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[PHC - JamCol]

The density of ethanol is 0.789 g/mL. How many grams of ethanol should be mixed with 225 mL of water to make a 4.5% (v/v) mixture?

 

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To answer this question, we need to first understand what is meant by a 4.5% (v/v) mixture.

A 4.5% (v/v) mixture means that the volume of ethanol in the mixture is 4.5% of the total volume of the mixture.

We can set up a proportion to solve for the amount of ethanol needed:

% ethanol / 100 = volume of ethanol / total volume

We know that the total volume will be 225 mL (the volume of water), so we can plug in the values we know and solve for the volume of ethanol:

4.5 / 100 = volume of ethanol / 225 mL

0.045 * 225 mL = 10.125 mL of ethanol

Now that we know the volume of ethanol needed, we can use the density of ethanol to calculate the mass:

mass = volume * density

mass = 10.125 mL * 0.789 g/mL

mass = 7.99 grams of ethanol

Therefore, we need to mix 7.99 grams of ethanol with 225 mL of water to make a 4.5% (v/v) mixture.