Chapter 9 (Kelly Pocian)

Kelly Pocian

Throughout chapter 8, we learned about the process of Stoichiometry and its relationship to the whole number ratios of chemical reactions. Chapter 9, however, was focused more on the applications of stoichiometry, or how we would use this process in real life, along with a couple more terms that are related to this process. Through worksheets, labs, and a whole ton of questions we answered through our studies.

We began this unit with the “Volume of a Mole of Gas” lab, in which we calculated the volume and took any other corresponding measurements of the Hydrogen gas produced through the reaction of a strip of Magnesium and Hydrochloric acid. We were then asked to find the following:

-The partial pressure of the Hydrogen gas

-its volume at standard temperature and pressure (STP)

-its mass

-how moles of Magnesium were used

-the number of moles of Hydrogen gas in our sample

-the volume of one mole of Hydrogen gas at STP

-and determine the percent error of our experimental value

All of this we calculated using what we had learned from past lessons (such as how to calculate partial pressure, the use of BCA and PVnT charts, mole ratios,and percentages) and knowledge that we had just recently acquired (such as the ideal gas law)

The “Ideal Gas Law” is an equation combining almost everything we’d ever need to measure for a gas, or the “ideal” gas. The Ideal Gas equation is PV=nRT. P=Pressure in atmospheres (atm), V= volume in liters (L), n= the number of moles of that substance, T= temperature (in Kelvin (K)), and R is the constant that ties all of the different units of measure together (0.0821 L*atm/mol*K). As long as we have enough data to calculate all but one of the variables, we are able to find the extra variable using this equation.

Our next lab or “challenge,” as it was referred to, consisted of calculating how much Carbon Dioxide was needed to fill a Ziplock bag, and how much Sodium Bicarbonate and Citric Acid would be necessary to successfully complete the inflation. In order to calculate the amount (in grams) of reactants needed, we used BCA charts and the Ideal Gas Law Equation.

Our last lesson was on Molarity (or Molar concentration). The main idea of this is how much of a substance (mol) is dissolved in a liquid (L), or grams per liter. Molarity (M) is calculated by taking the number of moles and dividing it by the number of liters it’s mixed into.

In order to expand on this topic and to practice calculations we completed the lab titled “Molarity Analysis of Kool-Aid Concentration.” In this lab we added different amounts of Kool-Aid mix to the same amount of water and then taste tested them. We then proceeded to calculate the molarity of each of the different cups to find out which one had the highest concentration (the one with the most mix!)