Ishwar S. answered • 06/25/20
University Professor - General and Organic Chemistry
Balanced chemical reaction:
2HNO3 (aq) + Ba(OH)2 (aq) → Ba(NO3)2 (aq) + 2H2O (l)
This is a strong acid + strong base reaction called a neutralization reaction. The products formed are a salt (Ba(NO3)2) and water. We first need to use the given volume and concentration to determine which reactant is the limiting reagent.
mol HNO3 = (75 cm3 x 1 dm3 / 1000 cm3) x 0.400 mol/dm3) = 0.0300 mol HNO3
mol Ba(OH)2 = (100 cm3 x 1 dm3 / 1000 cm3) x 0.200 mol/dm3) = 0.0200 mol Ba(OH)2
Use the mole ratio from the balanced chemical reaction to convert mol of one reagent to another. It does not matter which one you select. In this case, I am going to convert mol HNO3 to mol Ba(OH)2.
0.0300 mol HNO3 x (1 mol Ba(OH)2 / 2 mol HNO3) = 0.0150 mol Ba(OH)2
This tells us that HNO3 is the limiting reagent since only 0.0150 mol Ba(OH)2 is needed to COMPLETELY neutralize 0.0300 mol HNO3.
Excess Ba(OH)2 remaining = 0.0200 - 0.0150 = 0.0050 mol Ba(OH)2
Since Ba(OH)2 is a strong base, its ionization reaction is written as:
Ba(OH)2 (aq) → Ba2+ (aq) + 2OH- (aq)
1 mol Ba(OH)2 forms 2 mol OH- ions, therefore, 0.0050 mol Ba(OH)2 will dissociate to form 2 x 0.0050 = 0.0100 mol OH- ions. Next calculate the pOH using the equation
pOH = - log [OH-] = - log 0.0100 = 2.00
pH of the solution can be calculated using the equation: pH + pOH = 14.00
pH = 14.00 - pOH = 14.00 - 2.00 = 12.00
This pH is valid because OH- is a strong base where the pH should be greater than 7!
