November 11th, 2013
Regarding the chapter 12 test
Definitions of "acid" and "base"
In this class we are going with the Bronsted-Lowry definitions of acids & bases.
An acid is a proton (H+) donor. For your purposes, if something loses a hydrogen, it is an acid.
A base is a proton acceptor. If it gains a hydrogen in a reaction, it is a base.
Definitions of "strong" and "weak"
A strong acid or base is one that breaks apart (dissociates) almost completely when added to water.
A weak acid or base is one that mostly stays intact when added to water.
The pH scale
pH is how we measure how acidic or basic something is. For purposes of this class, the pH scale goes from 0 to 14.
A change of one unit on the pH scale corresponds to a ten-times change in acidity or basicity.
Regardless of where you start on the scale, if the pH goes down you are getting more acidic, and if the pH goes up you are getting more basic.
Common acids and bases
There is a section in the chapter on common acids and another on common bases. I want you to know a couple common acids and a couple common bases. I also want you to be able to tell me a couple common uses of acids and a couple common uses of bases.
- Molecules don't heat up, they speed up.
- When I ask you to describe something "on a molecular level", what I want to see is something about molecules. "The liquid is getting hotter" says nothing about molecules. "The molecules of the liquid are speeding up" is a description on a molecular level.
- A compound that is nothing but carbon and hydrogen is not polar.
- Gases flow.
- I was a bit generous in my grading on some items. On the final I will not be so forgiving, as by then you'll have had my lectures, the text book, whatever notes and auxiliary documents I put up on the Weebly site, your tests, whatever comments I made on those, and the answer keys for the tests. I figure that, with all that stuff available, you ought be able to give me an answer that doesn't require much interpretation.
Definitions of "acid" and "base"
In this class we are going with the Bronsted-Lowry definitions of acids & bases.
An acid is a proton (H+) donor. For your purposes, if something loses a hydrogen, it is an acid.
A base is a proton acceptor. If it gains a hydrogen in a reaction, it is a base.
Definitions of "strong" and "weak"
A strong acid or base is one that breaks apart (dissociates) almost completely when added to water.
A weak acid or base is one that mostly stays intact when added to water.
The pH scale
pH is how we measure how acidic or basic something is. For purposes of this class, the pH scale goes from 0 to 14.
- A neutral substance, like pure water, is no more acidic than it is basic. The pH of a neutral substance is 7. (A neutral substance can act as an acid or a base in the presence of a base or acid. Water is neutral, but add hydrochloric acid to water and the water acts as a base.)
- An acid has a pH less than 7. The lower the number, the more acidic the substance is.
- A base has a pH greater than 7. The higher the number, the more basic the substance is.
A change of one unit on the pH scale corresponds to a ten-times change in acidity or basicity.
- If substance A has a pH of 4 and substance B has a pH of 3, substance B is ten times more acidic than substance A. If substance C has a pH of 2, it is 100 (10 x 10) times more acidic than substance A.
- Substance X has pH of 8, substance Y has pH of 9, and substance Z has pH of 10. Substance Z is ten times more basic than substance Y, and 100 (10 x 10) times more basic than substance X.
Regardless of where you start on the scale, if the pH goes down you are getting more acidic, and if the pH goes up you are getting more basic.
- Solution F has a pH of 12, while solution G has a pH of 10. Solution G is more acidic than solution F, even though solution G is still a base.
Common acids and bases
There is a section in the chapter on common acids and another on common bases. I want you to know a couple common acids and a couple common bases. I also want you to be able to tell me a couple common uses of acids and a couple common uses of bases.