[lingo_belle]

Hi all,

I've measured 50ml of H2SO4 (98%) into 150ml of water. May I check if the concentration is abt 4.6M?

thank you

belle

[Arkcon]

What's the density of 98% H2SO4, and how did you calculate the molarity?

[Guitarmaniac86]

I checked on Wikipedia and the density is 1.84 g cm3 so I ll use that.

Mass H2SO4 = density x volume = 1.84 x 50 = 92 g

Moles = Mass / RMM = 92 / 98

Moles = 0.9388 moles.

Conc = (Moles x 1000)/ Volume = (0.9388 x 1000) / 150

Conc = 6.26 M

Edit:

On working backwards, if you got a value of 4.6 M the density would be: 1.3524 g cm3. If thats what you were given then 4.6 M would be correct.

[Arkcon]

You should check the bottle if you're in the lab, or the text of the question if you're doing homework.  The density of  concentrated acids can vary, so this is one example of when wikipedia is a bad choice..  Look at the bottle in a lab sometime, you'll see the density is often typed, not mass production printed, on the bottle's label.  Beyond that, your formulas are correct.

[Guitarmaniac86]

You should check the bottle if you're in the lab, or the text of the question if you're doing homework.  The density of  concentrated acids can vary, so this is one example of when wikipedia is a bad choice..  Look at the bottle in a lab sometime, you'll see the density is often typed, not mass production printed, on the bottle's label.  Beyond that, your formulas are correct.

We had that problem at my lab. The density on the bottle was 0.61 for cyclohexanol. The actual density was 0.962 but the lab tech slapped the wrong label on so everyone assumed the density was 0.61. Boy was it fun correcting all the calculations with the correct density.

I had a hissy fit because I was getting stressed with the synthesis of cyclohexene. It just went ... Wrong

Anyway Im spamming :S

[AWK]

Conc = (Moles x 1000)/ Volume = (0.9388 x 1000) / 150

You poured 50 ml of H2SO4 into 150 ml of water. Your volume will be approximately 200 m

[Guitarmaniac86]

Conc = (Moles x 1000)/ Volume = (0.9388 x 1000) / 150

You poured 50 ml of H2SO4 into 150 ml of water. Your volume will be approximately 200 m

Someone cant count

>_>

<_<

Ok taking that into consideration its: 4.694 M

Sorry... My bad :S

[Arkcon]

We had that problem at my lab. The density on the bottle was 0.61 for cyclohexanol. The actual density was 0.962 but the lab tech slapped the wrong label on so everyone assumed the density was 0.61. Boy was it fun correcting all the calculations with the correct density.

I had a hissy fit because I was getting stressed with the synthesis of cyclohexene. It just went ... Wrong

Anyway Im spamming :S

Hardly spamming, this is a serious factoid.  Occasionally these percentage problems come up, and you're left without density.  And nowhere to go.

You poured 50 ml of H2SO4 into 150 ml of water. Your volume will be approximately 200 m

Good catch.  And nice of you to say approx.  For various solutions: 50 ml + 50 ml ≠ 100 ml.  Even more so for conc. H₂SO₄, which will raise the temperature, and expand.

[AWK]

Even when cooled to the starting temperature the final volume wil be about 189 ml!

[Borek]

CASC does such calculations automatically, taking all density changes into account (thanks to built in density tables). In a way it was fun to code - IIRC internally everything is converted to mass and mass percentages first, as these things can be always calculated exactly.

In this particular case:

[lingo_belle]

hi all,

thx for the help, at least i know i'm somewhere there in the calculation!

THx!

belle