LAB # 6 MASS RELATIONSHIPS IN CHEMICAL CHANGES October 22, 2012 Patricia D Partner: Mike C MASS RELATIONSHIPS IN CHEMICAL CHANGES PURPOSE The purpose of this experiment was to study the fundamental idea that in chemical reactions, or changes, all particles of one substance will have the same average mass, but particles of different substances will have average masses different from each other. These changes occur in ratios, and rarely occur in simple whole numbers.
When a chemical reaction occurs, how do the masses of reactants and products compare? In this experiment we will be making a comparison between the masses of reactants and products and the number of moles of reactants and products.
PROCEDURE Polish the zinc strip using steel wool and then determine its mass. Allow the strip to sit in lead acetate for approximately an hour and observe the changes in the zinc strip.
The zinc starts to accumulate particulate matter (lead particles) on its surface.
This is cause by the chemical reaction that occurs between the lead acetate and the zinc strip. The strip is then rinsed in water and acetate and then dried. The particles of lead are scraped off the strip and dried thoroughly and then weighed. The mass is recorded and the zinc strip is polished again and weighed. Calculations are then done to determine the amount of zinc dissolved and the amount of lead formed. Convert the masses of the reactants and products to moles using their molar masses.
Using the mole ratios from the balanced chemical equation, it is possible to determine how much material should react or be produced. These calculated values are then compared to the observed values. DATA ATTACHED: DISCUSSION: In a balanced equation, the total mass of the reactants is equal to the total mass in the products. By using mole-mole factors, you can predict the moles of the product that can be produced. In this experiment we attempted to show the mass relationship in a chemical change between zinc and lead acetate.
This mass relationship between Zinc and Lead Acetate in this experiment in moles was equal to the coefficients of 1:1. Theoretically, we should have 1 mole of lead formed for every mole of zinc dissolved. However, due to extraneous circumstances and our inability to perform the experiment under the conditions set forth, the results that were calculated are not what they should be. The moles of lead produced were 3. 2 times that of the moles zinc dissolved.
It is my hypothesis that because the zinc that was left in the drawer for 2-3 weeks open to air, it had oxidized with the oxygen in the room and caused the end product of lead to be more than it should’ve been. This experiment was an example of a single replacement reaction in which the element zinc reacted with the compound lead acetate to form zinc ion and lead. According to the calculation, 0. 390 g Pb should have been produced. See below. 1. 23 g Zn x 1 mole Zn/65. 41 g Zn x 1 mole Pb/1 mole Zn x 207. 2 g Pb/1 mole Pb = . 390 g Pb
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