Archived posting to the Leica Users Group, 2002/06/23
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Dan-
One way you can overcome this is to simply dry your pentahydrate. Place
approx. 150 grams in a beaker then in an oven (it's not toxic and will not
go anywhere) and dry it for about 12 hrs at 150 degrees C -- Then you'll
have the anhydrous form that you can take 100 grams of!
Otherwise you must figure out the number of MOLES of sodium thiosulfate
(anhydrous) in 100 grams by dividing 100g by the Molecular Wt (g/mole) of
the compound, in this case sodium thiosulfate. Once you have the number of
moles you need , multiply that by the Molecular Wt of sodium thyosulfate
pentahydrate (5 water molecules with each Sodium thiosifate ( which would be
the anhydrous Wt + (5x18 g/mole) 18 g/mole is the molecular wt of water. and
that would give you the number of grams of the pentahydrate you need to
equal 100g of the anhydrous, You can look up the molecular weight on the
side of the bottle, or in a General Chem textbook.
I'll figure it out for you if you write me back off- forum (I just can't
run to a book right this second!) if you'd like. I always keep my photo
stuff desiccated and dry to make things easier.
But off the top of my head I think the pentahydrate form is about 250
grams/mole making it about 64 percent water. So if you weigh out 165 grams
instead of 100 grams, you'd be mighty close!!
EC
And who says high school chem wasn't fun!!
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> From: owner-leica-users@mejac.palo-alto.ca.us (Leica Users digest)
> Reply-To: leica-users@mejac.palo-alto.ca.us
> Date: Sun, 23 Jun 2002 02:20:32 -0700 (PDT)
> To: leica-users-digest@mejac.palo-alto.ca.us
> Subject: Leica Users digest V22 #321
>
> Friends
>
> What is the weight of anhydrous sodium thiosulphate which is equivalent to
> 100 grams of the "hypo" (pentahydrate) variety? Thanks.
>
> Dan K.
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