Solutions

A solution is defined as a homogeneous mixture.
- Solvent: The substance present in the largest amount in the solution.
- Solutes: Other substances that are dissolved within the solvent.
- Aqueous solution: A specific type of solution where water is the solvent.

Ionic Substances: These substances break up into their constituent cations and anions when dissolved in a solvent.
Solubility of Ionic Substances:
- Polar water molecules interact with the positive and negative ions in the ionic compounds.

An example of a polar substance that is soluble in water is ethanol, which has a polar OH group.
Sugar and Water: The question arises, why is solid sugar soluble in water?

For a molecule to be classified as polar, two conditions must be met:
1. The molecule must contain polar bonds.
2. The spatial arrangement of these bonds must lead to a separation of charge within the molecule.

Nonpolar substances, such as oil, do not interact with polar solvents like water.
- Water-water hydrogen bonds prevent the mixing of nonpolar molecules with water.
To dissolve a solute in water, a "hole" must be created in the water structure for each solute particle, leading to replacing the lost water-water interactions with new water-solute interactions based on the principle: "like dissolves like".

Solubility of a solute is limited:
- Saturated solution: Contains the maximum amount of solute that can dissolve at a given temperature.
- Unsaturated solution: Has not reached the solubility limit; more solute can still be added.
- Supersaturated solution: This occurs when a saturated solution is cooled after allowing more solute to dissolve, remaining in solution. This state is unstable; adding a crystal can cause precipitation.

A solution can vary in concentration based on the amounts of solute and solvent:
- To describe concentration qualitatively:
- Concentrated solution: Contains a relatively large amount of solute.
- Dilute solution: Contains a relatively small amount of solute.

The formula for calculating mass percent concentration is as follows:
- \text{Mass Percent} = \left( \frac{\text{mass of solute}}{\text{mass of solution}} \right) \times 100\%
- Alternatively: \text{Mass Percent} = \left( \frac{\text{grams of solute}}{\text{grams of solute} + \text{grams of solvent}} \right) \times 100\%

To calculate the percent by mass of glucose in a solution:
- If 5.5 g of glucose is dissolved in 78.2 g of water:
- \text{Percent by mass} = \left( \frac{5.5 g}{5.5 g + 78.2 g} \right) \times 100 = 6.6\%

The formula for calculating molarity (M) is defined as:
- M = \frac{\text{moles of solute}}{\text{liters of solution}}
Example:
- If 6 moles of HCl is dissolved to give 2 liters of solution, then:
- M = \frac{6\text{ moles}}{2\text{liters}} = 3 M

If provided with 1.00 mol of sugar in 125.0 mL solution:
- Convert mL to L: 125.0 mL = 0.1250 L
- Calculate molarity:
- M = \frac{1.00 mol}{0.1250 L} = 8.00 M

If you dissolve 500.0 g of potassium phosphate and make 1.50 L of solution:
- Convert 500.0 g to moles: 500.0 g \div 212.27 g/mol = 2.355 mol
- Calculate molarity:
- M = \frac{2.355 mol}{1.50 L} = 1.57 M

Determine the volume needed of a 10.0 M sugar solution to obtain 2.00 mol of sugar:
- \text{Volume} = \frac{2.00 mol}{10.0 M} = 0.200 L

Given two HCl solutions (Solution A and Solution B), with Solution A having a higher concentration:
- If equal volumes are compared, Solution B must contain more moles of HCl.
- If comparing equal moles, Solution B must have a greater volume.
- To achieve equal concentrations, water must be added to Solution B.
- Adding more moles of HCl to both will increase their concentration.

Determine which of the following contains the greatest number of ions:
- a) 400.0 mL of 0.10 M NaCl.
- b) 300.0 mL of 0.10 M CaCl2.
- c) 200.0 mL of 0.10 M FeCl3.
- d) 800.0 mL of 0.10 M sucrose.

Calculate the molarity of a solution prepared by dissolving 0.185 mol Na2SO4 in enough water to make 450 mL of solution.