Unit 4, Lessons 17 and 18

Lesson 17:

Substances can be classified as acids, bases, or neutral solutions. Whether or not a solution gets classified as one of those three depends on its pH, which is a measure of the concentration of hydrogen and hydroxide ions. Acids have a very low pH number (anything less than 7). Bases sit on the complete other side of the scale and have pHs above 7. Any solution with a pH of exactly 7 is neutral. Table salt and pure water are neutral; lemon juice is an acid (FUN FACT: so is milk!), and soap is a base. Acids and bases are both very corrosive and sometimes unsafe to handle. How exactly does one tell if a solution is acidic or basic? Through the use of an indicator, a molecular substance that changes colors in acidic and basic environments. There are two common types of indicators: cabbage juice (easily accessible at home) and Universal Indicator (not as easily acquired, but much  more accurate).

Problems:

1.) What are some observable properties of acids and bases? Acids are typically sour, if they're safe to eat. Bases, like soap, taste bitter and sometimes foam up in water. Both acids and bases can be corrosive.

2.) What is the pH scale? The pH scale is a colored number line, essentially, that associates different types of solutions with colors to help one determine if they're basic or acidic. Basic solutions are usually in darker greens, blues, and purples on the scale; acids show up as vibrant reds, oranges, and yellows.

Lesson 18:

The laws for identifying basic, neutral, and acidic solutions have changed over time. Most of the laws, though, have always involved the hydrogen and hydroxide ions that pH measures. In a chemical reaction, acids give away one H+ ion, which shows up in the products. The product that has one more H+ ion than before is the starting acid (reactant)'s corresponding base. Oppositely, bases give off OH- ions in their reactions, and the product that receives the base's OH- is its corresponding acid. In these processes, which are defined Arrheniously, Bronsted-Lowry's law comes into play. It states that acidic solutions are proton donors (since H+ ions are simply stray protons) and basic solutions are proton acceptors.

Problems:

2.) How is the Bronsted-Lowry theory of acids similar to the Arrhenius theory? How is it different? These two theories are similar in that they both deal with the identification of solutions as acids/bases through whatever ions are present. They're different in that the Arrhenius theory doesn't explain how solutions without OH- ions in their chemical formulas can be bases, too.

7.) Explain why aqueous washing soda, NaCO3, is a basic solution. It is a basic solution because it has one OH- ion in its composition. (Also, it's a kind of soap, which is also a giveaway).