Direction: order to receive credit. Make sure your answers to look the Ka values
ID: 542973 • Letter: D
Question
Direction: order to receive credit. Make sure your answers to look the Ka values of some acids. es that require problem solving, you need to show the calculation set up leading to the answer in s contain the correct units, You will need a Table of Ionization Constants For exercis A. Acid Base and Titration Does the pH of the solution increase, decrease, or stay the same when you A. Add solid sodium oxalate, Na CO, to 50.0 mL of 0.015 M oxalic acid, HC,O? Explain 1. for credit. B. Add solid ammonium chloride to 75 mL of 0.20 M HF? Explain for credit. C. Add 20.0 g of NaCI to 1.0L of 0.10 M sodium acetate, CH,COONa? Explain for credit. D. Add aqueous ammonium nitrate to 30.0 mL of 1.0 M NH? Explain for credit.Explanation / Answer
1]
a) will certainly become less acidic. The pH will increase. That's because the oxalate ion concentration has increased, so the equilibrium between
H2C2O4 <---> 2H+ + C2O4-2
will have to shift back to the left to re-establish.
So some of the freshly introduced oxalate ions combine with protons and form the oxalic acid molecule.
b) the ammonium ion is capable of releasing protons. If you add it to a neutral or alkaline solution it will release
protons to form ammonia.
However, in the presence of a strong acid the effect will hardly be noticeable.
NH4+ ---> NH3 + H+
in theory it would reduce the pH by dissociating into NH3 and H+, but the actual change in pH would be very small.
c) there is not even a theoretical reason for any change in pH in this example. Both salts dissociate completely. The acetate ion itsself will cause the solution to be weakly alkaline, but addition of NaCl won't change anything.
d]
NH4+ ----> NH3 + H+
equilbrium shifts to left due to the presence of NH3
so
less number of H+ ions
which results in pH increase
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