Which one of the following isnotan example of an oxidation reaction?
A white substance is formed when an aqueous solution of barium chloride is mixed with sodium sulphate solution
Identifying Non-Oxidation Reactions in Chemistry
The question asks us to identify which of the given chemical processes is NOT an example of an oxidation reaction. To answer this, we need to understand what an oxidation reaction is and then examine each option.
What is an Oxidation Reaction?
Oxidation is a chemical process that involves:
- Gain of oxygen
- Loss of hydrogen
- Loss of electrons (increase in oxidation state)
Often, oxidation occurs along with reduction (gain of hydrogen, gain of electrons, decrease in oxidation state). Reactions where both oxidation and reduction occur are called redox reactions.
Analyzing Each Option
Let's look at each option presented and determine if it involves oxidation.
Option 1: Taste of butter changes if left for a longer period
This describes the phenomenon of rancidity in fats and oils like butter. Rancidity often occurs due to the oxidation of unsaturated fatty acids present in the butter. This process breaks down the fats into smaller compounds, which have unpleasant smells and tastes. Therefore, this is an example of an oxidation reaction.
Option 2: A white substance is formed when an aqueous solution of barium chloride is mixed with sodium sulphate solution
This reaction involves mixing barium chloride (\(\text{BaCl}_2\)) and sodium sulphate (\(\text{Na}_2\text{SO}_4\)) in water. The reaction that takes place is a double displacement or precipitation reaction:
\(\text{BaCl}_2\text{(aq)} + \text{Na}_2\text{SO}_4\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)} \downarrow + 2\text{NaCl}\text{(aq)}\)
Here, barium sulphate (\(\text{BaSO}_4\)) is formed as a white solid substance (precipitate). Let's examine the oxidation states of the elements involved:
| Substance | Element | Oxidation State in Reactant | Oxidation State in Product |
|---|---|---|---|
| \(\text{BaCl}_2\) | Ba | +2 | - |
| Cl | -1 | - | |
| \(\text{Na}_2\text{SO}_4\) | Na | +1 | - |
| S | +6 | - | |
| O | -2 | - | |
| \(\text{BaSO}_4\) | Ba | - | +2 |
| S | - | +6 | |
| O | - | -2 | |
| \(\text{NaCl}\) | Na | - | +1 |
| Cl | - | -1 |
As you can see from the table, the oxidation states of barium (+2), chlorine (-1), sodium (+1), sulfur (+6), and oxygen (-2) remain the same before and after the reaction. Since there is no change in oxidation states, no electrons are gained or lost by any species. Therefore, this reaction is NOT an oxidation or reduction reaction (it's not a redox reaction).
Option 3: A reddish-brown powder gets coated on articles made of iron
This describes the rusting of iron. Rust is primarily hydrated iron(III) oxide (\(\text{Fe}_2\text{O}_3 \cdot n\text{H}_2\text{O}\)). Rusting is a complex process that involves the oxidation of iron (\(\text{Fe}\)) by oxygen (\(\text{O}_2\)) in the presence of water. The oxidation state of iron changes from 0 (in solid iron) to +3 (in iron(III) oxide). This gain in oxidation state indicates oxidation. Therefore, rusting is an example of an oxidation reaction.
\(\text{Fe}\text{(s)} \rightarrow \text{Fe}^{2+}\text{(aq)} + 2\text{e}^- \quad (\text{Oxidation})\)
Followed by further oxidation to \(\text{Fe}^{3+}\) and formation of hydrated oxides.
Option 4: Wine gets sour with time
When wine is exposed to air (oxygen), the ethanol (\(\text{CH}_3\text{CH}_2\text{OH}\)) present in it can be oxidized to ethanoic acid (\(\text{CH}_3\text{COOH}\), acetic acid), which is the main component of vinegar. This process is often catalyzed by microorganisms like *Acetobacter*. This conversion involves the oxidation of ethanol.
\(\text{CH}_3\text{CH}_2\text{OH}\text{(aq)} + \text{O}_2\text{(g)} \rightarrow \text{CH}_3\text{COOH}\text{(aq)} + \text{H}_2\text{O}\text{(l)}\)
In terms of oxidation states of the carbon atoms, the carbon bonded to the -OH group in ethanol has a lower oxidation state compared to the carbon in the -COOH group of ethanoic acid. Alternatively, considering the loss of hydrogen and gain of oxygen relative to the carbon framework, this is clearly an oxidation process. Therefore, this is an example of an oxidation reaction.
Conclusion
Based on the analysis, the reaction where a white substance (\(\text{BaSO}_4\)) is formed from barium chloride and sodium sulphate solutions is a double displacement precipitation reaction, not an oxidation reaction. The other three options describe processes that involve oxidation.
Revision Table: Oxidation Reactions
| Process | Type of Reaction | Involves Oxidation? | Why? |
|---|---|---|---|
| Butter becoming rancid | Oxidation of fats | Yes | Fats/oils are oxidized by air. |
| \(\text{BaCl}_2 + \text{Na}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + \text{NaCl}\) | Double displacement/Precipitation | No | No change in oxidation states of ions. |
| Rusting of iron | Oxidation of iron | Yes | Iron is oxidized from \(\text{Fe}^0\) to \(\text{Fe}^{+3}\). |
| Wine becoming sour | Oxidation of ethanol | Yes | Ethanol is oxidized to ethanoic acid. |
Additional Information on Redox Reactions
Redox reactions are fundamental in chemistry and are involved in many processes, including:
- Combustion (burning)
- Respiration in living organisms
- Photosynthesis in plants
- Electrochemical cells (batteries)
- Corrosion (like rusting)
Remember the mnemonic "OIL RIG" to help identify oxidation and reduction:
- Oxidation Is Loss (of electrons)
- Reduction Is Gain (of electrons)
In the double displacement reaction between barium chloride and sodium sulphate, ions simply swap partners, forming an insoluble compound. This type of reaction does not involve the transfer of electrons or changes in oxidation states, unlike the oxidation reactions described in the other options.
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