Question

An iron nail was attached to a zinc metal strip and wrapped with a paper napkin that had been soaked in dilute solution of sodium nitrate.Explain how the rate of iron would be affected.
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Answer 1

Answer:

decrease

Explanation:

the reaction rate of iron is decrease d in the presence of zinc

Answer 2

2() + 2₂() + ₂() → 2²⁺ () + 4⁻()

Explanation:

The rusting of iron is the result of a redox reaction that takes place  between iron, oxygen, and water, in a process called galvanic corrosion.  The iron is oxidized and the oxygen is reduced, to produce ferrous ions  and hydroxide as follows:

() → ²⁺ () + 2⁻

2₂() + ₂() + 4− → 4− ()

To produce an overall reaction:

2() + 2₂() + ₂() → 2²⁺ () + 4⁻()

The iron ions and the hydroxide ions, react to produce Fe(OH) ₂ which,  alongside other similar compounds, such as iron oxide (Fe₂O₃), is the  ‘rust’ that is observed.

In this redox reaction, the  anode and cathode can be identified using the two indicators:  phenolphthalein and potassium ferricyanide.

Phenolphthalein, typically clear, turns a bright pink colour in the presence  of OH− ions in solution. Thus pink appears where the reduction reaction  occurs (the cathode). Similarly, potassium ferricyanide turns Prussian blue when it reacts with Fe²⁺ in the solution to produce iron (II) hexacyanoferrate (III).

²⁺() + ₃()₆() → ²⁺() + [()₆]₂()

• As a result, sites that turn blue indicate where the iron is being oxidised,  and thus identify the anode.
• The anode is usually found at each end of the  object, or at any position at which the oxidation reaction can readily take  place and is indicated by blue spots.
• The remaining length of the nail is  surrounded by pink, indicating the reduction reaction that takes place in  the water surrounding the nail.

• This corrosion process can be prevented through the use of a sacrificial  anode. In this case, a more reactive metal (i.e. a metal that is more readily  oxidised) is wrapped around the iron.
• This metal is then oxidised rather  then the iron and rusting is prevented. Zinc coating is often  used to protect iron in a process known as galvanisation, as it acts as a  sacrificial anode in the place of iron and thus protects it from corrosion.
• In  these instances, the blue indicator will not be activated, as the iron has  not been ionised into Fe²⁺; however, the solution will still turn pink, as the  OH⁻ has been produced through the reaction with the sacrificial anode  and the surrounding environment.

• The common ion effect refers to the lowering of the solubility of a

substance due to the presence of a common ion in the solution.  

• This is because there is a point of saturation at which a  solution can absorb no more of a given solute.

• When an ion is already  present in the solution, the amount of this ion that can be added by  dissolving is limited.

For example, the solubility of sodium chloride in  sodium nitrate solution is limited, due to the common ion, sodium (Na⁺).

• In order for corrosion to occur, the ion of the metal being oxidised must  dissolve. Thus, by increasing the concentration of this ion in the solution, the degree to which the metal corrodes is expected to be lowered.

• This  will be tested for sacrificial anodes identified in this experiment.