pressure: This factor affects the solubility of gases, with solubility also increasing with pressure.

The Science Behind Solubility

Put simply, a substance is considered to be soluble if it can be dissolved, most commonly in water. When a solute, such as table salt, is added to a solvent, such as water, the salt’s molecular bonds are broken before combining with the water, causing the salt to dissolve.

However, for the salt to remain soluble and dissolve completely, there must be a larger concentration of water than salt in the solution. A solution becomes saturated when the solvent can dissolve no more solute. But adding heat or pressure can help to increase the solubility of the solute, depending on its state.

Check out Chemistry Rocks! 3 Simple Science Experiments To Teach Students Chemistry for more activity ideas!

Testing the Solubility of Substances

For this experiment, your students will explore basic chemistry concepts by testing the solubility of different substances in water. From the example above, we know that table salt is highly soluble in water. What other substances can dissolve in water?

What You Need

• Clear containers, such as cups, beakers, or bowls
• Materials to test, such as sugar, sand, chalk, baking soda and Epsom salts
• Stirring rods
• Measuring spoon
• STEM journals (optional)
• Begin by discussing the science of solubility, and have students write down their predictions about which materials are soluble or insoluble. Students can also document the scientific process in their STEM journals.
• Fill each container with lukewarm tap water.
• Add a specific amount—for example, 1 tablespoon—of a test material to a container using the measuring spoon. Repeat, adding an equal amount of a different material to each container of water.
• Use the stirring rods to mix the contents in each container.
• Observe which materials dissolved in the water and which did not. Did students make the right predictions?

Discussion Questions

Once the experiment is complete, use the following questions to deepen students’ understanding of solubility and how it works:

• What are the qualities of the soluble materials versus those of the insoluble materials? For example, the soluble materials are likely powdery and dry, while insoluble materials may have a hard, grainy texture.
• For the materials that dissolved in the water, what do you think will happen if you keep adding more to the water?
• What are other examples of soluble substances?
• What are other examples of insoluble substances?

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