CRS – Organic Chemistry

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Organic Chemistry
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Chemistry of Carbon
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Chemistry of Carbon
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Organic Chemistry
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State 4 reasons why carbon is so special
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– 4 outer electrons – 4 covalent bonds – forms chains or rings – huge number of possible variations
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State the 4 types of formulae found in Organic Chemistry
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– molecular -structural -displayed -skeletal
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molecular formula
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structural formula
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CH3CH2CH3
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displayed formula
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skeletal formula
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What is a functional group?
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– groups of atoms that are attached to carbon skeletons -they confer a characteristic set of properties and reactions -they give rise to homologous series
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– groups of atoms that are attached to carbon skeletons -they confer a characteristic set of properties and reactions -they give rise to homologous series
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Functional groups
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What is a homologous series?
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-group of molecules that have the same functional group but differ in the length and structure of the carbon chain
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Group of molecules that have the same functional group but differ in the length and structure of the carbon chain
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Homologous series
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State the 8 homologous series.
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– Alkanes – Alkenes -Arenes -Halogenoalkanes – Aldehydes -Ketones -Carboxylic acids
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What is the general formula of alkanes?
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CnH2n+2
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Which homologous series has this general formula: CnH2n+2?
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Alkanes
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What 2 types of bonds do alkanes have?
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C-C and C-H
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Why are alkanes not very reactive?
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because C-C bonds are not polar and C-H bonds are not significantly polar.
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Why are alkanes said to be saturated hydrocarbons?
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because they only have single bonds (C-C and C-H)
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How are alkanes classified wrt their bonding.
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saturated hydrocarbons
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What are the bonds present in alkanes consisting of an overlapping between atomic orbitals?
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Sigma Bonds
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State the 10 prefixes used to name the carbon chains.
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1. meth- 2. eth- 3.prop- 4. but 5. pent- 6. hex- 7. hept- 8. oct- 9. non- 10. dec-
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How many carbon does a methane chain have?
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1
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How many carbon does an ethane chain have?
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2
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How many carbon does a propane chain have?
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3
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How many carbon does a butane chain have?
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4
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How many carbon does a pentane chain have?
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5
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How many carbon does a hexane chain have?
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6
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How many carbon does a heptane chain have?
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7
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How many carbon does an octane chain have?
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8
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How many carbon does a nonane chain have?
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9
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How many carbon does a decane chain have?
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10
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What suffix is added to name an unbranched chain?
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-ane
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What suffix is added to name a branched chain?
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-yl
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What prefix is added to name a ring structure?
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cyclo-
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What is the general formula of alkenes?
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CnH2n
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What homologous series has the following general formula: CnH2n?
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Alkenes
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What bonds do alkenes have?
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C=C
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How are alkenes classified according to their bonding?
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Unsaturated hydrocarbons
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Why are alkenes said to be unsaturated hydrocarbons?
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Because they have C=C double bonds
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Why are alkenes more reactive than alkanes?
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Because the electrons are not held between the carbons but within an electron cloud above or below the molecule. Positive things are likely to be attracted to the high electron density.
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Which homologous series has a free rotation around its bonds?
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Alkanes
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Which homologous series has a restricted rotation around its bonds?
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Alkenes
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Which chain is the principle chain in alkanes?
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The longest chain
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Which chain is the principle chain in alkenes?
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the chain with the double bond.
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Which suffix is added to the principle chain when naming alkenes?
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-ene
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Which carbon number do we use to indicate the position of the double bond in alkenes?
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the lowest number
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How are arenes classified according to their structure?
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aromatic hydrocarbons
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What functional group do arenes have?
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a benzene ring
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How are the electron spread in arenes?
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They exist in an overlapping p orbital which produces a system of Pi molecular orbitals spread over the entire ring structure.
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How many Carbons and Hydrogens does a benzene ring have?
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6 carbons 6 hydrogens
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How do you recognise a benzene ring?
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6 carbons 6 hydrogens
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How does benzene achieve the maximum overlap?
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it has a planar structure
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Why does benzene have a planar structure?
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To achieve the maximum orbital overlap
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State the 3 main properties of arenes.
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– high degree of energetic stability -undergoes combustion, found in crude oil and petrol – relatively unreactive
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Why are arenes relatively stable?
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Because of their delocalised Pi molecular orbitals.
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What property of arenes is due to their delocalised Pi molecular orbitals?
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high degree of energetic stability
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Where are arenes found?
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– in crude oil – in petrol
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What word do we add to name arenes?
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-benzene
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What are the 2 other names for halogenoalkanes?
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– haloalkanes – alkyl halides
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What are the 2 other names for haloalkanes?
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-halogenoalkanes – alkyl halides
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What are the 2 other names for alkyl halides?
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– halogenoalkanes – haloalkanes
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Which atoms are found in halogenoalkanes?
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halogen atoms
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State the 4 halogen atoms
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– fluorine – chlorine -bromine – iodine
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What does aliphatic mean?
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straight chain
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How is a straight chain compound called?
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Aliphatic
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How is a ring compound called?
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Aromatic
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What is the opposite of aliphatic?
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aromatic
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What is the opposite of aromatic?
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Aliphatic
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What is the general formula of alcohols?
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CnH2n+1OH
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What suffix do we add when naming alcohols?
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-ol
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What common functional group do aldehydes and ketones have?
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carbonyl group (C=O)
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Which homologous series have a carbonyl group?
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– Aldehydes – Ketones
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What functional group do alhedydes have?
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Carbonyl (C=O)
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What functional group do ketones have?
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Carbonyl (C=O)
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Where is the carbonyl group found in aldehydes?
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at the end of the carbon chain
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Where is the carbonyl group found in ketones?
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in the middle of the chain
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What suffix do we add when naming aldehydes?
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-al
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What suffix do we add when naming ketones?
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-one
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What is the functional group found in carboxylic acid?
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Carboxyl (-COOH)
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How do we name branched carboxylic acids?
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count from the carbon atom in the -COOH group
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What homologous series has a hydroxyl group?
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alcohols
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What homologous series has a carboxyl group?
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Carboxylic acids
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What is the common name of methanoic acid?
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Formic acid
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What is the common name of ethanoic acid?
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Acetic acid
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What is the common name of propanoic acid?
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Propionic acid
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What is the common name of butanoic acid?
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Butyric acid
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What is the common name of pentanoic acid?
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Valeric acid
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What is the common name of hexanoic acid?
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Caproic acid
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What is the actual name of Formic acid?
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Methanoic acid
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What is the actual name of Acetic acid?
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Ethanoic acid
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What is the actual name of Propionic acid?
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Propanoic acid
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What is the actual name of Butyric acid?
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Butanoic acid
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What is the actual name of Valeric acid?
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Pentanoic acid
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What is the actual name of Caproic acid?
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Hexanoic acid
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What is the natural origin of methanoic acid?
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ants
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What is the natural origin of ethanoic acid?
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vinegar
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What is the natural origin of propanoic acid?
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acne bacteria
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What is the natural origin of butanoic acid?
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sheep, buffalo milk
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What is the natural origin of pentanoic acid?
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valeria plant
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What is the natural origin of hexanoic acid?
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goat
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What is the natural origin of Formic acid?
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ants
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What is the natural origin of Acetic acid?
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vinegar
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What is the natural origin of Propionic acid?
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acne bacteria
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What is the natural origin of Butyric acid?
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sheep, buffalo milk
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What is the natural origin of Valeric acid?
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valeria plant
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What is the natural origin of Caproic acid?
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goat
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Which acid is found in ants?
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Formic acid (=methanoic acid)
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Which acid is found in vinegar?
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Acetic acid (=ethanoic acid)
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Which acid is found in acne bacteria?
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Propionic acid (=propanoic acid)
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Which acid is found in sheep and buffalo milk?
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Butyric acid (=butanoic acid)
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Which acid is found in valeria plant?
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Valeric acid (=pentanoic acid)
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Which acid is found in goats?
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Caproic acid (=hexanoic acid)
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What is a Fatty acid?
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a long-chain unbranched carboxylic acid
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What is the common name of dodecanoic acid?
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lauric acid
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What is the common name of tetradecanoic acid?
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myristic acid
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What is the common name of hexadecanoic acid?
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palmitic acid
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What is the common name of hexadecan-9-enoic acid?
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palmitoleic acid
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What is the common name of octadecanoic acid?
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stearic acid
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What is the common name of octadecan-cis-9-enoic acid?
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Oleic acid
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Where is malic acid found?
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in various fruits
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Where is pyruvic acid found?
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it’s a metabolic intermediate
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Where is niacin found?
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it’s a vitamin
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Where is citric acid found?
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in citrus fruits
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Where is biotin found?
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its a cell growth factor
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Where is abietic acid found?
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in pine resin
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Where is cholic acid found?
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in bile
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What governs the physical properties of carboxylic acids?
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their ability to form hydrogen bonds
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How does the boiling points of carboxylic acids vary in comparison to those of alcohols of similar sizes?
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The boiling point of carboxylic acids is higher than that of alcohols of similar sizes.
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Explain why the boiling point of carboxylic acids is higher than that of alcohols of similar sizes.
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-The higher boiling point of carboxylic acids is due to hydrogen bonds. -In a pure carboxylic acid, hydrogen bonding can occur between 2 molecules to form a dimer. -This dimer immediately doubles the size of the molecule -As the molecule is bigger, the number if instantaneous dipole – induced dipole and intermolecular forces is increased (between one of these dimers and its neighbours). -So it is more difficult to separate the molecules -So carboxylic acids have a higher boiling point than equivalent alcohols
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Describe the solubility in water of carboxylic acids.
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– in water, carboxylic acids don’t dimerise – carboxylic acids containing up to 4 carbon atoms will mix up with water in any proportion -solubility of larger acids decreases with size
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Explain why carboxylic acids don’t dimerise in water but they do in non polar solvents.
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– in water, carboxylic acids form a lot of hydrogen bonds with water molecules – in polar solvents, there is no other bond possible so dimers are formed, inducing permanent dipoles
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Explain why carboxylic acids are acids.
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-An acid is a compound that donates H+ in solution – carboxylic acids can give out the H present on the hydroxyl group (OH)
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Explain why carboxylic acids are more acidic than alcohols.
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1. C=O – the C=O bond has an effect on the O-H bond – it draws the e- away (towards it), making the O-H bond weaker (more likely to dissociate and release an H+) 2. Anion Stability – the interactions of Pi orbitals alows the delocalisation of e- around the carboxylic acid -so the charge is no longer localised to 1 atom -this stabilises the anion (resonance structure)
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Give the 2 main reasons why carboxylic acids are more acidic than alcohols
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1. C=O e- drawing effect 2. Anion stability
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What is the resonance structure in carboxylic acids?
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-its is the interaction of Pi orbitals which allows the delocalisation of e- around the carboxylic acid in the anion (spread of the negaive charge between the 2O) -it stabilises the anion -that is one of the reasons why carboxylic acids are more acid than alcohols of similar sizes
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Give the equation of the dissociation of ethanoic acid.
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– CH3COOH + H2O CH3COO- + H3O+ or -CH3COOH(aq) CH3COO- + H+
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What type of acids are carboxylic acids?
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weak acids
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Explain why carboxylic acids are said to be ‘weak acids’?
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Their dissociation is reversible and only partial
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In the dissociation of ethanoic acid, what portion of ethanoic acid reacts to form ions at any one time?
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1%
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Describe the dissociation of carboxylic acids in one sentence.
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In solution, a H+ ion is transferred from the carboxylic acid to a water molecule.
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Recall how the pKa relates to the pH.
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– The lower the pKa, the lower the pH, the stronger the acid (the more dissociation occurs)
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Which substituents make a weaker carboxylic acid?
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alkyl groups
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Which substituents make a stronger carboxylic acid?
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halogens
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What effect has the addition of alkyl groups on a carboxylic acid?
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– the alkyl groups push the e- towards the carboxyl group -this makes the anion more negative, so less stable (more likely to reform the acid) -and it makes the O-H bond more stable (prevents it from becoming an ion by preventing the shift of the H e- to go towards the O) -so adding an alkyl goup makes it a weaker acid.
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What effect has the addition of halogens on a carboxylic acid?
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– halogens draw e- away (towards them) – this makes the anion less negative, so more stable (by spreading the negative charge) -and it makes the O-H bond weaker (e- are shifted towards thr H which is more likely to break) -so adding a halogen makes it a stronger acid. -the closer the halogens are from the carboxyl group, the stronger the effect
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How does the drawing effect of halogens vary with their proximity to the carboxyl group in carboxylic acids?
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The closer the halogens are to the carboxyl group, the stronger their effect.
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Describe how you would distinguish between a carboxylic acid, an aldehyde, an ketone and an inorganic acid (4 ways).
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– pH: Highest pH for carbonyls (aldehydes & ketones) – less acidic – Benedict’s: no further oxidation of ketones – Brady’s: no reaction with carboxylic acids – Neutralisation
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What are the 2 functional groups involved in an ester bond?
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– carboxylic acid -COOH – alcohol -OH
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What type of reaction forms ethyl ethanoate?
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esterification
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Which two substances react together in an esterification reaction to form ethyl ethanoate?
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– ethanol – ethanoic acid
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Which catalyst is usually used to form ethyl ethanoate?
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concentrated sulphuric acid
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What is the role of concentrated sulphuric acid in the formation of ethyl ethanoate?
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catalyst
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State the two main things involved in esterification?
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– association of -COOH with -OH – release of a water molecule
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In esterification, which compound provides 1 H atom for the formation of a water molecule?
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the carboxylic acid
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In esterification, which compound provides 1 H and 1 O atom for the formation of a water molecule?
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tthe alcohol

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