Question on online problems for Dilution

[404602335]

26. If an 800 mL aqueous solution contains 12.4 g of ethanol, CH3CH2OH, what is molarity of ethanol in this solution?

[JasonLiu_2J]

Remember that the units for molarity are moles/liter (number of moles/volume of solution). From the question, you know that you have 800ml, or 0.8 L of solution. What you need to find is how many moles of ethanol are in 12.4 grams of ethanol (CH3CH2OH). To do this, you would divide the amount in grams you have by the molar mass of ethanol, which is 46.07 grams/mole. Dividing 12.4 grams by 46.07 grams/mole leaves you with 0.269 moles of ethanol in the solution. Finally, to calculate molarity, you would simply to the number of moles of ethanol divided by the volume of the solution. Doing this calculation (0.269 moles / 0.8L) gives you 0.336 mol/L, which is the molarity of ethanol in the solution.

[Rachel Yu 1G]

First, calculate the molar mass of ethanol (CH3CH2OH) which ends up being 46.07 g/mol. We can use this value to calculate the moles of ethanol in 12.4g by dividing (12.4g)/(46.07g/mol) to get 0.269 moles of ethanol. Remember the equation for molarity: Molarity = (number of moles/volume in Liters). Since the given volume (800 mL) is in milliliters, we need to convert the value to liters by dividing by 1000, giving us 0.8 L. Now we can calculate the molarity by dividing 0.269 moles of ethanol by 0.8 L, giving us in 0.336 mol/L for the molarity of ethanol.