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Unformatted text preview: C O H O Lewis Acids accept a pair of electrons. Bases donate a pair of electron (Lewis definition). Brnsted Acids donate H + Bases accept H + (Brnsted-Lowry definition) ALL Brnsted acids are Lewis acids too, but not all Lewis acids are Brnsted acids Page 1 of 5 WHEN IN DOUBT CONVERT TO MOLES Version 2002 ANALYSIS OF ASPIRIN BY TITRATION WITH STANDARDIZED NaOH Now that you have a solution of 0.1 M NaOH for wich you know the concentration to 3 significant figures, you can use it to assess the purity of the aspirin you made last week. Aspirin is an acid, and reacts with sodium hydroxide: H C H C C H C H C C O A s p i r i n , C 8 H 7 O 2 C O O H + N a + M W = 1 8 0 . 1 5 g / m o l H P- + O H- P = + H 2 O F I G U R E 1 C O O C O C H 3 H T h e a c i d p a r t o f a s p i r i n H C H C C H C H C C O C O O- C O C H 3 N a + S o d i u m a c e t y l s a l i c y l a t e + O H- T h e b a s e p a r t o f s o d i u m h y d r o x i d e H O H + 1 mole of aspirin will react with 1 mole of sodium hydroxide. Like the reaction of KHP with NaOH, this is an ACID- BASE reaction. Aspirin (like KHP) is an acid this piece of aspirin donates an H + to the - OH ion, which is a base (the Br nsted-Lowry definition) . Also H + from aspirin accepts a pair of electrons from the - :OH ion (Lewis definition). FIRST Calculate how much of your aspirin you need: a. BEFORE YOU COME TO LAB, calculate how many moles of NaOH there are in 25.0 mL of 0.10 M NaOH ( a convenient volume to use in a buret) b. BEFORE YOU COME TO LAB Calculate how many moles of aspirin you will need to react with the moles of NaOH you calculated in part a above. c. BEFORE YOU COME TO LAB Calculate how many GRAMS of aspirin corresponds to the number of moles of aspirin you calculated in b above. Titrate your aspirin at LEAST 3 times. 4 times is recommended. You will be scored on your precision , so the more times you repeat this, the better for you. Submit MW of aspirin from each trial, the average and the standard deviation, the % error and the % absolute error. WHEN IN DOUBT CONVERT TO MOLES Page 2 of 5 WHEN IN DOUBT CONVERT TO MOLES Version 2002 PROTOCOL NaOH is Caustic! Keep it off your skin and out of your eyes! If you standardized your NaOH today, life is good. You can omit steps 1-3! 1. Retrieve and shake up your 0.1 M NaOH solution which you standardized. If the NaOH solution is not well mixed, your experiment WONT WORK. Make sure the cap is on tightly and invert the bottle of solution at least 30 times....
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This note was uploaded on 10/01/2011 for the course CHEM 3332 taught by Professor Thummel during the Spring '08 term at University of Houston.
- Spring '08