Calcium dihydrogen phosphate, Ca(H2PO4)2, and sodium hydrogen carbonate, NaHCO3,
ID: 942343 • Letter: C
Question
Calcium dihydrogen phosphate, Ca(H2PO4)2, and sodium hydrogen carbonate, NaHCO3, are ingredients of baking powder that react with each other to produce CO2, which causes dough or batter to rise:
Ca(H2PO4)2(s) + NaHCO3(s) CO2(g) + H2O(g) + CaHPO4(s) + Na2HPO4(s)[unbalanced]
If the baking powder contains 31.0% NaHCO3 and 35.0% Ca(H2PO4)2 by mass:
(a) How many moles of CO2 are produced from 1.59 g of baking powder?
mol CO2 =
(b) If 1 mol of CO2 occupies 37.0 L at 350°F (a typical baking temperature), what volume of CO2 is produced from 1.59 g of baking powder?
L=
Explanation / Answer
balanced reaction is
Ca(H2PO4)2 + 2NaHCO3 --> 2CO2 + H2O + CaHPO4 + Na2HPO4
Mass of Ca(H2PO4)2 = ( 35/100) x 1.59 = 0.5565 g
Moles of Ca(H2PO4)2 = mass/ molar mass = 0.5565 /234.05 = 0.002378
Mass of NaHCO3 = ( 31/100) x 1.59 = 0.4929 g
Moles of NaHCO3 = ( 0.4929/84) = 0.00587
as per reaction NaHCO3 and Ca(H2PO4)2 react in 2:1 , hence for 0.00587 moles NaHCo3 we need ( 1/2) 0.00587 = 0.00294 moles Ca(H2PO4)2 moles but we had only 0.002378 moles Ca(H2PO4)2
hence Ca(H2PO4)2 is limiting reagent ,
CO2 moles = 2 x Ca(H2PO4)2 moles = 2 x 0.002378 = 0.004756
b) 1 mol occupies 37 L
0.004756 moles CO2 occupies = 37 x 0.004756 = 0.176 L