Water of Crystallization and Empirical Formula of a Hydrate

Introduction Introduce the background material necessary in order to understand the experiment. State the purpose of the investigation in the form of a sentence – do not phrase it as a question.

When crystallization occurs due to evaporation of the water from an aqueous salt solution, water molecules may become incorporated into the structure of the crystal. When this occurs, the resulting salt is known as a hydrate. A hydrate may have any number of water molecules incorporated into its structure, but the ratio of water molecules to salt units will always occur in simple whole number ratios. By heating the hydrated salt, the water molecules can be driven off by evaporation, producing the anhydrous form of the salt. The purpose of this investigation is to dehydrate a hydrated salt of copper (II) sulphate, CuSO4·n H2O, in order to determine its chemical formula.

Apparatus and Materials Apparatus refers to the equipment used, where materials refers to the chemicals/substances. Only list items that you used in the experiment, as you may have been asked to deviate from the items listed in your lab sheet.

Apparatus Materials apron 4 grams of CuSO4·x H2O eye protection crucicle and lid crucible tongs iron ring ring stand bunsen burner wire gauze x 2 centigram balance

Procedure

1. A clean, dry crucible and lid were placed on wire gauze in a ring stand, with the lid slightly ajar. 2. Using the Bunsen burner, the crucible and lid were heated strongly for three minutes. 3. The crucible and lid were removed from heat using the tongs, and placed on another piece of wire gauze to cool. 4. The hydrate was placed in the crucible, and massed. 5. With the lid slightly ajar, the crucible and its contents were heated gently for approximately 15 minutes. 6. The crucible and contents were removed from heat and allowed to cool on wire gauze. 7. The mass of the crucible, lid and contents were recorded. 8. The procedure above was repeated once more. 9. The copper (II) sulphate was disposed of, and lab stations were cleaned. Observations Unless you are instructed to do otherwise, do not include indirect observations in your observation section. This means calculations derived from your raw data. Only include the observations (qualitative and quantitative) that you observed during the lab itself.

Object Mass (g) Qualitative observations crucible + lid (empty) 25.77 crucible, lid + hydrated salt 29.80 Salt is a dry, blue crystal crucible, lid + anhydrous salt 28.35 Salt is a dry, whitish-gray powder 28.35(Trial 1 ) (Trial 2) Analysis You must show all work (formulas used, subbing in), and clearly separate your steps so that it is easy to interpret. If you are doing multiple similar calculations (e.g., finding number of moles from molar mass), you only need to sho w one full calculation with the formula.

1. Calculate the mass of anhydrous salt (residue after driving off the water).

2. Calculate the moles of anhydrous copper(II)sulfate.

3. Calculate the mass of the water driven from the hydrate.

4. Calculate the number of moles of water driven off.

5. Calculate the mole ratio of water to anhydrous salt.

6. The reaction for the experiment is: where n = numbers of moles CuSO4 * nH2O (s) à CuSO4 (s) + n H2O

______What is “n”’s value

Calculations Table Mass of anhydrous solid Grams Moles of anhydrous solid Moles Mass of water driven from solid Grams Moles of water driven from solid Moles Mole ratio of water to anhydrous solid Mole / Mole Using the data below find formulas for MgSO4 * n H2O, MgxOy, NaxOy, and AlxOy.

MgSO4 * n H2O MgxOy NaxOy AlxOy Crucible and lid 24.30 g Crucible and Lid 38.73 g 24.350 g 28.90 g Crucible, Lid, Hydrate 25.28 Metal 38.95 g 25.73 g 29.44 g Crucible, Lid, Anhydrous 24.78 g Metal Oxide 39.08 g 26.21 g 29.92 g

Discussion Discuss how you analyzed your data, and the results of your analysis. Do not be overly verbose; the point is to provide a concise overview of your analysis so it is not necessary to include a description of every single step. The steps you undertook should be apparent in your analysis section. Identify any possible sources of error. You may also want to suggest improvements to the lab procedure that would help minimize error. Again, use past passive tense – never speak in the first person. When in doubt, state ev ery thi ng a s a fa ct (n ev er u se “I th in k. .. ” ).

After two trials of dehydrating the CuSO4·x H2O, the mass was found to be constant and so no more trials were performed. The arithmetic mean of the two trials was used as the experimental value when analyzing the data. The mole ratio of anhydrous CuSO4 to H2O was determined to be approximately 1:5, allowing identification of the hydrated salt as CuSO4·5 H2O. The actual mole ratio of CuSO4 : H2O was 1 : 4.97. Possible sources of error include human error during the process of transferring and measuring the salt. The mole ratio, however, was sufficiently close enough to simple whole numbers such that the chemical formula derived from the dehydration analysis can be deemed accurate.

Conclusion Simply restate the purpose of the lab, provide a concise summary of the lab procedure, and restate the conclusion of your analysis. Never introduce any new information in the conclusion; this should all have been established in your introduction or discussion, if necessary. There is no need to restate all the background information from your introduction; avoid redundancy. If anything went horribly wrong to the point where no valid conclusion can be reached from your data, you should mention it here as well as in your discussion.

The purpose of this lab was to determine the number of water molecules incorporated into the structure of CuSO4. Through dehydration analysis, the chemical formula of the hydrated salt was determined to be CuSO4·5 H2O.

Final points on organization: · Put all sections in the correct order · Use proper grammar and spelling · Subscripts · Data tables that are redundant or difficult to interpret will cost you marks · Never split up data tables/steps of analysis on separate pages. Use a page break if you have to – a little blank space is better than splitting elements up. · D o no t u se th e wo rd “ rev ea l /rev eal ed” . Try “id en ti f y” o r “d etermi n e” . · No ti ce th e wo rd “ co n ci se” wa s u sed sev era l ti mes. BE CONCI SE! !! !