An aqueous solution is 13.0% by mass ethanol, ch3ch2oh, and has a density of 0.978 g/ml. the molarity of ethanol in the solution is

Mass percentage of ethanol is 13%. Density of ethanol is 0.978 g/mL.
I mL of ethanol solution weighs 0.978 therefore 1 L of solution will weigh 978 g.
Since mass percentage is 13%, the weight of ethanol in 1 L of solution will be 
- 978 g x 13 % = 127.14 g
molar mass of ethanol is 46 g/mol
Therefore number of ethanol moles in 1 L - 127.14 g/ 46 g/mol = 2.76 mol
Molarity of ethanol solution - 2.76 mol/L = 2.76 M

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