Unit 3: Topic 8 - Representations of Solutions

Question 1

What are aqueous solutions? What are some different types of aqueous solutions?

Answer 1

• Aqueous solutions are solutions with water as the solvent.
• An electrolyte is an aqueous solution containing ions. As a result of the presence of ions, they have the ability to conduct electricity.
• Any substance that forms an aqueous solution containing no ions is called a nonelectrolyte. Since they do not contain ions, they will not conduct electricity.
• For example, saltwater can be considered an electrolyte, while the dissolution of sugar in water can be considered a nonelectrolyte.

Question 2

What are the steps to solution formation?

Answer 2

Step 1: Expanding the solute by breaking solute-solute interactions. This usually involves breaking intermolecular forces, and this requires energy(endothermic).

Step 2: Expanding the solvent by breaking solvent-solvent interactions (endothermic). This also involves breaking intermolecular forces, which require energy(endothermic).

Step 3: Allowing the solute and solvent to form solute-solvent interactions (intermolecular forces) to create a solution. This step would be exothermic because forming bonds will always release energy.

Question 3

What should a particle diagram depicting solution formation look like?

Answer 3

• Look at the formula of the solute to determine the mole ratios of the ions. For example, in Ca(NO3)2, you would want to make sure to draw two NO3 anions for each Ca cation. This indicates the relative concentrations of the ions.
• It’s also important to indicate the relative sizes of the components. Anions are typically larger than cations.
• Solvent molecules should surround the solute molecules with the correct orientation on all sides. Usually, the solvent we will be dealing with is water.
• Note that depending on whether the substance is a weak electrolyte or not, you may have to include drawings of the initial molecule to show that the substance did not fully dissociate.

Question 4

How are solute and solvent molecules oriented inside a solution?

Answer 4

Water, a polar molecule, is often the solvent involved in solutions, and it induces ion-dipole interactions with the solute molecules.

To illustrate the various ion-dipole interactions between the solute and the solvent(water):
- Align the partial negative ends of the water, namely the oxygen molecule, towards the positive cations of the solute.
- Align the partial positive ends of the water, namely the hydrogen molecules, towards the negative anions of the solute.

Each ion formed from the dissociation of the solute will be surrounded on all sides by the solvent particles with the aforementioned orientation.

Question 5

What are strong and weak electrolytes?

Answer 5

• Electrolytes that are present in solution entirely as ions are known as strong electrolytes. This means that the substance will fully dissociate into ions. These include soluble salts, strong acids, and strong bases.
• Electrolytes that are present in solution partly as ions and partly as molecules are known as weak electrolytes. This means that the substance does not fully dissociate into ions. These include weak acids and weak bases.
• In particulate diagrams, you can identify strong or weak electrolytes by looking at whether the diagram has only ions or if it has both ions and molecules.

Question 6

What are some examples of particulate diagrams?

Answer 6

Here are the diagrams we will analyze:
- In diagram 1, the solution contains both ions and molecules. This means that the original substance had only partially dissociated into cations(positive ions) and anions(negative ions), suggesting that it is a weak electrolyte.
- In diagram 2, the solution only contains ions. This means that the original substance was able to completely dissociate, suggesting that it is a strong electrolyte.
- In diagram 3, the solution only contains molecules. This means that the original solution was not able to dissociate at all, suggesting that it is a non-electrolyte.
- In diagram 4, AgNO3 is dissolved in water. The partial negative ends of the water molecule(oxygen) are oriented to point to the Ag+ cations, and the partial positive ends of the water molecule(hydrogen) are oriented to point to the NO3- anions.

• The number of moles of a molecule is based on its chemical formula. In this example, since there is an equal number of green and red balls in the first 3 diagrams, we can assume that the mole ratio of the ions is 1:1.