Experiment 4 Buffer Lab Answers to Application of Principles
Problems (pages 4-6 to 4-8)
1. NH4NO3 is the salt that contains the conjugate acid.
NH4 + is the conjugate acid of NH3.
(ammonia gas in water).
Write ammonia as NH3 (gas) or NH4OH
A second method would be to add a small amount of strong base (NaOH) to react with NH4
+
the acid and make some base.
NH4 +
+
OH –
NH3
+
H2O
2. To be a buffer you must contain a weak acid and its conjugate base (as part of a salt)
like HCHO2 , NaCHO2 and
NaH2PO4, K2HPO4
or
contain a weak base and its conjugate acid (as part of a salt)
like N2H4 , N2H5Cl
3.
pH = 7.73
4.
pH = 4.62
5.
A. pH = 8.19;
6. Kb
B. new pH = 8.15 (more acidic added HCl)
= 4.4 x 10 –6 to 4.5 x 10 –6
 pH = 0.04