The fizz produced when an Alka-Seltzer tablet is dissolved in water is due to th

Question

The fizz produced when an Alka-Seltzer tablet is dissolved in water is due to the reaction between sodium bicarbonate (NaHCO_3) and citric acid (H_3C_6H_5O_7): 3 NaHCO_3(aq) + H_3C_6H_5O_7(aq) rightarrow 3CO_2(g) + 3H_2O(l) + NaC_6H_5O_7(aq) In a certain experiment 1.00 g of sodium bicarbonate and 1.00 g of citric acid are allowed to react, (a) Which is the limiting reactant? (b) How many grams of carbon dioxide form? (c) How many grams of the excess reactant remain after the limiting reactant is completely consumed?

Explanation / Answer

a) NaHCO3 is the limiting reagent.
For reaction to completely consume both the reactants the ratio should be 1:3 (sodium bicarbonate:citric acid). but here 1gm NaHCO3 = 1gm/84.066g/mol = 0.0119 mol
and citric acid = 1gm/192.124g/mol = 0.0052 mol which is more than 1/3 of NaHCO3. Hence, NaHCO3 is the limiting reagent.

b)  0.0119 mol of NaHCO3 forms  0.0119 mol of CO2 i.e., 0.0119 mol x 44.01gm/mol = 0.523 gm of CO2 will be produced.

c) The use of 0.0119 mol of NaHCO3 should consume (1/3rd) or 0.00397 mol citric acid. Which means 0.763 gm citric acid will be consumed when 1 gm of NaHCO3 is completely used.

Therefore, 1 - 0.763 = 0.237 gm will remain unreacted after the limiting reactant is competely consumed.

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