Chemistry 123 Lab 12 Abstract: The affect affect of buffers buffers and the factors factors that that influe influence nce their capaci capacity ty to regula regulate te pH was determined by three different tests. A phosphate buffer containing 1.0M NaOH and 0.5 M H 2PO4 was made to model the human blood buffer system. The phosphate buffer was titrated with appreciable amounts of hydrochloric acid, HCl, and sodium hydroxide, NaOH, to explain the response of the human blood buffer. A pH probe was used to monitor the pH of the solution. Introduction In order for life sustaining sustaining chemical chemical reactions reactions to occur, the human body must maintain maintain a pH of blood between 7.35- 7.45. Acidosis is the lowering of blood pH to lower than 7.35 and can have severe consequences. During strenuous exercise, glucose is known to convert to pyruvic acid, which will further convert to lactic acid due to the lack of oxygen. This process causes the blood pH to lower, as well as soreness in the skeletal muscle (Virk 1994). Eleven well-trained cyclists were chosen to complete a 70s all-out cycling effort. A control sample of blood was taken before the start of the exercise, and was compared with samples taken 0, 5 and 8 minutes after the exercise. At the end of the trial, acidosis was found where the pH of blood was 7.20 (Thomas et al. 2015). In this experiment, human blood buffer was modeled by a phosphate buffer. The experiment was conducted to examine the behaviour of the human blood buffer and its response to increased amounts of acid and base in the blood stream. The phosphate buffer was titrated with HCl and NaOH, and the pH was determined using a pH probe. Furthermore, a simulation of acidosis was done. The amount of ‘Restoration Solution required to restore a patient’s blood from a pH of 7.0 back to 7.45 was determined. Experimental Section Mixing 36.00 mL of 0.50M H2PO4 and 11.50mL of 1.0M NaOH created a phosphate buffer of pH 7.55. This solution was then transferred into a volumetric flask and filled with water. The initial pH titration curve was obtained through the titration of 25.00mL of phosphate buffer with 0.100M HCl until the pH dropped by 1unit. The second pH titration curve was obtained with a similar technique but with 0.100M NaOH added to 25.00mL of buffer solution until the pH increased by 1 unit. Lastly, a titration curve using “testing blood” was obtained upon the addition of restoration solution until a pH of ~7.45 was reached. This was then used to calculate the amount of restoration solution needed to “save the patient” and get a pH of 7.45 Results and Calculations (some calculations are attached ) (D1)
i) volume ume (mL (mL) of H2PO4- required to make phosphate buffer: −¿ =0.06477 mol / L ( 0.100 L )=0.006477 mol
mol H 2 PO 4
¿
2−¿ =0.1150 mol / L ( 0.100 L )= 0.01150 mol
mol mol HPO HPO4
¿
starting material material =0.006477 mol + 0.01150 mol =0.017977 mol ∴ most starting 0.017977 mol 0.5 M
=35.95 mL
(ii) Volume (mL) of NaOH required to make phosphate buffer:
2−¿ =
0.1150 mol
L ( 0.100 L )
= 0.01150 mol ¿
mol mol HPO HPO 4
0.01150 mol 1.0 M
(D2) (D2)
=11.50 mL
Aci Acid buf buffe ferr cap capac acit ity: y: [(0.0224LHCl)*(0.10MHCl)]/0.025L = 0.0896M
(D3) (D3)
Base Base buff buffeer cap capac acit ity: y: [(0.00750L NaOH)*(0.10M NaOH)]/0.025L = 0.0300M
D5)
Amount Amount of Rest Restora oratio tion n Solutio Solution n require required d to resto restore re pH from from 7.00 7.00 to 7.45 7.45 (25.00 (25.00 mL sampl sample): e): 971 drops restoration solution x 0.036489 mL/drop = 35.43mL
(D7)
Amount of Restorat Restoration ion Soluti Solution on required required to restore restore pH from from 7.00 7.00 to 7.45 (7.0 (7.0 L of patient patient blood): 7 L÷ L ÷ 0.0250 L=280, so 280 × 0.03543 L=9.920 L of Restoration Solution
(D8)
Table 1. Volumes Volumes (mL) (mL) of Restoratio Restoration n Solution Solution required required for patients patients with acute acute acidosis. acidosis.
pH
Volumes (mL) of Restoration Solution
7.40
1080
1188
1296
1404
1512
1620
1728
7.30
3080
3388
3696
4004
4312
4620
4928
7.20
4760
5236
5712
6188
6664
7140
7616
7.10
5880
6468
7056
7644
8232
8820
9408
7.00
7080
7788
8496
9204
9912
10620
11328
Weight
50 kg
55 kg
60 kg
65 kg
70 kg
75 kg
80 kg
Discussion
36.00mL of
−2
H 2 P O4
and
11.50 mL NaOH NaOH
was used to create the phosphate buffer
(D1). The acid buffer capacity was 0.0896M (D2), while the base buffer capacity was 0.0300M (D3). The acid buffer capacity is reater than the base buffer capacity. This can be accounted for because metabolic processes usually result in lowerin blood p! thus, blood must ha"e a hiher acid buffer D4). 35.43mL of #estoration $olution was capacity to be able to compensate for the low p!s ( D4). re%uired to brin the p! of the patient bac& to '.)* (D5). $ince the initial p! of the blood was .00, the con+u con+uat atee base, base, −2
HP O 4
−2
HP O 4
, must be added to raise the p! to '.)*. This is because as
increases, it reacts with
+¿
H 3 O
¿
, lowerin the acidic content of the solution. (D6). f
0.0-*L of blood re%uired 35.43mL of restoration solution, then increasin the "olume by -80 times will also increase the amount of restoration solution needed by -80 times, therefore 9.9-0L of restoration solution is needed (D7). The addition of !l to the buffer was done in efforts to simulate acidosis. /ssentially since the p! rane is no loner within the rane of .3*.)*, an estimation of "olumes of restoration solution is needed for the acidosis patients to obtain a p! bac& in the normal rane. n the case where the p! is dropped to a danerous le"el, restoration solution 1treated the patient2 because it contained
a wea& base solution. The restoration fluid raises the p! since it contains the con+uate base, 4 )-, thus reducin the concentration of hydroen ions, resultin in a p! within the normal rane.
Bibliography Thomas, C.; Delfour-Peyrethon, R.; Bishop, D. J.; Perrey, S.; Leprêtre, P.-M.; Dorel, S.; Hanon, C. Effects Of Pre-Exercise Alkalosis on the Decrease in VO2 at the End of All-out Exercise. Eur. J. Appl. Physiol. 2015, 2015, 116 , 85–95. Virk, R.S. The Effect of Vitamin B-6 Supplementation on Fuel Utilization and Plasma Amino Acids During Exhaustive Endurance Exercise in Men. Physiol. 1994