A sample of dolomitic limestone containing only #CaCO_3# and #MgCO_3# was analyzed. When a 0.2800 gram sample of this limestone was decomposed by heating, 75.0 mL of #CO_2# at 750 mmHG and 20°C were evolved. How many grams of #CO_2# were produced?

1 Answer
Jan 8, 2017

Answer:

#MCO_3(s) + Delta rarr MO(s) + CO_2(g)uarr#

Approx. #140 *mg# gas are evolved.

Explanation:

We use the Ideal Gas equation to access the moles of carbon dioxide evolved:

#n=(PV)/(RT)# #=# #((750*mm*Hg)/(760*mm*Hg*atm^-1)xx75.0xx10^-3*L)/(0.0821*L*atm*K^-1*mol^-1xx293*K)#

#=3.1xx10^-3mol#.

#"Mass of carbon dioxide produced"=3.1xx10^-3molxx44.0*g*mol^-1=??g#

The key to doing this problem was (i) knowing that #760*mm*Hg-=1*atm#; and (ii) using the right gas constant, #R#. I have always liked #R=0.0821*L*atm*K^-1*mol^-1# because it uses units that chemists would habitually use. The other gas constants tend to use whack, non-intuitive units.