Which two of the following reactions are oxidationreduction...

Which two of the following reactions are oxidationreduction reactions? Explain your answer briefly. Classify the remaining reaction. (a) $\mathrm{CdCl}_{2}(\mathrm{aq})+\mathrm{Na}_{2} \mathrm{S}(\mathrm{aq}) \rightarrow \mathrm{CdS}(\mathrm{s})+2 \mathrm{NaCl}(\mathrm{aq})$ (b) $2 \mathrm{Ca}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CaO}(\mathrm{s})$ (c) $4 \mathrm{Fe}(\mathrm{OH})_{2}(\mathrm{s})+2 \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})$

Which two of the following reactions are oxidationreduction reactions? Explain your answer briefly. Classify the remaining reaction.
(a) $\mathrm{CdCl}_{2}(\mathrm{aq})+\mathrm{Na}_{2} \mathrm{S}(\mathrm{aq}) \rightarrow \mathrm{CdS}(\mathrm{s})+2 \mathrm{NaCl}(\mathrm{aq})$
(b) $2 \mathrm{Ca}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{CaO}(\mathrm{s})$
(c) $4 \mathrm{Fe}(\mathrm{OH})_{2}(\mathrm{s})+2 \mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 4 \mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{s})$

Key Concepts

Oxidation-Reduction (Redox) Reactions

These reactions involve the transfer of electrons from one chemical species to another, resulting in changes to the oxidation states of the atoms involved. In redox reactions, one substance undergoes oxidation (loss of electrons) while another undergoes reduction (gain of electrons). Identifying redox reactions typically involves assigning oxidation numbers to elements in the reactants and products and detecting changes that indicate electron transfer.

Oxidation States

The concept of oxidation states or numbers is a bookkeeping tool used to keep track of electrons in atoms during chemical reactions. By assigning numerical oxidation states to elements in compounds, chemists can determine whether oxidation or reduction has occurred. This method of analysis is essential for recognizing redox processes by highlighting shifts in electron density between reactants and products.

Precipitation Reactions

Precipitation reactions are a type of chemical reaction where two soluble salts in aqueous solution combine to form an insoluble solid, known as a precipitate. Unlike redox reactions, precipitation reactions do not involve changes in oxidation states but are classified based on the insolubility of the product formed. They are often identified by the formation of a solid from clear solutions when the product exceeds its solubility limit.

Transcript

00:01 Hello everyone.

00:02 We are going to examine three oxidation or three reactions and determine which two are oxidation reduction and which one isn't.

00:10 Let's assign oxidation numbers to our first problem.

00:17 Excuse me.

00:19 Okay, we're looking at the blue reaction and cadmium on the reactant side has a 2 plus and cadmium on the product side also has a 2 plus.

00:32 Chlorine on the the reactant side has a negative 1 and chlorine on the product side as a negative 1.

00:40 Sodium is a plus 1 and a plus 1 and sulfur is a 0 minus 1, minus 2 and a minus 2.

00:50 This has no change in any oxidation number.

00:54 It is not a redox.

00:56 If you take a look at it, this is a precipitation reaction, which is a double replacement reaction.

01:10 Okay, the next one's pretty fast to look at.

01:12 Elements in their natural and combined state have an oxidation number of zero.

01:18 So both calcium, elemental calcium, and diatomic oxygen are zero.

01:24 Calcium combined is 2 plus and oxygen is 2 minus.

01:30 Calcium is losing electrons.

01:36 Therefore, it is undergoing oxidation.

01:39 It is oxidized.

01:44 Oxygen is gaining electrons, therefore it is being reduced.

01:58 Okay, for our next problem, let's go ahead and figure out the oxidation numbers of these.

02:08 Hydrogen has a plus 1, and there are two of them, so hydrogen has a 2 plus...

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