# Can anyone explain to me how is the molar concentration, or should I say the number of moles of water equal to 55.5? I need it with some explanation.

Jul 6, 2015

Yes, one liter of water does contain 55.5 moles of water.

#### Explanation:

You can determine how many moles of water can be found in one liter of water by using water's density and its molar mass.

At room temperature, you can approximate the density of pure water to be equal to 1 g/mL. This means that the mass of a liter of water at room temperature will be

1cancel("L") * (1000cancel("mL"))/(1cancel("L")) * "1 g"/(1cancel("mL")) = "1000 g"

You can determine how many moles this much water would contain by using water's molar mass, which tells you how much 1 mole of water weighs.

1000cancel("g") * "1 mole water"/(18.01528cancel("g")) = "55.5 moles"

Since molarity is defined as moles per liter (regardless if you're dealing with moles of solute or not), you can say that the molar concentration of water is equal to

${C}_{\text{water" = n/V = "55.5 moles"/"1 L" = "55.5 M}}$