retort stand.
- 25 cm³ of the sulphuric acid solution in the calorimeter was pipetted into a
beaker.
- The sulphuric acid solution was titrated against the 1M of sodium hydroxide
solution so that the molarity of the sulphuric acid can be determined.
Part 2(i): Determination of the Enthalpy of Reaction between Nitric Acid and Sodium
Hydroxide
- The calorimeter of known constant was mixed with a mixture of 50 cm³ of
sodium hydroxide solution and 50 cm³ of water.
- The solution in the calorimeter was stirred and the temperature observation
recorded at interval of 1 minute over a period of 5 minutes. The reading of
temperature obtained and was recorded.
- After the period of time, the solution in the calorimeter was added with 5cm³ of
10M nitric acid solution from a graduated pipette.
- The solution in the calorimeter was continually stirred and the temperature of
the solution was continually measured and recorded at interval of 1 minute
over a period of 10 minutes.
- At the end of the period of time, the solution was added with 3 drops of methyl
orange indicator to ensure the acidity of the solution. If the solution was found to be alkaline, it must be titrated with 0.1M of hydrochloric acid, and vice versa..
Part 2(ii): Determination of the Enthalpy of Dilution of Nitric Acid
- 100 cm³ of distilled water was pipetted into the calorimeter by graduated
pipette.
- The distilled water was stirred with thermometer and the temperature of water
was measured and recorded at interval of 1 minute over the period of 5 minutes.
- At the end of the period of time, nitric acid was introduced into the distilled
water in the calorimeter.
- The solution in the calorimeter was continually stirred and the temperature
was continually recorded at interval of 1 minute over the period of 10 minutes.
MATERIALS : Dewar flask, stopwatch, thermometer, suction bulb, 25 cm³
graduated pipette, 10 cm³ graduated cylinder, burette, retort stand, beaker, concentrated sulphuric acid (H₂SO₄), concentrated nitric acid (HNO₃), 1M of sodium hydroxide (NaOH), 0.1M of hydrochloric acid (HCl)
RESULT AND CALCULATION :
Table 1:Temperature of the water before and after adding sulphuric acid, H2SO4 solution in the calorimeter
Volume of NaOH solution titrated = 17.50 cm³
Table 2:Temperature of sodium hydroxide solution before and after the addition of nitric acid in calorimeter
Table 3: Temperature of water before and after the addition of nitric acid solution in the calorimeter.
From graph 1,
The change in temperature, ∆T = 5.0 ̊C
Volume of NaOH solution = 17.50 cm³
2NaOH + H₂SO₄ →Na₂SO₄ + 2H₂O
17.50 cm³ of 1M sodium hydroxide solution required to titrate the 25.0 cm³ of sulphuric acid solution
1 mole of sodium hydroxide produces 1 mole of hydroxide ions when dissolved in water.
Number of moles of NaOH required in the titration = MV
1000
= (17.50 cm³ )(1M)
1000
= 0.0175 mole
Number of moles of hydroxide ions = 0.0175 mole
1 mole of sulphuric acid produces 2 moles of hydroxonium ions when dissolved in water.
1 mole of hydroxonium ions reacts with 1 mole of hydroxide ions; therefore, 0.0175 moles of hydroxonium ions react with 0.0175 moles of hydroxide ions.
Number of moles of hydroxonium ions = 0.0175 mole
Number of moles of sulphuric acid = 0.0175mol
2
= 0.00875 mole
MV = 0.00875 mole
1000
(25.0 cm³ )(M) = 0.00875 mole
1000
Molarity of sulphuric acid = 0.35M
By plotting the graph of heat liberated against molarity of sulphuric solution, the enthalpy of reaction can be determined from the graph obtained.
From graph 2,
∆H = 3.016 KJ
Ccal = ∆H
∆T
= 3.016 KJ
5.0 ̊C
= 0.603 KJ/oC
From graph 3,
The change of temperature, ∆T = 3.5 ̊C
∆H = Ccal. ∆T
= (0.603 KJ/ ̊C) (3.5 ̊C)
= 2.11 KJ
However, the enthalpy obtained from the calculation above is still incorrect; the enthalpy of dilution of nitric acid must be considered.
From graph 4,
The change of temperature, ∆T = 0.0 ̊C
∆Hdilution = Ccal. ∆T
= (0.603 KJ/ ̊C) (0.0 ̊C)
= 0.0 KJ
Given that ∆Hreaction = ∆H - ∆Hdilution
= 2.11 KJ – 0.0 KJ
= 2.11 KJ
= -2.11 KJ
DISCUSSION :
Calorimeter is a device which is used to measure the of heat flow, either in a chemical reaction or a physical heat exchange experiment. Similarly, a calorimeter should neither absorb nor give out heat. It meant it should be perfectly insulated. However, every calorimeter has its own heat capacity. Heat capacity is the heat required to increase the temperature of any substance by 10 C. Specific heat is the heat required to raise the temperature of 1g of the substance by 10 C. Now it can be seen that heat capacity is mass in grams times the specific heat capacity. Since neither the mass nor the specific heat capacity of the calorimeter changes, the heat capacity remains constant. Hence this quantity is what is known as the calorimeter constant, K.
The reaction in which an acid and a base react to give a salt and water is called neutralization reaction. Neutralization reactions are exothermic in nature. The heat change when one gram equivalent of an acid is completely neutralised by a base or vice versa in dilute solution, is called heat of neutralization.
It is important that the term gram equivalent is used in the definition of heat of neutralization. This is because neutralization involves 1 mole of H+ ions and 1 mole of OH- ions to form 1mole of water and 57.1 kJ of heat is liberated.
One gram equivalent of various acids on complete dissociation liberates one mole of H+ ions. But one mole of the acid may produce more than one mole of H+ ions in solution depending upon its basicity; for example 1mol of H2SO4 gives 2 mol of H+ ions and 1mol of H3PO4 gives 3 mol of H+ ions on complete dissociation. But 1gram equivalent of both (H2SO4 or H3PO4) produces only 1 mol of H+ ions.
Thus, it is more appropriate to use the term gram equivalent in the definition of enthalpy of neutralization.
Below reaction that happens when NaOH reacts with nitric acid.
NaOH + HNO3→ NaNO3 + H2O
Sodium Nitrate is also called as Chile saltpeter and Peru saltpeter. In mineral form Sodium Nitrate, NaNO3 is called as nitratine (soda niter). Resin is produced by combining iron hydroxide and Sodium Hydroxide, NaOH.The reaction of Sodium Hydroxide, NaOH with Nitric Acid, HNO3 can be very useful particularly in mining of this compound has created a very good industry for production of Sodium Nitrate, NaNO3.
2NaNO3 (s) → 2NaNO2 (s) + O2 (g)
Sodium nitrate is slightly deliquescent and gets wet. Hence it cannot be used in making gun powder like the potassium salt.
By mixing Sodium Hydroxide, NaOH with sulphuric acid, H2SO4 nitric acid,HNO3 can be produced. Further fractional distillation of HNO3will produce sodium bisulphate.
All the acids have hydrogen in common. The hydrogen present in acids is such that when acid is dissolved in water, it separates out as positively charged hydrogen ions and enters the solution as H+ ions.It is the presence of hydrogen ions in hydrochloric acid solution, which makes it behave like an acid.Hydrogen ions do not exist as H+ ions in solution, they attach themselves to the polar water molecules to form hydronium ions, H3O+Thus, the acidic behaviour of an acid solution is due to the presence of hydrogen ions in it.
On the basis of these replaceable hydrogen ions, acids are of following types:
-
A monobasic acid is the acid that has one replaceable hydrogen atom to give to the base in any acid-base reaction such as HCl, HNO3
-
A dibasic acid has two replaceable hydrogen atoms for the reactions such as H2SO4.
-
A tribasic acid has three replaceable hydrogen atoms such as H3PO4.
Monobasic acid, HCl has few properties which explain an acid. When hydrochloric acid, HCL reacts with sodium hydroxide, NaOH solution, then a neutralization reaction takes place to form sodium chloride, NaCL and water. Solution of hydrochloric acid, HCl reacts with crushed eggshells to give a gas (carbon dioxide) that turns lime water milky.
REFERANCE :
