Test-exam 2

0 1014 571 1010 5 k a 175 10 4 01 x x 10 x 571

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Unformatted text preview: 2 0.1 x 0.1 7. Suppose you are given a monoprotic weak acid solution, HA (pKa = 3.83), and its solid sodium salt, NaA (FW=98.00). What is the weight of the solid sodium salt that must be added to 400.00-mL of 1.00-M HA to produce a buffer solution with a pH of 4.00. Assuming that when the solid sodium salt is added to the acid, there is no change in volume; it maintains at 400.00-mL. a. 58.0-g* b. 58.0-mg c. 43.5-g d. 43.5-mg e. 0.285-g Ans. HA H A [ A ] pH pK a log [ HA] Let x be the number of grams of NaA that is needed, then x 98.00 4.00 3.83 log 0.400 1.00 8. When 194-mL 0.200-M HCl is added to 250.0-mL of 0.300-M sodium mandelate (C6H5CHOHCOONa), how much mandelic acid (C6H5CHOHCOOH) (Ka = 4.0 x 10-4) is produced? a. 75.0-mmol b. 38.8-mmol* c. 36.2-mmol d. 36.2-mol e. Can not be determined because the Ka value for mandelic acid is too small. Ans. Let A be C6H5CHOHCOO. NaA Na A soluble. HC H C strong acid. H A HA K 1 2.5 103 4 4.0 10 Therefore, before reaction mmolH 194 0.200 38.8 mmolHA 0 mmol A...
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