0.3 Colorful copper  (Page 4/2)

Experiment 3: colorful copper

Objective

• To observe, describe and explain the products of a number of chemical reactions of the transition metal copper.
• To use several techniques in recovering copper from solution.
• To understand the concept of percent yield.

Grading

• Pre-lab (10%)
• Lab Report (80%)
• TA points (10%)

Before coming to lab…

• Read the lab instructions
• Complete the pre-lab, due at the beginning of the lab.

Introduction

Copper is a soft metal with a characteristic color that we often call "copper-colored", a bright orange-brown color. Copper is relatively inert chemically; it does not readily oxidize (react with oxygen) in air and is react when exposed to simple mineral acids such as sulfuric or hydrochloric acid. One of the most popular uses of copper is in the computer industry where it is used to build the integrated circuits and chips. It is beginning to replace aluminum for this application due to the resulting decrease in costs. Copper is also good at conducting electricity because it has so many free electrons that allow for the efficient flow of current.

In this lab you will preform a series of reactions with copper and observe a variety of distinctive and colorful products. Most chemical syntheses involve the separation and then purification of a desired product from unwanted side products. The common methods of separation are filtration, sedimentation, decantation, extraction, chromatography and sublimation.

This experiment is designed as a quantitative evaluation of your laboratory skills in carrying out a series of chemical reactions, purification and analyses with copper. You will employ two fundamental types of chemical reactions, namely oxidation-reduction (redox) and metathesis (exchange) reactions to recover pure copper with maximum efficiency. The chemical reactions involved are the following.

Redox: $\text{Cu}(s)+{\text{4HNO}}_3(\text{aq})\to \text{Cu}({\text{NO}}_3{)}_2(\text{aq})+{\text{NO}}_2(g)+{\text{2H}}_{2}O(l)$ [1]

*Metathesis: $\text{Cu}({\text{NO}}_3{)}_2(\text{aq})+2\text{NaOH}(\text{aq})\to \text{Cu}(\text{OH}{)}_2(s)+{\text{2NaHO}}_3(\text{aq})$ [2]

Dehydration: $\text{Cu}(\text{OH}{)}_2(s)+\text{heat}\to \text{CuO}(s)+H_{2}O(g)$ [3]

Metathesis: $\text{CuO}(s)+H_2{\text{SO}}_4(\text{aq})\to {\text{CuSO}}_4(\text{aq})+H_{2}O(l)$ [4]

Redox: ${\text{3CuSO}}_4(\text{aq})+2\text{Al}(s)\to {\text{Al}}_2({\text{SO}}_4{)}_3(\text{aq})+\text{Cu}(s)$ [5]

Each of these reactions proceeds to completion and in the case of a metathesis reaction, completion is reached when one of the components is removed from the solution in form of a gas or an insoluble precipitate. This is the case for reactions [1], [2], and [3]. In reactions [1]and [3] a gas is formed and in reaction [2]an insoluble precipitate is formed (Reaction [5] proceed to completion because copper is more difficult to oxidize than aluminum).

Metathesis (Exchange) Reaction Defined in Chapter 4 of your textbook: 'One of the following is needed to drive a metathesis reaction: the formation of a precipitate, the generation of a gas, the production of a weak electrolyte, or the production of a nonelectrolyte.'

Oxidation-Reduction (Redox) Reactions. This involves the loss of electrons from one components and an addition of electrons to the other component as the reaction proceeds (the are transferred from one atom to another). The component that loses electrons is said to be oxidized; the one that gains electrons is then reduced. Such reactions are important for the production of electricity due to the energy produced from an electron transfer.