C. Some Properties of Buffers buffer sys- On the lab bench can be used to make t

Question

C. Some Properties of Buffers buffer sys- On the lab bench can be used to make three different common tems. These we have o.1 M stock solutions that are HCO, -CO NH -NH carbona acetic acid-acetate ion ammonium ion-ammonia hydrogen buffer The sources of the i will be sodium and ammonium salts containing those ions. Select one of these systems for your experiment. 1. Using a cylinder, out 15 ml of the acid component of your buffer into a 100-mL beaker. The acid graduated measure Quo M NH,CI. o.10 M NaHCO3 will be one of the following solutions: M O 15 mLof the conjugate base of your Rinse out the graduated cylinder distilled water and use it to add calculate pK.for the acid. buffer Measure the pH of your mixture and record it on the Data page, 2. Add 30 mL water to your buffer mixture, mix. and pour half of the resulting solution into another 100 mL Measure the pH of the diluted buffer Calculate plk, again. Add five drops of 0.10 M NaOH M to the diluted and measure the pH again. To the other once 5 drops 0.10 half of the diluted buffer add buffer HCI, and again measure the pH. Record your results. Make a buffer mixture containing 2 mL of the acid component and 20 mL of the solution containing the conjugate base. Mix, and measure the pH. Calculate a third value for pKa To that solution add 3 mL0.10 M NaOH. Measure the pH. Explain your results.

Explanation / Answer

4. Concentration of H+=[OH-]=10^-7 So PH=-log[H+]=-log(10^-7)=7

When 5 drops=0.25 ml(considering 20 drops of HCl=1 ml) HCl is added to the 25 ml distilled water [H+]=25*0+0*25*0.1/25.25=9.99*10^-4

PH=4-log9.9=3.004

Now 10 drops(0.5 ml) 0.1 N naOH was added.

[HO-]=(0.5*0.1-0.25*0.1)/25.75=9.708*10^-4=3.012

PH=14-3.012=10.998

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