Presentation on theme: "Unit 8: Solutions Mathematicians have Problems, But Chemists have Solutions."— Presentation transcript:
Unit 8: Solutions Mathematicians have Problems, But Chemists have Solutions
Water Water is a polar molecule. This means the oxygen side is negatively charged and the hydrogen side is positively charged. This charge allows water molecules to be attracted to other water molecules through intermolecular forces. H H O
The forces that hold water molecules together are called hydrogen bonding. Because of water’s strong hydrogen bonding, it is a liquid at normal temperatures even though is has such a low molecular weight. It is also the reason it has such an unusually high boiling point (100 o C) and high specific heat capacity. (this means it takes a lot of energy (4.18 J/g o C )to raise the temperature of liquid water!)
Physical Properties of Water Surface Tension—The resistance of a liquid to increase in surface area The Result : Water beads as a drop instead of spreading out --Cohesive forces are those holding the liquid together to present the minimum of surface area. Water has a very high surface tension due to strong hydrogen bonding!
Capillary Action—The spontaneous rising of liquid in a narrow tube due to two forces Cohesive and Adhesive forces. Adhesive forces are those connecting a liquid and its container. For Water- Adhesive forces are stronger than the cohesive forces, the liquid is higher nearer the container and lower in the middle (the meniscus is concave.)
Solutions are mixtures… SOLUTIONS are HOMOGENOUS MIXTURES. They cannot be separated by filtration or settling. They cannot be separated by filtration or settling. Solutions have two components- 1. SOLUTE- the solid that gets dissolved, or the liquid that is present in smaller amount. 2. SOLVENT- the liquid that does the dissolving. It is always present in a larger amount. Solvation – The dissolving process where solute particles are surrounded by solvent molecules.
Example: Salt water What is the solute?___________ What is the solute?___________ What is the solvent?___________ What is the solvent?___________ Example – 70% ethanol solution. Solute _______________ Solute _______________ Solvent________________ Solvent________________ Salt water Water ethanol
Solubility Principle Solutes will dissolve in solvents with similar polarity. “Like Dissolves Like” Polar substances will dissolve in polar solvents and nonpolar substances will only dissolve in nonpolar substances. Water is considered a universal solvent because it can dissolve both ionic and polar covalent compounds Example – Alcohol will dissolve in water because both are polar molecules.
Like Dissolves Like Q: Why does salad dressing separate into its oil and vinegar components? The polarity of vinegar and oil are not the same. Oil is non-polar and vinegar is polar. Therefore, they do not mix.
Ionic Compounds In an aqueous solution, water is the solvent. HCl (aq), NaCl(aq), CuSO 4 (aq) Ionic compounds are considered polar Ionic compounds will separate into its ionic parts when dissolved in water. NaCl + water K 2 SO 4 + water Na + + Cl - 2K + + SO 4 2-
Solvation Water dissolves ionic solutes through a process called solvation. Steps to solvation: 1. An ionic solute is added to water. 2. Water molecules bombard the ionic compound until it breaks into its ions. 3. The positive “H’s” in water molecules surround the negative solute ion. 4. The negative “O” in water molecules surround the positive solute ion. Ions that are completely surrounded by water molecules form hydration spheres and are said to be “hydrated”.