Introduction+to+Voltaic+Cells

Introduction to Voltaic Cells

Before doing this exercise you need to know how to assign oxidation states and write oxidation and reduction half reactions. So let's review:

Oxidation-reduction reactions occur when electrons are transferred from one element to another. The species **gaining** the elections is **reduced** and known as the **oxidizing agent**. The species **losing** the electrons is **oxidized** and known as the **reducing agent**.

Example: 2AgNO3 (aq) + Cu (s) --> Cu(NO3)2 (aq) + 2Ag (s) Oxidation states of reactants: Ag = +1 N = +5 O = -2 Cu = 0 Oxidation states of products: Ag = 0 N = +5 O = -2 Cu = +2

So... because the oxidation state of silver decreases it is reduced and the oxidation state of copper increases it is oxidized. The oxidation states in the nitrate ion don't change because it is the spectator ion.

Oxidation half-reaction: 2Ag+ + 2e- --> 2Ag Reduction half-reaction: Cu --> Cu2+ + 2e-

You have to keep the coefficients because equal amounts of electrons have to be received and given in order for the reaction to be balanced.

Now you try!

1) Write the oxidation states for elements the following compounds: a) sodium peroxide b) strontium oxide c) nitrogen d) water e) calcium hydride f) phosphorus trichloride g) methane

2) Copper (II) sulfate reacts with iron. a) Write a balanced equation for this reaction. b) Classify this type of reaction. c) What are the oxidation states of the reactants? d) What are the oxidation states of the products? e) Which substance is oxidized (oxidation state increases)? f) Which substance is reduced (oxidation state decreases)? g) Write a half-reaction for the oxidation (remember... it's when you show the element losing electrons). h) Write a half-reaction for the reduction (remember... it's when you show the element gaining electrons).

3) Magnesium metal reacts with hydrochloric acid. a) Write a balanced equation for this reaction. b) Classify this type of reaction. c) What are the oxidation states of the reactants? d) What are the oxidation states of the products? e) Which substance is oxidized (oxidation state increases)? f) Which substance is reduced (oxidation state decreases)? g) Write a half-reaction for the oxidation (remember... it's when you show the element losing electrons). h) Write a half-reaction for the reduction (remember... it's when you show the element gaining electrons).

Now check your work by going to the SHARED drive SSubotic and looking in the SmartBoard presentation Oxidation States.

Now... read your packet and go to the following site:

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