redox reaction

Homework one

1)Our first metal is a chunk of solid calcium metal. When we place it in distilled water, we observe a vigorous chemical reaction. Bubbles of hydrogen gas are created, the calcium dissolves, and the resulting solution tests as strongly basic (which tells us that hydroxide is now present at high concentration). 

We also place it in a highly acidic solution, and see a vigorous reaction there as well. 

Select a balanced ionic equation that describes the reaction in water, remembering that both mass and charge have to be balanced for a reaction to be correct. 

2) For each element in the above reaction, select the oxidation number both before (reactant side)  and after (product side) the reaction. 

Calcium metal 

-1

+2

0

+1

-2

Calcium ion

1

+2

0

+1

-2

Hydrogen in water 

1

+2

0

+1

-2

 

Hydrogen in hydrogen gas

1

+2

0

+1

-2

hydrogen in hydroxide

1

+2

0

+1

-2

Oxygen in water 

1

+2

0

+1

-2

Oxygen in hydroxide

1

+2

0

+1

-2

3) Based on the oxidation numbers and how they changed, identify the reducing agent and the oxidizing agent in the reaction.

-Oxidizing Agent

-Reducing Agent

In addition, say what happened to each element as it became a product:

-Calcium to calcium ion

-Hydrogen in H2O to hydrogen in hydrogen gas

-Hydrogen in H2O to hydrogen in hydroxide

-Oxygen in H2O to oxygen in hydroxide

4)

In the above reaction, which element gave up electrons?

-oxygen

-calcium

-hydrogen

Which element received the electrons?

oxygen

-calcium

-hydrogen

In the balanced chemical equation, how many total electrons were transferred?

1 moles

2moles

3moles

4 moles

0 moles

5) Our next metal is a chunk of solid zinc metal.

When we put it in water, no reaction happens.

But if we put it in the strongly acidic solution, it reacts with the hydronium ions in the solution to generate bubbles of hydrogen gas, and the zinc dissolves into solution. Testing the solution afterward shows that it is no longer acidic, but is now a neutral solution. 

Select the correctly balanced ionic equation that describes this reaction. Remember that it must be balanced for both mass and charge. 

6)

Analyze the oxidation numbers in the correct equation above and identify the following: 

- Oxidizing agent:

-reducing agent:

7) Copper metal is placed in water, and no reaction happens. 

Cu(s) + H2O(l) --> no reaction

Copper metal is also placed in highly acidic solution, and no reaction happens. 

Cu(s) + H3O+(l) --> no reaction

Now we want to compare the reactivity of these three metals, calcium, zinc, and copper. In each case, the metals were potential reducing agents. Based on the reactions we saw in both water and in acidic solution (hydronium ions present)  place them in order from strongest to weakest reducing agents

Strongest reducing agent

Calcium             Zinc             Copper         

Middle reducing agent

Calcium             Zinc             Copper      

   

Weakest reducing agent

Calcium             Zinc             Copper      

8) Based on the short activity series we just created in the above question, predict which of the following two reactions will happen, and which will not happen. 

Here is the activity series you should have created:   Ca > Zn > Cu

Two potential redox reactions written as net ionic equations: 

Reaction A: Zn(s) + Cu2+(aq) --> Cu(s) + Zn2+(aq)  (zinc donates electrons to copper ions in solution)

Reaction B: Cu(s) + Zn2+(aq) --> Zn(s) + Cu2+(aq) (copper donates electrons to zinc ions in solution)

Which reaction will occur as written?      

["Reaction B", "", "Reaction A"]           

Which reaction will not occur? 

["Reaction B", "", "Reaction A"]