Hydrated Copper (II) Sulphate Experiment Report

Introduction

The objective of this experiment is to determine the amounts of the component parts of hydrated copper (II) Sulfate. These components are: water, sulfate ions and copper ions. The experiment aims at determining the empirical formula of hydrated copper (II) sulfate. Empirical formula is the smallest numeral ratio of atoms that are in a compound. Gravimetric analysis is the methodology that will be used in determining the empirical formula of copper (II) sulfate. In this methodology, the compound being analyzed is reacted with another substance to form a solid compound. The reaction employed is such that it is possible to know the components of the products.

Three procedures are performed in this experiment and the first one is the analysis of the copper ions. Here, the hydrated copper (II) sulfate is reacted with oxine to form a complex called copper (II). Because we know the makeup of the complex we can get the amount of copper ions that were in the initial sample of the copper sulfate (hydrated).In getting amount of water in the hydrated copper (II) sulfate a sample is heated to drive off all the water. The water present is the difference in mass, if the sample mass is measured before heating and after heating. The third procedure is the scrutiny of sulfate ion in a sample of copper sulfate (hydrated). Here, the hydrated copper sulfate is reacted with barium chloride to form barium sulfate.

Experimental methods

Scrutiny of copper ions by precipitating the hydrated copper (II) sulfate with oxine

Oxine is an 8-hydroxy-quinoline organic compound. When reacted with Cu (II) or other metallic ions it behaves like a monoprotic acid and a metal complex is formed. The composition of the complex formed when hydrated copper (II) sulfate is reacted with oxine is Cu (C₉H₆ON) ₂ with 351.85g/mole formula weight.

The following steps are followed:

1. Approximately 3g hydrated copper sulfate is weighed to the closest milligram.
2. The copper sulfate is dissolved in 100ml of water that is distilled and contained in a big beaker.
3. 5ml of acetic acid (glacial) is added and 1.5g of ammonium acetate is also added.
4. The solution is heated in a hot plate toward approximately 75°C.
5. 3% oxine (in ethanol and water in the ratio 95:5) is added drop wise while stirring awaiting completion of the precipitation and the reagent is in excess. Approximately 17-20 milliliters of the oxine solution are needed for this experiment.
6. For 5 minutes, and at 65-70°C the mixture is heated and then stirred vigorously, after which the precipitate is allowed to settle. If adequate reagent is used the resultant liquid will be orange-yellow or yellow in color.
7. A filter paper is folded and weighed and a beaker is labeled with grease pencil.
8. The filter paper is placed in a glass funnel placed on an Erlenmeyer flask.
9. A large amount of the liquid is decanted into the filter set up. The remaining mixture is stirred and filtered.
10. Using hot water the residue and the beaker are washed.
11. A rubber policeman is used to scrub the beaker.
12. The residue is transferred to a small beaker or casserole which is dry, clean and has been weighed previously.
13. The beaker or casserole is covered with aluminum foil which is perforated and the system is allowed to dry.
14. Weight of product, after drying is used to get the percentage of copper.

Determination of the amount of water in hydrated copper (II) sulfate.

In this experiment, care should be taken because crucibles that are cold and those that are hot look alike.

Steps to be followed are:

1. For 5 minutes a clean, dry crucible is heated on the stand apparatus and then allowed to cool.
2. The crucible is weighed.
3. By a difference of 2g, hydrated copper sulfate is weighed into the crucible.
4. The system is returned on the clay triangle. The lid is kept such that the crucible is partially covered.
5. The crucible is heated gently on a small flame.
6. In the heating process the material is stirred periodically.
7. 15 minutes after heating the system the crucible is covered completely and allowed to cool.
8. The crucible and its contents are weighed after they are cooled and the lid removed.
9. For 5 minutes the system is heated once again and allowed to cool.
10. The crucible is weighed when cool, and still covered.
11. The procedure is repeated until consecutive weighing does not fluctuate by more than a centigram.
12. The data is used to calculate the amount of water in hydrated copper sulfate.

Data and results

1. Part A data
   1. Copper sulfate hydrate: 0.307 grams
   2. Filter paper: 0.806 grams
   3. Weight of product (precipitate):1.296 grams
2. Calculation of the percent of copper ions in hydrated copper sulfate
   1. Mass of Cu in Cu (C₉H₆NO) ₂
   2. M=0.089
3. Part B Data
   1. Crucible Wight: 25.457
   2. Crucible + copper sulfate hydrate: 27.748 grams
   3. Cool crucible Wight: 26.748 grams
   4. Crucible Wight after heating then cooling again: 26.755 grams
4. Calculation of the amount of water in hydrated copper sulfate
   1. Mass of H₂O= 0.702grams
   2. % of H₂O= 35.1%
5. Calculation of the amount of sulfate in hydrated copper sulfate
   1. SO₄ %= 36.07%
   2. The empirical formula of copper sulfate hydrate is Cu SO₄. 5H₂O

Errors in the experiment

1. (Errors when getting the percent of copper ions in copper sulfate.
   1. The calculated percentage of the cation would have increased if he mass of the precipitate had been too high.
   2. The possible reason that too much precipitate might be collected in the lab is the existence of foreign cations for example ferric iron and calcium which are co-precipitated.
   3. If the mass of the precipitate had been too low the percentage of the cation would have reduced.
   4. Some of the possible reason why too little precipitate may be collected in the lab is that the substance to be weighed is not readily removable by filtration
2. Errors when getting the amount of water in hydrated copper sulfate
   1. If the mass of the heated crucible had been too high the calculated amount of water would have reduced.
   2. One reason why the mass of the crucible after heating could be too high is the failure to remove all the water from the hydrate.
   3. If the mass of the heated crucible had been too low the calculated percentage of water would have increased.
   4. A reason why the mass of the crucible after heating could be too low is decomposition of the hydrated copper (II) sulfate by overheating.