s11Q4W5 - CHEM 0120 Golde SPRING 2011 QUIZ 4 WEEK 5 b...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
CHEM 0120 SPRING 2011 Monday 1:00 PM Golde QUIZ 4 WEEK 5 January 31, 2011 Name_______________________________ For ax 2 + bx + c = 0, x = - ± - b b ac a 2 4 2 ; K w = 1.00 x 10 -14 1. Assign each of the following as a strong acid, a weak acid, a weak base or a strong base: HNO 3 ; NH 3 2. Assign each of the following salts as acidic, basic or neutral. Give your reasoning. Hints: identify any active and any spectator ions; also see Question #1! a) CaBr 2 b) NH 4 NO 3 3. The weak acid, formic acid HCHO 2 , ionizes as follows: HCHO 2 (aq) + H 2 O(l) H 3 O + (aq) + CHO 2 - (aq), K a = 1.70 x 10 -4 A solution is prepared, which initially contains 0.085M HCHO 2 and no H 3 O + ions. Determine [H 3 O + ] and the pH in the solution, when the reaction comes to equilibrium . ANSWERS 1. HNO 3 : strong acid; NH 3 : weak base 2. a) CaBr 2 splits into Ca 2+ and Br - . Ca 2+ is the conjugate of Ca(OH) 2 , a strong base, and thus has no acid-base properties. Similarly, Br - is the conjugate of HBr, a strong acid, and has no acid-base properties. Thus CaBr 2 gives a neutral solution. b) NH 4 NO 3 splits into NH 4 + and NO 3 - ions. NO 3 - is the conjugate of HNO 3 , a strong acid, and thus has no acid-base properties. NH 4 + is the conjugate of NH 3 , a weak base, and thus acts as a weak acid. Thus NH 4 NO 3 is weakly acidic in solution. 3. HCHO 2 + H 2 O CHO 2 - + H 3 O + I 0.085 0 0 C –x +x +x E 0.085 - x x x x 085 . 0 x 2 - = 1.70 x 10 -4 . Apply the approximation 0.085 - x = 0.085 x 2 = 1.70 x 10 -4 x 0.085 = 1.44 x 10 -5 x = 3.80 x 10 -3 (exact method, e.g. using SOLVER, yields x = 3.72 x 10 -3 ) [H 3 O + ] = 3.80 x 10 -3 M; pH = 2.42 CHEM 0120 SPRING 2011 Monday 6:00 PM Golde QUIZ 4 WEEK 5 January 31, 2011 For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
Background image of page 1

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

View Full DocumentRight Arrow Icon
Name_______________________________ 1. H 3 PO 4 is a triprotic acid, with acid ionization constants as follows: K a1 = 6.9 x 10 -3 ; K a2 = 6.2 x 10 -8 ; K a3 = 4.8 x 10 -13 . Also K w = 1.0 x 10 -14 as usual Using this information, determine a) K a of H 2 PO 4 - ; b) K b of H 2 PO 4 - Show your work or give your reasoning! 2. A certain weak base, B, ionizes in water as follows: B(aq) + H 2 O(l) BH + (aq) + OH - (aq) A sample of B was dissolved in water to make a 0.175M solution of B (initial value). The pH of the solution was measured to be 9.432 (equilibrium value). a) Determine [H 3 O + ] and [OH - ] for this solution b) By creating an I-C-E table or otherwise, determine the equilibrium concentrations of BH + and of B. c) Hence, determine the base ionization constant, K b , of B. ANSWERS 1. a) K a of H 2 PO 4 - is just K a2 , i.e. 6.2 x 10 -8 b) H 2 PO 4 - is the conjugate base of H 3 PO 4 . Thus K b = K w /K a1 K b = 1.0 x 10 -14 /6.9 x 10 -3 = 1.4 x 10 -12 2. a) [H 3 O + ] = inv log(-9.432) = 3.70 x 10 -10 M [OH - ] = 1.00 x 10 -14 /3.70 x 10 -10 M = 2.70 x 10 -5 M b) [BH + ] = [OH - ] = 2.70 x 10 -5 M [B] = 0.175 – 2.70 x 10 -5 = 0.175M c) K b = -5 2 (2.70 x 10 ) 0.175 = 4.18 x 10 -9 CHEM 0120
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/20/2011 for the course CHEM 110 taught by Professor Dr.huston during the Spring '06 term at Pittsburgh.

Page1 / 9

s11Q4W5 - CHEM 0120 Golde SPRING 2011 QUIZ 4 WEEK 5 b...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online