Question

How many moles of water, H2O, contain 2.0×1022 molecules of water? (See the hints for assistance in interpreting scientific notation.)
Express the quantity in moles to two significant figures.

Answer 1

Answer : The number of moles of water is, $3.3\times 10^{-2}$

Solution : Given,

Number of water molecules = $2.0\times 10^{22}$

As we know that 1 mole of water molecule contains $6.022\times 10^{23}$ number of water molecules.

As, $6.022\times 10^{23}$ number of water molecules present in 1 mole  of water molecule

So, $2.0\times 10^{22}$ number of water molecules present in $\frac{2.0\times 10^{22}}{6.022\times 10^{23}}=3.3\times 10^{-2}$ mole  of water molecule

Therefore, the number of moles of water is, $3.3\times 10^{-2}$

Answer 2

0.033 moles of water (H2O) contain 2.0 × 10²² molecules of water.

HOW TO CALCULATE NUMBER OF MOLES:

• The number of moles of a substance can be calculated by dividing the number of molecules in the substance by Avogadro's number:

• no. of moles = no. of molecules × 6.02 × 10²³

• According to this question, there are 2.0 × 10²² molecules of water. The number of moles can be calculated as follows:

• no. of moles = 2.0 × 10²² ÷ 6.02 × 10²³

• no. of moles = 2/6.02 × 10²²-²³

• no. of moles = 0.332 × 10-¹

• no. of moles = 0.033 moles

• Therefore, 0.033 moles of water (H2O) contain 2.0 × 10²² molecules of water.

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