CHEM 504Name:

Lab - Molar heats of reaction

The aim of this experiment is to determine molar heats of dissolution and neutralization of different chemical compounds.

Materials:

  • Thermometer
  • 50 ml graduated cylinder
  • 3 polystyrene cups
  • Electronic balance
  • Weighing boat
  • 250 ml beaker
  • Ring stand
  • Thermometer clamp
  • Glass stirring rod
  • 2.0 g of potassium nitrate powder (KNO3)
  • 2.0 g of NaOH pellets (NaOH)
  • 25.0 ml of 0.50 M hydrochloric acid, HCl
  • 25.0 ml of 0.50 M sodium hydroxide, NaOH
  • 25.0 ml of 0.25 M sulfuric acid, H2SO4
  • 25.0 ml of 0.50 M potassium hydroxide, KOH

Procedure A – Dissolution

  1. Measure 20.0 ml of water using the graduatedcylinder
  2. Pour water into polystyrene cup
  3. Record initial temperature
  4. Mass 2.0 g of KNO3 on electronic balance using weighing boat
  5. Pour KNO3 into cup and insert thermometer
  6. Stir gently with glass stirring rod to dissolve solid
  7. Record the temperature every 30 seconds
  8. Record the final temperature of the solution (once you have obtained 3 consecutive identical readings)
  9. Pour solution in the appropriate waster beaker, rinse cup at your bench, rinse stirring rod
  10. Repeat steps 1-9 with NaOH

Procedure B – Neutralization

  1. Place polystyrene cup in 250 ml beaker. Place beaker on the base of ring stand.
  2. Attach thermometer to thermometer clamp
  3. Ensure graduated cylinder is dry before use
  4. Measure 25.0 ml of HCl in the graduated cylinder and pour into cup
  5. Record initial temperature
  6. Measure 25.0 ml of NaOHin graduated cylinder and pour into cup
  7. Gently stir with glass stirring rod
  8. Record the temperature every 30 seconds
  9. Record the final temperature of the solution (once you have obtained 3 consecutive identical readings)
  10. Pour solution in the appropriate waste beaker, rinse cup at your bench, rinse and dry graduated cylinder
  11. Repeat steps 1-9 using 25.0 ml of H2SO4 and 25.0 ml of KOH and a NEW polystyrene cup
  12. Rinse and dry all materials, they will be used by all groups.

Results:

Table 1 (5 marks)

Mixtures / Ti(oC ± 0.05 oC) / Tf(oC ± 0.05 oC) / ∆T (oC ± 0.05 oC) / Endothermic
reaction / Exothermic reaction
Dissolutions
Water + KNO3 / □ / □
Water + NaOH / □ / □
Neutralizations
HCl + NaOH / □ / □
H2SO4 + KOH / □ / □

Analysis of results:

  1. Among the mixtures made in the lab, which are: (2 marks)

a)Physical transformations? ______

b)Chemical transformations? ______

  1. Based on your data, calculate the molar heat of dissolution of both KNO3 and NaOH. (4 marks)

KNO3: ______NaOH: ______
  1. Compare your calculated values to the accepted values on p.420 in your textbook. Calculate percent error for both. (4 marks)

KNO3: ______NaOH: ______
  1. Based on your data, calculate the molar heat of neutralization of HCl and H2SO4. (4 marks)

HCl: ______H2SO4: ______
  1. Calculate the percent error for your experimental heats of neutralization based on the accepted values of -56.0 kJ/mol for HCl and -112.0 kJ/mol for H2SO4. (4 marks)

HCl: ______H2SO4: ______

  1. For each of the reactions performed in the lab write the thermochemical equation with heat energy in the equation as well as in ∆H format. (4 marks)

a)Dissolution KNO3 :

______

______

b)Dissolution NaOH:

______

______

c)Neutralization HCl:

______

______

d)Neutralization H2SO4:

______

______