Lesson 2.2: The Gain and Loss of Electrons
Completion requirements
Unit A: Chemical Change
Lesson 2.2: The Gain and Loss of Electrons
Check the water pipes in your home. Are they made of copper? Although water pipes may be made of plastic these days, copper has traditionally been used for water pipes as well as for electrical wire.- Read pages 69 to 70 if you are interested in the historical use of copper in Canada.
Copper was likely the first metal to be separated from rock (refined) and used by people. It occurs in a fairly pure form, but in compounds of sulfur or oxygen. Making pure copper requires a chemical reaction that allows copper to take electrons from oxygen to change it from a copper compound into a pure element. This reaction could be represented like this:
The video on the right shows what this may have looked like.
Cu2+ + 2e- ----> Cu
The video on the right shows what this may have looked like.
In this lesson you will learn to understand the movement of electrons, identify oxidation and reduction, and represent oxidation and reduction with half reactions. The first skill is to identify the movement of electrons as ions become ionic compounds.
What transfer of electrons makes the following compounds
Look at the anion, oxygen, which has a charge of 2- . So iron has a charge of 2+. How many electrons were gained or lost to make Fe2+, the ion in iron oxide?
Fe lost 2 electrons to become Fe2+ .
Fe lost 2 electrons to become Fe2+ .
The charge of phosphate is 3-. There are three lithium ions in the compound, so each one must have a charge of 1+. How many electrons were gained or lost to make Li+ ?
One Li loses 1 electron to become Li+
One Li loses 1 electron to become Li+
The charge on sulfur is 2- . Three sulfur ions give a total charge of 6- , so each gold must have a charge of 3+ (2 x 3- = 6+) How many electrons were gained or lost to make Au3+ ?
Au loses 3 electrons to become Au3+
Au loses 3 electrons to become Au3+
- Complete the table on page 71 and check below.
Science 20 Text. Courtesy Alberta Education
- Read "transfer of Electrons" page 71 - 73. Answer the Practice Questions as you go. View the video below left. It would be very useful to make notes on oxidation and reduction. Be sure to give examples, and include the memory aid 'OiL RiG'
- Do practice question #18 on page 74. This is exactly the kind of question you will see again. Check the practice answers below.
- Read "Single Replacement Reactions" and "Redox Reactions" on page 74 and 75. View the short video above right. You should be able to identify the reduction and oxidation half reactions and the spectator ion. Do practice problem # 18 on page 20 (important!) and check your answers below.
Science 20 Text. Courtesy Alberta Education
- Read “2.2 Summary” on page 75 of the textbook. Then, complete “2.2 Questions” # 2 - 5 (6 if needed). These questions are just like questions on the Final Exam. Check your answers below.
Science 20 Text. Courtesy Alberta Education