[myalpineshines]

I got a summer packet prior to going into AP chem and i am dumbfounded on one of the questions as follows:
    "In the human body, the toxic compound hydrogen cyanide is neutralized by the acid, H2S2O3, according to the reaction  HCN + H2S2O3 yields HCNS + H2SO3.  If 1.000 mg of H2S2O3, is available in the body, will this be enough to neutralize 2.000 mg of HCN swallowed by a person?"
    Any help is greatly appreciated.

[kissoftalons]

I'm am not 100 % sure about this...but this is the way I would approach the question and my reasoning...


Find out how many mols of H2S2O3 you have....so 1 mg = 0.001 gram
0.001 / 114.12 = 0.000008763 or 8.763 x 10^-6 mols of H2S2O3

2mg = 0.002 grams of HCN
0.002 / 27.0477 = 0.000073947 or 7.3947 x 10^-5 mols

Since HCN and H2S2O3 are in a 1:1 ratio ...the one you have less mols of is the limiting reagent, in this case the H2S2O3

So ... there is not enough H2S2O3 to neutralize the HCN swallowed (since you have less H2S2O3 in the reaction than needed to react with all of the HCN)

Hope this has helped!

[xiankai]

thats a good approach. convert all given data to moles, and work out the limiting reageant based on molar ratios in the equation.