2/1/11

HAPPY TWO DAY SNOW DAY EVERYONE!

Announcements: There will be a quiz tomorrow reviewing Stoich with Density.
**Remember** If you get 100% on 5-7 quizzes, you will get extra credit points so study hard.

Homework: Finish page 23 and 24

In class we reviewed Stoich. Page 20, "Stoich 3" was our homework but it was kind of hard because it involved density. So in class we also started to learn Stoich with Density (page 23). Mr. Paek taught us how to convert using density like milliliters per grams. A good example of a tough problem that might be on the quiz is shown below (since I can't upload pictures, I just typed it up).


// = FRACTION BAR

EQUATION: C2H6O + 3O2 ---> 2CO2 + 3H2O

2. c) If the density of O2 is 0.00143 g/ml, what mass of ethanol will be needed to react with 950 ml of O2?

950 ml * .00143g of O2 // 1 ml of O2 * 1 mol of O2 // 32g of O2 * 1 mol of ethanol // 3 mol of O2 * 46g of ethanol// 1 mol of ethanol = .65g of ethanol


*** Things to remember:
1. If it says g/ml, that means you start with one of them (in ^^ that case, ML) and put the other unit (^^ Grams) on top.
2. Make sure your units always cancel out. If you have Grams on top, you have to have grams on bottom in the next one.
3. Use the equation to look at how many moles each unit will need to react with the one above or below it
4. Always write the elements name (for ex: 3 mols of >C2H6O<) after how many units it is, UNLESS you want to lose points on a quiz :)


You can refer back to previous posts for more examples on how to do normal stoich without density.