Chapter 7: Unit 2. Solutions Definition

Solutions Definition

A solution is a homogeneous mixture made of a solute and a solvent. A solute is a chemical compound that is limited in the amount and soluble in the solvent. The solvent in a chemical compound that has the ability to dissolve the solute and it has excess amount compared with the solute amount. To assure solubility both solute and solvent share similar polarity.

An example of a homogenous mixture is the solubility of sodium chloride NaCl in water. Sodium chloride is considered as a solute with the least amount and water is considered as a solvent with a large amount.

Also solubility of an oil (none polar compound) in cyclohexane solvent (none polar) makes a homogenous mixture.

If the solute and solvent have different polarities, then they form heterogeneous mixture which is not considered as a solution.

The Phet Simulation Activity of the different solubility outcome of sugar and salt in water. Both sugar and salt are soluble in water. However, the solubility of salt in water will produce ions which can conduct electricity.

The simulation can be accessed and downloaded through the link below:Click to run

https://phet.colorado.edu/en/simulation/legacy/sugar-and-salt-solutions

You will have to download this Phet simulation first.

You will:

• Compare the behavior of sugar and salt in water
• Identify sugar and salt as either an electrolyte or a nonelectrolyte
• Draw a particulate representation of salt in water and sugar in water
• Propose an explanation for why a light bulb glows or does not glow
• Extend the definition of electrolytes versus nonelectrolytes to other substances and qualitatively relate bond type to this observation

Procedure

Part I: Open Exploration

1. Students may share how the conductivity tester works; how to shake the shaker; how to add

water to the container; and how the evaporation slider works.

Part II: Macro (First Tab)

Fill in the Table below with your findings:

Questions:

1. Which of these compounds are electrolyte and which are nonelectrolytes?

2. Which of these compounds are conducting electricity and which are not?

Part III: Water (Third Tab)

What happens as you add sugar or salt to water?

Fill in the Table below with your findings:

Questions:

1. Using the observations made with salt in water and sugar in water in the first tab (macro); propose one possible explanation for the bulb glowing?

2. If the evaporation is allowed to continue until all of the water is gone, a thin white layer forms on the bottom of the container representing the salt and the sugar. What happens if the conductivity tester is left in the beaker during evaporation with the salt first? And then with sugar?

3. Which compound breaks apart into ions and which compound does not?

Part IV: Micro (Second Tab)

What happens when other compounds are added to water?

Fill in Table below with what your findings:

Activities:

1. Using the “Periodic Table” button, work with your partner to identify two other combinations of elements that might be considered an ionic compound. Explain your reasoning.

2. Using the “Periodic Table” button, identify two combinations of elements that might be considered a covalent compound. Explain your reasoning

The conclusion of the simulation activity above is given below:

Salt dissolution in water:

NaCl_(s)   +   H₂O_(l)    à Na_(aq)⁺     +    Cl_(aq)⁺        [Two ions are produced from solid NaCl]

The two ions produced are responsible of conducting electricity. The lamp will be lit when its electrodes are immersed into the salt solution.

Sugar dissolution in water:

C₆H₁₂O_6(s)    +   +   H₂O_(l)  à  [C₆H₁₂O₆]_(aq)         [No ions are produced]

The sugar solution does not produce any ions and hence no electricity is conducted and the lamp will not be lit.

The dissolution of the solute in water can also be practiced in the simulation created by Molecular Workbench. The solid solute is surrounded by water molecules.

At the beginning the solid crystals are sitting very packed together. Water molecules are approaching the solid salute crystals and penetrate through the crystal network with addition of more water and more given time, water will separate the crystal network of the solid salute and start producing ions out the dissolved solute.

The simulation can be accessed and downloaded through the link below:

http://mw.concord.org/nextgen/#interactives/chemistry/solubility/dissolving-chemistry

No water is added:

Impact on potential energy when a substance dissolves in water.

Add water to a substance and observe the impact on potential energy as the substance dissolves. Observe the interactions between molecules as the substance dissolves over time and watch what happens to the potential energy of the system as dissolving occurs.

Questions:

1. Write your observation regarding the potential energy and the molecules at the beginning of the experiment when no water is added?

2. Write your observation regarding the potential energy and the molecules at the beginning of the experiment when water is added?

After some time water is able to dissolve the solid salt and ions are produced.

Water is a polar solvent with oxygen has the highest electronegativity compared with hydrogen. Oxygen has partial negative charge and hydrogen has partial positive charge.

The patial positive charged hydrogen will be attracted to the negative ion of the solute and oxygen partially negative charged will be attracted to the positive ion of the solute.

Molecular Workbench Simulation activitity can illustrate this type of attractions.

http://mw.concord.org/nextgen/#interactives/chemistry/solubility/dissolving-chemistry-experimental

Explore how molecules of different polarity interact when mixed.

Select the polarity of two different molecules and simulate what happens when these two molecules of different (or the same) polarities are mixed. Speed up the simulation to reach an outcome faster, or keep it slow to observe the interactions between atoms. Then draw conclusions about how polarity impacts how different substances dissolve.

Questions:

1. Are molecules with same polarities attracted to each other or repelled each other? Explain your answer.

2. Are molecules with different polarities attracted to each other or repelled each other? Explain your answer.