Heat of Combustion of Magnesium Lab

 

 

Purpose:

 

������ The purpose of this lab is to experimentally determine the heat of combustion of magnesium using Hess�s Law.

 

Procedure:

 

������ Part 1

 

  1. Pour 100.0 ml of 1.0M HCl into a Styrofoam cup and record the temperature of the acid.
  2. Add 0.1 to 0.2 g of Mg.� Stir constantly but slowly.
  3. Record the final temperature achieved.
  4. Rinse out the Styrofoam cup.

 

������ Part 2

 

  1. Pour 100.0 ml of 1.0M HCl into a Styrofoam cup and record the temperature of the solution.
  2. Add about 1.5 g of MgO.� Stir constantly.
  3. Record the final temperature achieved.
  4. Rinse out the Styrofoam cup.

 

Data and Observations:

 

������ (Create your own data table.)

 

Calculations:

 

  1. Write out the molecular equation for each reaction that occurs.
  2. Calculate the DH for each reaction for the amount of each reactant (Mg and MgO) that you actually used by assuming that the 1.0M HCl solution is just water.
  3. Calculate the DH per mole of Mg and MgO, respectively, for each reaction.
  4. Using the values calculated above and the value for the heat of formation of liquid water, apply the Law of Hess to calculate the heat of combustion for magnesium (the DH for the reaction of Mg plus oxygen gas to yield magnesium oxide).

 

 

Error Analysis:

 

Using the textbook value of the heat of formation of MgO, perform a percent error calculation.� (Is the heat of combustion of magnesium the same as the heat of formation for magnesium oxide?)