Question

Use dimensional analysis to find out approximately how many grams of borax will be needed if the molecular weight is 381.37 g/mol and we need 0.104 moles/liter to make 100 ml of the solution?

Answer 1

Molarity of borax solution is 0.104 moles/liter and volume of solution is 100 mL. Molarity is defined as number of moles of solute in 1 L of solution.

It is mathematically represented as follows:

`M=(n)/(V)`

Here, n is number of moles of solute and V is volume of solution.

Thus, number of moles can be calculated as follows:

`n=M* V`

Putting the values,

`n=(0.104 mol/L)* (100 mL)((10^(-3) L)/(1 mL))=0.0104 mol`

Thus, number of moles of borax is 0.0104 mol. The molar mass of borax is 381.37 g/mol, mass can be calculated as follows:

`m=n* M=(0.0104 mol)(381.37 g/mol)=3.96 g`

Therefore, mass of borax is 3.96 g.