The Properties of Nitric Acid

... 3+(aq) produces as brown ppt of Fe(OH)3(s) when the mixture is reacted with NaOH(aq)

Probable brown fumes of NO oxidation.

Brown fumes

Clear solution +HNO2

(darkgreen ppt)

+ NaOH(brown ppt)

Sulphur dioxide

Mixture of acid and SO2 reacts to give

White precipitates of BaSO4(s) with a mixture of BaCl2

Mixture +BaCl2® white ppt.

Conclusions:

HNO2 has the tendency to act as an oxidant and oxidised the above reactants, approved by the observation and standard tests carried out. A detailed explanation of the mechanisms observed was given in the discussion.

Reducing properties

Reagents

Predictions

Observations

Bromine water

Br2(l) reduces to Br-(aq)

Br-(aq) + Ag+(aq)®

AgBr(s) creamy ppt

Brown +HNO2(clear)

+ AgNo3(aq) creamy ppt.

Pottasuim maganate(VII)

Purple Mn7+ reduces to colourless Mn2+

Colour change

Purple +HNO2(colourless)

Sodium dichromate (VI)

Anticlockwise rule applies that Orange Cr6+(aq) reduces to greenCr3+

Orange+HNO2(green)

Conclusion:

Conclusive evidence from the above tests suggests that HNO2(aq) has the tendency to behave as a reducing specie.

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Discussion

Using the anticlockwise rule had clearly with in effect suggested the mechanism in which the reactions occurred. A much negative E value increases the tendency for HNO2 to act as a reducing agent, and a more positive E value allows the tendency to act as an oxidising agent. The reason to which why these chemical reactions occur will be discussed in relation to Gibbs energy. The following data summarises the findings of the HNO2 reactions.

As an Acid , the results were obtained as predicted. Effervescence produced by the reaction with magnesium, warmed the test tube as it was an exothermic reaction. Brown fumes were however produced from this reaction without being predicted. The exothermic nature of this reaction could account for the oxidation of NO(g). A high confidence level in results was confirmed with the 'pop' test for hydrogen gas and with limewater in the carbonate reaction to check for CO2(g). Significantly the carbonate reaction had outlined HNO2 to be a stronger acid compared to carbonic acid as it had protonated the carbonate ion to release carbondioxide.

As an Oxidising agent, the E chart illustrates as to why the observations of the reactions fit into the prediction pattern. In this case HNO2 has more tendency to acc ...