Question

Kemmi pipets 25.00 ml of pure 1-propanol (c3h7oh, a liquid organic alcohol) into a 100.0 ml volumetric flask. she dilutes it with di water. help her calculate the strength of her diluted solution. volumes: 25.00 ml volumetric pipet, 100.00 ml volumetric flask. molar mass of pure 1-propanol: 60.09 g/mol. density of pure 1-propanol: 0.803 g/ml calculate the number of moles in exactly 25.00 ml of 1-propanol. (3 significant digits; units of mol) [x] calculate the molarity of the diluted solution. (3 significant digits; units of m or mol/l) [y]

Answer 1

Q1)
As Kemmi pipettes a volume of 25.00 ml of the solution
density of pure propanol is 0.803 g/ml
This means that in 1000 ml of solution - 0.803 g of pure propanol
Therefore in 25.00 ml of solution - 0.803 g x 25.00 ml / 1000 ml
                                                     = 0.0201 g
Using molar mass, number of moles can be calculated= 0.0201 g / 60.09 g/mol
                                                                                       = 3.35 x 10⁻⁴ mol
therefore the number of pure propanol moles in exactly 25.00 ml is
3.35 x 10⁻⁴ mol

Q2)
molarity is the concentration of the solution. It can be defined as the number of moles of solute per liter of solution
we know the number of moles in 25.00 ml of solution. When its diluted in a 100.00 ml volumetric flask, number of moles remain constant but now the volume over which the moles of solute are dissolved is increased.
therefore number of moles = 3.35 x 10^(-4) mol
volume over which its dissolved - 100.00 / 10³ dm³
                                                    = 1.0000 x10⁻¹ dm³
the molarity = 3.35 x 10⁻⁴ mol / 1.0000 x10⁻¹ dm³
                    = 3.35 x 10⁻³ mol/dm³