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Determine the crystallisation temperature of the solution potassium nitrate at different concentrations and use information to find out the standard enthalpy of potassium nitrate.

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Introduction

Introduction Stability Stable. Strong oxidizer - contact with combustible material may cause fire. Incompatible with combustible materials, and strong reducing agents. Toxicology Harmful if swallowed. May cause reproductive disorders. Aim The aim of this experiment is to determine the crystallisation temperature of the solution potassium nitrate at different concentrations and use information to find out the standard enthalpy of potassium nitrate. Equipment and reagents * Boiling tubes * Dark card * Bunsen burner * Thermometer * Weighing scale * Burette (50cm3) * Clamp * Stand * Potassium nitrate * Deionised water/ distilled water Safety * Wear goggles for eye protection at all times. * Laboratory coats must be worn at all times. * Wear gloves to avoid chemical contact to skin, potassium nitrate. * Long hair was tied back when Bunsen burners were used. Procedure 1. 10g of potassium nitrate were weighed out and placed into a boiling tube, and then the exact mass was noted in a result table. 2. Exactly 8.0cm3 of deionised water was added to the boiling tube containing the potassium nitrate. This was done by using a burette. 3. The tube was then heated gently until the crystals were dissolved and then the heat source was removed. 4. The tubes were allowed to cool for safety reasons. The temperature at which the crystals were first appeared was noted. A dark card was used for this purpose. The results were recorded. ...read more.

Middle

of the line of best fit I was able to estimate the SD of the values I had calculated for S and H the following table shows the results. R.in cn 1/T values (a) 1/T values calculated from best fit line (b) Difference for each 1/T value, as a fraction of the best fit value.(a-b)/b Difference2 (R = 8.21 Jmol-1 K-1) K-1 K-1 20.90 0.00298 0.002925 0.0188 3.5344 x10-4 19.04 0.00304 0.00303 3.300 x10-3 1.089 x10-5 17.53 0.00313 0.003113 5.461 x10-3 2.9822521 x10-5 16.24 0.00319 0.00319 -6.2696 x10-3 3.93 x10-5 Calculations Molar mass (KNO) = K= 39 N= 14 O= 3 X16 = 39 + 14 + 48 = 101.11g Number of moles : Amount = mass = 10.00 = 0.0989 mol dm-3 Molar mass 101.11 Concentration: Concentration = amount Volume (a) 8 cm3 : C = 0.0989 = 12.36 mol dm-3 8/1000 (b) 10 cm3 : C = 0.0989 = 9.89 mol dm-3 10/1000 (c) 12 cm3 : C = 0.0989 = 8.24 mol dm-3 12/1000 (d) 14 cm3 : C = 0.0989 = 7.06 mol dm-3 14/1000 R.In cn: (a) 12.36 mol dm-3 : ln (12.36) = 2.514 = R X ln (concentration) =8.31 x 2.51 =20.90 (b) 9.89 mol dm-3 : ln (9.89) = 2.2915 = R X ln (concentration) =8.31 x 2.29 =19.04 (c) 8.24 mol dm-3 : ln (8.24) = 2.1090 = R X ln (concentration) =8.31 x 2.11 =17.53 (d) ...read more.

Conclusion

Plus, it was hard to actually say what amount of particles formed, was the right amount to take the solution off the heat source and note the results. In my own opinion I think that my method was a suitable one because it gave me accurate results and didn't take up too much time to proceed. Improvements The improvements that could have been made to make my experiment more accurate are to be more careful in measuring reagents and also to use a more accurate thermometer. In addition, a larger scaled graph could have been used as results would have been plotted more accurately. Confidently in future I would be more experienced in carrying out the experiment and would be more precise at spotting the crystals when they form. Conclusion and % error Thermometer 0.10 620 : % error = 0.1 x 100 = 0.2% 62 560 : % error = 0.1 x 100 = 0.2% 56 470 : % error = 0.1 x 100 = 0.2% 47 420 : % error = 0.1 x 100 = 0.2% 42 Average % error = 0.2% Burette 0.1cm3 8cm3 : % error = 0.1 x 100 = 1.3% 8 10cm3 : % error = 0.1 x 100 = 1% 10 12cm3 : % error = 0.1 x 100 = 0.8% 12 14cm3 : % error = 0.1 x 100 = 0.7% 14 Average % error = 1.3 + 1+ 0.8 +0.7 = 0.95% 4 Weighing scales + 0.01g % error = 0.01 x 100= 0.1% ...read more.

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