• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Confirming Hess's Law Experiment

Extracts from this document...


LAB Hess' Law Lab HYPOTHESIS The heat of combustion for magnesium can be calculated by determining the heat of reaction for the following reactions: 1) Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g) 2) MgO(s) + 2HCl(aq) --> MgCl2(aq) + H2O(l) 3) H2(g) + 1/2 O2(g) --> H2O(l) Once these values have been obtained, one can add or subtract these values in order to achieve the heat of combustion for magnesium. VARIABLES Independent: � Type of chemicals used � Amount of chemicals used Dependant: � Change in enthalpy Controlled: � Elevation � Air pressure � Room temperature � Equipment � Humidity OBSERVATIONS Qualitative: Hydrochloric acid solution: - transparent, water-like liquid Magnesium metal strip: - dull silver, grey strip - extremely ductile Magnesium oxide: - fine, white powder - flour-like appearance Reaction #1 between hydrochloric acid solution and magnesium metal strip: - soft fizzing noise coming from the calorimeter - calorimeter is warm to touch Reaction #1 upon removing the Styrofoam cup cover: - clear solution - magnesium metal strip has fully dissolved in the hydrochloric acid solution - pungent smell - bubbles are apparent at the side of the cup Reaction #2 between hydrochloric acid solution and magnesium oxide: - calorimeter is slightly warm to touch - no apparent noise Reaction #2 upon removing the Styrofoam cup cover: - clear solution ...read more.


0.05 J -1158 ? 0.05 J 0.0248 ? 0.001 mol 0.0248 ? 0.001 mol - 53.59 ? 0.040 kJ - 46.69 ? 0.040 kJ Trial #1: 1) Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g) ?H = - 468.5 kJ/mol 2) MgO(s) + 2HCl(aq) --> MgCl2(aq) + H2O(l) ?H = - 53.59 kJ/mol 3) H2(g) + 1/2 O2(g) --> H2O(l) ?H = -285.8 kJ/mol (www.chm.davidson.edu/ChemistryApplets/Calorimetry/HeatOfCombustionofMethane.html) (1) + (-2) + (3) = Mg(s) + 1/2 O2(g) --> MgO(s) ?Hcomb = (- 468.5 kJ/mol) + (46.69 kJ/mol) + (-285.8 kJ/mol) = - 700.71 kJ/mol Trial #2: ?Hcomb = (- 468.5 kJ/mol) + (53.59 kJ/mol) + (-285.8 kJ/mol) = - 707.61 kJ/mol CONCLUSION Theoretical value of heat of combustion of magnesium = 601.8 kJ/mol (cstl-csm.semo.edu/Hathaway/CH085/Heat%20of%20Reaction.doc) Trial #1: Trial #2: The heat of combustion for magnesium was determined algebraically by adding the molar enthalpies of three intermediate chemical reactions. For two out of the three reactions, the molar enthallpies were determined experimentally. A temperature probe was used to calculate the temperature change in both of the reactions. This value was then used in the equation Q = -mc?T. Since both of these reactions are exothermic, the negative sign reflects this nature. Also the specific heat capacity value used in the equation was that of water (4.18 J/g?C) ...read more.


Finally, due to the time restrictions and chemical limitations implemented during this lab, further trials were unable to be completed to ensure the accuracy of this lab. However, these would have aided in determining a more accurate heat of combustion of magnesium, as an average of all results would be obtained that best reflected the actual result. Also, these values would be more accurate with more practise. All these errors could be prevented or eliminated in order to improve this experiment. To ensure that the temperature probe is within the hydrochloric acid solution, a small cup should have been used. Therefore, the rubber stopper could have blocked the hole which was escaping air, and this would not have prevented the temperature probe from reaching the solution. Also, any gaps between the paper cups could have been blocked using tape to guarantee a tight fit, however, this would have been tedious to perform during the lab. To ensure the even distribution of magnesium, magnesium powder should have been used instead of the magnesium strip, which would allow for a better reaction due to the larger surface area. During calculations, the density of the hydrochloric acid should also have been determined, instead of assuming it was equal to water. Finally, through the benefit of more trials, the heat of combustion could have been calculated more accurately. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our International Baccalaureate Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related International Baccalaureate Chemistry essays

  1. hess's law

    �C Change in Enthalpy (?Ha) = mc?? = 50 X 4.18 X (7.5 � 1.0) = 50 X 4.18 X (7.5 � 13%) = 1567.5 � 13% � 1568 � 13% = 1568 � 204 Joules Note: The above enthalpy change value obtained is for the total no.

  2. Experiment - The Empirical Formula of Magnesium Oxide

    the reactions were not fully completed; 2) the readings of the masses were incorrect since it took a while for the electronic balance to reach the real mass. Thus, if the experimenter did not wait till the readings stopped changing; the recorded data would be smaller than they were supposed to be. These could cause random errors.

  1. Rate of reaction of Magnesium with Hydrochloric acid

    One of which was the fact that the surface area of the Magnesium and the mass were not the same for every coil of Magnesium used, another variable we were not controlling was the temperature. As the experiment was unfoldingwe could see that the temperature of the substance was increasing,

  2. Acids/Bases Design Lab. How does a change in the pH value of a solution ...

    As part of the procedure, the investigator is measuring out a pre-determined volume of concentrated hydrochloric acid (12 mol dm-3) and eventually it is combined with a larger quantity of distilled water. The distilled water to be used for all of these should be distilled water, and come from the same source water tank.

  1. Hesss Law Lab, use Hesss law to find the enthalpy change of combustion of ...

    Reaction: 1 (hydrochloric acid (HCl) solution and magnesium (Mg) metal strip) It made a soft fizzing noise and the cup was a bit warm after the reaction started. At the end of the reaction we were left with a clear solution.

  2. Determination of the molar mass of Magnesium from the reaction of magnesium and ...

    Then to make the gas inside the eudiometer have the same pressure as the air pressure in the room the eudiometer was lifted up to making the water level inside it equal to the water level in the measuring cylinder.

  1. The aim of this experiment is to examine the enthalpy of combustion of the ...

    * c (H2O) * ΔT (H2O) Q – heat energy M – mas of water C- heat capacity of water , the value is 4.20 J g-1 K-1 ΔT – change in temperature In the method it has been said that the volume of water is 40 cm ³.

  2. Bomb calorimetry. The goal of this experiment was to use temperature data over ...

    done by the bomb during the reaction (Mashkevich, 1995). However, the combustion takes place in a sealed container with constant volume, the work done on or by the system is also zero, so that âcU=0 (5) Considering the combustion of the system for both sample and the cotton fuse, âcUsample + âcUcotton = 0 (6)

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work