Ib Chemistry Hl Topic 10

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1. Describe the features of a homologous series.

Homologous series do not exhibit any similarities in chemical properties and physical properties.

Include the same general formula, neighbouringmembers differing by CH2, similar chemicalproperties and gradation in physical properties.
Homologous series: A series of compounds (usually hydrocarbons) that display similar chemicalproperties and functional groups but different physical properties (generally boiling point), oftendiffering by one repeating unit, usually a CH2/CH3 molecule. They can be given a general formula, egCnH2n+2
Organic chemistry is the chemistry of carbon compounds(excluding compounds such as metal carbonatesand oxides).
The ability of carbon atoms to form chains leads to theexistence of a series of compounds that have the samefunctional group (and hence similar chemical properties)and only differ from each other by the presence of anadditional carbon atom and its two associated hydrogenatoms in the molecule (which causes the physical propertiesto change in a regular manner).

Homologous series do not have a general formula and do not show gradation in physical properties.

Homologous series consist of compounds that have completely different chemical properties and functional groups.

Homologous series are characterized by compounds with similar chemical properties and functional groups, differing by CH2 in neighboring members, and showing a regular gradation in physical properties. This concept is essential in understanding organic chemistry and the behavior of hydrocarbons.

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About This Quiz

Explore the intricacies of organic chemistry with this focused set of flashcards, designed for students preparing for the IB Chemistry HL Topic 10. This educational tool enhances understanding... see moreof complex chemical reactions, bonding, and structures, vital for academic success in higher-level chemistry. see less

2. Distinguish between empirical, molecular and structural formulas.

Molecular formula: The representation of a compound showing the actual numbers and types of atoms present.

Condensed formula: A formula that provides a detailed diagram of the molecular structure.

Empirical formula: The simplest ratio of the atoms in a chemical compound.
A structural formula is one that showsunambiguously how the atoms are arrangedtogether. A full structural formula (sometimes called agraphic formula or displayed formula) shows everyatom and bond.
A condensed structural formula can omit bondsbetween atoms and can show identical groupsbracketed together, for example, for hexane: CH3CH2CH2CH2CH2CH3 or CH3(CH2)4CH3.
The use of R to represent an alkyl group and (RING) to represent the benzene ring can be used incondensed structural formulas.
Although skeletal formulas are used for morecomplex structures in the Chemistry data booklet,such formulas will not be accepted in examinationanswers.

Structural formula: A formula that only shows the elements present in a compound without indicating their arrangement.

The empirical formula represents the simplest ratio of atoms, while the molecular formula shows the actual numbers and types of atoms. Structural formulas provide a detailed arrangement of atoms within a compound.

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3. Describe structural isomers as compounds with the same molecular formula but with different arrangements of atoms.

Structural isomers are compounds with the same molecular formula and the same arrangement of atoms.

Structural isomers only differ in their physical properties, not their chemical properties.

Isomers are molecules that have the same name but different molecular formulas.

No distinction need be made between differenttypes of structural isomerism, such as chain
and position isomerism and functional groupisomerism. Knowledge of stereoisomerism is notrequired in the core.
Isomer: Two molecules with the same general formula but different structural formula (ie containing the same amounts of each atom but bonded differently) are said to be isomers of each other.
Two Types:
structural isomers, in which the atoms are joined ina different order so that they have different structuralformulae.
stereoisomers, in which the order that the atoms arejoined together is the same, but the molecules havea different arrangement of atoms in space and hencedifferent three dimensional shapes.

Structural isomers specifically refer to compounds with the same molecular formula but different arrangements of atoms. Isomers have different structural formulas despite having the same general formula.

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4. Identify primary, secondary and tertiary carbon atoms in alcohols and halogenoalkanes.

Primary carbon atoms are only found in alcohols, not in halogenoalkanes.

Tertiary carbon atoms can only be identified through NMR spectroscopy, not by structural analysis.

The terms primary, secondary and tertiary canalso be applied to the molecules containing thesecarbon atoms.

Secondary carbon atoms are those directly attached to oxygen in alcohols and to halogens in halogenoalkanes.

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5. Explain the low reactivity of alkanes in terms of bond enthalpies and bond polarity.

Alkanes are highly reactive due to low bond enthalpies and lack of bond polarity.

The reactivity of alkanes is not related to bond enthalpies or bond polarity, but rather to their molecular structure.

The low reactivity of alkanes is due to high bond enthalpies and bond polarity.

See notes.

Alkanes, being saturated hydrocarbons, have strong carbon-carbon and carbon-hydrogen bonds with high bond enthalpies, making them less reactive. Additionally, these bonds are nonpolar, thus lacking regions of partial positive or negative charge, further reducing reactivity.

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6. Describe, using equations, the complete and incomplete combustion of alkanes.

Incomplete combustion of alkanes only produces water vapor.

Complete combustion of alkanes can result in the formation of sulfur dioxide.

Alkanes do not undergo combustion reactions.

The most familiar reaction of the alkanes is combustion.Like almost all organic compounds, the alkanes areflammable and oxidise when burnt in the air to formcarbon dioxide and water if sufficient oxygen is present.
Incomplete = CO and H2O vapor

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7. Describe, using equations, the reactions of methane and ethane with chlorine and bromine.

Alkanes can also react with chlorine or bromine in asubstitution reaction, to give an initial product in whichone hydrogen atom is replaced by the halogen. Usuallythese reactions are brought about by exposure to ultravioletlight or sunlight, though they will also occur without light at high temp.

Alkanes react with chlorine and bromine to form hydrocarbons with a higher number of carbon atoms.

Alkanes react with chlorine and bromine to form alkenes.

Alkanes do not react with chlorine or bromine.

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8. Describe, using equations, the reactions of alkenes with hydrogen and halogens.

Alkenes react with nitrogen to form ammonia.

Alkenes react with metals to form ionic compounds.

Alkenes react with oxygen to form water and carbon dioxide.

The general formula for thealkene homologous series is CnH2n.
A reaction in which the double bond of an alkene isconverted to a single bond and two new bonds are formedto the species it reacts with is known as an additionreaction and they are typical of alkenes and alkynes.

The correct answer describes the general formula for alkenes and the addition reactions typical of alkenes and alkynes. The three incorrect answers mention reactions that do not involve alkenes reacting with hydrogen and halogens.

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9. Describe, using equations, the reactions of symmetrical alkenes with hydrogen halides and water.

Symmetrical alkenes react by forming alkanes without any byproducts.

Symmetrical alkenes react by producing aldehydes with hydrogen halides and water.

Symmetrical alkenes react by undergoing oxidation reactions with hydrogen halides and water.

See notes.

The correct answer is 'See notes.' as the specific equations depend on the type of symmetrical alkene and the conditions of the reaction. It is important to refer to detailed notes or textbooks for the exact reactions.

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10. Outline the economic importance of the reactions of alkenes.

Include the hydrogenation of vegetableoils in the manufacture of margarine, the hydrationof ethene in the manufacture of ethanol, andpolymerization in the manufacture of plastics.

The oxidation of alkenes for water treatment

The combustion of alkenes for energy production

The reduction of alkenes for pharmaceutical synthesis

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11. Describe, using equations, the oxidation reactions of alcohols.

An appropriate reducing agent is acidified potassium dichromate(VI).

Obtaining aldehyde requires heating the reaction mixture under reflux.

A suitable oxidizing agent is acidified potassiumdichromate(VI). Equations may be balanced using the symbol [O] torepresent oxygen supplied by the oxidizing agent. Include the different conditions needed toobtain good yields of different products, that is,an aldehyde by distilling off the product as it isformed, and a carboxylic acid by heating underreflux.

Balancing equations for oxidation reactions of alcohols is not necessary.

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12. Determine the products formed by the oxidation of primary and secondary alcohols.

Water and carbon dioxide

Esters and aldehydes

See image.

Carboxylic acids and ketones

The oxidation of primary alcohols leads to the formation of aldehydes and then carboxylic acids, while the oxidation of secondary alcohols results in the formation of ketones.

Explanation

The oxidation of primary alcohols leads to the formation of aldehydes and then carboxylic acids, while the oxidation of secondary alcohols results in the formation of ketones.

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13. Explain the substitution reactions of halogenoalkanes with sodium hydroxide in terms of SN1 and SN2 mechanisms.

Both primary and tertiary halogenoalkanes follow the SN1 mechanism while secondary halogenoalkanes follow the SN2 mechanism.

Reference should be made to heterolytic fission. Curly arrows should be used to represent themovement of electron pairs. For tertiary halogenoalkanes the predominantmechanism is SN1, and for primary halogenoalkanesit is SN2. Both mechanisms occur for secondaryhalogenoalkanes.

Only secondary halogenoalkanes follow the SN1 mechanism, while primary and tertiary halogenoalkanes follow the SN2 mechanism.

The reaction with sodium hydroxide does not involve any mechanism, it is a direct chemical reaction.

When explaining the substitution reactions of halogenoalkanes with sodium hydroxide, it is important to consider the mechanisms SN1 and SN2. This involves understanding the role of heterolytic fission and the use of curly arrows to represent electron pair movements. Tertiary halogenoalkanes primarily follow the SN1 mechanism, while primary halogenoalkanes follow the SN2 mechanism. Secondary halogenoalkanes can undergo both SN1 and SN2 mechanisms.

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14. Deduce reaction pathways given the starting materials and the product.

Conversions with more than two stages will not beassessed. Reagents, conditions and equations should beincluded. For example, the conversion of but-2-ene tobutanone can be done in two stages: but-2-enecan be heated with steam and a catalyst to formbutan-2-ol, which can then be oxidized by heatingwith acidified potassium dichromate(VI) to formbutanone.

Only one-stage conversions will be considered.

Equations and reagents are not necessary for deducing reaction pathways.

All conversion pathways will be assessed equally.

The correct answer clearly states that conversions with more than two stages will not be assessed, and emphasizes the importance of including reagents, conditions, and equations for each stage of the reaction pathway.

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