Question 1180854
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You need a 95% alcohol solution. On hand, you have a 15 mL of a 10% alcohol mixture. 
How much pure alcohol will you need to add to obtain the desired solution?
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<pre>
The given starting mixture contains 0.1*15 mL = 1.5 mL of the pure alcohol.

The rest  15 mL - 1.5 mL = 13.5 mL is <U>water</U>.



Now, we are going to add pure alcohol - so we do not change the mass of water, those 13.5 mL.

These 13.5 mL are going to become 5% = 100% - 95% of the final mixture.



    Hence, the volume of the final mixture must be  {{{13.5/0.05}}} = 270 mL.



It means that the volume of the pure alcohol to add is  270 mL - 15 mL = 255 mL.



<U>ANSWER</U>.  255 mL of pure alcohol should be added, and the final volume of the mixture will be 270 mL.
</pre>

Solved.


It is how &nbsp;COMMON &nbsp;SENSE &nbsp;helps to solve problems without using any equations.