Buffer Lab, Lab 7 Data sheet .71; Calculation space: Preparation of Buffer A, pH : 5-_ ml of 0.300 M Acetic Acid · 'll b ~ ~g of Sodium acetate theoretical • \Ltl ~ . g of Sodium acetate actual 5 tJrl:; pH measured \ C9i2.J:4('._Final total volume ~ M in acetic acid ·£2P) M. Calculation space: Preparation of Buffer B, pH ~ (5".o ) (.Ko) "" ( (oo) (11..t -w.. A,( 2...'L·?o I74- s-1~ 5. / i. l ·Cl\ \ '0 )l.. Titration of Buffer: Buffer ID~ Vol of buffer ~ "'-'l Titrant ID # c._\ ·O'L 1; ~ Trial 2 Volume initial Volume final Total volume titrant Moles of titrant pH initial pH final Changein pH Analysis , 1. Using the masses of sodium acetate and the beakers you weighed it in, determine the exact mass of sodium acetate you added to each buffer. Was the actual amount of sodium acetate needed different than the theoretical amounts? Why might this be? I 2. 1 • Calculate the concentration of hydronium ion of the buffer solutions at their starting pHs. Calculate the moles of hydronium ion present in 20.0 mL of the buffers. 3. A change of pH by l unit means a change in hydronium ion concentration by a factor of 10. Calculate the number of moles ofNaOH that would theoretically be needed to decrease the moles of hydronium you calculated in ''2" by a factor of 10. · 4. Using your results from the careful titrations (Part C)and the concentration for your standard NaOH solution, calculate the moles of titrant (NaOH) needed to change the pH by 1 unit for each buffer. : 5. Calculate the number of moles ofHCJ that would theoretically be needed to increase the moles l of hydronium you calculated in "2" by a factor of 10. ( 6. Using your results from the careful titrations (Part C) and the concentration for your standard HCl solution , calculate the moles of titrant (HCl) needed to change the pH by 1 .L., unit for each buffer. • Conclusions 1. Compare your experimental results (Question 4 and 6) with the theoretical calculation (Q 3, 5) Why are these numbers different? 2. Which buffer had a higher buffering capacity? Why? 3. Express your Buffer capacity in the following form: Buffer Capacity= (number of moles of base or acid) (pH change)(volume of buffer in L) 4. If you wanted to make a buffer with an even higher buffering capacity, what change(s) would you make to the recipe? 3
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