CHEM 211 Laboratory - Chemistry and Biochemistry



CHEM 212 Laboratory

Determination of Water of Hydration

Reference: General Chemistry Laboratory Experiments, Suzanne W Slayden, 1999, 3rd edition, Pages 127-130

Data: After you have noted down all the masses, enter your own data into the appropriate Web-based data entry form, using a computer in the lab. In your measurements and calculations, remember to pay attention to uncertainties and significant figures.

Results: Outside of class, retrieve your data in spreadsheet form (along with that of the entire class) from: . Then use Excel to calculate the Weight of hydrated salt, Moles of hydrated salt, Weight of anhydrous salt, Moles of anhydrous salt, Weight of H2O lost, Moles of H2O lost, Moles of water released per mole anhydrous salt, Theoretical weight percent of water in hydrated salt, Actual weight percent water in hydrated salt, and % Error.

Your lab report should include the following in addition to the pages from your lab notebook:

• An Excel sheet “Raw Data” showing the raw data for the entire class (as downloaded).

A typical example of the raw data sheet is shown below:

|DATA ANALYSIS SUPPLEMENT |

|RAW DATA |

| |A |B |

|1 |g_K3FeOx3_3H2O |g_K3FeOx3 |

|2 |12.123 |10.345 |

|3 |11.867 |9.453  |

|Explanation: | | | | | |

|g_K3FeOx3_3H2O = Weight of hydrated salt | | |

|g_K3FeOx3= Weight of anhydrous salt | | |

• A 2nd Excel worksheet “Results” showing the calculated results for each student in the class – each in a separate row. Make sure to show an example calculation for each column. This can be done by copying the equation to a blank cell below the elements in the table. An apostrophe in front of it makes it text instead of an equation. Each table should be formatted as in previous classes with lines separating the table headings from the contents. A line below the contents should also be drawn.

A typical example of the results sheet is shown below:

| |A |

|2 |massH2O lost |mass%H2O |

|A2 |massH2Olost |mass of H2O lost from the compound after heating. Obtained by subtracting the mass after heating |

| | |in the oven from the mass after heating. E.g. A3 in the results table is calculated by |

| | |subtracting the contents of B2 from the contents of A2! |

| | |Sample calculation: =RawData!B2-RawData!A2 |

|B2 |mass%H2O |mass % of water in the hydrated compound. |

| | |E.g. =100*A3/RawData!A2 |

|C2 |molH2Olost |moles of water lost from the hydrated sample |

| | |E.g. =A2/18.01 |

|D2 |molHydratedSalt |moles of the hydrated salt used |

| | |E.g. =RawData!A2/491.25 |

|E2 |molH2O/ molHydrated Salt |Mole of water divided by the mole of hydrated compound |

| | |E.g. =C3/D3 |

|F2 |%Error |E.g. = =100*abs(E2-3)/3 |

• An Excel chart showing a histogram of the distribution of Actual weight percent results. Use equally spaced “bins” chosen to display the “spread” in the class results. Refer to the histogram tutorial on the website.

Printing Tables:

• Large tables should be printed in the landscape mode and sometimes it might be necessary to go to “page setup” and select “Fit to 1 page” to make the page fit on one page.

• Include column and row headings on the printout so that the instructor can more easily understand equations used. This can be done by going to File → Page Setup → Sheet tab → Select “Row and Column Headings”.

Discussion: In your discussion section address the following questions:

o What is a Hydration number?

o How are water molecules bonded to the metal ion or anion? What happens to them on heating?

o What may happen to the crystal structure and color of a compound when it is dehydrated?

o What are the possible sources of error in this experiment? Refer in your answer to the class histogram as well as to your own results.

o Discuss your % Error in terms of errors in measurements. What is the major source of error?

o Using the histogram, discuss how your mole ratio compares with the mole ratio of the rest of the class.

o Discuss the shape of the histogram. What does it tell you about the nature of the error in the class’ measurements?

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