Thermochemistry

(A) Determination of Water Equivalent of Calorimeter

Materials Required

  • Calorimeter
  • Wooden box with lid
  • Stirrer  
  • Thermometer  
  • Distilled water
  • Cotton  
  • 250 ml beakers
  • Hot plate
  • Measuring jar                                

Real Lab Procedure

  • Using a measuring jar, take 50 ml of distilled water in the calorimeter.
  • Using a thermometer, measure the temperature of water in the calorimeter. Let it be t1 °C.
  • Place the calorimeter in the wooden box and fill cotton in the space between the calorimeter and the wooden box to avoid heat loss.
  • Now insert a stirrer in the calorimeter.
  • Using the measuring jar, pour 50 ml of distilled water in a beaker.
  • Heat water in the beaker to a temperature 10-20 °C (~47 °C) higher than that of room temperature.
  • Stop heating and note the temperature of this warm water. Let it be t2 °C.
  • Add the warm water into the calorimeter without any loss of time.
  • Immediately close the wooden box.
  • Quickly insert the thermometer into the calorimeter.
  • Now, stir the water using the stirrer and note the thermometer reading.
  • Continue stirring until the temperature becomes constant. Let it be t3 °C.

Observations

  • Volume of water taken in the calorimeter = 50 ml

Therefore, mass of water = 50 g (assuming specific density of water is unity)

  • Temperature of water = t1 °C
  • Volume of warm water added = 50 ml
  • Therefore mass of warm water = 50 g
  • Temperature of warm water = t2 °C
  • Temperature after mixing = t3 °C

Calculations:

 

(B) Determination of Enthalpy of Dissolution of Salt in Water at Room Temperature

Materials required

  • Calorimeter
  • Wooden box with lid
  • Stirrer  
  • Thermometer  
  • Distilled water
  • Cotton  
  • Measuring jar
  • Sample
  • Ammonium chloride

Real Lab Procedure

  • Using the measuring jar, take 50 ml of distilled water in the calorimeter.
  • Note the temperature of water using the thermometer. Let it be t1 °C.
  • Place the calorimeter in the wooden box and fill cotton in the space between the calorimeter and the wooden box to avoid heat loss.
  • Insert a stirrer in the calorimeter.
  • Add 5 g of ammonium chloride into the calorimeter.
  • Immediately close the wooden box.
  • Quickly insert the thermometer into the calorimeter.
  • Now stir the water using the stirrer and note the thermometer reading.
  • Continue stirring until the temperature becomes constant. Let it be t2 °C.
  • At this temperature, the substance just dissolves.

Observations

  • Weight of ammonium chloride dissolved, w = 5 g
  • Volume of water taken in the calorimeter = 50 ml
  • Therefore, mass of water taken in the calorimeter = 50 g (assuming specific density = 1)
  • Temperature of water = t1 °C
  • Temperature after dissolving ammonium chloride = t2 °C
  • Water equivalent of calorimeter, W = 11.11 g
  • Molecular mass of ammonium chloride, M = 53.49 g/mol

Calculations

Assuming density and specific heat of the solution to be same as that of water, heat evolved or absorbed for dissolution of w g of the solute,

Precautions

  • Do not stir the liquid in the calorimeter vigorously because vigorous stirring does cause some increase in temperature.  
  • The space between the calorimeter and the wooden box should be filled with cotton to avoid heat loss.

                                   

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