The mole is defined as the number of atoms in exactly 12 g of carbon-12. The mol

Question

The mole is defined as the number of atoms in exactly 12 g of carbon-12. The mole equals 6.022×1023 items of whatever you are counting. This number is also called Avogadro's number, after Amadeo Avogadro (1776–1856). Molar mass is the mass of 1 mol of atoms of an element; for compounds, molar mass is the mass of 1 mol of molecules or formula units. Molar mass can be used to convert mass to moles for any element or compound.

How many grams are in 4.60 mol of sodium chloride (NaCl)?

How many water molecules are in a block of ice containing 2.25 mol of water (H2O)?

Explanation / Answer

Molar mass of NaCl = At.mass of Na + At.mass of Cl

                             = 23 + 35.5

                             = 58.5 g/mol

We know that number of moles , n = mass/molar mass

So mass of NaCl , m = number of moles x molar mass

                               = 4.60 mol x 58.5 (g/mol)

                              = 269.1 g

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We know that 1 mole contains 6.023x1023( avagadro number) of molecules

                     2.25 mole of water contains M molecules

                       M = ( 2.25x6.023x1023) / 1

                           = 1.355x1024 molecules

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