Experiment 2 Part 1 - Chemical Reactions

Most students today finished within 1.5hrs, and my last student left after 2.5 hrs. It is helpful to divide students into three groups and have each group start with a different part of the lab so that they aren't all waiting in line for the same chemicals. Also watch for students bringing chemical bottles back to their benches - they usually forget to put them back.

PRE-LAB - I first went over the grading for the lab reports from the past two weeks and discussed common mistakes - incorrect sig figs, missing units, missing observations, missing or illegible calculations and again what I expect to see in a good purpose, procedure and conclusion. There is plenty of time in lab today, so I wanted to make sure that my students understand my expectations - they pay more attention now than they did on check-in day since they already have experience with writing reports and have received grades back.

I gave examples of acid-base and precipitation reactions, including the molecular, complete ionic and net ionic equations for these types of reactions. They should have already covered this in class, but several still needed a review. We also discussed possible observations and what they mean (bubbles, color change, texture change, heat, turns cloudy). I also discussed the difference between 'clear' and 'colorless' since most students use these interchangably.

PART C - Almost every student thought that Na2CO3 should be a solid in the reaction and then wouldn't break up into ions. Some students thought this was a ppt rxn because they used too much Na2CO3 and assumed the solid in the bottom was a product (NaCl (s)) rather than leftover reactant. Make sure they stir/shake the reaction mixture.

Q4 - You can make up your own question, or omit - I had my students answer this question before doing Part C. I had them design an experiment to verify whether Na2CO3 is solid or aqueous. I expect them to be able to put a small amount of Na2CO3 into a test tube and add DI water to see whether it dissolves. They could verify the presence of ions using conductivity.

Waste - 2 beakers - the one with Ag waste goes in jug. Acid/base beaker gets neutralized and poured down the drain. Send them to look at the colors on the back of the universal indicator bottle to see the yellow/green a neutral solution should be. You might want to have them check with you when they get to this step - many add too much acid or base and then swing back and forth ending up with 500mL of waste at the end.

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This page contains a single entry by amaxwell published on February 7, 2011 4:19 PM.

Experiment 1 Part 3 - Titrations using Conductivity was the previous entry in this blog.

Experiment 3 Synthesis of Calcium Carbonate is the next entry in this blog.

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