Monday, October 25th

In chemistry today, we started out by receiving our grades. Mr Henderson also reminded us of our Test on Thursday along with our delicious bookmark which is due at the end of the unit. Then we moved on to our lesson of the day which was mass composition and empirical and molecular formulas. Our lesson for today was on the packet page 13. We started out by finding the molecular or empirical formula’s of certain compounds with a given molar mass. As an example in the compound Octane, the molar mass was 114.2 g/mol, and the molecular formula was given to be C8H18. Mr. Henderson then explained that the empirical formula was C4H9 because it was the simplest ratio of the molecular formula.

In a second example, we were given the compound Benzene and the molar mass was 78.1 g/mol. The empirical formula CH was given and there are many possibilities for a molecular compound from this formula, so the Mr Henderson explained how you can find the molecular formula through the molar mass. For this problem we found that the mass of Benzene was six times that of the empirical formula, so therefor the molecular formula would be C6H6.

We then did a word problem together where we had to determine the empirical and molecular formula of an unknown carbohydrate when given the percent ratios of the elements and the molar mass. We solved this by assuming that that there was 100.00g of this substance, then we multiplied each of the percentages by their molar masses and from this we got the empirical formula which we compared with the molar mass to get the molecular formula.

Finally we finished the class with the Formula of a Hydrate Lab. In this lab we had to determine the chemical formula of the hydrate of copper sulfate by weighing the copper sulfate before and after we burned all the moisture out of it.