The Mole and Atomic Mass | Chemistry | Visionlearning
In this online course, learn in-depth knowledge of general, organic and analytic chemistry through topics such as chemical equilibrium and chromatography. To calculate the number of atoms, molecules or formula units in a . Click here to visit our frequently asked questions about HTML5 video. . For example, to convert moles of a substance to mass, we use the relationship. One mole is equal to the number of atoms in 12 grams of . out the nature of atoms, gas particles, and those particles' relationship with gas volume. . While the mole is very useful for scientists, it is not without its problems and controversies.
We also described the law of multiple proportions, which states that the ratios of the masses of elements that form a series of compounds are small whole numbers.
The problem for Dalton and other early chemists was to discover the quantitative relationship between the number of atoms in a chemical substance and its mass. In the laboratory, for example, the masses of compounds and elements used by chemists typically range from milligrams to grams, while in industry, chemicals are bought and sold in kilograms and tons.
To analyze the transformations that occur between individual atoms or molecules in a chemical reaction it is therefore absolutely essential for chemists to know how many atoms or molecules are contained in a measurable quantity in the laboratory—a given mass of sample. The unit that provides this link is the mole mol.
The Mole and Atomic Mass
The quantity of a substance that contains the same number of units e. Many familiar items are sold in numerical quantities that have unusual names. For example, cans of soda come in a six-pack, eggs are sold by the dozen 12and pencils often come in a gross 12 dozen, or Sheets of printer paper are packaged in reams ofa seemingly large number.
Atoms are so small, however, that even atoms are too small to see or measure by most common techniques.
- Avogadro, Gay-Lussac, Dalton, and the history of the mole concept
- Worked Examples of Moles-Avogadro Number Calculations
- The mole and molar mass
Any readily measurable mass of an element or compound contains an extraordinarily large number of atoms, molecules, or ions, so an extraordinarily large numerical unit is needed to count them. The mole is used for this purpose. A mole is defined as the amount of a substance that contains the number of carbon atoms in exactly 12 g of isotopically pure carbon According to the most recent experimental measurements, this mass of carbon contains 6.
Just as 1 mol of atoms contains 6.
Since the mass of the gas can also be measured on a sensitive balance, knowing both the number of molecules and their total mass allows us to simply determine the mass of a single molecule in grams.
The mole provides a bridge between the atomic world amu and the laboratory grams. It allows determination of the number of molecules or atoms by weighing them. The numerical value of Avogadro's number, usually written as No, is a consequence of the arbitrary value of one kilogram, a block of Pt-Ir metal called the International Prototype Kilogram, and the choice of reference for the atomic mass unit scale, one atom of carbon A mole of C by definition weighs exactly 12 g and Avogadro's number is determined by counting the number of atoms.
It is not so easy. Avogadro's number is the fundamental constant that is least accurately determined. The definition of a mole—that is, the decision to base it on 12 g of carbon—is arbitrary but one arrived at after some discussion between chemists and physicists debating about whether to use naturally occurring carbon, a mixture of C and C, or hydrogen.
ChemTeam: Using Avogadro's Number in Calculations
The value I will use for Avogadro's Number is 6. Types of problems you might be asked look something like these: When the word gram replaces mole, you have a related set of problems which requires one more step. So keep in mind that there are 4 example problems just above. Calculate the number of molecules in 1. Once again, replacing mole with gram adds one step to the procedure.
Here is a graphic of the procedure steps: Pick the box of the data you are given in the problem and follow the steps toward the box containing what you are asked for in the problem. In example 10, I do a problem that will require three steps. The first two steps will be laid out below and I will then introduce the third step at example Make sure to take a look at it. Start from the box labeled "Moles of Substance" and move to the right to the box labeled "Number of Atoms or Molecules.
The Mole and Atomic Mass | Chemistry | Quiz | Visionlearning
That's right - multiply by Avogadro's Number. The question then is WHAT per mole?
The answer is that it depends on the problem.