activity

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The activity series is a ranking of metals based on the ease with which they are oxidized. Oxidation involves the loss of one or more electrons, while reduction is the gain of one or more electrons. Metals which are high on the activity series are easily oxidized. Metals which are low on the activity series are not easily oxidized. The activity series can be used to predict whether or not a redox reaction will take place. As an example, consider the following possible reaction: Zn (s) + Cu+2 (aq) ——> Zn+2 (aq) + Cu (s) Does this reaction take place? In other words, if zinc metal is placed in contact with aqueous copper ion, will zinc displace copper ions from solution? Another way to phrase this is, “Will Zn reduce Cu+2?” (or, equivalently, “Will Cu+2 oxidize Zn?”) As a general rule, an element will be displaced from solution or its compounds by another element higher on the activity series. An abbreviated version of the activity series is given below, where the top of the series is to the left, and the bottom to the right. Most Active ——> Least Active (Easily oxidized) ——> (Not easily oxidized) We see that zinc is above (to the left in this list) copper. Thus, zinc metal will displace copper ions from solution since Zn is more easily oxidized than Cu. The activity of a metal can be correlated to its electron configuration. Some elements lose electrons (//i.e.,//are oxidized) readily. Why? What is it about the electron configuration of these elements that make them so active? Are there any trends or regular patterns in the activity of the metals, and if so, how do the trends relate to the elements’ position on the periodic chart? How can these trends be explained?
 * Lab on Activity Series**
 * Na — Mg — Zn — H2 — Cu — Ag**

Lab Procedure: 1) Receive instructions from teacher about which reactions to do. 2) For each reaction, put 10 mL of the solution in a test tube. 3) Place metal into the tube. 4) Wait for two minutes and observe and record results ( you may have to let reactions with iron to sit for longer). State whether a reaction occurred. 5) Record the results on the chart. 6) Clean Up test tubes.

Given the metals and metal nitrates that will be used, student's must come up with their own "activity series", or, list of metals from most reactive to least reactive. To make sure that student's don't just randomly guess, they must be able to defend their choices, or at least give a reasonable basis as to their order. Having been introduce to most of the trends in the periodic table, they should be able to base their choices on at least one of these. This list should be handed in at the beginning of the lab, to ensure that changes do not take place during the lab. Also, students could be asked to come up with as many controlled variables as possible for the entire lab. These include: temperature, concentration of solutions, time the metal is left in the solution, the type of compounds (we suggest all nitrates), amount of solution used. Then, the students could be directed to what exactly we are looking for. This would force the students to read the lab before hand and (hopefully) understand what they will be doing! Another question could be ... "Why do we have to sand the metals before using them?" and "Is this important?" A good thing to emphasize with the students, is, "What are we looking for that will give us a proof that a reaction has taken place?" Perhaps even doing one with the students (like zinc metal in copper nitrate), will show them what to expect. Also, point out that a wet metal also changes colour slightly.

Post-lab Activities: Since we suggest coming up with the final Activity Series as a class, this would not constitute part of the lab write-up. However, a reasonably logical reason as to why the activity series ended up as it did should be submitted. Another good idea to see if students got the hang of it, is to give them a couple metals that were not used in the lab, and ask them to place them, to the best of their ability, with justification, in the appropriate spot in the activity series. A good discussion question to ask could be related to mining and mineral extraction from ores. "If a mine had a rich copper ore, in which the copper was mostly found as a sulfate, what other, less expensive metal could be used to precipitate the copper out of solution?" If zinc was running $4.00/kg and iron was $2.10/kg, which do you think would be the best choice to use? Why? This is a "beyond the turf" type question. They really do not have enough knowledge to answer it. However, it makes them think. If zinc is very reactive, it should precipitate more copper than the iron would. (It does). The students could make an executive decision as to what they think is more efficient based on reactivity and cost.

__Justification for Changes :__ We added a more detailed pre-lab that included a demonstration of what a reaction would look like so that students would be able to distinguish between a reaction occurring and the metal just being wet. We also added pre-lab questions about variables that might affect the experiment to get students thinking about what was occurring during the lab. This would help the students do the lab more smoothly and understand it better. In the debugged lab we decided to make students hand in part of the conclusions and some relevant questions to ensure they understood the class discussion when the activity series was composed. We also added suggestions for questions to be used during the class discussion to give teachers ideas for applications of the activity series and beyond the turf material.