[stlboy]

acid base reaction
    2-            +
CO      +     2H      ====>    H  O   +  CO
    3                                       2         2

7.8L of co2 is collected at STP, cannot figure the molarity of th HCL solution used in the reaction
if 140 ml of HCL was needed, in M.  Tried limiting reagent, but wrong path.

[Borek]

Use subscripts and supperscripts to format reaction equation:

CO₃^2- + 2H⁺ -> H₂O + CO₂

How many moles of CO₂ were collected?

[stlboy]

Thanks for your patience.  I am assuming you are guiding me.
1 mole =22.4 at STP so

1 mole   =  22.4
------       --------
x mole        7.8

which gives me .348 moles of CO₂

still stuck...

[Borek]

OK, now, assuming 0.348 moles of CO₂ were produced, how many moles of HCl reacted?

[stlboy]

Lets see, use the mole ration in the balanced equation to get moles of H+ (from HCl)
Now you have moles as each HCL molecule gives you one H+
THen divide by solution in litres and have molarity

thanks for guiding

[Borek]

Just don't forget about significant digits.