2. What is a solution? A solution is any mixture of two or more materials, where the solute and solvent are mixed homogenously.
3. Wait, what? For a mixture to be considered a solution, the solute (what’s being dissolved) and the solvent (what’s doing the dissolving) must have a specific ratio throughout the mixture (homogenous)
4. Is it a solution? Milk and cereal? No, the cereal isn’t dissolved in the milk Sea water? Yes, the salt is dissolved by the water Milk? No, the different fats and proteins in milk are unaffected by the water in it Air? Yes, the air we breathe is an evenly mixed combination of Nitrogen, Oxygen, Argon, and Water Vapor
5. Tips and Tricks Almost every mixture you can see through is a solution. Even if the mixture is colored (like lemonade) if light can pass through it, it’s a solution. Any material you cannot see through (like milk) is a mixture, as the light is scattering off of the materials suspended in the mixture. Any mixture of gasses is ALWAYS a solution.
6. Like dissolves like A substance can only be dissolved into another substance if they share a similar polarity. Non-polar substances can only be dissolved by other non-polar substances, and polar substances can only be dissolved by polar substances.
7. Polarity A compound’s polarity is determined by how evenly the electrons are distributed in the molecule. If a molecule is symmetrical around the central atom, then it is non-polar If a molecule is asymmetrical around the central atom, then it is polar.
9. Water: Love It or Hate It Some compounds are very easily dissolved in water, and are known to be hydrophilic. “hydro”= water, “philia”= love Others won’t dissolve in water at all. These are known to be hydrophobic. “hydro”= water, “phobos”= fear
10. Hydrophilaphobia-wha? Some compounds, like soap or cell membranes, have parts that are hydrophilic (likes the water) and parts that are hydrophobic (repels the water).
11. Universal Solvents Some solvents are known as “universal” because they can dissolve a wide variety of materials. For example, water can dissolve sugar, salt, honey, vinegar, soap, food coloring, chocolate syrup, and oxygen (among tons of other things) No solvent can be truly universal, however, because no solvent can dissolve every single solute
12. Acids and Bases In water, the pull of the oxygen atom on the hydrogen atom is so strong that it can actually draw one from another water molecule (dissociation). When this occurs, you end up with two molecules: H+ and OH- Pure water has these two ions in equal concentrations.
13. Acids When a water molecule is broken apart, the H+ ion usually pairs up with another water molecule to form H3O+, known as a hydronium ion. When the number of hydronium ions in a solution outnumbers OH- ions, the solution is said to be acidic
14. Bases The OH- molecule is known as a hydroxide ion When a solution has more hydroxide ions than hydronium ions, it is said to be basic, or alkaline Bases often feel slippery, because the OH- molecules react to the oil on our skin to form a soap.
15. pH pH stands for “potential for Hydrogen” The pH scale is a measurement for how acidic or basic a solution is Acids have lower pH values and bases have higher pH values A change from one level to the next represents a tenfold change in either acidity or alkalinity. In other words, an acid with a pH of 3 has ten times as many H3O+ ions as does an acid with a pH of 4.
16. Buffers Buffers are substances that counteract a small amount of either an acid or base so that the solution stays a specific pH. Huh? Since many organic substances need to remain a constant pH, they’ll use buffers to cancel out enough of the acid or base to keep the whole area within a safe range
17. Properties of Water As we learned earlier, water is a polar molecule. The oxygen portion is slightly negative, and the hydrogen portions are slightly positive
18. Hydrogen Bonding Since there are positive and negative regions in each water molecule, they are attracted to the oppositely charged regions in other molecules. The negatively charged oxygen will be attracted to the positively charged hydrogens.
19. Cohesion and Adhesion Cohesion is the attractive forces between molecules of the same compound. This is what gives water properties like surface tension. Adhesion is the attractive forces between molecules of differing compounds You can see this when water clings to a cold glass (capillarity)
