The Properties of Nitric Acid.

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The Properties of Nitric Acid


Page No. .

.Introduction 1

. Plan : 3

Outline of method


. Results: 7

Acidic properties

Oxidizing properties

Reducing properties.

. Discussion: 9


. Bibliography 14

. Chemical equipment's and lists. 15

Introduction: An investigation on the properties of Nitrous acid.

The study under this investigation was concerned with the acid base and redox reactions of Nitrous acid.

Nitrous acid is a weak acid of ka 4.7 x 10-4 formed from the reaction:

NaNo2(aq) + HCl(aq) ® HNO2(aq) +NaCl(aq).

(nitrous acid)

Related studies have shown that a pale blue solution is formed from this reactions a result of an unstable oxide N2O3 and that HNO2 is an unstable compound because it decomposes very fast at room temperature. It was hence used up immediately after being made from its constituent's reactants, Sodium nitrite and Hydrochloric acid.

The instability of the compound means that it disproportionates at standard room temperature .

HNO2(aq) ----- HNO3(aq) +NO (g)

(nitric acid) (nitrogen monoxide)

Disproportionation occurs when one of the reactant molecule in a reaction forms two products, one product which is obtained by the oxidation of the reactant molecule and the other by reduction. To limit this effect, Le Chatelier's principle applied that cooling the system will shift the equilibrium to the exothermic direction of the equation to minimise the temperature decrease. In this case an ice bath was used to drive the reaction towards the left-hand side. This inevitably limits the dispropornation reactions.

To demonstrate the acidic properties of Nitrous acid, the three standard tests were set.

Acid + base/alkali ® Salt + water

Acid + Metal ® Metal Salt + Hydrogen

Acid + Carbonate ® Salt + Carbondioxide + Water

The redox reactions involve reductions and oxidations. To question the view that HNO2 behaved as either a reductant, oxidant or both, scientific theories and experiments were applied based on the fact that it displays the characteristics set by the following standards

As a reducing agent it reduces another specie by donating electrons to it.

As an oxidising agent it oxidises another specie by removing electrons from it.

To practically demonstrate the acid base, redox reactions of HNO2 the following reagents were used based on factors concerned with cost, availability and the nature of their reactions.



Acidic reactions

Magnesium solid

Sodium hydroxide solution

Sodium Carbonate solid

Reduction reactions

Bromine water

Pottasuim manganate (VII) solution

Sodium dichromate (VI) solution

Oxidation reactions

Pottasium iodide solution

Iron (II) sulphate solution

Sulphur dioxide solution

In all the cases, the anticlockwise rule was applied to make predictions on whether a reaction took place and possible outcomes of the products. Appropriate tests were carried out in some of the reactions to distinguish formation of products if any from that of a mixture of the reactants. Prior to making an aqueous solution of HNO2, consideration were given to the small scale laboratory procedure and the following safety precautions:

· Use standard laboratory concentrations of 2M.

· Wear laboratory coats and goggles.

· Avoid inhaling toxic nitrogen monoxide gas (use fume cupboard)


Plan : Preparation of Nitrous acid

An aqueous solution of 2M HNO2 was made from cold acidified aqueous solution of sodium nitrite from the equation.

NaNo2(aq) + HCl(aq) ® HNO2(aq) + NaCl(aq)


Moles of NaNo2 and HCL, ratio 1:1

Amount needed = 100cm3 of 2M HNO2

Amount of HCl = 50cm3 of 2M HCl

50 x 2 = 0.1 moles


Moles of NaNo2 = 0.1 moles

Mass = 0.1 x (RMM 69g)


6.9g of NaNo2 makes up 50cm3 of 2M solution.

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Outline of method:

· Set up a conical flask placed into an ice bath.

· Weigh 6.9g of solid NaNo2 and dissolve in 50cm3 of distilled water.

· Pour solution into conical flask inside ice bath.

· Cool down to a temperature range of (0 - 5)0C in ice bath.

· Add 50cm3 of 2M HCl to conical flask

· Place apparatus in fume cupboard

· Carry out tests with the conical flask placed in ice bath.

Procedure: 3cm3 of Nitrous acid was used to react in all cases to 3cm3 and small portions of reactant solutions and solids . A table of results was ...

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