N (4) A laboratory technician needs to make at least 1 L of 0.10 M histidine buffer WH at pH 7.54. Recall that histidine

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N 4 A Laboratory Technician Needs To Make At Least 1 L Of 0 10 M Histidine Buffer Wh At Ph 7 54 Recall That Histidine 1 (61.12 KiB) Viewed 57 times

N (4) A laboratory technician needs to make at least 1 L of 0.10 M histidine buffer WH at pH 7.54. Recall that histidine (structure shown at left) has three ionizable groups": a carboxylate with H2N pKa of 1.80, an amino group with pka OH of 9.33 and an imidazole group with pKa of 6.54. I.e. histidine monohydrochloride (His*HCI) has a pKa of 6.54. Which of the following statements related to making this buffer or its properties are correct? (indicate all that are correct, 1 pt each correct) (i) To obtain the desired buffer, the laboratory technician can mix 1.0 L of 0.10 M His*HCI with 0.1 L of 0.10 M of histidine (ii) To obtain the desired buffer, the laboratory technician can mix 0.1 L of 0.10 M His*HCI with 1.0 L of 0.10 M of histidine (iii) To obtain the desired buffer, the laboratory technician can mix 1.91 g (0.01 moles) His*HCI with 15.5 g (0.10 moles) histidine with sufficient water to make a 1.1 L solution (iv) Since the average net charge of histidine is +0.5 at pH 6.54 and -0.5 at pH 9.33, the pl of histidine is (6.54+9.33)/2 = 7.94 (v) The pl of histidine is (9.33 + 1.80)/2=5.57 (vi) The pl of histidine is equal to the sidechain pKa, i.e. it is 6.54 (vii) The pl of aspartate is (1.80 +6.54 +9.33)/3 = 5.89