Hydrated Compounds

 

Hydrated compounds have water as part of their chemical formula. Anhydrous compounds have had their water removed from them. The formula of a hydrate is written a bit differently. An example of this is

The following video provides a good explanation on how to solve hydrate problems. https://www.youtube.com/watch?v=KCuYQ3ayFNM Practice problems can be found at http://www.chemteam.info/Mole/Determine-formula-of-hydrate.html

 

% Composition and Empirical/Molecular Forms

We discussed percent composition in class last week. These problems are solved by simply taking the mass of each element in the compound and dividing it by the mass of the entire compound and then multiplying it by 100. You can then use the percent composition of that element and calculate the mass of it in a certain size sample by multiplying the % comp by the mass of the sample. An example of this can be found in the following video. https://www.youtube.com/watch?v=lywmGCfIUIA
We also talked about empirical form vs. molecular form. Empirical formula is the lowest number ratio, but molecular gives the actual number of atoms in the compound. Below is a chart to help show the differences.

To find the empirical formula we used this process: 

Examples of this can be found on the following link. http://www.chemteam.info/Mole/EmpiricalFormula.html

Using empirical formula you can find the molecular formula by taking gram formula mass and dividing it by the empirical formula mass to get a whole number, and then distributing it to the empirical formula. Some practice problems can be found on the following links. http://www.chemteam.info/Mole/Empirical-MolecFormulas.html and http://chemistry.about.com/od/chemistry-test-questions/tp/Molecular-Formula-Practice-Test-Questions.htm



Formula of a Hydrate lab

We completed a lab on Monday in class working with hydrates and anhydrous compounds. To start, we measured out about a thumb width of hydrated crystals into a test tube and took its mass by weighing by difference. Using and bunson burner, we heated the test tube gently for a few minutes and then on medium heat for 5-10 minutes or until it was completely white and allowed it to cool before taking it's mass once more. We reheated the test tube again to ensure all water was driven off and took the mass one last time after it was cooled. Using the data we determined the formula of the hydrate.

The Mole

The mole is expressed as 6.02 × 10²³ and is a unit of measurement. These problems can be solved using the mole road map:

When converting from mass to moles or vice versa, use atomic mass off the periodic table for elements and molar mass for compounds. The following link incudes a video for more explanation and examples of using the road map: https://www.youtube.com/watch?v=mBVL0PHPrhg