How many mL of alcohol and how many mL of water are needed to prepare a 35.0%
alcohol solution containing 15.0 mL

Here we want to mix a volume of water and a volume of alcohol in such a way that we end with a 35.0% alcohol solution.

We will conclude that we must use 9.75 mL of water and 5.25 mL of alcohol.

Now let's see how to get the solution:

First, we should define the variables:

We want to have a 15 mL solution, then we will have:

x + y = 15 mL

And the 35% of this must be alcohol, then we will have that the quotient between the volume of alcohol and the total volume should be equal to 0.35

y/15mL = 0.35

That can be rewritten as:

y = 0.35*15ml = 5.25mL

Now we can reaplace this in the first equation to get the volume of water that we must use:

x + y = 15mL

x + 5.25mL = 15mL

x = 15mL - 5.25 mL = 9.75mL

So we can conclude that we must use 9.75 mL of water and 5.25 mL of alcohol.

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15.00 ml ROH + 27.86 ml H₂O => 42.86 ml of solution

Explanation:

Assuming the 15.0 is the volume of alcohol ...

Vol ROH = 15.00 ml = 35% of X where X = total volume of solution

X = 15.00 ml/0.35 = 42.86 ml total volume of solution

∴ Volume of water in 42.86 ml of solution = 42.86 ml - 15.00 ml = 27.86 ml

1.43 x 10^-11 j the guy commented the awnser just making sure u see it .

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.