High School Chemistry
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[edit] High School Chemistry
Introduction
Chemistry is easy! Chemistry, like most new subjects, is easy as long as you know it's easy. Just as swimming or riding a bike was difficult at first, chemistry or most other new skills will have you stumbling and crawling before you walk and run. This is true of just about any skill you will ever attain. If you know you can do it, and keep at it, you will succeed.
Unless you have a feel for what the numbers you're about to be exposed to really mean, you don't really know what you're doing and will likely run into problems. To prevent this problem, the following will help:
Get a good feel of what objects between 1 gram and 500 grams feel like, and look like in various objects.
Get a good feel of what objects between 1 millimeter and 100 meters really look like.
Experiment with several items, classifying them by weight and volume. You find that an object may be a far different size and shape than another object of the same weight. This is due to density. Remember that this is true.
If you make sure to get a good feel for what weights and measurements really feel like and look like, suddenly, you'll find that when you come up with an answer to a question you are able to look at that answer and immediately realize if its wrong. You know, when you're trying to figure out how fast you drove on a trip that if you end up with a number like 73829.3498 or 0.000034 you did something wrong because those numbers are just silly. Why? Because you know what you're doing and what you're looking for.
Weight vs. Mass
Weight and mass are not the same thing. On earth, they will be the same thing, but if you go outside of earth, suddenly, the mass is the same, but the weight may change based on where you are in the universe due to gravity in different locations.
The SI (Metric) System
The world, outside of the United States, almost exclusively uses the metric system. Why? Because it's so easy!
The imperial measure system (What we use) approach: 12 inches = 1 foot, 5,280 feet = 1 mile
The metric system approach: 10 millimeter = 1 centimeter, 100 centimeter = 1 meter, 1000 meter = 1 kilometer
This is far easier to work with, and easy is very good in this situation.
1 meter is the distance travelled by light in absolute vacuum in 1/299,792,458 of a second.
In the metric system, there are 7 basic units of measurement. From these units, all other metric units are derived.
You can find the 7 basic units and their uses here.
In order to allow for the simplification of numbers used to represent measurements, the metric system uses a variety of prefixes to accompany the basic units.
You can find the prefixes and their uses here.
Periodic table of elements
The periodic table of elements is a representation of all atoms known to make up all matter as we know it.
You can find a periodic table of elements here.
Density
The official SI representation of Density = kg / m3
Density (kg/m3) = Mass (kg) / Volume (m3)
Using this official form you end up with stuff like this:
3.45 g/cm^3 = 3450 kg/m^3
A number like this is hard to imagine, so, to get a better feel for what you're dealing with you can multiply the result by 1000 to get the result in g/cm3, which is a little easier to wrap your head around.
A material with high density, like uranium (19.1 g/cm3), may be small as well as heavy.
A material with a low density, like water (0.917 g/cm3, solid ice), may be large as well as light.
So, if you may have some uranium and some ice, both of which weigh the same, but because the uranium has a far higher density, it will have a far smaller volume than the ice, so it may look small but it'll be exactly as heavy as the larger block of ice.
Moles
A mole is an amount of a substance which has a set number of molecules in it. Because some molecules are more or less dense than others, the same amount of molecules of something like table sugar (aka: Sucrose; Chemically: C12H22O11; Molar mass: 342.29648 g/mol) has a much larger molar mass than water (Chemically: H2O; Molar mass: 18.0153 g/mol).
This means that 1 mole of water and 1 mole of sugar, while they have the exact same number of molecules, will not necessarily be the same size or weight.
Avogadro's number (For determining the mass of solids)
Molecules in 1 Mole: 6.0221415 x 1023
For common usage you can usually use: 6.02 x 1023
1 Mole = weight of sample (g) / molar weight (g/mol)
Loschmidt's number (For determining the mass of gases)
IMPORTANT: Assumes STP (Standard Temperature and Pressure) @
Absolute pressure of 100 kPa (1 bar) at a temperature of 273.15 K (0 °C)
Vol = 22.414 L / Mole
