Question

What is the molality of a solution in which 2.3 g `O_2` gas dissolved in 355 g of water?

Answer 1

`0.20m`

Explanation:

Molality can be found using the equation below:

What you want to do now is determine what the solute and solvent are. A solute is dissolved in the solvent and the solute is the "minor component in a solution."The solvent is usually water or it is the substance that you have more of. In our case, the solute is `O_2` and the solvent is water.

As we can see from the equation, the solute and solvent have the wrong units. Let's start by converting grams of `O_2` to moles of `O_2`. We do this by using the molar mass of `O_2` as a conversion factor.

`2.3cancel"g"O_2xx (1mol O_2)/(32.00cancel"g")= 0.0719 mol O_2`

Now we need kg of solvent instead of the grams that we're given. Let's use this relationship:

`355cancel"g" H_2O xx (1kg)/(1000cancel"g") = .355kg H_2O`

Now all we do is plug the values into the equation like this:

`molality = (0.0719 mol)/(0.355kg)` = `0.20 m`