The concentration of water molecules in pure water at 298 K is

Options

A. `10^(-7)M`
B. `55.5M`
C. `5.55M`
D. `7.26M`

Answer

B

Explanation

Molarity is defined as the number of moles of solute per liter of solution, Thus, the molarity of pure water means the number of moles of water in one litre of water.
Volume `(H_(2)O)=1 L=1000 ml`
Density `(H_(2)O)= 1 g mL^(-1)`
Mass `(H_(2)O)=` Density x Volume
`= (1g mL^(-1))(1000 ml)`
`= 1000 g`
Number of moles of `H_(2)O = ("Mass")/("Molar mass")`
`= (1000g)/(18g mol^(-1))=55.5 mol`
Since we have `55.5` mol of `H_(2)O` in 1 L of water, the molarity of pure water is `55.5` mol of `H_(2)O` in 1 L of water, the molarity of water is `55.5 mol L^(-1)`.