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

Chemistry Internal Assessment Hesss Law

Extracts from this document...


Chemistry Internal Assessment DCP and CE “Hess’s Law” 2014 Raw data table: Observations: * The solution with MgSO4 a white precipitate formed * In the experiment using MgSO4 the thermos got warm * The solution with MgSO4.7H2O turned a cloudy white * In the experiment using MgSO4.7H2O the thermos got cooler Measurement Mass (g) ±0.001 Volume –measuring cylinder (mL) ±1 Mass of MgSO4 3.801 Mass of MgSO4.7H2O 7.958 Volume of H2O 50 Full Equations of Reactions 1) MgSO4(s) → Mg2+(aq) + SO42-(aq) 2) MgSO4.7H2O(s) → Mg2+(aq) + SO42-(aq) + 7H2O(l) Literature Values Constant Value Source Specific Heat Capacity of Water 4.18 J g-1K-1 http://www.sphsgator.net/sphsteachers/domanskil1/databooknew.pdf A Raw Data Table Showing the Relationship between Time Elapsed and the Temperature of the Reaction of Hydrous and Anhydrous Magnesium Sulphate using a logger pro temperature sensor. Time (seconds) ± 0.1 seconds Anhydrous MgSO4 Temperature (°C) ±0.1°C Hydrated MgSO4 Temperature (°C) ±0.1°C 0 20.7 17.3 10 20.7 17.3 20 21.8 16.8 30 23.3 15.9 40 24.4 15.7 50 25.3 15.6 60 26.1 15.6 70 26.6 15.7 80 27.1 15.7 90 27.4 15.7 100 27.7 15.8 120 28.0 15.8 130 28.0 15.9 140 28.1 15.9 150 28.1 15.9 160 28.1 16.0 170 28.1 16.0 180 28.1 16.0 190 28.1 16.0 200 28.0 16.0 210 28.0 16.1 220 28.0 16.1 230 28.0 16.1 240 28.0 16.1 250 28.0 16.1 260 27.9 16.1 270 27.9 16.1 280 27.8 16.1 290 27.7 16.2 300 27.7 16.2 310 27.7 16.2 320 27.6 16.2 330 27.6 16.2 340 ...read more.


+ 7H2O(l) ? MgSO4.7H2O(s) 37% Conclusion Theoretical or Accepted Result Experimental or Actual Result Percentage Error 37% Calculated random error Our percentage error or deviation from the expected value was 37%, which is much larger than the calculated random error of 2.46%. This implies that the experiment was significantly affected by systematic errors. Evaluation General, as the percentage error for our two experiments was relatively similar at 38% and 31.3% I can assume that the systematic errors effect both experiments reasonably evenly. Limitation Explanation Effect on results Significance of Limitation Improvements Heat Loss The thermos warmed up slightly when we added MgSO4 to the water. This suggests that heat energy, released as a result of this experiment was dissipating into the surroundings: the thermos, the temperature probe, and the air. This would have lowered the value of ?T and therefore lowered the value of ?H. Although we extrapolated our line to minimize the effect of heat loss this still would have been very significant, and is the most probably cause of our percentage error. This experiment could be improved, if the experiment was carried out in a more insulated container, which would allow heat to escape at a much slower pace. An airtight lid would also not allow heat to be lost to air. Heat Gain The thermos cooled down slightly when we added the MgSO4.7H2O to the water, which suggests that heat was gained from the surroundings. ...read more.


Though this wouldn?t have affected the accuracy of the results. It would have decreased the precision of our results. This may have had a significant effect as more repeats may have decreased our percentage error. If I was to repeat the experiment I would ensure that I did at least three repeats with each chemical. The surface area of anhydrous and hydrated crystals is different. The anhydrated MgSO4 was a powder while the hydrated MgSO4 was crystalline. This meant that the surface area of the chemicals was different. The larger surface area of the hydrated MgSO4 would have meant that it took longer time to react, as there would be less collision. Thus more heat could have been gained during the experiment causing ?T to decrease and therefore lowered the value of ?H This would not have been very significant. If I was to repeat this experiment I would powder the hydrated MgSO4 with a pestle and mortar prior to using it. Ensuring a more consistent surface area. Incomplete Reaction The MgSO4 may have not completely reacted in the water. As the right amount of bonds would not have been formed/broken, more heat could have been gained/lost during the experiment causing ?T to decrease and therefore lowered the value of ?H This may have been very significant but we have no evidence that an incomplete reaction occurred. We could stir the mixture faster by using a magnetic stirrer and stir bar, which was kept at 700rpm. ________________ [1] Experiments in Seventh Form Chemistry- a Laboratory Manual. Dept of Education New Zealand, 1978 ...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. A comparison of various proprieary antacids

    gel and Eno powder is approximately 3 times more effective than the Zolicid gel. Calculating Errors: Errors for the first step of the experiment( adding the Hydrochloric acid to the conical flask) Moles HCl= Volume in litres x concentration(this was as standardized solution with no errors)

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

    (28 + 0.5)�C (27 + 0.5)�C (28 + 0.5)�C EXPERIMENT 1 A time/s(�1sec) Temp.0C (�0.50C ) HCl 0 21 30 21 60 21 90 21 120 21 150 21 180 21 HCl+Mg 190 22 200 24 210 26 220 28 230 30 240 31 250 32 260 33 270 34

  1. Using Hess's law to calculate enthalpy change

    + 100H2O(l) MgSO4(aq,100H2O) * Q = m x c x delta T * M= 45.1 + 3.02 = 48.1g * C = 4.18 J/g.K * Delta T = 21 - 18 = 3.00 K * Q = 603J *

  2. Validating Hess's law

    Stir and record the maximum temperature reached. Calculate the enthalpy change of this process in kJmol-1. Measurement of ?H?3 Pour 50cm3 of 1M sodium hydroxide into an empty polystyrene cup and record its temperature as accurately as you possibly can.

  1. IB Chemistry Kinetics Exam Questions and Answers

    The reaction between nitrogen and oxygen in the atmosphere under normal conditions is extremely slow. Which statement best explains this? This is an IB exam question - narrow down your choices, then if two choices are almost the same thing, pick the 4th!

  2. IB chemistry revision notes

    * The majority are metals. Physical Properties * A covalent radius is half the4 minimum distance between the nuclei of 2 atoms of the same element covalently bonded in a diatomic molecule. * A Van der Waal's radius is half the minimum distance between the nuclei of two atoms in the same element, which are NOT chemically bonded.

  1. To determine the standard enthalpy of formation of Magnesium Oxide using Hess Law.

    1 × lab coat The lab coat is used to prevent damages from any spillage of chemicals onto clothing. 1 × covered shoes Covered shoes are needed to prevent any damages to the feet that could be due to spillage of corrosive HCl.

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

    There are five such bonds in ethanol so 410 is multiplied by five to get 2050 joules. The same calculations are done for other alcohols. Methanol has the least number of Carbon atoms in the chain and also has the lowest enthalpy change of combustion.

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