- Mole, Mass & Avogadro Constant An amount of substance containing 6.02 × 10 23 particles is called a mole (often abbreviated to mol). 6.02 × 10 23 is called the Avogadro Constant or Avogadro's Number. The following diagram shows how to convert between Mass, Mole and Number of particles.
- Find the number of moles of oleic acid. First find the volume of pure oleic acid (assuming 0.10 mL of the solution was used). Then find the mass of oleic acid (density = 0.895 g/mL) From the molar mass (282 g/mol), calculate the moles of pure oleic acid. Find the number of molecules of oleic acid.
The Mole And Avogadro's Number Key
Calculations related to Avogadro's law. Enter known values (e.g. Volume or number of moles) and select which value you want to find out (e.g. Molar volume) and we'll show you step-by-step how to transform basic formula and reach your result in desired units. Scientists call this value Avogadro's number, NA, in honor of the Italian scientist Amedeo Avogadro (1776–1856), and it is often cited with units of reciprocal moles, 6.02 × 10 23 mol −1. The unit (read as either “inverse mole” or “per mole”) reminds us that there are 6.02 × 10 23 objects per one mole.
A flat tire is not very useful. It does not cushion the rim of the wheel and creates a very uncomfortable ride. When air is added to the tire, the pressure increases as more molecules of gas are forced into the rigid tire. How much air should be put into a tire depends on the pressure rating for that tire. Too little pressure and the tire will not hold its shape. Too much pressure and the tire could burst.
Avogadro's Law
You have learned about Avogadro's hypothesis: equal volumes of any gas at the same temperature and pressure contain the same number of molecules. It follows that the volume of a gas is directly proportional to the number of moles of gas present in the sample. Avogadro's Law states that the volume of a gas is directly proportional to the number of moles (or number of particles) of gas when the temperature and pressure are held constant. The mathematical expression of Avogadro's Law is:
[V = k times n]
or
[dfrac{V_1}{n_1} = dfrac{V_2}{n_2}]
where (n) is the number of moles of gas and (k) is a constant. Avogadro's Law is in evidence whenever you blow up a balloon. The volume of the balloon increases as you add moles of gas to the balloon by blowing it up.
If the container holding the gas is rigid rather than flexible, pressure can be substituted for volume in Avogadro's Law. Adding gas to a rigid container makes the pressure increase.
Example (PageIndex{1})
Avogadro's Number Calculator
A balloon has been filled to a volume of (1.90 : text{L}) with (0.0920 : text{mol}) of helium gas. If (0.0210 : text{mol}) of additional helium is added to the balloon while the temperature and pressure are held constant, what is the new volume of the balloon?
Solution
Steps for Problem Solving | |
|---|---|
| Identify the 'given' information and what the problem is asking you to 'find.' | Given: (V_1 = 1.90 : text{L}) (n_1 = 0.0920 : text{mol}) Find: (V_2 = ? : text{L}) |
| List other known quantities. | Note that the final number of moles has to be calculated by adding the original number of moles to the moles of added helium. (n_2 = 0.0920 + 0.0210 = 0.1130 : text{mol}) |
Plan the problem. | First, rearrange the equation algebraically to solve for (V_2). [V_2 = frac{V_1 times n_2}{n_1}] |
Calculate. | Now substitute the known quantities into the equation and solve. [V_2 = frac{1.90 : text{L} times 0.1130 : cancel{text{mol}}}{0.0920 : cancel{text{mol}}} = 2.33 : text{L}] |
| Think about your result. | Since a relatively small amount of additional helium was added to the balloon, its volume increases slightly. |
Exercise (PageIndex{1})
A 12.8 L volume of gas contains .000498 moles of oxygen gas. At constant temperature and pressure, what volume does .0000136 moles of the gas fill?
0.350 L
Summary
- Calculations for relationships between volume and number of moles of a gas can be performed using Avogadro's Law.
Contributions & Attributions
This page was constructed from content via the following contributor(s) and edited (topically or extensively) by the LibreTexts development team to meet platform style, presentation, and quality:
Why Is A Mole 6.022 X10 23
CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.
Marisa Alviar-Agnew (Sacramento City College)
Henry Agnew (UC Davis)
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