gchem problem

[113zami]

an aqueous sulfuric acid solution is 39.2% H2SO4 by mass and has a specific gravity of 1.25. How many milliliters of this solution are required to make 100mL of a 0.2M H2SO4 solution?
ansr= 4mL

spent nearly an hour on this one, read the explanation but it went right over my head, hopefully someone here can help me figure it out "hopefully", thanks alot

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[REH]

I don't know if this is correct, but here's the answer that I came up with. First, I calculated the molarity of the solution:

1L * 1000mL/1L * 1.25g/mL*39.2g H2SO4/100gSol'n * 1molH2SO4/98g *1/1L = 4.48 M

Now, I need to determine how many mLs of this solution I need:

100mL * 1L/1000mL * 0.2 mol/L * 1L/ 4.48 * 1000mL/1L = 4.46 mL

Hope this helps.

REH.

 

[doc toothache]

an aqueous sulfuric acid solution is 39.2% H2SO4 by mass and has a specific gravity of 1.25. How many milliliters of this solution are required to make 100mL of a 0.2M H2SO4 solution?
ansr= 4mL

spent nearly an hour on this one, read the explanation but it went right over my head, hopefully someone here can help me figure it out "hopefully", thanks alot

ml x n= g/eq wgt
100ml of 0.2M would need .1 x.2 x 98=1.96g of H2SO4
1 ml of 39.2% H2SO4 contains 1.25 x .392= .49 g of H2SO4

since you need 1.96 g 1/.49=x/1.96 or x= 1.96/.49= 4 ml

Ok. For those who like to dive into m1v1=m2v2

A solution of 39.2% sulfuric acid will have 39.2 x 1.25 g/100ml of solution=49.0g/100ml or 490g/liter. Since 1 M requires 98g/liter we are dealing with 5M solution.

then 5V1=100x 0.2
solving for V1= 100x0.2/5=4ml

 

[113zami]

..

what do you mean... really dumb question right, gosh I don't even know why such people even try to study for the dat, they're so dumb they should just give up,

 

[doc toothache]

what do you mean... really dumb question right, gosh I don't even know why such people even try to study for the dat, they're so dumb they should just give up,

You are being too hard on yourself. As the old saying goes, the only dumb question is the one you didn't ask. (There was a previous post on this subject, but it was easier to re calculate the problem then to find the post. That was the reason for the ....). See the above edited post for calculations.

 

[113zami]

thanks doc i over reacted under frustration
thanks REH

 

[rose786]

What is specific gravity exactly? My book doesn't cover it.

 

[Montserrat]

It's probably covered in the "Density" section.

It's just the ratio of the density of substance is in question to the density of water.

x
1g * cm^3 = sp. gr.