How many moles of NaCl are in 255 g of a 1.24 m NaCl solution?

Question

If you could work me through the steps, that'd be great. Thanks

Answer 1

First, let's assume that you mean molal by 1.24 m.  If you mean molar, then it should be 1.24 M.

1.24 m means 1.24 moles of NaCl per kg of solvent

 

First find the mass of 1.24 moles of NaCl1.24 moles NaCl x 58.44 g/mole = 72.47 g NaCl

 

1 kg of water (solvent) = 1000 g assuming a density of 1g/ml, thus 1.24 m NaCl = 72.47 g NaCl/1000 g H2O

Total mass of solution = 72.47 g + 1000 g = 1072.47 g 

What fraction of 1072.47 g is 255 g?  It is 255/2072.47 = 0.123

Moles of NaCl in 255 g of 1.24 m = 0.123 x 1.24 = 0.153 moles