Video: Applying Knowledge of Reducing Agents in the Reaction of Sodium and Chlorine

For statements (I) and (II), state for each if they are true or false. (I) When sodium reacts with chlorine, sodium acts as the reducing agent. (II) Sodium is reduced in the reaction of sodium chlorine. If both are true, state if (II) is a correct explanation for (I).

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Video Transcript

For statements (I) and (II), state for each if they are true or false. (I) When sodium reacts with chlorine, sodium acts as the reducing agent. (II) Sodium is reduced in the reaction of sodium chlorine. If both are true, state if (II) is a correct explanation for (I).

Sodium metal, which exists as a silver-colored solid under standard conditions, with symbol Na, and chlorine, which exists as a diatomic yellow-green gas under standard conditions, with formula Cl2, react with each other according to the following balanced equation. The reaction produces sodium chloride, NaCl, which is a crystalline solid under standard conditions.

Sodium chloride is the main component in table salt that we use on our food. However, the sodium chloride that we use we usually get from evaporated water of salt pens and not produced by this reaction. The reaction given here is an example of a redox reaction, which is a reaction in which both reduction and oxidation occur.

Oxidation is the loss of an electron or electrons by a chemical species such as an atom or an ion of an element in a reaction. And reduction is the gain of an electron or electrons by a chemical species in a reaction. So in a redox reaction, one of the chemical species undergoes oxidation, or loss of electrons, and another chemical species undergoes reduction, or gain of electrons.

We can remember what oxidation and reduction are using the acronym OIL RIG, where OIL stands for “oxidation is loss” of electrons and RIG stands for “reduction is gain” of electrons.

We can use the oxidation state or oxidation number to understand how many electrons have been lost or gained by an element in redox reactions. Oxidation number is the number of electrons lost or gained by a neutral atom of an element in a compound. For the neutral atom sodium, we assign an oxidation number of zero. We know that sodium being a neutral atom has the same number of protons as electrons. So it has neither lost nor gained electrons. In other words, it has neither been oxidized nor reduced in the state.

Cl2, which consists of two neutral chlorine atoms bonded together covalently, each having an oxidation state of zero, gives the element molecule Cl2 an oxidation state overall of zero. Sodium chloride, however, is an ionic compound composed of ions, the sodium plus ion and the chloride minus ion. Because of the positive charge on the sodium ion, we know that the sodium atom used to form it must have lost one electron. And so the oxidation number of Na+ is plus one, which we write above the Na symbol.

For the chloride iron, we know that it was formed from a neutral atom of chlorine that gained one electron to give the one minus charge. So the oxidation number of the chloride ion is minus one. And we write this above the Cl symbol.

In the reaction, we can see that sodium has undergone an oxidation. It has lost an electron to form a sodium ion. And each chlorine atom has undergone reduction or gained an electron to form a chloride iron. We know that sodium is oxidized and chlorine is reduced, but it is the oxidation of sodium or the loss of an electron by sodium which causes the chlorine to be reduced or to gain an electron. In other words, the electron lost by sodium is gained by chlorine. So a sodium atom reduces a chlorine atom. We say that sodium is the reducing agent, and oppositely we can say that chlorine causes sodium to lose an electron. In other words, chlorine oxidizes sodium. So chlorine is an oxidizing agent.

Looking at statement (I), which says “When sodium reacts with chlorine, sodium acts as the reducing agent,” we can see that this is true. And statement (II), sodium is reduced in the reaction of sodium and chlorine, we know is false. Sodium is oxidized in the reaction of sodium and chlorine. Because only one statement is true, we need not address the last statement.

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