Redox Reactions How to solve balance and identify

Redox Reactions How to solve, balance, and identify your oxidizing and reducing agents

What is a redox reaction? § A redox reaction is where ion charge changes from one side of the reaction to the other. § Very often they are reversible reactions. § In a redox reaction there is always an oxidizing agent and a reducing agent.

How to Balance a Redox reaction § To balance a redox reaction the first thing to be done is to find all of the charges for every element in the reaction. This will tell us which ion’s charge changes. KMn. O 4 + H 2 S + HCl = KCl + Mn. Cl 2 + H 2 O + S +1 +7 -2 +1 -1 +2 -1 +1 -2 0 § Once you have the charges you must decide which ion had a charge that changed. Here we can see that Mn went from +7 to +2 and S went from -2 to 0.

Balancing a Redox Reaction § Once the elements with the changing charges are identified then we can write a simplified ionic reaction for each one. Mn+7 + 5 electrons = Mn+2 S-2 = S 0 + 2 electrons § We can now balance the charges between these two reactions. We must have equal numbers of free electrons. Since we cannot multiply 2 by anything to get 5 we must use the least common multiple, which is 10.

Balancing a Redox Reaction 2 ( Mn+7 + 5 electrons = Mn+2) 5 (S-2 = S 0 + 2 electrons) This produces: 2 Mn+7, 10 electrons, and 2 Mn+2 Also: 5 S-2, 5 S 0, and 10 electrons § We can now take those coefficients and put them into our full equation with the compounds that contained the above ions. 2 KMn. O 4 + 5 H 2 S + HCl = KCl + 2 Mn. Cl 2 + H 2 O + 5 S § This leaves us with an unbalanced equation so we must balance the rest of the equation with coefficients. 2 KMn. O 4 + 5 H 2 S + 6 HCl = 2 KCl + 2 Mn. Cl 2 + 8 H 2 O + 5 S

How do I Identify the Oxidizing and Reducing Agents? § Oxidizing involves losing electrons so the element that lost electrons is the oxidized element. § Reducing involves gaining electrons so the element that gained electrons is the reduced element. § There is an easy mnemonic device to help you remember: LEO the lion goes GER § LEO: Losing electrons oxidizing § GER: Gain electrons Reducing

Oxidized and Reduced Elements § So in our example: Mn was a +7 and became a +2. To write it another way: Mn+7 +5 electrons = Mn+2 Since Mn gained electrons this makes it our reduced element. S was a -2 and became a 0, to write it out: S-2 = S 0 + 2 electrons Since S lost electrons this makes it our oxidized element.

So what is the difference between a oxidized element and an oxidizing agent? § The element that loses the electrons is the oxidized element but the element that gained those electrons is the oxidizing agent and vice versa. § So in our example the S was the oxidized element which means that the Mn was the oxidizing agent, it caused S to lose it’s electrons. § To summarize: S: oxidized element, reducing agent Mn: reduced element, oxidizing agent