Identifying The Oxidized Substance In The Redox Reaction Co(s) + 2 HCl(aq) → CoCl2(aq) + H2(g)

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In the world of chemistry, redox reactions, short for reduction-oxidation reactions, are fundamental processes that involve the transfer of electrons between chemical species. Identifying the substance that undergoes oxidation in a redox reaction is a crucial skill for students and chemists alike. This article will provide a comprehensive explanation of how to determine the oxidized substance in the given reaction: Co(s) + 2 HCl(aq) → CoCl2(aq) + H2(g). We will delve into the concepts of oxidation states, oxidation, reduction, and the mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain) to make the process clear and straightforward. Through a detailed analysis of the reaction, we will identify the substance that loses electrons and, therefore, is oxidized.

Understanding Redox Reactions

To accurately identify the oxidized substance, it is essential to grasp the core principles of redox reactions. Redox reactions are chemical reactions where there is a change in the oxidation states of the atoms involved. These reactions always involve two simultaneous processes: oxidation and reduction. In simpler terms, oxidation is the loss of electrons, while reduction is the gain of electrons. It's important to remember that oxidation and reduction always occur together; one cannot happen without the other. The substance that loses electrons is said to be oxidized, and the substance that gains electrons is said to be reduced. A helpful mnemonic to remember this is OIL RIG, which stands for Oxidation Is Loss (of electrons) and Reduction Is Gain (of electrons).

In any redox reaction, there are key players known as the oxidizing agent and the reducing agent. The oxidizing agent is the substance that causes oxidation by accepting electrons and is itself reduced. Conversely, the reducing agent is the substance that causes reduction by donating electrons and is itself oxidized. Identifying these agents is crucial in understanding the complete picture of electron transfer in a redox reaction. For instance, in a reaction where substance A oxidizes substance B, A is the oxidizing agent, and B is the reducing agent. The oxidation state of an atom is a concept that helps us track the movement of electrons in a chemical reaction. It is a hypothetical charge that an atom would have if all bonds were completely ionic. Oxidation states are assigned based on a set of rules, which we will discuss in detail later. By comparing the oxidation states of atoms before and after a reaction, we can determine whether they have been oxidized (oxidation state increased) or reduced (oxidation state decreased).

Understanding oxidation states is crucial for identifying redox reactions and the substances involved in oxidation and reduction. The oxidation state, also known as the oxidation number, represents the hypothetical charge an atom would have if all its bonds to other atoms were completely ionic. By comparing the oxidation states of elements before and after a chemical reaction, we can determine whether they have gained or lost electrons. Assigning oxidation states follows a set of rules:

  1. The oxidation state of an element in its free or elemental state is always 0. For example, the oxidation state of Co(s) is 0, and the oxidation state of H2(g) is 0.
  2. The oxidation state of a monoatomic ion is equal to its charge. For example, the oxidation state of Cl- is -1.
  3. The oxidation state of oxygen is usually -2, except in peroxides (such as H2O2) where it is -1, and when combined with fluorine (OF2) where it is +2.
  4. The oxidation state of hydrogen is usually +1, except when it is bonded to metals in metal hydrides (such as NaH) where it is -1.
  5. The sum of the oxidation states of all atoms in a neutral molecule is 0. The sum of the oxidation states of all atoms in a polyatomic ion is equal to the charge of the ion.

These rules provide a systematic approach to assigning oxidation states and are essential for analyzing redox reactions. By mastering these rules, you can confidently determine which substances are oxidized and reduced in any given chemical reaction.

Analyzing the Given Redox Reaction

Now, let's apply our knowledge to the given redox reaction: Co(s) + 2 HCl(aq) → CoCl2(aq) + H2(g). To identify the oxidized substance, we need to determine the oxidation states of each element before and after the reaction. This involves applying the rules for assigning oxidation states, which we discussed earlier. By comparing the oxidation states, we can pinpoint which element has undergone oxidation (loss of electrons) and which has undergone reduction (gain of electrons). This step-by-step analysis will provide a clear understanding of the electron transfer process in this specific reaction.

Step 1: Assign Oxidation States

Let's assign oxidation states to each element in the reaction:

  • Co(s): Cobalt in its elemental form has an oxidation state of 0.
  • HCl(aq): Hydrogen usually has an oxidation state of +1. Chlorine, being more electronegative, has an oxidation state of -1. So, in HCl, H is +1 and Cl is -1.
  • CoCl2(aq): To determine the oxidation state of Co in CoCl2, we know that the total charge of the molecule is 0. Since there are two chlorine atoms, each with an oxidation state of -1, the total negative charge is -2. Therefore, the oxidation state of cobalt must be +2 to balance the charge. So, Co is +2 and Cl is -1.
  • H2(g): Hydrogen in its elemental form has an oxidation state of 0.

Step 2: Identify Changes in Oxidation States

Now, let's compare the oxidation states before and after the reaction:

  • Cobalt (Co) goes from 0 in Co(s) to +2 in CoCl2(aq).
  • Hydrogen (H) goes from +1 in HCl(aq) to 0 in H2(g).
  • Chlorine (Cl) remains at -1 in both HCl(aq) and CoCl2(aq).

Step 3: Determine Oxidation and Reduction

From the changes in oxidation states, we can see that:

  • Cobalt's oxidation state increases from 0 to +2. This means cobalt has lost electrons and has been oxidized.
  • Hydrogen's oxidation state decreases from +1 to 0. This means hydrogen has gained electrons and has been reduced.
  • Chlorine's oxidation state does not change, so it is neither oxidized nor reduced.

By systematically assigning oxidation states and tracking the changes, we have successfully identified the substance that is oxidized in the reaction. The increase in oxidation state clearly indicates that cobalt has undergone oxidation.

The Oxidized Substance

Based on our analysis, we can definitively identify the oxidized substance in the reaction Co(s) + 2 HCl(aq) → CoCl2(aq) + H2(g). We have established that oxidation is the loss of electrons and is indicated by an increase in oxidation state. By assigning oxidation states to each element before and after the reaction, we observed that the oxidation state of cobalt (Co) increases from 0 in Co(s) to +2 in CoCl2(aq). This increase in oxidation state signifies that cobalt has lost electrons during the reaction. Therefore, the substance that is oxidized in this redox reaction is cobalt (Co).

This conclusion aligns perfectly with the definition of oxidation. Cobalt, by losing two electrons, transforms from its elemental form to an ionic form within the compound CoCl2. The electrons lost by cobalt are gained by hydrogen ions (H+) from HCl, which are reduced to form hydrogen gas (H2). This electron transfer is the essence of the redox reaction. The systematic approach of assigning oxidation states and tracking changes is a reliable method for identifying oxidized and reduced substances in any redox reaction.

Conclusion

In summary, the substance oxidized in the redox reaction Co(s) + 2 HCl(aq) → CoCl2(aq) + H2(g) is D. Co. By understanding the principles of redox reactions, assigning oxidation states, and carefully analyzing the changes, we have clearly demonstrated that cobalt loses electrons and is, therefore, oxidized in this reaction. This process underscores the importance of mastering redox chemistry concepts for a comprehensive understanding of chemical reactions.

Understanding redox reactions is fundamental to chemistry, and the ability to identify oxidized and reduced substances is a critical skill. By breaking down the reaction and applying the rules for oxidation states, we can confidently determine the electron transfer processes occurring. This knowledge not only helps in answering specific questions but also builds a solid foundation for further studies in chemistry.