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Questions and Answers
What type of reaction occurs when alkanes combust?
What type of reaction occurs when alkanes combust?
Which law states that equal volumes of gases at the same conditions contain the same number of molecules?
Which law states that equal volumes of gases at the same conditions contain the same number of molecules?
During the combustion analysis of a hydrocarbon, what products are typically formed?
During the combustion analysis of a hydrocarbon, what products are typically formed?
What is the primary reason why alkanes are considered relatively inert?
What is the primary reason why alkanes are considered relatively inert?
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In combustion analysis, if 80 mL of the mixture after combustion is carbon dioxide, what information does it provide about the hydrocarbon?
In combustion analysis, if 80 mL of the mixture after combustion is carbon dioxide, what information does it provide about the hydrocarbon?
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What is the significance of the residual volume measured after combustion analysis?
What is the significance of the residual volume measured after combustion analysis?
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The reaction of methane with chlorine exemplifies which type of reaction?
The reaction of methane with chlorine exemplifies which type of reaction?
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What can be determined through combustion analysis of a known hydrocarbon?
What can be determined through combustion analysis of a known hydrocarbon?
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What is the main characteristic of bromine compared to chlorine or fluorine in terms of selectivity?
What is the main characteristic of bromine compared to chlorine or fluorine in terms of selectivity?
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In the bromination reaction of alkane, what is a likely product when light is applied?
In the bromination reaction of alkane, what is a likely product when light is applied?
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Which of the following statements about free radicals is true?
Which of the following statements about free radicals is true?
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What reaction typically occurs when alkanes react with chlorine in the presence of light?
What reaction typically occurs when alkanes react with chlorine in the presence of light?
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During the termination phase of free radical reactions, what typically happens?
During the termination phase of free radical reactions, what typically happens?
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What is a likely outcome of a reaction involving bromine and an alkane when using light as a catalyst?
What is a likely outcome of a reaction involving bromine and an alkane when using light as a catalyst?
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What is the purpose of determining the percent composition of elements in a compound?
What is the purpose of determining the percent composition of elements in a compound?
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What type of diseases can be explained by reactions of free radicals with biological substances?
What type of diseases can be explained by reactions of free radicals with biological substances?
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Which of the following products is typically expected from the reaction of alkanes with bromine in the presence of light?
Which of the following products is typically expected from the reaction of alkanes with bromine in the presence of light?
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Which formula represents the empirical formula of a compound?
Which formula represents the empirical formula of a compound?
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In the context of percent composition, what does the variable 'n' represent?
In the context of percent composition, what does the variable 'n' represent?
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During free radical halogenation, what is the primary role of the initiation step?
During free radical halogenation, what is the primary role of the initiation step?
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Which of the following statements is true regarding the stability of free radicals in halogenation reactions?
Which of the following statements is true regarding the stability of free radicals in halogenation reactions?
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What is formed during the dihalogenation of an alkane?
What is formed during the dihalogenation of an alkane?
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What is the primary risk associated with the use of fluorine in free radical halogenation?
What is the primary risk associated with the use of fluorine in free radical halogenation?
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In the molecular formula determination, what is the final step after obtaining the mole ratios?
In the molecular formula determination, what is the final step after obtaining the mole ratios?
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What type of substitution reaction results in multiple halogen atoms being added to an alkane?
What type of substitution reaction results in multiple halogen atoms being added to an alkane?
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What happens during the termination step of free radical halogenation?
What happens during the termination step of free radical halogenation?
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Study Notes
Organic Chemistry Lecture 4
- Organic chemistry lecture 4 covers reactions of alkanes, combustion analysis of hydrocarbons, free radical halogenation, reactions of higher alkanes, cycloalkanes, and double bond equivalents.
Reactions of Alkanes
- Alkanes have non-polar, covalent bonds, making them relatively inert.
- They do not typically react with acids, bases, or reducing agents.
- Alkanes are used as fuels.
- Combustion (burning) of alkanes releases heat and light.
- The general combustion reaction for methane is CH₄ + 2O₂ → CO₂ + 2H₂O + heat.
Combustion Analysis of Hydrocarbons
- Gay-Lussac's Law: Volumes of gases in a reaction are numerically related at standard temperature and pressure (STP).
- Avogadro's Law: Equal volumes of gases at STP contain equal numbers of molecules.
- Combustion analysis involves reacting a known volume of hydrocarbon with a known volume of oxygen.
- The volume of products and unreacted oxygen after cooling is measured.
- This method determines the molecular weight of the alkane.
Free Radical Halogenation
- The reaction of methane with chlorine is an example of free radical halogenation, a process with three steps.
- Initiation, propagation and termination
- The substitution reaction produces different products depending on the carbon’s position (primary, secondary, tertiary).
- Bromine is more selective than chlorine or fluorine.
Cycloalkanes
- Cycloalkanes are saturated hydrocarbons with at least one ring of carbon atoms.
- Their general formula is CₙH₂ₙ.
- They are named by adding the prefix "cyclo" to the corresponding alkane name.
- Cis-trans isomerism is possible in cycloalkanes.
Double Bond Equivalents (DBE)
- DBE provides information on the number of double bonds or rings in an organic compound.
- DBE is related to the degree of saturation/unsaturation of the compound.
- The formula for calculating DBE is: DBE = 1 + C - (H/2) - (X/2) + N/2
Past Paper Questions
- Several past paper questions are included for practice, involving calculations and mechanisms. Example: 2-Methylpropane reacts with bromine (July/August 2004).
Determination of Molecular Formulae using Percent Composition
- Percent composition (by mass) of elements in a sample is obtained experimentally.
- It is used for determining the empirical and molecular formula of a compound.
- Empirical formula shows the relative proportions of elements in a molecule. Calculation involves converting percent composition to moles, and then to mole ratios.
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Description
Explore the intricacies of alkanes in this lecture covering their reactions, combustion analysis, and properties. Learn about free radical halogenation and understand the significance of cycloalkanes and double bond equivalents. This foundational knowledge is key for mastering organic chemistry.
