Question

Calculate the number of moles of methanol in 5 liters in 2m solution.

Answer 1

if the density of the solution is 0.981 kg/L.( molar mass=32.0 g/mol) (should be given)


First, calculate the mass of the solution:

5 * 0.981 = 4.905kg = 4905g (volume * density )

Now, for every 1000g of solvent, there is 2 moles of methanol. As the molecular mass of methanol is 32 g, 2 moles is 64 g. Therefore the total mass of a solution containing 2 moles of methanol is 1064 g.

So, how many times does this known mass of solution fit into the 5 litres?
4905 / 1064 = 4.6099624

So a 4.6099624 lots of 2m solution of 1000g solvent are needed to make 5 litres of the solution.

Therefore, you need 4.6099624 lots of 2 moles of methanol to make 5 litres.
2 * 4.6099625 = 9.2199248 moles of methanol