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# Chemistry Internal Assesment - Stoichiometry (measuring 'x' in salt)

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Introduction

BACKGROUND As it is commonly known, salt is just the compound of ions, as for example the daily salt we use to regulate the taste of our dinner, NaCI, or some other as BaSO4. What is more, some salts are hygroscopic. That is why we often put the small package of salt to our shoes to avoid the humidity damaging them. Here the question is: what are hydrated salts? The answer is coming quickly: those are salts containing water in themselves; those are salts having H2O attached.1 The worth of attention of the internal is the fact those salts are still in solid state. Below are examples of those salts: * CuSO4�5H2O copper (II) sulfate pentahydrate * CoCl2�6H2O cobalt (II) chloride hexahydrate * SnCl2�2H2O stannous (or tin (II)) chloride dihydrate2 During the experiment I will observe the loss of mass of the chosen hydrated salt by heating the proper amount of salt to dryness and calculate the ratio of the chosen salt to water. RESEARCH QUESTION What is the value of "x" in the formula of hydrated salt: sodium carbonate Na2CO3 * xH2O? AIMS 1) To observe the loss of mass in salts 2) To calculate the whole number ratio in the formula: (1) Na2CO3 *(x)H2O VARIABLES CONTROLLED -->time (s) -->mass (g) EQUIPMENT a) sample of salt: sodium carbonate Na2CO3 b) crucible c) burner d) tongs e) weight f) Petri scale PROCEDURES 1) ...read more.

Middle

water 0,0444 / 0,0113 = 3,9292 � 4 The ratio, in that case, is 1:4. Since there were some drawbacks during the experiment, as the uncertainty in measuring the crucible, because the weight was showing two results in that case during different stages of the experiment, I decided to do the experiment once again, with other crucible and with better precise in measurement and time control. SECOND ATTEMPT RESULTS I found the mass of crucible: 25,9+0,1g I measured the amount of salt: 3,0+0,1g - the salt was white, crystalline The whole mass: 28,9+0,1g I decided to use now 4-minutes breaks. time the whole mass the mass of salt loss of mass before - 10:49 28,9+0,1g 3,0+0,1g x 10:54 28,7+0,1g 2,8+0,1g -0,2+0,1g 10:58 27,7+0,1g 1,8+0,1g -1,2+0,1g 11:02 27,6+0,1g 1,7+0,1g -1,3+0,1g 11:06 27,4+0,1g 1,5+0,1g -1,5+0,1g 11:10 27,4+0,1g 1,5+0,1g -1,5+0,1g Table 2: The procedure of losing salt's mass while heating during the second attempt. mass of hydrated salt before: 3,0+0,1g mass of hydrated salt after: 1,5+0,1g loss of mass: 1,5+0,1g= mass of water CALCULATIONS 1) masses in g c) salt 1,5+0,1g d) water 1,5+0,1g 2) masses in g * mol-1: c) salt 2 * Na + C + 3 * 0 = 46 + 12 + 48 = 106 d) water 2 * H + O = 2 + 16 = 18 3) number of moles c) salt 1,5 / 106 = 0,0142<-- the smallest number d) ...read more.

Conclusion

The school equipment and poor fire could not heat crucible properly and I did not pay special attention to it. Salt wasn't kept in good conditions - the headmaster had not wanted to finance the Chemistry Room for years. Of course, there is also the problem of the error in measurement - I am not sure I had the proper samples of salt in those attempts. There could also be powder on the weight. The biggest error was the immediate measurement after getting the object off the burner. The crucible was hot and it was the cause of other result and weight, which conducted to the wrong calculations. If the crucible was cool, the result would be different and the ratio bigger. The thing I regret is only two attempts to do the experiment. In my future the most probable result will be gained with the minimum three researches with different data, BUT THE SAME material. Other ideas for improving the experiment are: * putting special attention to the measurement * detailed cleaning the equipment before it is used * keeping the crucible in high temperature, at least 100oC, while heating in order to vaporize water completely * cool the crucible before writing the result I am sure with that the result could be fine. CHEMISTRY SL - INTERNAL ASSESSMENT Finding a formula of a hydrated salt Candidate's name: Bartosz Wytrzyszczewski Candidate's number: ____________________________ School: Paderewski Private High School, Lublin Session: May 2010 1 http://answers.yahoo.com/question/index?qid=20090627062611AATunUB 2 http://en.wikipedia.org/wiki/Water_of_crystallization ?? ?? ?? ?? ...read more.

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