Apparatus:
- Standard Thermometer
- 1 M HCl
- Magnesium Oxide (MgO)
- Magnesium Ribbon (Mg)
- Probe (GLX)
- Graduated Cylinder (100 ml)
- Beaker (250 ml)
- Styrofoam Cup X 2
Method:
A Styrofoam cup was set up and placed in a beaker. 50 ml of I M HCl was measured and poured into a Styrofoam cup. A temperature probe was placed in hole at the top of cup and the initial temperature was recorded. 0.25 g Magnesium was added to the solution. Temperature was recorded until the trend stabilized. The solution was then disposed. The same process was repeated with 0.5 g Magnesium Oxide and HCl.
Variables:
- Dependent: Temperature Change, Enthalpy Change
- Independent: Reactants
- Control: Room temperature, Time of recording temperature
Raw Data:
Table 1: Measurements recorded during reactions of MgO and Mg with HCl
Figure 1: Temperature change of the reaction MgO(s) + 2 HCl(aq) → MgCl2(aq) + H2 O(l)
Figure 2: Temperature change over time of the reaction Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
Processed Data:
Table 2. Processed data for the Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g) and MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)
Reaction Enthalpy for Mg(s) + 1/2 O2 (g) → MgO (s) reaction = -591.4 KJ/ mol
Percent Error: (601.8-604.6/601.8) * 100 = 0.46 %
Calculations for acquired Processed Data:
Using the following reactions, Hess’ Law was applied to find out reaction enthalpy of MgO was found indirectly. Also using this formula for reaction enthalpy: ∆H= (-Q / n)
-
Mg(s) + 1/2 O2 (g) → MgO (s)
-
MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)
-
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
-
H2(g) + 1/2 O2 (g) → H2O(l)
Temperature change= final temperature – initial temperature = 27.6 -21.6 = 7.4
Moles of HCl = (ml of HCl /1000) * Molarity of HCl = (48.30 / 1000) *1 = 0.04830
Moles of MgO = g of MgO / molar mass = 0.52/(24.3+16.0) = 0.01290
Reaction Enthalpy = (temp change * 4.18 * mass of HCl /1000 * -1) / moles of limiting reagent
(7.4*4.18*48.30/1000) / 0.01290 ) * -1 = - 115.8KJ/ mol
-> Similar calculations were done for the reaction of Mg with HCl.
Reaction Enthalpy of :
Mg(s) + 1/2 O2 (g) → MgO (s) using Hess’ Law was calculated like this:
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g) -434.6
+H2(g) + 1/2 O2 (g) → H2O(l) -285.8
+MgCl2(aq) + H2O(l) → MgO(s) + 2HCl(aq) +115.8
Mg(s) + 1/2 O2 (g) → MgO (s) -604.6
Percent Error: | (accepted value – experimental) | / accepted value * 100
| 601.8-604.6 | / 601.8 * 100 = 0.46 %
Conclusion: The oxidization of Magnesium was found to have the enthalpy of -604.6 KJ/ mol, which proved to be exothermic, since the value of reaction enthalpy is negative. Therefore, the Hypothesis proved to be correct, since we got an almost close value.
Evaluation: The almost perfect results with a 0.46 % error in this experiment can proved to be a great result for the determination of enthalpy of oxidization of Magnesium. Numerous errors could have been affected the results achieved in this experiment. The likeliness of heat loss from the probe itself and heat loss into the system could affect the enthalpy of reaction of MgO and Mg with HCl. Another error could be that the specific heat capacity used was for water when in the liquid was solution had other impurities in it, which could have resulted in the slightly off results. These errors could be avoided in other experiments by making use of an insulated cup and by considering the proper specific heat capacity of solutions used in the experiment. The lab also faced the plight of not being experimented under standard conditions.
