Tuesday, October 21, 2008
Tues-Day 2
AP Chem- we discussed the meaning of balanced chemical equations with which we can determine the limiting and excess reactants given actual (mass or mole) quantities of said reactants.
Balance chemical equations only and ever give MOLE ratios or reactants and products, NEVER mass ratios of reactants and products.
For example, from the balanced equation, 2 moles of H2 react with 1 mole of O2 to form 2 moles of H2O. This CANNOT mean that 2 grams of H2 react with 1 gram of O2 to form 2 grams of H2O due to the great difference in molecular masses of H2 and O2. In fact, as you can see and measure, 4.032 g of H2 reacts per 32.0 grams of O2 to form 36.032 grams of water, which is not a 2 to 1 to 2 mass ratio.
We then did a problem in which we converted grams of each reactant to moles of each reactant, plugged those molar quantities right into the balanced equation to see which reactant had the lowest mole ratio; this reactant is the limiting reactant, which we use to determine the theoretical maximum number of moles or grams of each product formed. We then determine the quantity of UNreacted/left over excess reactant.
Given ACTUAL experimental quantities of products (called the "yield"), one can determine the "percent yield" for a given particular experiment i.e. if 120.00 g of product A were predicted from the limiting reactant and balanced equation BUT only 90.00 g of product A were formed (due to side reactions, etc.), the percent yield for that particular experiment is 90.00/120.00 or 75.00%.
Your hydrate lab is due tomorrow; we will start a new stoichiometry lab tomorrow, also.
Bio 6- by using actual electron microscope photographs of cells in various phases of mitosis and cytokinesis, we clarified and reviewed the steps involved in cell division.
We then discussed one of the differences in plant vs. animal cell division: animal cells undergo cytokinesis by "pinching in" the cell membrane (forming a "cleavage furrow") until there are two separate cells; plants form separate cells by forming a "cell plate" that forms a new cell wall and membrane between the two separate cells.
Bio 7/8- we finished the onion cell osmosis and "cell membrane" transport/use of indicators lab.
We will continue with mitosis and cytokinesis tomorrow.
Balance chemical equations only and ever give MOLE ratios or reactants and products, NEVER mass ratios of reactants and products.
For example, from the balanced equation, 2 moles of H2 react with 1 mole of O2 to form 2 moles of H2O. This CANNOT mean that 2 grams of H2 react with 1 gram of O2 to form 2 grams of H2O due to the great difference in molecular masses of H2 and O2. In fact, as you can see and measure, 4.032 g of H2 reacts per 32.0 grams of O2 to form 36.032 grams of water, which is not a 2 to 1 to 2 mass ratio.
We then did a problem in which we converted grams of each reactant to moles of each reactant, plugged those molar quantities right into the balanced equation to see which reactant had the lowest mole ratio; this reactant is the limiting reactant, which we use to determine the theoretical maximum number of moles or grams of each product formed. We then determine the quantity of UNreacted/left over excess reactant.
Given ACTUAL experimental quantities of products (called the "yield"), one can determine the "percent yield" for a given particular experiment i.e. if 120.00 g of product A were predicted from the limiting reactant and balanced equation BUT only 90.00 g of product A were formed (due to side reactions, etc.), the percent yield for that particular experiment is 90.00/120.00 or 75.00%.
Your hydrate lab is due tomorrow; we will start a new stoichiometry lab tomorrow, also.
Bio 6- by using actual electron microscope photographs of cells in various phases of mitosis and cytokinesis, we clarified and reviewed the steps involved in cell division.
We then discussed one of the differences in plant vs. animal cell division: animal cells undergo cytokinesis by "pinching in" the cell membrane (forming a "cleavage furrow") until there are two separate cells; plants form separate cells by forming a "cell plate" that forms a new cell wall and membrane between the two separate cells.
Bio 7/8- we finished the onion cell osmosis and "cell membrane" transport/use of indicators lab.
We will continue with mitosis and cytokinesis tomorrow.
# posted by C @ 1:52 PM 
