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Explain these three measures of moles: (mass/Mr), (concentration/vol) and (volume/24).

One can think about a mole as a measure of mass or quantity of a substance. A mole of a substance contains 6.023 x 10^23 atoms (or molecules, if the substance is a compound). That is to say, one mole of the element iron contains 6.023 x 10^23 atoms of iron, while one mole of oxygen gas consists of 6.023 x 10^23 molecules of oxygen gas. One can obtain the moles of a substance by...

One can think about a mole as a measure of mass or quantity of a substance. A mole of a substance contains 6.023 x 10^23 atoms (or molecules, if the substance is a compound). That is to say, one mole of the element iron contains 6.023 x 10^23 atoms of iron, while one mole of oxygen gas consists of 6.023 x 10^23 molecules of oxygen gas. One can obtain the moles of a substance by using the three formulas your teacher mentioned:


  • The number of moles of a substance is the ratio of the mass of a substance and its molar mass or Mass/Mr. For example, water (H2O) has a molar mass of 18 g, thus, 50 g of water contains 50 g /18 g = 2.78 moles of water.

  • The concentration of a solution is often expressed in terms of molarity, which is the ratio of moles of solute to volume of solution. Thus, the number of moles of a solute can be calculated as the product of molarity and volume. For example, 1 lt of 2 molar solution of sulfuric acid contains 1 l x 2 M = 2 moles of acid.

  • One mole of a gas occupies 24 lt volume at room temperature, thus the moles of a gas can be calculated as the ratio of volume (in lt) to 24. That is, moles = volume/24.

Thus, the three formula mentioned by your teacher will help you calculate the moles of solids, liquids and gases.


Hope this helps.  

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