# 302 ho 9 - dar566 hw05 McCord (53580) This print-out should...

This preview shows pages 1–2. Sign up to view the full content.

1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points The term “ K a For the ammonium ion” de- scribes the equilibrium constant For which oF the Following reactions? 1. NH 4 Cl(solid) + H 2 O NH + 4 + Cl 2. NH 3 + H 2 O NH 4 + + OH 3. NH 3 + H 3 O + NH + 4 + H 2 O 4. NH + 4 + H 2 O NH 3 + H 3 O + correct 5. NH + 4 + OH NH 3 + H 2 O 6. The term is misleading, because the am- monium ion is not an acid. Explanation: 002 10.0 points Hydroxylamine is a weak molecular base with K b = 6 . 6 × 10 9 . What is the pH oF a 0.0500 M solution oF hydroxylamine? 1. pH = 8.93 2. pH = 9.48 3. pH = 7.12 4. pH = 10.37 5. pH = 4.74 6. pH = 9.26 correct 7. pH = 3.63 Explanation: Hydroxylamine is a weak base, so use the equation to calculate weak base [OH ] con- centration (note that this is the approximate equation. Why? Because K b is very small and the concentration is reasonable) : [OH ] = r K b C b = R (6 . 6 × 10 9 )(0 . 0500) = 1 . 82 × 10 5 AFter fnding [OH ], you can fnd pH using either method below: A) pOH = log ( 1 . 82 × 10 5 ) = 4 . 74 pH = 14 4 . 74 = 9 . 26 or B) [H + ] = K w [OH ] = 1 . 0 × 10 14 1 . 82 × 10 5 = 5 . 52 × 10 10 pH = log ( 5 . 52 × 10 10 ) = 9 . 26 003 (part 1 oF 2) 10.0 points Calculate the pH oF the solute in an aque- ous solution oF 0 . 09 M C 5 H 5 N(aq) (pyridine) iF the K b is 1 . 8 × 10 09 . Correct answer: 9 . 10476. Explanation: C pyridine = 0 . 09 M K b = 1 . 8 × 10 09 C 5 H 5 N + H 2 O C 6 H 5 NH + + OH 0 . 09 0 0 x + x + x 0 . 09 x x x K b = [C 6 H 5 NH + ][OH ] [C 5 H 5 N] 1 . 8 × 10 09 = x 2 0 . 09 x x 2 0 . 09 x = [OH ] = R 0 . 09(1 . 8 × 10 09 ) = 1 . 27279 × 10 05 mol / L . The pOH is

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 11/07/2009 for the course CH GenChem taught by Professor Mccord during the Spring '09 term at University of Texas at Austin.

### Page1 / 5

302 ho 9 - dar566 hw05 McCord (53580) This print-out should...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online