One of the greatest things you can do in life is to teach something truthful and useful to someone.
Have you ever heard of this riddle: "What weighs more 50 pounds of sand or 50 pounds of feathers?" Well, if you said sand, you're thinking like I used to when it came to Moles. The answer to the question is "neither" because they both weigh the same: 50 pounds. First, of all, a pillow filled with feathers, indeed, will be lighter than if filled with of sand. The thing is: weight is not the same as density.
Every thing in the physical world that can be measured must be measured with units. For example: time, distance, weight, density and so on. In mathematics, you can always find handy information from previous knowledge like measurements and conversions.
Density can be calculated by dividing mass by volume. Mass is sometimes the same as weight, but it depends where. Your mass will always be the same where ever you are, but you will weigh more on the Earth than on the Earth's Moon. That's due to the force of gravity.
In Chemistry, we use a similar formula for finding how much of substance is dissolved in a bigger substance. For example, a couple of spoonfuls of table salt is stirred in a cup of water. The salt will be the solute, the water will be the solvent, both constitute the solution and how much salt is in this solution can be measured in what is called "concentration." Concentration is measured in units called "molarity" (M). (By the way, this salt is Sodium Chloride (NaCl) the salt we use on the dinner table. Yet, in Chemistry we call any ionic molecule that is made of a nonmetal with a metal a salt.)
When you think of concentration in molarity, picture "frozen juice concentrate" which is mixed in water. That solute was dense, hard, but when you add it to water, it's a liquid (aqueous.) Yes, you can melt the frozen juice and it will be liquid, but that's not the point. In reality, the taste and the color of the juice tells you if it's close to 100% juice or if water has been added to it. In those terms, notice that ready-to-drink cranberry juice is never bottled as 100% juice. If 30% or less of cranberry juice is sour imagine what 100% concentration of cranberry juice will taste like.
The formula for molarity is: moles divided by Liters. Notice something? Molarity is like density; moles are like mass; and, liters are like. . . Well, liters are used to measure volume, like cups, pints, and gallons. Liters are used in the metric system, so you can use miliLiters, but the other measurements of volumes previously mentioned (cups, etc.) are found in the English System and are not given in multiples of 10 like Liters. In other words, we do not have milicups nor kilogallons.
The moles as mass? Well, let's recall measuring in volume. Notice that comparing cups to liters was different. Within in the Engish system: A gallon has 8 pints, a pint has 2 cups, a cup has 8 ounces. Within the metric system: a liter is 1000 mililiters. Well, the English system doesn't have a pattern, where the metric system has a pattern of 10. The metic system allow us to write up small quantities in like 0.00000045 as 4.5*10^-7 and big quantities like 6,700,000,000,000,000 as 6.7*10^15. It helps us with the zeros by sticking to tens.
Now, moles can and are used with the metric system. For example, there are 1000 milimoles in a mole. A mole is 6.022*10^23 of any element; this is Avogadro's number. Wait! An atom of Oxygen doesn't weigh the same as an atom of Carbon, so how can this be??? Well, a mole tells you how many particles are there, but not how much they weigh. A mole of an element means that you have the same units in grams as you do in the molecular formula. Since Oxygen has 16 amu's, a mole of Oxygen will weigh 16 grams. Carbon has 12 amu's, so a mole of Carbon will weigh 12 grams. You can calculate a mole of sugar this way: take the formula of sugar and multiply the amu's of each element and remember to multiple by how many of each element, for example: H2 is 1.00*2 = 2.00. This 2.00 is the formula weight (fw) of the molecule. (By the way, that "2.00" multiplied by 1 mole means 2 grams of the hydrogen molecule; 1 mole of the hydrogen gas molecule weighs 2 grams.)
Molar mass (italicized "M") is the mass of one mole of a substance. One molar mass of the hydrogen atom is 1.007 grams. One molar mass of hydrogen gas is 2.014 grams.
Now, do you get the mole?
My name is Celia A. Escalante. I am a Miami-Dade College Alumna. E-mail me your subject-related questions at celiaescalante@yahoo.com or visit my web page at http://www.geocities.com/celiaescalante/. I'm a college tutor and the author of Mood Rollercoaster available on www.lulu.com/celiaescalante and the founder of MiamiBulletin.com.
