Chemistry acidic 3~

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Chemistry acidic 3~
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  1. What is ionisation
    The dissociation of molecules or compounds into smaller charged particles called ions
  2. What is the Bronsted-Lowry Theory of acids
    • -An acid is a proton donor
    • -A base is a proton acceptor
  3. Describe the ionisation of acids in water
    - Acids ionise in water to release hydrogen ions

    • - Acid molecules react with water by donation a proton to form a hydronium ion (H3O+)
  4. Identify Acetic acid
    (Ethanoic acid)

    • -CH3COOH
    • - Used in vinegar (around 4% of vinegar is acetic acid)

    -Manufactured industrially
  5. Identify Citric acid
    (2-hydroxypropane-1,2,3-tricarboxylic acid)

    - C6H8O7

    - Occurs naturally in fruit

    - Added to food as preservative and flavouring
  6. Identify Hydrochloric acid
    (HCl)

    - Found in the stomach of humans

    -Produced industrailly on a large scale
  7. Identify Sulfuric acid
    (H2SO4)

    - Can be produced from volcanic eruptions

    -Can be produced from smelting of ores

    - Used as an acid catalyst

    -Used as a dehydrating agent
  8. Describe the use of the pH scale in comparing acids and bases
    - Allows us to measure acidity of various samples by comparing concentrations of Hand OHions in solution
  9. Describe acids and their solutions with the appropriate use of the terms strong, weak, concentrated and dilute
    - "Concentrated" and "Dilute" refer to the amount of acid added relative to volume of water

    -"Strong" and "Weak" refer to the extent to which an acid dissociates into its ions in solution in water
  10. Identify pH as -Log10[H+] and explain that a change in pH of 1 means a ten-fold change in [H+]
    -A formula is used to determine pH given the concentration of hydronium ions:

    pH= -log[H+]

    - A change in pH of 1 means a ten-fold change in [H+]
  11. Compare the relative strengths of equal concentrations of citric, acetic and hydrochloric acids and explain in terms of the degree of ionisation of their molecules
    -HCl is a strong acid and completely ionises in solution

    -Citric acid is a weak acid and only partially ionises in solution

    - Acetic acid is an even weaker acid and is monoprotic
  12. Describe the difference between a strong and a weak acid in terms of an equilibrium between the intact molecule and its ions
    Strong acids

    • -Strong acids completely ionise in water to produce hydronium ions in solution
    • -No equilibrium
    • -e.g.

    Weak Acids 

    • -Weak acids only partially ionise in water
    • -Equilibrium is established between acid molecules and its ions

    -e.g.

    Strong Bases

    -Strong bases completely ionise in warter to produce hydroxide ions in solution 

    • -e.g. 

    Weak Bases

    - Some molecules or ions react with water to form hydroxide ions in aq solution

    • -e.g. 

  13. Explain the use of acids as food additives
    • - Improves taste
    • - Preserves food

    -Common acids added: acetic, citric, phosphoric, propanoic
  14. Outline Lavoisier's theory of acids
    Proposed that acids were substances that contained oxygen

    • Limitations
    • -Some acids contained no oxygen e.g. HCl
    • -Metal oxides formed bases in solution
  15. Outline Davy's theory of acids
    Proposed that acids were substances that contained replacable hydrogen

    • Limitations
    • -Could not explain why some hydrogen containing substances were not acidic
  16. Outline Arrhenius's theory of acids
    Proposed acids were substances that ionized in solution to produce hydrogen ions

    • Limitations
    • - Only applied to aqueous solutions
    • - Does not explain why some salts act as acids
  17. Identify conjugate acid/base pairs
    -Products of acid-base reactions are the conjugate acids and bases

    -When an acid donates a proton, it forms its conjugate base

    -When a base accepts a proton, it forms its conjugate acid

    • Generalisation
    • -Strong acids will have weak conj bases
    • -Strong bases will have weak conj acids
    • -Weak acids will have stronger conj bases
    • -Weak bases will have stronger conj acids
  18. Identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic nature
    -Neutral salts contain ions that do not react with water

    -Basic salts contain ions that react with water to from OHions

    - Acidic salts contain ions that react with water to form H3O+ions

  19. Identify amphiprotic substances and construct equations to describe their behaviour in acidic and basic solutions
    -Amphiprotic substances can accept or donate protons

    -This means they can act as either an acid or a base

    - An amphoprotic substance must contain a donateable hydrogen ion

    -All amphiportic substances are amphoteric but not all amphoteric substances are amphiprotic

    E.g. Water

    • Acting as an acid

    • Acting as a base

    Self ionisation of water

    -One molecule of water acts as an acid and one molecule of water acts as a base

  20. Identify neutralisation as a proton transfer reaction which is exothermic
    -Neutralisation reactions are acid-base reactions involving a proton transfer which is exothermic

    -It is exothermic since it forms covalent bonds between hydrogen and oxygen when water is formed
  21. Qualitatively describe the effect of buffers with reference to a specific example in a natural system
    Effect of Buffers

    -Buffer solutions resist changes to pH when small amounts of acids or bases are added

    -Buffers are an aq mixture in roughly equal amoujnts of a weak acid and its conjugate base or a weak base and its conjugate acid

    Buffers in a natural system

    -The buffer system used in blood is carbonic acid and hydrogen carbonate ions
  22. Describe the differences between the alkanol and alkanoic acid functional groups in carbon compounds
    -Alkanols have at least one hydroxly (-OH) group bonded to a carbon

    -Alkanoic (carboxylic) acids have at least one carboxyl group (-COOH)
  23. Identify the IUPAC nomenclature for describing the esters produced by reactions of straight-chained alkanoic acids from C1 to C8 and straight-chained primary alkanols from C1 to C8
    Esters are named in 2 parts

    • First Part
    • - Comes from alkanol
    • -e.g. ethyl (suffix '-anol' changes to '-yl')

    • Second Part
    • - Comes from acid
    • -e.g. Butanoate (suffix '-oic' acid changes to 'oate')
  24. What is an ester
    A reaction between an alkanol and an alkanoic acid forms an organic compound called an ester
  25. Explain the difference in melting point and boiling point caused by straight-chained alkanoic acid and straight-chained primary alkanol structures
    In Alkanols

    • -C-O and O-H bonds are polar
    • - Able to form hydrogen bonds: strong intermolecular forces between alkanol molecules

    -Thus higher b.p. than corresponding alkanes/enes

    In Alkanoic Acid

    • -Additional C=O bond
    • -forms even stronger hydrogen bonds: even stronger intermolecular forces

    -Even more energy needed to separate molecules


    Both, alkanols and alkanoic acids have higher m.ps than hydrocarbons of similar molecular mass
  26. Identify esterification as the reaction between an acid and an alkanol and describe, using equations, examples of esterification
    -Esterification is the condensation reaction between an alkanoic acid and an alkanol to form an ester

    -Esterification is reversible

    • e.g. 
    • conc.H2SO4 as catalyst
  27. Describe the purpose of using acid in esterification for catalysis
    -Conc. H2SOis needed to lower activation energy

    - Conc. H2SO4 increases yield, as it is a dehydrating agent therefore shifts the equilibrium to the right according to Le Chat
  28. Explain the need for refluxing during esterification
    Refluxing is the process of ehating a reaction mixture in a vessel with a cooling condenser attached

    - Cooling condenser prevents loss of any volatile reactant or product

    -Esterification requires thermal energy to reach equilibrium , therefore, without refluxing it would take days to reach equilibrium
  29. Outline some examples of the occurrence, production and uses of esters
    Esters are frequently found in many parts of nature

    Esters have pleasant, sweet, fruity odours

    Occurence

    -Many odours and scents of fruits and flowers are caused by the presence of esters

    -Solid animal fats and plant oils are esters

    Production

    -There is a substantial industry that manufactures and develops synthetic flavours and perfumes

    Uses

    • -Food: margarine, flavours, fragrances
    • -Soaps
    • -Solvents
    • -Cosmetics
  30. Identify and describe the uses of esters as flavours and perfumes in processed foods and cosmetics
    -Esters are widely used as flavours and perfumes in processed foods and cosmetics

    • Ethyl Ethanoate
    • -has a pear and wine-like odour
    • -used in nail polish remover and perfumes

    • Butyl Ethanoate
    • -Pleasant odour
    • -used in flavouring of confectionary and ice cream
    • -alse used as solvent

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