For each of the following oxidation–reduction reactions,...

For each of the following oxidation–reduction reactions, identify which element is being oxidized and which is being reduced. $$ \begin{array}{l}{\text { a. } \mathrm{Ca}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s, a q)+\mathrm{H}_{2}(g)} \\ {\text { b. } \mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \rightarrow 2 \mathrm{HF}(g)} \\ {\text { c. } 4 \mathrm{Fe}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)} \\ {\text { d. } 2 \mathrm{Fe}(s)+3 \mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{FeCl}_{3}(s)}\end{array} $$

For each of the following oxidation–reduction reactions, identify which element is being oxidized and
which is being reduced.
$$
\begin{array}{l}{\text { a. } \mathrm{Ca}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s, a q)+\mathrm{H}_{2}(g)} \\ {\text { b. } \mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \rightarrow 2 \mathrm{HF}(g)} \\ {\text { c. } 4 \mathrm{Fe}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)} \\ {\text { d. } 2 \mathrm{Fe}(s)+3 \mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{FeCl}_{3}(s)}\end{array}
$$

Key Concepts

Oxidation–Reduction (Redox) Reactions

Redox reactions are chemical processes involving the transfer of electrons between species. In these reactions, one reactant loses electrons (oxidation) while another gains electrons (reduction). Understanding redox reactions is fundamental to predicting reaction outcomes and balancing chemical equations in many fields, including inorganic chemistry, biochemistry, and industrial processes.

Oxidation

Oxidation refers to the process by which an element loses electrons, leading to an increase in its oxidation number. This loss of electrons makes the element more positively charged, and it is often paired with the reduction of another species that gains these electrons. Recognizing oxidation steps is crucial for analyzing redox reactions and determining the direction of electron flow.

Reduction

Reduction is the process in which an element gains electrons, resulting in a decrease in its oxidation number. Gaining electrons makes the element less positively charged or more negatively charged, balancing the electron loss from the oxidized species. The concept of reduction is integral to understanding how substances interact and transform in redox reactions.

Oxidation Numbers

Oxidation numbers or oxidation states are assigned to atoms to keep track of electron distribution in compounds and reactions. By comparing the oxidation states before and after a reaction, one can determine which species have been oxidized (increase in oxidation number) and which have been reduced (decrease in oxidation number). The proper assignment of oxidation numbers is an essential tool in systematically analyzing redox processes.

Transcript

00:01 Okay, so in this video we're going to go over reduction in oxidation.

00:06 Again, labeling our oxidation states very carefully and then identifying our reduction in oxidation based on those states.

00:14 And so for the first example here, we have calcium solid, water liquid going to calcium hydroxide and hydrogen gas.

00:21 So we're going to start with calcium, solid.

00:24 We know that's a zero.

00:25 And breaking down this water here, we have a minus two charge on that oxygen, a plus one charge.

00:31 On that hydrogen, again, for completion's sake, times two.

00:36 It's going to lead us to a plus two overall to balance out that oxygen.

00:40 And then moving right along to the right here.

00:43 So we know that hydroxide overall is associated with a negative one charge.

00:49 And since we have two of them, we have a minus 2 charge.

00:56 And to break that down further, we know that oxygen is still minus 2, hydrogen is still plus 1.

01:04 And then here, calcium is a plus 2 charge.

01:08 Again, it's the second group of the periodic table.

01:11 Calcium has that plus 2 ionic charge.

01:14 And h2 gas, we know, is always going to be a 0.

01:17 And so then to go back, identify our reduction in our oxidation, we notice that calcium has a plus 2.

01:23 Charge over here, but it started as a zero.

01:27 That is a loss of electrons, and so we know that's our oxidation.

01:31 And then over here, we see what's our other atoms involved? well, we have a hydrogen gas over here, and we know that this is a zero, but it started as a plus one.

01:41 And so that is going to be our reduction in charge, and therefore be our reduction.

01:46 Awesome.

01:47 And we noticed that this oxygen atom over here stayed the exact same.

01:52 It started as a minus two.

01:54 And it stayed as a minus 2 over here.

01:58 So we don't need to worry about oxygen in this case.

02:01 All right, moving right along.

02:03 We have hydrogen gas, fluorine gas goes to two hydrofluorine.

02:06 So we have a zero over here, and we have another zero over here.

02:11 And then this ionic compound hydrogen fluorine.

02:14 So we have hydrogen is always a plus one.

02:17 Fluorine is always a minus one.