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How can a metal reactivity series be constructed and justified with…
How can a metal reactivity series be constructed and justified with evidence? (Chan & Kate)
Displacement Reactions
Process: using spotting tiles to react each metal with every other metal solution and using a table to record whether a metal displacement reaction occurred. (e.g. if zinc displaced iron from iron sulphate, it can be concluded that zinc is more reactive than iron and thus, higher on the reactivity series).
Advantages: The exact position of the metal on the metal reactivity series can be determined once each metal has been reacted with every other metal.
Limitations: when using this technique on its own, it can be very time consuming and inefficient as each metal must be each other. It is also occasionally difficult confirm whether a displacement reaction occurred or not just from observing it.
Variables
Controlled: concentration of solutions, each metal must be fully submerged
Dependent: the type of solid metal and the type of solution being reacted with it
Independent: whether a displacement reaction occurs or not
Safety Hazards and Considerations
Glass: If broken, any glass equipment used in the experiment may potentially cut or scratch and cause injury. Therefore, any glass handled will need to be done so with caution not to drop or smash the glass to avoid potential injury. However, a teacher will be present to supervise the experiment and will be notified if glass does become broken.
Acids: If any acid solution were to be ingested or come into contact with the naked eye or exposed skin, it may cause potential injury. Caution must be taken in order to not ingest the acid, and personal protective equipment (gloves, safety glasses and lab coats) will be worn to limit any potential contact to bare skin.
Personal protective equipment must be worn (i.e. gloves, safety glasses, lab coats)
Metals: Students must avoid ingesting any metals involved with the experiment.
Galvanic Cell
Process: Two individual metal electrodes are placed in an ionic solution of themselves, and the galvanic cell completed with conducting wires and a salt bridge connecting the two 'half cells', accomodating the flow of ions between the two. By measuring the voltage produced by the galvanic cell, an estimate of how far apart the two metals are on the reactivity series can be made
Advantages: This is a relatively simple and safe process. The higher the voltage created by the metals in the galvanic cell directly indicates how far apart the two metals that make up the electrodes are on the reactivity table, which can give a rough indication of what the table will look like.
Limitations: Extremely time ineffective as it will take lengthy amounts of time to prepare galvanic cells for each individual metal to be tested against each other. Additionally, may be costly to create many galvanic cells, taking into account cost of the metals required and doesn't give specific information on where the metals are on the reactivity series or which one is higher than the other and should be used in conjunction with another technique.
Variables
Independent: voltage created by the galvanic cell
Dependent: metal element (electrode and ion solution)
Controlled: salt bridge, beaker size, size of metal electrode, volume of metal ion solution, voltmeter
Reaction with Acid
Process: the metal is placed in hydrochloric/sulphuric acid to see whether it will react or not. If the metal reacts with hydrochloric/sulphuric acid, it can be concluded that it is located on the higher portion of the reactivity series.
Advantages: By being able to make a rough estimate of where the metals are on the reactivity series, it allows for them to be split into two groups (higher and lower) which makes it easier and more efficient to perform other tests within each group to establish their exact positions
Limitations: This component alone gives a very rough estimate of how reactive the metal is and cannot be used to find the exact order of the metals
Variables
Controlled: each metal is completely submerged in acid, similar surface area, type of acid, acid concentration
Independent: whether or not the metal reacts with the acid
Dependent: type of metal being reacted with the acid
Materials needed for chosen experiment design
350mL acid solution (sulphuric or hydrochloric)
250mL glass beakers x6
Stopwatch
Salt bridge
Voltmeter
Electrode
Voltmeter wires
Metals
Magnesium
Tin
Lead
Iron
Zinc
Copper/copper sulphate
Aluminium/aluminium sulphate
Personal Protective Equipment
Lab Coats
Safety goggles
Gloves
Final Verdict: Reaction with Acid, Metal Displacement reactions and Galvanic Cells
Variables
Independent:
The metal being reacted with the acid
the metal/ionic solution combination
Dependent:
whether the metal reacts with acid
whether the metal and ionic solutions produce a metal displacement reaction
Controlled: Each metal is completely submerged during both the acid reaction and metal displacement reactions, similar surface area of each metal, type of acid used, acid and metal solution concentrations, time given for metal to react with acid/ionic solution
Final Decision
Reasoning: by combining these three components, the positions of the metals on the reactivity series can be determined. This is because the reaction with acid will split the metals into two broad groups (high reactivity and low reactivity) which makes the spotting tiles process a lot more efficient as the number of combinations of metals and solutions is roughly halved. After this, the galvanic cells can be used effectively to check the order of the reactivity series by using the most reactive metal for one electrode and the other metals for the other in order of least reactive to second most reactive. If the voltage gradually decreases, it can be confirmed that the reactivity series is accurate.
Limitations: It may still be difficult to determine at times whether a displacement reaction occurred during the spotting tile portion of the method. This may be fixed by using small beakers instead of spotting tiles to get more of the metal reacting with the solution to allow for a clearer view of the reaction. Furthermore, although the reaction with acid was included in order to increase the efficiency of metal displacement reactions, it may still be time consuming as each metal must be reacted with every other metal.