Substitution Reactions: Halogenation of Alkanes
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Questions and Answers

What is the expected observation when ketones are tested with Fehling's solution?

  • A red precipitate forms
  • No change is observed (correct)
  • The solution turns yellow
  • Bubbles are produced
  • What is the first step in the Tollen's reagent procedure?

  • Heating the solution in a water bath
  • Adding ethanal to the test tube
  • Mixing silver nitrate with sodium hydroxide (correct)
  • Dissolving the precipitate with concentrated sulfuric acid
  • What gas is produced when magnesium is tested in a solution, as observed?

  • Hydrogen is produced (correct)
  • Oxygen is released
  • Carbon dioxide is generated
  • Nitrogen is emitted
  • When anhydrous sodium carbonate is added to a test tube, which of the following observations is expected?

    <p>The lighted taper is extinguished</p> Signup and view all the answers

    Which is NOT a step in the mass spectrometry process?

    <p>Formation of more complex molecules</p> Signup and view all the answers

    What occurs during the ionisation stage of mass spectrometry?

    <p>Electrons are knocked off the sample particles</p> Signup and view all the answers

    What is formed as a result of the polymerisation reaction of chloroethene?

    <p>Polychloroethene (PVC)</p> Signup and view all the answers

    Which breakdown product is associated with the thermal cracking of 1,2-dichloroethane?

    <p>Chloroethene</p> Signup and view all the answers

    What must occur for ethane to be formed in a chain reaction involving chloromethane?

    <p>Two methyl free radicals must combine.</p> Signup and view all the answers

    Which substance acts as a catalyst in the esterification process mentioned?

    <p>Sulfuric acid</p> Signup and view all the answers

    In an addition reaction, what is a key characteristic of the bonds involved?

    <p>They occur on double or triple bonds.</p> Signup and view all the answers

    What is the primary outcome when the C=C double bond in ethene is polarized by Br2?

    <p>A carbonium ion is formed.</p> Signup and view all the answers

    What happens to the geometry of the molecules during an addition reaction on a double or triple bond?

    <p>It changes from planar to tetrahedral.</p> Signup and view all the answers

    Which of the following statements about free radicals in the reaction is true?

    <p>Only reactions using free radicals will speed up with the addition of more free radicals.</p> Signup and view all the answers

    What is the role of the brine in the soap preparation process?

    <p>It allows the soap to precipitate out of solution.</p> Signup and view all the answers

    What is the primary function of anti-bumping granules in the soap preparation process?

    <p>To prevent bumping and ensure smooth boiling.</p> Signup and view all the answers

    What determines whether particles pass through the spectrometer to the detector?

    <p>The particles' mass</p> Signup and view all the answers

    What does the height of a peak in a mass spectrum indicate?

    <p>The relative abundance of particles of that mass</p> Signup and view all the answers

    Which factor influences the separation in paper chromatography?

    <p>Solubility of materials in the mobile phase</p> Signup and view all the answers

    In gas chromatography, what does the gaseous mobile phase carry?

    <p>Gaseous samples</p> Signup and view all the answers

    What is the stationary phase in column chromatography?

    <p>Silica gel</p> Signup and view all the answers

    Which application is NOT typically associated with mass spectrometry?

    <p>Gel electrophoresis</p> Signup and view all the answers

    What happens during the elution process in column chromatography?

    <p>The solvent is passed through the column</p> Signup and view all the answers

    In paper chromatography, where should the spot of the sample mixture be placed?

    <p>1 cm above the water line</p> Signup and view all the answers

    What type of reaction produces ethene from ethanol?

    <p>Elimination reaction</p> Signup and view all the answers

    Which of the following statements is true regarding polymerization?

    <p>Polymers are made up of repeating units called monomers.</p> Signup and view all the answers

    When a primary alcohol is oxidized, it is converted to which compound?

    <p>Aldehyde</p> Signup and view all the answers

    What is formed when a secondary alcohol reacts with acidified sodium dichromate?

    <p>Ketone</p> Signup and view all the answers

    What is the primary product formed when ethene undergoes the addition of bromine in the presence of chlorine ions?

    <p>1,2-dibromethane</p> Signup and view all the answers

    Which reagent is used in the mandatory experiment to oxidize ethanal?

    <p>Potassium permanganate</p> Signup and view all the answers

    What is the purpose of adding dilute sulfuric acid in the experiment with ethanal and potassium manganate(VII)?

    <p>To provide acidity for oxidation</p> Signup and view all the answers

    In the oxidation experiment using Fehling's solution, what is the initial color of the solution?

    <p>Blue</p> Signup and view all the answers

    What is the role of the mobile phase in gas chromatography?

    <p>To carry the sample through the column</p> Signup and view all the answers

    How does high-performance liquid chromatography (HPLC) achieve effective separation of components?

    <p>By employing a high-pressure pump to force the liquid through the packed column</p> Signup and view all the answers

    What type of information can ultraviolet (UV) spectroscopy provide that infrared (IR) spectroscopy cannot?

    <p>It can analyze the concentration of a compound</p> Signup and view all the answers

    In what application is gas chromatography frequently used?

    <p>Measuring alcohol levels in urine samples</p> Signup and view all the answers

    Which bonded structure would absorb infrared radiation at a different frequency than C=O in IR spectroscopy?

    <p>O-H bond</p> Signup and view all the answers

    What is one of the main uses of infrared (IR) spectroscopy?

    <p>To identify illegal drugs</p> Signup and view all the answers

    What does the coiled column in gas chromatography primarily serve as?

    <p>The stationary phase for separating components</p> Signup and view all the answers

    During the mandatory experiment of separating ink components using paper chromatography, how is the mobile phase initially prepared?

    <p>By pouring the solvent into a tank to a depth of 10 mm</p> Signup and view all the answers

    What is the primary purpose of refluxing during the preparation of soap?

    <p>To allow time for reaction without losing volatile material</p> Signup and view all the answers

    What type of reaction occurs in Stage 1 of soap preparation?

    <p>Saponification</p> Signup and view all the answers

    Which substance is removed during the distillation in Stage 2?

    <p>Ethanol</p> Signup and view all the answers

    What is the function of the brine in Stage 3 of the soap preparation?

    <p>To precipitate the soap</p> Signup and view all the answers

    Why is it important to wash the soap thoroughly in Stage 4?

    <p>To remove sodium hydroxide</p> Signup and view all the answers

    What co-product is formed during the soap preparation process?

    <p>Propane-1,2,3-triol</p> Signup and view all the answers

    How does sodium stearate interact with oils and salts in sweat?

    <p>Its non-polar tail dissolves oils while the ionic head attracts salts</p> Signup and view all the answers

    What is the maximum possible yield of soap from 4.45 g of glyceryl tristearate?

    <p>4.59 g</p> Signup and view all the answers

    Study Notes

    Substitution Reactions

    • A substitution reaction is a chemical reaction where an atom or group of atoms in a molecule is replaced by another atom or group.
    • Alkanes undergo substitution reactions with halogens in the presence of ultraviolet light.
    • Example: CH4 + Cl2 → CH3Cl + HCl (methane reacts with chlorine to form chloromethane and hydrogen chloride).

    Halogenation of Alkanes

    • Halogenation is a type of substitution reaction.
    • Halogen atoms replace hydrogen atoms in an alkane molecule.
    • Continued halogenation can lead to the formation of di-, tri-, or tetrachloromethanes.

    Mechanism of Monochlorination of Methane

    • The mechanism of a reaction is a step-by-step description of how the overall reaction proceeds.
    • The mechanism of monochlorination of methane is a free-radical substitution mechanism.

    Initiation

    • A chlorine molecule is broken down into two chlorine atoms in the presence of ultraviolet light.
    • This creates chlorine free radicals.

    Propagation

    • A chlorine free radical attacks a methane molecule, forming hydrogen chloride and a methyl free radical.
    • The methyl free radical attacks another chlorine molecule, forming chloromethane and a chlorine free radical.

    Termination

    • When most reactants are used up, remaining chlorine and methyl radicals combine to form Cl2, chloromethane, and ethane, ending the chain reaction.

    Evidence for the Mechanism

    • Reaction occurs when exposed to UV light.
    • Thousands of chloromethane molecules are formed for every photon of light absorbed.
    • Ethane is a product of the reaction.
    • Free radicals speed up the reaction.

    Addition Reactions

    • An addition reaction is a reaction where two or more molecules combine to form a single molecule.
    • Addition reactions always occur at double or triple bonds.
    • The geometry of the molecule changes from planar to tetrahedral bonds.
    • Examples include hydrogenation of vegetable oils and the formation of plastics.

    Polarisation

    • The C=C double bond in ethane has a high concentration of negative charge.
    • As Br2 approaches ethane, electrons are repelled, polarising the Br2 molecule.

    Heterolytic Fission

    • The Br2 molecule splits into Br⁺ and Br⁻ ions.

    Carbonium Ion Formation

    • The Br⁺ ion attacks the electron-rich C=C double bond.
    • This forms a carbonium ion.

    Ionic Addition

    • The carbonium ion is attacked by the Br⁻ ion.
    • This results in the formation of 1,2-dibromethane.

    Polymerisation Reactions

    • Polymers are long chain molecules made by joining together many small molecules.
    • Polymers are repeating structures consisting of thousands of monomers linked together.
    • Polyvinyl chloride (PVC) is a common plastic.
    • The repeating unit of a polymer is the part whose repetition forms the complete polymer chain, excluding end groups.

    Elimination Reactions

    • An elimination reaction is a reaction where a small molecule is removed from a larger molecule, often producing a double bond in the larger molecule.

    Redox Reactions

    • When a primary alcohol reacts with an oxidizing agent, the primary alcohol is converted into an aldehyde.
    • Two hydrogen atoms are removed from the primary alcohol.
    • If a secondary alcohol reacts with acidified sodium dichromate, a ketone is formed.
    • Aldehydes and ketones can be reduced back to alcohols using hydrogen and a nickel catalyst.

    Mandatory Experiment: To Prepare Soap

    • Detailed procedures are outlined (using 2.5g of lard, 2.5g KOH, and 20cm³ ethanol, in a reflux apparatus using a water bath, then distillation, dissolution in water, and precipitation in brine followed by filtration).
    • Testing the soap is also outlined.

    Mandatory Experiment: To Study Reactions of Ethanal

    • Experiments on ethanal using acidified potassium permanganate, Fehling's reagent, and ammoniacal silver titrate are described.
    • Observations and analysis are discussed for each step.

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    Description

    Explore the intricacies of substitution reactions, specifically focusing on the halogenation of alkanes. This quiz delves into mechanisms, examples, and processes involved in the reaction of alkanes with halogens under ultraviolet light. Test your understanding of these essential chemical concepts!

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