Question

How many milliliters of pure liquid methanol (ch3oh, mw = 32.04 g/mol) are needed to prepare 500.0 ml of an aqueous solution of 12.0 g/l methanol? the density of pure liquid methanol is 0.791 g/ml?

Answer 1

Answer:- 7.59 mL.

Solution:- We want to make 500.0 mL of an aqueous solution of methanol whose density is $12.0\frac{g}{L}$. This has to be made from a given pure liquid methanol with density $0.791\frac{g}{mL}$ . It asks to calculate the volume of pure liquid methanol.

We know that, mass = volume*density

Let's calculate the mass of aqueous solution from it's given volume and density. need to convert volume unit from mL to L as the density is given in grams per liter:

mass of aqueous methanol solution = $500.0mL(\frac{1L}{1000mL})(\frac{12.0g}{L})$

= 6 g

From above calculations, we need to use 6 g of pure liquid methanol. It's density is known, so we could calculate it's volume as:

$volume=\frac{mass}{density}$

Let's plug in the values in it:

$volume=6g(\frac{1mL}{0.791g})$

= 7.59 mL

Hence, we need to take 7.59 mL of pure liquid methanol.