[onkodat12]

Hello everyone, I am new to this forum. I tried to find one of my topics but I was not able to. I have a small problem concerning weight fractions.

So the task is:
25litres of 80% (w%) sulfuric acid (ρ=1,70kg/l) should be diluted to 16% solution. What volume of water (ρ=1kg/l) should be added?

So my approach is the following that I use [itex]w_{ percent }=\frac  { m_{ solute } }{m_{ solvent } + m_{ solute } }*100[/itex]


First I calculate the [itex]m_{ solvent}[/itex] to know how much H20 is in the solution of 80%

I need to dilute the whole solution by adding [itex]m_{ uknown}[/itex] . [itex]m_{ solute }[/itex] stays constant and since I need to dilute the whole solution I would add  [itex]m_{ uknown}[/itex] into the calculation and just solve it.

[itex]w_{ 16 }=\frac  { m_{ H2S04 } }{m_{ H20 } +  m_{ uknown}+ m_{ H20 } }*100[/itex]

Now I wondering if my assumption is right. Cause it sounds logic to me but the result is not right.

Thank you all for your help

[chenbeier]

The Problem is sulfuric acid get volume contraction if diluted.
You have to convert the volume to mass, then use the cross rule. Write on the left side the percentage what you have, in the middle the percentage what you want to have. The subtraction gives the weight parts for the 80% sulfuric and the water. But look up the specific gravity of 16% . Convert this to the volume and add the difference as water.

[Borek]

[itex]w_{ 16 }=\frac  { m_{ H2S04 } }{m_{ H20 } +  m_{ uknown}+ m_{ H20 } }*100[/itex]

Now I wondering if my assumption is right. Cause it sounds logic to me but the result is not right.

Logic looks OK to me, show your numbers. Why do you think the result you are getting is not correct?

As long as you operating with masses only, volume contraction and density changes are irrelevant.