How to Answer a Gravimetric Stoichiometry Question?

Question

The two questions are

“How many moles of chorine gas are required to produce 1.000kg of laundry bleach (CaOCl2 (s) or Ca(OCl2*CaCl2(s)) from solid lime and chlorine? (Lime is calcium dioxide)”

“What mass of lye (NaOH) can be produced from the reaction of 148g of slaked lime (Ca(OH)2(s)) reacting with sufficient soda ash (Na2CO3(s))?

Answer 1

Hi Ana G.,

First of all, you have to correct the chemistry. The substances expected in "calcium bleaching powder" are:

Ca(OCl)₂ , Ca(OH)₂ , and Ca (Cl)₂ . And lime is not calcium dioxide; that would imply two atoms of oxygen for each one of calcium. It's only CaO . Frequently in lab reactions, lime is 'slaked' = reacted with water, to make Ca(OH)₂ . This may react faster with other chemicals, since it carries its own little bit of "water" with it, so to speak (and dry ingredients tend not to react at all!)

1) So, for each reaction there, write your reaction, and balance it.

2) Convert a given mass into moles, using the molecular weight of the species (I'm guessing you have to add them up, from a periodic table, right?).

3) Using the coefficients in the balanced equation, figure the required or co-produced moles of the target species. Convert back to mass units. Done!

P.S. What drives the second reaction? You should know the major drivers of reactions: production of .... or .....!

Cheers, -- Mr. d.