Identification of an Unknown Compound through Mass Correlations

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2 pages pre lab for this experiment

Identification of an Unknown Compound through Mass Correlations
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Identification of an Unknown Compound through Mass Correlations
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Experiment 5 – Identification of an Unknown Compound Through Mass Correlations I. Purpose Study of hydrates, percent water in a compound and complete the chemical formula of a compound. II. Introduction As the world’s population increases, the consumption of energy also increases. Scientists are looking for alternative ways to generate energy since fossil fuels are depleting rapidly. Recent efforts have been focused on obtaining methane, the main component of natural gas, from the seafloor sediments. Methane is found thousands of feet below sea level as methane hydrates, which is chemically different than inorganic hydrates. A methane hydrate is a methane molecule trapped in a cage of ice, called a clathrate. It is estimated that 700 quadrillion cubic feet of methane are trapped under the sea, which 1% of this may meet America’s energy needs for 170,000 years. III. Materials Part 1 MgSO4•nH2O CuSO4•nH2O MnSO4•nH2O Na2CO3•nH2O Part 2 NaHCO3 Na2CO3 KHCO3 K2CO3 6 M HCl IV. Safety Precautions Be cautious with the handling of acids and bases, and dispose chemicals as instructed. V. Experimental Procedure Part 1. Identification of an Unknown Compound by Water of Hydration Determination 1. Weigh and record the mass of a clean and dry crucible with lid using a top loading balance. Obtain an unknown compound. The unknown compound may be MgSO4•nH2O, CuSO4•nH2O, MnSO4•nH2O, or Na2CO3•nH2O. 2. Weigh and record about 1 g of the unknown compound directly into the crucible. 3. Secure an iron ring on a ring stand, making sure to leave enough space underneath the iron ring for a Bunsen burner. 4. Place a clay triangle on top of the iron ring. 5. Place the crucible containing the sample on the clay triangle. Make sure the crucible lid is placed ajar on the crucible. 46 6. Place a Bunsen burner underneath the iron ring and gently heat the sample for 5 minutes. 7. Increase the intensity of the flame and heat for an additional 10 minutes. The high intensity flame should cause the bottom of the crucible to glow reddish in color. 8. Allow the crucible to cool for at least 10 minutes. 9. When the crucible is no longer hot, weigh and record the mass of the crucible with lid and sample. 10. Heat the crucible with lid and sample again for an additional 5 minutes. 11. Allow the crucible to cool, and weigh and record the mass. 12. Repeat the heating and cooling process until constant mass is reached. 13. Determine the chemical formula of the unknown compound. Part 2. Identification of an Unknown Compound by Stoichiometric Mass Correlations 1. Weigh and record the mass of a clean and dry crucible with lid using an analytical balance. 2. Obtain an unknown compound. The unknown compound may be NaHCO3, Na2CO3, KHCO3, or K2CO3. 3. Weigh and record about 0.4 g of the unknown compound directly into the crucible. 4. Secure an iron ring on a ring stand, but make sure to leave enough space underneath the iron ring for a Bunsen burner. 5. Place a clay triangle on top of the iron ring. 6. Place the crucible containing the sample on the clay triangle. Make sure the crucible lid is placed ajar on the crucible. 7. Place a Bunsen burner underneath the iron ring and gently heat the sample for 5 minutes. 8. Increase the intensity of the flame and heat for an additional 10 minutes. The high intensity flame should cause the bottom of the crucible to glow reddish in color. 9. Allow the crucible to cool for at least 10 minutes. 47 10. When the crucible is no longer hot, weigh and record the mass of the crucible with lid and sample. 11. Repeat the heating and cooling process until constant mass is reached. (If the sample is sodium bicarbonate, it would decompose into sodium carbonate, water, and carbon dioxide.) 12. Slowly add 6 M HCl, one drop at a time, to the sample inside the crucible. 13. After each drop swirl the mixture until there is no appearance of a chemical reaction before adding another drop. 14. Continue adding drops and swirl until all the solids dissolves, but do not exceed a total of 30 drops. 15. Gently heat the crucible with the lid very slightly ajar for about 10 minutes. It is important that the flame is set at a very low intensity to prevent any HCl excess from boiling out of the crucible. 16. After 10 minutes, turn off the flames and check to see if the sample appears dry. 17. Continue to gently heat if the sample is not dry. If the sample appears dry, set the flame at a high intensity and heat for an additional 10 minutes. The high intensity flame should cause the bottom of the crucible to glow reddish in color. 18. Allow the crucible to cool for at least 10 minutes. 19. When the crucible is no longer hot, weigh and record the mass of the crucible with lid and sample. 20. Repeat the heating and cooling process until constant mass is reached. 21. Using the masses obtained, determine the unknown compound. VI. Questions 1. In part 2 of the experiment, a balanced equation can be written for the decomposition of sodium bicarbonate upon heating: 2 NaHCO3(s)  Na2CO3(s) + H2O(g) + CO2(g) If 2.0 grams of sodium bicarbonate was added into a crucible and heated with the lid ajar to constant mass, how many grams of product will remain? 48 VII. Discussion Questions 1. In part 2 of the experiment, what would happen to the data if not enough hydrochloric acid is added to dissolve the solid? VIII.References 1. How Frozen Fuel Works. Website accessed on November 14, 2010: http://science.howstuffworks.com/environmental/green-tech/energyproduction/frozen-fuel.htm. 2. Murov, S., Experiments in General Chemistry, Identification of a Compound by Mass Relationships, (2006) 5th Ed., Thomson Brooks/Cole 3. Randall, J., Advanced Chemistry with Vernier, The Determination of the Percent Water in a Compound, (2007) 2nd Ed., Vernier Software & Technology, Beaverton, OR 49 ...
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Attached.

Running head: UNKNOWN COMPOUND AND MASS CORRELATIONS

Experiment 5: Unknown Compound and Mass correlations
Pre-Lab Report
Student’s Name
Institution
Date of Submission

1

UNKNOWN COMPOUND AND MASS CORRELATIONS

2

Pre-Lab Report
Purpose of the Experiment: The purpose of this experiment will focus on the study of hydrates.
Also, the experiment will involve the study of the percentage of water in a compound. In doing
so the experiment will be conducted in two parts that is part 1 and Part 2
Materials: The following materials will be used during the experiment.
Part 1;
1. MgSO4•nH2O
2. CuSO4•nH2O
3. MnSO4•nH2O
4. Na2CO3•nH2O

Part 2;
1. 6 M HCl
2. NaHCO3
3. Na2CO3
4. KHCO3
5. K2CO3
Procedure:
Part 1: Identification of an Unknown Compound by Water of Hydration


This will be the first part of this experiment.



First, the mass of cle...

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