#4 Lab report metal ion reactions PDF

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Metal Ion Reactions Practical lab report...

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#4 Metal Ion Reactions Objectives:     

To reduce Cu^2+, Mg^2+ and Fe^2+ ions to their metals. To investigate the oxidation behaviour of transition metal cations. To explore the reactivity of the metals Sodium and Magnesium. To observe the various colours associated with transition metal ions. To study oxidation-reduction reactions.

Theory: A more reactive metal will displace a less reactive metal from a solution of one of its salts. The oxidising species (agents) remove electrons from other species and can force them to become reducing agents, thereby releasing electrons. Metals always react by losing electrons, oxidation. Metals are the reducing agents. However, if a metal is in competition with metal ions the more reactive metal can obligate the less reactive metal (in the form of ions) to accept electrons. This is called a displacement reaction. If it is observed that there is a reaction between a metal and another metal ion in solution, it can be deduced that the Solid metal is more reactive than the metal of the dissolved metal ions. In part one of this Experiment Cu^2+, Mg^2+ and Fe^2+ ions are reduced to their metals by their reaction with magnesium and iron. The Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. The more positive the reduction potential, the more likely the ion is to be reduced. Reduction potential is measured in volts (V) or millivolts (mV). Each species has its own specific value for reduction potential. Part two of this experiment explored the oxidation of transition metal ions. Most transition metals differ from those metals in groups one, two and thirteen in that they are capable of forming more than one cation with different ionic charges. Ionic formation for transition metals is complicated by the fact that these elements have unfilled inner d shells. Although the next higher S electrons are the ones that are removed during ionisation. The ionisation energy is the energy required to remove one mole of the most loosely held electrons from one mole of gaseous atoms to produce one mole of gaseous ions with charge 1+. Theoretically, 2+ ions from elements on the left are easier to oxidise, because as you go left to right in the periodic table it becomes more difficult to lose electrons due to the fact that there is a greater number of protons. The additional protons are holding the electrons more tightly and hence increasing the ionisation energy. Molecular Oxygen, Hydrogen Peroxide and Sodium bismuthate were used as the oxidising agents in this experiment. It is expected that Sodium bismuthate will be the best oxidising agent, followed by hydrogen peroxide. Part three of this experiment explored the reactivity of the metals Sodium and Magnesium. A metal and an alcohol react to produce an alkoxide. Alkoxides can be produced by several methods starting from an alcohol. Highly reducing metals react directly with alcohols to give the corresponding metal alkoxide. The Alcohol serves as an acid, hydrogen is produced as a by-product. In the case of Sodium and ethanol the equation for the reaction is as follows;

Metals react with oxygen within the air to produce metal oxides. When Magnesium reacts with oxygen found within the air it reacts to produce Magnesium oxide. Magnesium gives up two electrons to oxygen to form this powdery product. This reaction is an exothermic

reaction, a reaction in which there is a net release of energy. The equation of this reaction is as follows; 2Mg (s) + O2 (g)→2MgO (s) + energy. And upon addition of water; Mg (s) + 2H2O→Mg (OH)2 (s) + H2 (g).

Experimental Procedure: Part 1- Six test-tubes were placed in a test-tube rack, some Mg, Fe, and Cu metals were added each to a separate test-tube. Hence, this step was repeated so that there was two test-tubes with each of the metal ions. Fe^2+ (2cm^3) was added to the Cu and the Mg metals, Mg^2+ (2cm^3) to the Cu and Fe metals and finally Cu^2+ (2cm^3) was added to the Mg and Fe metals. Observations and results were recorded. Part 2- Twelve test-tubes were placed in a test-tube rack. Cr^2+, Mn^2+, Fe^2+ and Co^2+ (2cm^3) were each added to a separate test-tube, this step was repeated so there was three test-tubes with each of the metal ions. Hence, each of the ions were exposed to the three different oxidising agents (O2, H2O2 and NaBiO3). Observations and results were recorded. Part 3- (i) A few cm^3 of Ethanol was added to a clock glass and a small piece of sodium was also added. The white deposit (NaOC2H5) was then dissolved in water and a few drops of universal indicator was added. Observations and results were recorded. (ii) Using thongs, a piece of Mg ribbon was ignited at one end in a Bunsen flame. The metal was removed from the flame and placed in a porcelain dish. The residue was transferred to a test-tube, Deionised water (2cm^3) was added alongside a few drops of universal indicator. The test-tube was placed into a beaker of water on a hot plate and heated until it boiled. The results were recorded and interpreted. Results: Part 1- Reduction of metal ions Test Cu + Fe^2+ Cu + Mg^2+ Fe + Mg^2+ Mg + Cu^2+ Mg + Fe^2+

Fe + Cu^2+

Observation Copper clumped together Copper clumped together Nothing happened Magnesium was dissolved a gas was visible Colour of solution changed from clear to dark blue solids were moving Iron was being oxidised, as it turned red in colour

Part 2- Oxidation of transition metal ions

Conclusion No reaction No reaction No reaction Reaction occurred Reaction occurred

Reaction occurred

Metal ions Cr^2+ Mn^2+ Fe^2+ Co^2+

Oxidising agents O2 Oxidation No oxidation No oxidation No oxidation..

H2O2 Oxidation No oxidation Oxidation No oxidation

NaBiO3 Oxidation Oxidation No Oxidation Oxidation

Part 3- Reactivity of metals Reaction

Observation Conclusion

Na + ethanol

Na dissolves

Mg combustion

Luminous white flame

NaOC2H5 has formed Mg is oxidised in the flame

Addition of water and Universal Indicator

Observation Conclusion

Goes from red to black Goes from red to green with purple

Sodium was oxidised The solution is basic

Upon the boiling of the Mg solution the Green solution with a hint of Purple turned to a much darker green colour. Discussion: In part one of the experiment it was found that there was no reaction for the first three tests (the metal ions were not reduced) and this was due to the fact that Copper is not a more reactive metal than Fe^2+ and Mg^2+ salts. In addition, iron is not more reactive than Mg^2+ either. The last three tests were successful in producing reactions and each of the metal ions were reduced, as magnesium is a more reactive metal than Cu^2+ and Fe^2+ and also Iron was more reactive than Cu^2+. In the case of the magnesium and copper ions the magnesium was dissolved as bubbles. When magnesium was added to iron ions the colour, in solution, the original clear solution changed to dark blue. Upon the addition of Iron to the solution of copper ions the solution transformed to a Red colour, exhibiting how the iron was being oxidised and therefore the copper ions were being reduced to form its metal atom. Likewise in the other two reactions the metal was forcing the metal ions to accept electrons and become metal atoms. It can be seen how in the first three reactions the less reactive metal is coating the surface of the more reactive metal, whereas in the last three tests the more reactive metal is gradually disappearing and reacting, as it was forming a solution. The order of ease of reduction of each ion to metal was found to be Cu^2+>>Fe^2+>>Mg^2+. This was deduced based on the reduction potentials of each of the metal ions. The ease of reduction of ion to metal compares alongside the order of their reduction potentials, as reduction potentials reveal which ion is the most easily reduced. The more positive the reduction potential the more likely the ion is to be reduced. Part two of the experiment showed how Cr^2+ was oxidised by all of the oxidising agents, meaning it lost electrons upon its reaction with each of the agents. Mn^2+ was only oxidised by the sodium bismuthate and this was because it is a very powerful oxidising agent. Fe^2+ was only oxidised by hydrogen peroxide and Co^2+ was only oxidised by sodium bismuthate, which helped to finally confirm that within the case

of this experiment Sodium bismuthate was the best oxidising agent, followed by Hydrogen peroxide which was expected in theory. It was evident in theory and hence experimentally confirmed that 2+ ions from elements on the left are much easier to oxidise, because as you move from left to right in the periodic table it becomes much more difficult to lose electrons, due to the greater number of protons. The additional protons are holding the electrons more tightly and the ionisation energy is thereby increased. Part three of the experiment was successful in displaying the reactivity of the metals. When sodium was added to ethanol it was observed that the sodium dissolved and hence that sodium ethoxide was formed. Upon the addition of water and indicator the solution went from red to black concluding how the sodium was being oxidised. Also suggesting Sodium ethoxide is a strong base, as it will completely ionise into metal and hydroxide ions when in solution. When magnesium combusted a luminous white flame was observed, which led to the conclusion that magnesium is oxidised in the flame of the Bunsen burner. Upon the addition of water and indicator the solution of deionised water and the residue of the magnesium ribbon went from red to purple, which led to the conclusion that the solution is a weak base ( Magnesium hydroxide), as it has limited solubility. The solution was hence boiled to dissolve it and the solution changed from purple to dark green, as it is being oxidised even further. Conclusion:          

A transition metal exhibits many different colours in its reactions. Cu^2+ is reduced to its metal atom by magnesium. Fe^2+ is reduced to its metal atom by magnesium. Cu^2+ is reduced to its metal atom also by iron. 2+ ions from elements on the left of The Periodic table are easier to oxidise. An alcohol and a metal react to produce an alkoxide. A more reactive metal will displace a less reactive metal from a solution of its salts. Sodium and Magnesium are relatively reactive metals. Oxidation is the removal of electrons. Reduction is the addition of electrons....