Organic Chemistry: Hydrocarbons and Alkanes
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Questions and Answers

How is the name of alkynes derived from their corresponding alkanes?

The name of alkanes is modified by changing the ending -ane to -yne.

What is the general formula for alkynes?

The general formula for alkynes is C_nH_{2n-2}.

Describe the process to prepare ethyne using calcium dicarbide.

To prepare ethyne, calcium dicarbide is placed in a test tube, and water is added until it reacts completely, producing ethyne gas.

What observation would you make when ethyne is ignited?

<p>Upon ignition, ethyne produces a bright flame and burns with high temperature.</p> Signup and view all the answers

What happens when a few drops of bromine water are added to ethyne gas?

<p>The bromine water decolorizes, indicating the reaction of ethyne with bromine.</p> Signup and view all the answers

What type of forces primarily hold cyclohexane molecules together?

<p>Van-der-Waals forces</p> Signup and view all the answers

Identify the state of cyclohexane when there are 15 or more carbon atoms.

<p>Waxy solids</p> Signup and view all the answers

What is the IUPAC name for a compound with six carbons and a C=C double bond starting at carbon atom 2?

<p>Hex-2-ene</p> Signup and view all the answers

How would you describe the flame produced when ethene is ignited?

<p>Yellow luminous flame which is slightly smoky</p> Signup and view all the answers

What observable change occurs when ethene reacts with limewater?

<p>Limewater turns milky</p> Signup and view all the answers

What happens to the color of bromine water when mixed with ethene?

<p>Bromine water turns from red to colourless</p> Signup and view all the answers

What is formed when potassium manganate(VII) is added to ethene?

<p>The solution turns from purple to colourless</p> Signup and view all the answers

Characterize the solubility behavior of ethene.

<p>Insoluble in water but dissolves in some organic solvents</p> Signup and view all the answers

What characterizes a saturated compound?

<p>A saturated compound is characterized by having only single bonds between the atoms in the molecule.</p> Signup and view all the answers

List the first four members of the alkane series and their states at room temperature.

<p>The first four members are methane (gas), ethane (gas), propane (gas), and butane (gas).</p> Signup and view all the answers

Why are alkanes insoluble in water?

<p>Alkanes are insoluble in water because they are non-polar and only exhibit Van-der-Waals forces between their molecules.</p> Signup and view all the answers

Define a homologous series in organic chemistry.

<p>A homologous series is a series of compounds with similar chemical properties that vary in physical properties by a CH₂ unit.</p> Signup and view all the answers

What are structural isomers?

<p>Structural isomers are compounds that have the same molecular formula but different structural formulas.</p> Signup and view all the answers

What makes carbon unique compared to other elements?

<p>Carbon is unique because it can form stable rings and chains of atoms, allowing for diverse organic compounds.</p> Signup and view all the answers

Name a common source of hydrocarbons.

<p>Common sources of hydrocarbons include coal, natural gas, and petroleum.</p> Signup and view all the answers

What are the two primary components of Liquefied Petroleum Gas (LPG)?

<p>Propane and Butane.</p> Signup and view all the answers

Why are mercaptans added to LPG?

<p>To give an unpleasant smell for gas leak detection.</p> Signup and view all the answers

What is the primary use of kerosene?

<p>As a domestic heating fuel and fuel for aircraft.</p> Signup and view all the answers

How does the length of the alkane chain affect the octane number?

<p>Shorter alkane chains result in higher octane numbers.</p> Signup and view all the answers

What is autoignition in the context of petrol engines?

<p>Premature ignition of the petrol-air mixture before the spark occurs.</p> Signup and view all the answers

What was the purpose of adding lead to petrol in the past?

<p>To reduce engine knocking.</p> Signup and view all the answers

What kind of compounds generally have a higher octane number?

<p>Cyclic compounds have a higher octane number than straight-chain compounds.</p> Signup and view all the answers

Name one use of naphtha in the petrochemical industry.

<p>As a source for medicine, plastics, and synthetic fibres.</p> Signup and view all the answers

What is the primary characteristic of benzene that contributes to its stability?

<p>Benzene's stability is due to the delocalization of electrons across the benzene ring.</p> Signup and view all the answers

What observable change occurs when bromine water is mixed with an alkene?

<p>Bromine water changes from red to colourless.</p> Signup and view all the answers

How does the process of fractional distillation separate crude oil?

<p>Fractional distillation separates crude oil based on the different boiling points of its components.</p> Signup and view all the answers

What type of flame does ethyne produce when burned, and what is the consequence of this combustion?

<p>Ethyne burns with a luminous smoky flame, producing a significant amount of soot.</p> Signup and view all the answers

Define aromatic compounds and provide an example.

<p>Aromatic compounds are organic compounds that contain a benzene ring, such as benzene (C6H6).</p> Signup and view all the answers

What happens to KMnO4 when it is used in reactions with unsaturated hydrocarbons?

<p>KMnO4 changes from purple to colourless.</p> Signup and view all the answers

Why are refinery gases essential for a refinery?

<p>Refinery gases, such as methane, ethane, propane, and butane, serve as important fuel sources for the refinery.</p> Signup and view all the answers

What distinguishes aliphatic compounds from aromatic compounds?

<p>Aliphatic compounds consist of open chains of carbon atoms, while aromatic compounds contain a benzene ring.</p> Signup and view all the answers

What is the initial temperature of the hydrochloric acid solution measured before mixing?

<p>Temperature of HCl solution before mixing = X°C.</p> Signup and view all the answers

What should be done immediately after the sodium hydroxide is added to the hydrochloric acid solution?

<p>Stir the mixture well and quickly place a lid on the cup.</p> Signup and view all the answers

In the equation heat liberated = m c ∆T, what does each variable represent?

<p>m represents mass in kg, c is the specific heat capacity, and ∆T is the temperature rise.</p> Signup and view all the answers

Why should the answer for the heat of reaction be given a negative sign?

<p>Because the reaction is exothermic, indicating heat is released.</p> Signup and view all the answers

State Hess's Law in your own words.

<p>Hess's Law states that the total heat change in a reaction is the sum of the heat changes in each stage.</p> Signup and view all the answers

In calculating the heat of formation of methane, which reaction's enthalpy change is required?

<p>C(s) + 2H2(g) → CH4 ΔH = ?</p> Signup and view all the answers

What is the heat of formation of water according to the provided data?

<p>The heat of formation of water is -285.8 kJ mol^-1.</p> Signup and view all the answers

Why is it important to avoid splashing when mixing the acid and the base?

<p>To prevent loss of solution and ensure accurate temperature readings.</p> Signup and view all the answers

Study Notes

Organic Chemistry

  • Organic chemistry is the study of carbon compounds.
  • Carbon forms stable rings and chains of its atoms.
  • Most organic compounds are covalent compounds.
  • Carbon has the ability to form covalent bonds with itself and other elements.

Hydrocarbons

  • A hydrocarbon is a compound containing only carbon and hydrogen.
  • Common sources are coal, natural gas, and petroleum.
  • Fossil fuels are formed from the remains of plants and animals millions of years ago.

Alkanes

  • Alkanes are hydrocarbons where all atoms are linked by single bonds.
  • They are saturated compounds.
  • Saturated compounds have only single bonds between atoms.
  • Example alkanes: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, and decane.
  • Each alkane and its molecular formula are listed in table.

Homologous Series

  • A homologous series is a series of compounds with similar chemical properties that show gradations in physical properties.
  • Each member differs from the previous member by a (CH2) unit.

Isomers

  • Structural isomers are compounds with the same molecular formula but different structural formulas.
  • Example of structural isomerism for butane is shown in the text(structural formulas).

Naming of Alkanes

  • IUPAC rules are used for naming organic compounds.
  • Side chains are called alkyl groups (e.g., methyl, ethyl).
  • Prefixes like "di-" are used when two identical groups are present.
  • Example of naming a compound with formulas and steps are shown in the text.

Alkenes

  • Alkenes are hydrocarbons with one or more carbon-carbon double bonds.
  • They are unsaturated compounds.
  • General formula for alkenes is CnH2n.
  • Example of alkenes: ethene (ethylene), propene, and butene(isomerism begins).
  • Properties of alkenes (soluble in non-polar solvents, insoluble in water) are noted.
  • Naming of alkenes (longest chain containing the C=C double bond, numbering the chain) are noted.

Alkynes

  • Alkynes are hydrocarbons containing carbon-carbon triple bonds.
  • They are highly unsaturated.
  • General formula for alkynes is CnH2n-2.
  • Example is ethyne (acetylene).
  • Properties of alkynes (insoluble in water due to Van der Waals forces)are noted.

Aromatic Hydrocarbons

  • Aromatic compounds contain a benzene ring structure.
  • Benzene has a delocalized electron system.
  • Aromatic compounds are often highly stable and not reactive.
  • Example given is benzene.

Oil Refining

  • Crude oil is a mixture of hydrocarbons, separated by fractional distillation.
  • Fractional distillation separates crude oil into various fractions (different boiling points).
  • Fractions have different uses, e.g., petrol, kerosene, diesel, etc.
  • Octane number is a measure of a fuel's tendency to resist knocking.
  • Catalytic cracking breaks down long-chain hydrocarbons into shorter ones.

Heat of Reaction

  • Heat of reaction is the heat change when a specific number of moles of reactants react completely.
  • ΔH (delta H) is used to indicate the heat change.
  • Exothermic reactions release heat (+ΔH), and endothermic reactions absorb heat (- ΔH).

Heat of Combustion

  • Heat of combustion is the heat change when one mole of a substance is completely burned in excess oxygen.
  • Bomb calorimetry is used to measure heats of combustion.

Heat of Neutralization

  • Heat of neutralization is the heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base

Other

  • Hydrogen production methods (steam reforming and electrolysis) are mentioned.

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Description

This quiz covers the fundamentals of organic chemistry, focusing on hydrocarbons and their classification as alkanes. Understand the properties and examples of each alkane, as well as the concept of homologous series in organic compounds. Test your knowledge of carbon compounds and their characteristics.

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