Stoichiometric Relationships in Chemical Reactions

Stoichiometric Relationships in Chemical Reactions

By:

Kodee Howell

Lab Partners:

Jessica Duncan

Bailey McGaha-potter

Jazmin Ortega

May 13th, 2015

Abstract-

This experiment focused on the stoichiometric relationships in two reactions.

There were two percent yields in this experiment because there were two separate reactions happening. In reaction one there was a very large error that resulted in an incorrect percent yield for the solid product in reaction one, the percent yield for reaction one was 224%. Reaction two however had no major errors which led to a very efficient reaction and a very accurate percent yield of 93.4%. As shown by the percent yields reaction 2 was much more efficient than reaction 1. Stoichiometry is very important to chemistry because it can help predict the outcome of an experiment. Calculated accurately stoichiometry can be used to predict how much product can be produced from a reaction or how much of a reactant is needed to cause a reaction.

Introduction-

Stoichiometry is a section of chemistry that uses the relationship and/or products in a chemical reaction to determine quantities dated for reactants or products in a reaction. Stoichiometry can be used to find how much of a product can be produced from a certain amount of a reactant or how much of a reactant is needed to produce a given amount of product. Stoichiometric can also be used to find the limiting reactant in a chemical reaction. The limiting reactant in a reaction is the reactant that limits how much product can be made. For example since a chemical formula is like a recipe for a reaction, the limiting reactant is like having enough eggs to make three cakes but only one box of cake mix. This means that any amount of product made us completely dependent on the amount of limiting reactant present. The formula for calculating the limiting reactant is grams of reactant present times one mole of reactant over molar mass of reactant times mole ratio of product to reactant (product/reactant) equals moles of product produced by amount of reactant present. Both reactants are entered into this equation and the reactant that produces the least amount of product is the limiting reactant. The equation to find the theoretical yield of a product of a reaction is moles of product produced by limiting reactant react multiplied by molar mass of product over one mole of product equals theoretical yield of product in grams. (Science in Motion)

Procedure-

To begin the experiment, and reaction one, the mass of four pellets of NaOH was measured o the top loading balance, once measured the pellets were put into a large test tube and the mass recorded in the data table for the first reaction on the hand out. After the mass of the NaOH was recorded, 1 scoop of CuCl2 was measured on the top loading balance and the mass recorded in the data table for reaction one, and then put into the same test tube as the NaOH. Twenty-five milliliters of distillers water was then added to the test tube containing the NaOH and CuCl2, then stirred with a piper rod until all solids in the tube have dissolved. All observations were written in the observation section of the handout. Reaction two was started by recording the mass of one scoop of NaI and then putting it into test tube along with one small scoop of Pb(NO3)2, after the mass of both reactants were recorded in the data table for reaction two. Just as in reaction one, twenty-five milliliters of distiller water was added to the test tube number two and a piper Rod was used to stir until all solids have appeared to dissolve. Then two pieces of filter paper were separately weighed and their mass recorded, then each one folded similarly to a coffee filter. Two Erlenmeyer flasks and funnels were then set up for gravity filtration of both solutions with the filter paper placed inside the cone of the funnel and the funnel tip placed inside the flasks. Both solutions were poured into the funnels to allow the precipitates of the reaction to filter out. During the filtration process the experiment handout allowed an extra twenty-five milliliters of distiller water to be added to each of the test tubes to remove any residue of the products of the reaction left in the test tube. While waiting for gravity to filter the solution the limiting reactant and the theoretical yield were calculated for the precipitant produced from both reactions. Once filtered the precipitants were left to dry overnight and weighed the next day and the percent yield calculated (Science in Motion). 

Results & Discussion- 20/30

Mass Table for Rxn 1:

The first reaction involved combining sodium hydroxide and copper chloride in distiller water to produce aqueous sodium chloride and solid copper hydroxide in a double replacement reaction

Balanced Chemical Equation:

2NaOH (aq) + CuCl2 (aq) -–––> 2NaCl (aq) + Cu(OH)2 (s)

The mass of the four pellets of NaOH was 0.40 grams, but that approximately halfway through the filtration it was realized that there was not enough NaOH for the experiment to be performed correctly, so four more pellets of NaOH were weighed and then added to what was still remaining in test tube number one, bringing the mass to 92g. The mass of the CuCl2 was 1.7045 grams, but since the CuCl2 was in granulated crystal form, some of it stuck to the weight boat it was measured in. After the NaOH, CuCl2 and 25 mL of distiller water had been added together the substance inside the test tube was a light blue in color and the outside of the test tube was warm to the touch. The warmth of the tube shows that the reaction was slightly exothermic, which was caused by the sodium in the sodium hydroxide reacting with water. The precipitants in the test tube for reaction one was a dark blue color. s per allowed by the hand out 25mL of distilled water was poured into the test tube #1 after the solution was poured into the funnel filter to try to get any of the solution that might have stuck to the walls of the test tube. Before the extra four pellets of NaOH were added, the water that passed through the filter was a very light blue, which indicated that there was not enough NaOH present in the solution. After more NaOH was added the water that was filtered out was clear. While the solution was filtering the limiting reactant was calculated using the formula: