Spring 09 Recitation Quiz 4

Spring 09 Recitation Quiz 4 - CHEM 0120 Golde SPRING 2009...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
CHEM 0120 SPRING 2009 Monday 1:00 PM Golde QUIZ 4 WEEK 5 February 2, 2009 Name_______________________________ 1. Assign each of the following salts as acidic, basic or neutral (no acid-base properties). Give your reasoning in each case. Hint: focus on the active species . a) Ca(NO 2 ) 2 (calcium nitrite) b) SrBr 2 (strontium bromide) 2. An aqueous solution is initially 0.335 M NH 4 Cl, and then undergoes hydrolysis, i.e. Bronsted-Lowry reaction with water. Determine [H 3 O + ] and pH at equilibrium in this solution. Hint: work with the active ion , get rid of any spectator ions. Then get on your B-I- K-E. Remember that K b of NH 3 is 1.82 x 10 -5 and that K w = 1.00 x 10 -14 . ANSWERS 1. a) Basic. Ca 2+ is the conjugate of a strong base and has no acid-base properties. The nitrite ion is the active species: it is the conjugate of the weak nitrous acid, and thus has weak base properties. b) Neutral. Both ions are neutral as they are conjugates of, respectively, a strong base and a strong acid. 2. NH 4 + is the active ion; Cl - is a spectator. + 4 NH + H 2 O NH 3 + H 3 O + , K a = K w /K b = 5.49 x 10 -10 I 0.335 0 0 C –x +x +x E 0.335 - x x x x 0.335 x 2 - = 5.49 x 10 -10 As 0.335/5.49 x 10 -10 is large, apply the approximation 0.335 - x ~ 0.335 x 2 = 5.49 x 10 -10 x 0.335 = 1.84 x 10 -10 ; x = 1.36 x 10 -5 (Solver gives same x) [H 3 O + ] = 1.36 x 10 -5 M; pH = 4.87 CHEM 0120 SPRING 2009 Monday 6:00 PM Golde QUIZ 4 WEEK 5 February 2, 2009 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. a) Write Bronsted-Lowry equations for the ionization of HCO 2 H (formic acid) in water and for the hydrolysis (by water) of the HCO 2 - ion (the formate ion). b) If K a of HCO 2 H is 1.72 x 10 -4 , show that the value of K b of the formate ion is 5.81 x 10 -11 . K w = 1.00 x 10 -14 . 2. A buffer solution is 0.150 M in HCO 2 H and 0.450 M in HCO 2 - . These can be considered to be equilibrium values. Calculate [H 3 O + ] and the pH of this solution. Is the solution acidic or basic? Use relevant information from Question #1. ANSWERS 1a) HCHO 2 + H 2 O H 3 O + + CHO 2 - CHO 2 - + H 2 O OH - + HCHO 2 b) K b = -14 w -4 a K 1.00 x 10 K 1.72 x 10 = = 5.81 x 10 -11 2. A suitable equilibrium is HCO 2 H + H 2 O HCO 2 - + H 3 O + K a = - + 2 3 2 [HCO ][H O ] [HCO H] ; 1.72 x 10 -4 = + 3 0.450 [H O ] 0.150 [H 3 O + ] = 5.73 x 10 -5 M pH = -log(5.73 x 10 -5 ) = 4.24; acidic CHEM 0120 SPRING 2009 Tuesday 8:00 AM Golde QUIZ 4 WEEK 5 February 3, 2009 Name_______________________________ For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
Background image of page 2
1. For each of the following, is the statement True or False? Give your reasoning. a) The reaction for the hydrolysis
Background image of page 3

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

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/06/2009 for the course CHEM 0120 taught by Professor Golde during the Spring '07 term at Pittsburgh.

Page1 / 8

Spring 09 Recitation Quiz 4 - CHEM 0120 Golde SPRING 2009...

This preview shows document pages 1 - 4. Sign up to view the full document.

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