The question asks to identify the electrode where oxidation occurs in an electrochemical cell. This is a fundamental concept in electrochemistry, defining the roles of the anode and cathode.
For example, in a galvanic cell, at the anode, a metal might lose electrons and go into solution as ions:
\[ \text{M} \rightarrow \text{M}^{n+} + n\text{e}^- \]A) Anode is the correct answer because, by definition, oxidation (loss of electrons) always occurs at the anode in an electrochemical cell, regardless of whether it's a galvanic (voltaic) cell or an electrolytic cell.
To identify the oxidized species in a redox reaction, we need to understand the definitions of oxidation and reduction in terms of electron transfer or change in oxidation states. Oxidation is the loss of electrons, which results in an increase in the oxidation state. Reduction is the gain of electrons, resulting in a decrease in the oxidation state.
Write down the given reaction:
\[ \text{Zn(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Zn}^{2+}\text{(aq)} + \text{Cu(s)} \]
Determine the oxidation state of each species on the reactant side:
Zinc metal (\(\text{Zn(s)}\)): In its elemental form, the oxidation state of Zn is 0.
Copper ion (\(\text{Cu}^{2+}\text{(aq)}\)): The charge on the ion indicates its oxidation state, so Cu is +2.
Determine the oxidation state of each species on the product side:
Zinc ion (\(\text{Zn}^{2+}\text{(aq)}\)): The charge on the ion indicates its oxidation state, so Zn is +2.
Copper metal (\(\text{Cu(s)}\)): In its elemental form, the oxidation state of Cu is 0.
Compare the oxidation states of each element from reactants to products:
For Zinc: The oxidation state changes from 0 (\(\text{Zn(s)}\)) to +2 (\(\text{Zn}^{2+}\text{(aq)}\)). This is an increase in oxidation state, which means Zn has lost electrons.
\[ \text{Zn(s)} \rightarrow \text{Zn}^{2+}\text{(aq)} + 2\text{e}^- \]
For Copper: The oxidation state changes from +2 (\(\text{Cu}^{2+}\text{(aq)}\)) to 0 (\(\text{Cu(s)}\)). This is a decrease in oxidation state, which means Cu has gained electrons.
\[ \text{Cu}^{2+}\text{(aq)} + 2\text{e}^- \rightarrow \text{Cu(s)} \]
Identify the oxidized species: Oxidation is the loss of electrons. Since Zinc (Zn) loses electrons and its oxidation state increases from 0 to +2, Zinc metal is oxidized.
Correct Option: A) Zinc metal (Zn), since it loses electrons to form the
The question asks for the primary forms of energy released during a combustion reaction. We need to recall the characteristics of combustion, which is a common chemical process.
A) Heat and light — Combustion is fundamentally an exothermic process, meaning it releases energy, primarily as heat. The rapid reaction often leads to incandescence, producing light (e.g., a flame). This option accurately describes the main energy forms released.
The question asks about the products of the complete combustion of methane (CH₄) in the presence of sufficient oxygen. Complete combustion of any hydrocarbon always yields carbon dioxide and water as the main products.
Correct Option: B) Carbon dioxide (CO₂) and water (H₂O)
The question asks about the products of incomplete combustion, which occurs when there is an insufficient supply of oxygen. Understanding the difference between complete and incomplete combustion is key to identifying the correct hazardous by-product.
A) Carbon monoxide (CO), a toxic gas, along with soot (unburnt carbon particles). This option accurately describes the characteristic products of incomplete combustion, highlighting the hazardous nature of carbon monoxide and the presence of soot.
The question asks to identify the primary harmful gases released during the combustion of fossil fuels like coal and petroleum, which contribute to environmental air pollution. We need to recall the common by-products of incomplete and complete combustion of hydrocarbons and other elements present in fossil fuels.
C) Carbon monoxide (CO), sulphur dioxide (SO₂), sulphur trioxide (SO₃), and nitrogen dioxide (NO₂)
These gases are indeed major air pollutants resulting from the combustion of fossil fuels. Carbon monoxide is toxic, sulfur oxides contribute to acid rain and respiratory issues, and nitrogen oxides contribute to smog, acid rain, and respiratory problems.