This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: ssh525 hw07 McCord (53580) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Which of the following indicators would be most suitable for the titration of 0.10 M lactic acid with 0.10 M KOH(aq)? For lactic acid, p K a = 3.08. 1. alizarin yellow (p K In = 11.2) 2. methyl orange (p K In = 3.4) 3. phenol red (p K In = 7.9) correct 4. thymol blue (p K In = 1.7) 5. bromophenol blue (p K In = 3.9) Explanation: 002 10.0 points The acid form of an indicator is yellow and its anion is blue. The K a of this indicator is 1 10- 5 . What will be the approximate pH range over which this indicator changes color? 1. 5 &lt; pH &lt; 7 2. 9 &lt; pH &lt; 11 3. 4 &lt; pH &lt; 6 correct 4. 8 &lt; pH &lt; 10 5. 3 &lt; pH &lt; 5 Explanation: The p K a of this indicator is 5, so the indi- cator will change colors around pH 5. Thus you would expect a color change between pH 4 and pH 6. 003 10.0 points The un-ionized form of an acid indicator is yellow and its anion is blue. The K a of this indicator is 10- 5 . What will be the color of the indicator in a solution of pH 3? 1. red 2. orange 3. yellow correct 4. blue 5. green Explanation: K a = 10- 5 pH = 3 HIn yellow +H 2 O H 3 O + + In- blue K a = 10- 5 p K a = log ( 10- 5 ) = 5 The color change range is pH = p K a 1. At pH values above 6 the indicator will be ionized and at pH values below 4 the indicator will be un-ionized. 004 10.0 points Methyl orange is an indicator with a K a of 1 . 8 10- 4 . Its unionized form is red, while its ionized form is yellow. At pH 3.15, this indicators color would best be discribed as which color? 1. for some reason, purple! 2. a yellowish orange 3. completely yellow 4. a perfect orange 5. completely red 6. a reddish orange correct Explanation: The p K a is 3.74 so that is where a perfect orange would be. You would see all red for pH 2.74 and lower, and all yellow for 4.74 and above. The pH 3.1 given is on the acidic side of the middle so it would have a reddish orange color. 005 10.0 points ssh525 hw07 McCord (53580) 2 The equivalence point for the neutralization of 10- 3 M NH 3 by HCl occurs at pH = 6.1....
View Full Document
This note was uploaded on 04/10/2008 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.
- Spring '07