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Shezan Khan Grade: 11

Explain Molar Mass an Molar Volume

8 years ago

Answers : (1)

askIITIians Expert
21 Points

Molar Mass and Molar Volume

We have studied in Section 1.7 that 1 mol consists of 6.022 × 1023 entities or particles; we can talk of 1 mol of an element or a compound. Thus, mass of 1 mol of any substance will be its molar mass (M). Thus 1 mol of sodium means 6.022 × 1023 atoms of sodium weighing 23.0 g. In brief we can write Molar mass of sodium, M = 23.0 g mol–1

    Similarly, 1 mol of oxygen molecule (O2) means 6.022 × 1023 molecules weighing 32.0 g or

    Molar mass of oxygen (O2), M = 32.0 g mol–1

    In case of NaCI is we say 1 mol of sodium chloride, we mean of
6.022 × 1023 formula units of NaCI, which will weigh 58.5 g. Therefore, molar mass of NaCI = 58.5 g mol–1 (1 mol formula unit of NaCl will contain 1 mol of Na+ and one mol of Cl– ions).

    In case of certain substances it is sometimes not very clear whether we are talking of 1 mol atom or 1 mol molecule. For example, if we say 1 mol of hydrogen, it means we are talking of naturally occurring form of hydrogen and it is H2 i.e. we are talking of 1 mol of hydrogen molecule. Sometime we specify very clearly, for example 1 mol atom of hydrogen. Here it is clear that we are talking of 1 mol atom not molecule. But if it is not mentioned, then we should infer that it is the natural form of that substance. In order to avoid this confusion the molecular forms of nitrogen, hydrogen and oxygen are called dinitrogen (N2), dihydrogen (H2) and dioxygen (O2).

    Molar Volume of a substance is volume of one mole of that substance. Molar volume of liquid and solids can be calculated easily if we know the molar mass and density at any given temperature and pressure as these do not change much with temperature and pressure. The molar volumes for gases change considerably with temperature and pressure. For an ideal gas  molar volume at 0oC and 1 atm pressure (1.01 bar) is 22.4L.

8 years ago
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