Question

A Janitor is burned after throwing 2 chemicals into a trashcan and reaching in. The first chemical is 20% by mass Na2S2O3 and the other is 6% by mass NaClO. We are supposed to determine whether or not the janitor burned himself (the skin reached 71 degrees Celsius for at least 0.5 seconds).

We were given mock data using Job's Method where we kept the total volume reaction at 25 mL and varied the individual reactant amounts. In the mock data, the highest temperature attained was 42 degrees C with 0.5 M of 0.01875 L Na2S2O3 and 0.5 M of 0.00625 L NaClO.

The professor gave the equation (M of trashcan / M in mock lab) X max temperature in lab = max temperature in trashcan.

However, I do not know what to put in the M of trashcan part of the equation?

I have ( ? / 0.5 M) X 42 = ?

Answer 1

The equation suggests that you have to get the value of M (mass) of trashcan because you know the maximum temperatures in mock lab, and the trashcan. You can derive the value of M (mass) in mock lab in the following way:

The balanced reaction between the two chemicals is

3 NaClO + Na₂S₂O₃$\rightarrow$ 3 NaCl + Na₂S₂O₆

Please see the hand written solution for further reading:

The moles of Naso in the morrlas sa 0.58001895 meleyay a 9.375*103 moles non The moles of Nacio in the mock lob 30.5 x 0.00625 molt 5 3.125 x 103 males no The molecular weight is most ma of war = 158.10 & more mw of Nacto = 24.44 amore Thus, 9.375810 Snake of rache= 9.375 x 10 x 156.10 Gunter = 148 g 3,125x10 mok of rack & 3.125x10 x 74.46 2 g mad totas n 50234 m = (1.48+0.23) g or with = 1.7 g (min mock las)

im in trash can = M trash m in mock lab ammolkoon s o max. temperature in mock las & Tmax - max. temperature in trang an & Tmaxe 9 given the equation' - no1 Marash - (Tmax trash) x Mmock t curre co lot 0.7l x 1.77 2 . 42 g su 2.89 grotest 2 Tmax-mock

The Naisoo is 20x by 2.898 = 2.89x20 07 -0.5789 The Nacio is 67. by 2.898 & 6x2.89 = 01173 g - 100 wy 0.578 g naro, & 0.578 g 158.10 tog mot = 365x103 md 0.173 g Nacioc 0.173 g 74.44 Gemot 5 2.32 x 103 mol To burn the generator 3 equivalents of Naclo is needed for l equivalent of Naszog. Thus for the burning af Janitor the mole of Nacio in rashcan needed is 365x 103x3 = 1.09x10 moles but the giren Noclo is 2.32x10 moles thers, Janitor will not burn Answer