Activity Series of Metals and Ionic Nitrate Solutions (Wet Lab)

Background:

An activity series is a ranking of elements based on how reactive the elements are in order from most reactive to least reactive. For the sake of this lab, the elements to be ranked are metals and they shall be ranked according to their tendency to oxidize.

Oxidation is an atoms loss of electrons or increase in oxidation state as a result of a reaction, such as:

Li -> Li ⁺¹ + e^-1

In this example, lithium metal with an oxidation state of 0 loses one electron becoming a lithium ion with an oxidation of +1. An oxidation reaction alone is considered a half reaction. Another half reaction that often occurs with an oxidation reaction is a reduction reaction. Reduction is an atoms gain of electrons or reduction of oxidation state, such as:

 Ag ⁺¹ + e ^-1 -> Ag

In this example, a silver ion with an oxidation state of +1 gains one electron becoming silver metal with an oxidation state of 0. An oxidation reaction and reduction reaction together are called a redox reaction, such as:

Li + Ag ⁺¹ -> Li ⁺¹ + Ag

The electron lost in the lithium oxidation reaction is gained in the silver reduction reaction. This reaction impossible because lithium metal has a higher tendency to oxidize than silver,thus lithium would be placed higher than silver in the activity series.

The transfer of electrons in a redox reaction can be used in batteries to power engines. The oldest models of batteries were based off of this transfer. In a basic galvanic cell, there are two metals and two solutions made of the metals ions. When the reaction of a galvanic cell occurs, a full redox reaction takes place and the current of electrons is used to power electronics. An activity series can be used to determine which metals should be used in a galvanic cell; the farther apart they are in the activity series, the greater flow of electrons through the cell occurs.

Purpose:

The purpose of this lab is to observe how specific metals react with specific nitrate solutions. Then these metals (Cu, Zn, Mg, Pb) can be ranked into an activity series. This will be used to determine which metals will be oxidized in a basic galvanic cells with the highest voltage potential.

Materials:

• Metals 
• Copper (Cu) 
• Zinc (Zn) 
• Magnesium (Mg) 
• Lead (Pb) 
• Solutions 
• Silver nitrate solution, AgNO₃(aq) 
• Copper (II) nitrate solution, Cu(NO­₃)₂­­(aq) 
• Zinc nitrate solution, Zn(NO­₃)₂(aq) 
• Magnesium nitrate solution, Mg(NO₃)₂(aq) 
• Lead (II) nitrate solution, Pb(NO₃)₂(aq) 
• 5 Beral pipets (optional if solutions come with droppers) 
• Well-plate 
• Forceps 
• Steel Wool 

Methods:

After rubbing the pieces of metal with steel wool, in the well plate, place five pieces of copper metal in separate wells in the same row. Do this with the other three types of metals in separate rows. Place several drops of AgNO₃ in the four separate wells with different metals in the same column so that the metals are each covered in solution. Do this with the five other solutions in the separate columns already filled with metals. Let the well plate sit for five minutes. Record observations for each combination at the end of the five minutes. Discard of waste appropriately.

Magnesium metal (strips were used instead of balls)

Zinc metal

          

Magnesium metal stripes

Lead metal

Data/Observations:

Observations Table

	Cu2+(aq)	Mg2+ (aq)	Pb2+(aq)	Zn2+(aq)	Ag+(aq)
Cu(s)	No reaction	No reaction	No reaction	No reaction	* Green/brown Ppt
Mg(s)	* Light blue Ppt, green solution	No reaction	^ Black Ppt	Small grey Ppt	^ Black Ppt
Pb(s)	* Black and light blue Ppt	No reaction	No reaction	No reaction	* Black Ppt
Zn(s)	(small amt.) black Ppt	No reaction	^ Black Ppt	No reaction	^ Black Ppt

(* strong reaction, ^ notable reaction)

Results:

The observations make sense. A trend of metals not reacting with their ions makes sense because they have the same tendency to give off electrons. It is surprising that magnesium ions reacted with nothing, but this would suggest a small tendency to receive electrons and high tendency to give off electrons.

Discussion/Analysis:

From the observations, it can be seen that the activity series should be (from most likely to oxidize to least likely): magnesium (Mg), zinc (Zn), lead (Pb), copper (Cu), silver (Ag). Magnesium reacted by giving off its electrons with the most solutions--four solutions total. It didn't react with magnesium ions because magnesium metal and magnesium ions have the same tendency to receive and give off electrons. Zinc metal reacted with the second most solutions, 3 total solutions, which would indicate that it is the second most reactive/likely to oxidize. Lead reacted with two out of five solutions which would indicate that it is the third most reactive. Copper reacted only with the AgNO₃, which shows that it is the least reactive of the metals used. Silver was added to the end of the activity series because the silver ions reduced with all of the metals used. This would suggest that silver metal wouldn't oxidize with any of the metals used and should be placed lowest in the activity series. This is supported by the observations made. Magnesium ions reduced with none of the metals, zinc ions didn't reduce with any except magnesium metal, lead ions reduced with magnesium and zinc, and copper ions reduced with magnesium, zinc, and lead.

Possible sources of error include: "rusted" or impure metal and already used and contaminated well plates and forceps. If the metal was “rusted” enough, it wouldn't be able to react with the solutions. When a metal it rusted, it is a form of oxidation, so if the metal were rested already, it shows that the metal has already reacted with its environment and wouldn't be able to oxidize with the solution. If the metal were impure, it wouldn't have reacted as it pure metal would've because the foreign components in the metal would react differently. If a foreign component were present, it would react with the solutions differently than the metal would, and this would foreign reaction would be in the observations. The same thought goes for contaminated well plates and forceps. The contaminants would be part of the reaction and affect the end result accordingly. For example, if a reaction between magnesium metal and magnesium ions was contaminated with silver ions, it would make it appear that magnesium metal and magnesium ions would react, when they shouldn't.

To counteract the possibility of rusted metal, the use of steel wool is employed. The purpose of the steel wool is to scratch off the top layer of the metal and with it, the rust. It is possible, however, that a piece could have been used without steel wool being used first. The presence of some rust shouldn't have affected the data as long as some not oxidize metal was still exposed. The only way to counteract impurities in the metals used would be to buy more expensive, better quality metals. The metals used were intended for scientific purposes however, so if any impurities were present, they would've been minimal and affected the data minimal if at all. To counteract contaminated materials, it is suggested that the well plates and forceps be wash before and after labs. If the well plate and forceps were washed after their prior usage, then any contamination would've been avoided. If they were not but were washed prior to current usage, contamination would've been avoided in that case as well.

Conclusion:

The intent of this lab was to test and organize several metals into an accurate activity series according to tendency to oxidize. It was concluded that the activity series should be: Mg, Zn, Pb, Cu, Ag. From this and notes made in the data, it can be seen that a galvanic cell using a combination of magnesium metal and silver nitrate solution would be very effective. Unfortunately, that would inversely require magnesium nitrate solution and silver metal, which is hard to obtain. The other observations in the table will be used accordingly when deciding which metals and ions to use in a galvanic cell. A combination of magnesium and copper might also be appropriate. This lab achieved its intended purposes and was helpful in teaching what an activity series is.