How many molecules of sucrose (table sugar), C12H22O11, dissolved in 450.0 g of water are needed to make a 1.81 m solution?

Answer 1

This is ever so slightly different from the others you've asked about, so I thought I'd weigh in.

1.81 m means 1.81 mols of sugar per kg of water.

How many kg of water do we have?

450.0 g H₂O x 1 kg/1000 g = 0.4500 kg H₂O

How many mols of sugar do we need in 0.4500 kg H₂O to make 1.81 mol / kg?

x mol / 0.4500 kg = 1.81 mol / 1 kg

x = 0.8145 mols sugar needed

Check:

0.8145 mols / 0.4500 kg = 1.81 mol/kg

Now, to get to the question ... how many MOLECULES is this?

0.8145 mols x 6.02x10²³ molecules / mol = 4.90x10²³ molecules