Higher Chemistry- topic 2

• How is an ester made?

  Esters are formed by the condensation reaction between an alcohol and a carboxylic acid. This is known as esterification. In a condensation reaction, two molecules join and produce a larger molecule whilst eliminating a small molecule. During esterification this small molecule is water. Esters have characteristic smells and are insoluble in water.

  
  

  To make an ester, a hydrogen atom must be removed from the hydroxyl group (-OH) of the alcohol.

  The -OH portion of the acid's carboxyl group must also be removed. The hydrogren atom and the -OH combine to form a water molecule (H2O).

  
• What is an ester link?


  The functional group (-COO) is known as the ester link.

  
• What are esters used for?


  The main use of esters is for flavourings and perfumes, however they can also be used in the chemicals industry as solvents.
• How to name an ester?

  1) change the name of the parent alcohol to end in -yl

  2) change the name of the parent acid to end in -oate

  3) alcohol name goes to the front, acid name to the back
• What is a hydrolysis reaction?

  a reaction in which a bond is broken by the addition of a water molecule

  The breaking up of an ester can be achieved by heating the ester with an alkali such as sodium hydroxide.

  This is an example of a hydrolysis reaction (the opposite of a condensation reaction) as a water molecule is added and breaks up the structure.

  
• What is a condensation reaction?


  When two molecules bond through the loss of a water molecule.

  
• What is esterification?


  a reaction of alcohol with an carboxylic acid to produce an ester and water

  
• how to increase the yield and speed of esterification?

  increase heat

  add concentrated sulphuric acid (acts as a catalyst)
• Making an ester experiment

  -use a water bath not Bunsen because alcohol is flammable

  -sulphuric acid removes water therefore acts as a catalyst and moves equilibrium to the right

  -place cotton wool as a stopper in beaker to catch any chemicals that may spurt out

  -soak a paper towel in cold water and wrap it around the neck of the test tube to act as a condenser when the reaction is being heated
• What is a carboxylic acid?


  Carboxylic acids all contain the carboxyl group (-COOH). When naming carboxylic acids, the same rules as before are followed, but the position of the carboxyl group does not need to be identified, as it is always on C1.

  
• how to name carboxylic acids

  The longest carbon chain in the molecule below contains four carbon atoms. As the carbon of the carboxyl group is the first of the chain, then both branches are on the third carbon.

  
• What is an alcohol?

  Alcohol molecules all contain the hydroxyl (-OH) functional group. They are a homologous series and have the general formula CnH2n+1OH. Their names all end in -ol.
• How to name an alcohol

  Find the longest carbon chain and name it.

  Number the carbon atoms in the chain so that the functional group (in this case, the hydroxyl group) has the lowest possible number.

  Identify any branches joined onto the main chain and name them.

  Identify each branch by a number indicating its position. If more than one branch is present then a prefix must be used.

  
  

  When naming branched chain alcohols, be careful to number the longest possible carbon chain first.

  When writing the name, you follow the convention of using commas between numbers and dashes between numbers and words.
• What are the types of alcohols?

  There are three types of alcohol molecules. The type of alcohol is determined by the position of the hydroxyl functional group.

  -Primary alcohols

  A primary alcohol is one in which the hydroxyl group (-OH) is attached to a carbon atom with at least two hydrogen atoms.

  This will only occur when the hydroxyl group is at the end of the molecule chain.

  Propan-1-ol is a primary alcohol.

  -Secondary alcohols

  A secondary alcohol is one in which the hydroxyl group (-OH) is attached to a carbon with only one hydrogen atom attached.

  This can happen somewhere in the middle of a carbon chain.

  Propan-2-ol is a secondary alcohol.

  -Tertiary alcohols

  A tertiary alcohol is one in which the hydroxyl group is attached to a carbon with no hydrogen atoms attached.

  This will normally mean that the hydroxyl group is joined to the same carbon atom as a branch.

  2-methylpropan-2-ol is a tertiary alcohol.

  Multiple hydroxyl groups

  -Alcohols can have more than one hydroxyl group:

  Alcohols with two hydroxyl groups are called diols

  Alcohols with three hydroxyl groups are called triols

  
• What are the properties of alcohols?

  Compared with alkanes, alcohols have significantly higher boiling points. The hydroxyl groups in alcohol molecules are responsible for hydrogen bonding between the alcohol molecules.

  As greater energy is required to overcome these strong intermolecular forces, the melting points and boiling points of alcohols are higher than those of alkanes with a corresponding chain length.

  Alcohols with a greater number of hydroxyl groups will have even higher boiling points. When an alcohol has two hydroxyl groups it is called a diol. A molecule with three hydroxyl groups is a triol.

  The large increase in the boiling point of alcohols as the number of hydroxyl groups increases is caused by a greater degree of hydrogen bonding between the molecules.
• What are fats and oils?

  naturally occurring esters, formed from condensation reactions between the alcohol glycerol and different long chain carboxylic acids (fatty acids).
• What are fatty acids?

  long chain carboxylic acids ranging from C4 to C28. Common fatty acids including stearic acid and oleic acid have eighteen carbon atoms in their chains.

  
• What's the difference between fats and oils?

  Oils (liquids at room temperature) contain more carbon to carbon double bonds than fats (solid at room temperature).

  The lower melting point of oils is related to the higher degree of unsaturation. The presence of carbon to carbon double bonds in the oil molecules distorts the long fatty acid chains and the molecule's shape. As a result the molecules cannot pack closely together.

  Fat molecules do not have the same degree of distortion and can pack closely together. This increases their melting point.

  The poorer packing in oils makes London dispersion forces between the oil molecules weaker than between fat molecules. Less heat energy is needed to separate oil molecules, so oils have lower melting points than fats.
• What is the structure of fats and oils?

  A glycerol molecule and 3 fatty acid tails

  
• How to tell if a substance is unsaturated or saturated

  The bromine test can be used to determine the level of unsaturation in a fat or oil. Bromine solution will decolourise quickly when it reacts with unsaturated compounds. The more double bonds present in the fat or oil then the more bromine solution that can be decolourised.
• How to increase the mp of an oil?

  To increase the melting point of an oil, addition reactions between the double bonds and hydrogen can take place. This reduces unsaturation and causes hardening.
• What are proteins?


  Proteins are the major structural material of animal tissue

  Proteins are natural condensation polymers formed by joining together thousands of amino acid molecules.

  All proteins contain the elements N,O,H and N

  
• What are fibrous proteins?

  strong/insoluble/inflexible material e.g. collagen and keratin

  held together by hydrogen bonding between N-H and C=O

  
• What are globular proteins?

  soluble proteins with a specific 3D shape e.g. enzymes, hormones, antibodies, haemoglobin

  polypeptide hains held together in spherical shape

  
• What is condensation polymerisation?


  Where monomers with two functional groups join together, usually losing small molecules such as water (which is why they are called condensation reactions)

  
• What is an amide group?

  O=C-NH2

  amide group of one molecule links to carboxyl group of another molecule to form an amino acid

  
• How are proteins broken down?

  hydrolysis during digestion

  
• What is refluxing?


  Refluxing is the boiling of a solution while continually condensing the vapor by cooling it and returning the liquid to the reaction flask

  
• How can you hydrolyse proteins in a lab?

  Reflux it in hydrochloric acid for several hours

  Amino acids can be identified from the paper from thin layer chromatography- a piece of chromatography is spotted with some amino acids suspected as being present and also hydrolysed with proteins
• What happens is you oxidise a primary alcohol?

  The first stage oxidation of a primary alcohol involves the molecule losing two hydrogen atoms to form an aldehyde.

  In the second stage, oxygen is added to the aldehyde molecule to form a carboxylic acid.

  
• What happens is you oxidise a secondary alcohol?

  Form ketones

  
• What happens when you oxidise tertiary alcohols?

  You cant
• What happens during oxidation of alcohols?

  When carbon compounds are oxidised, the oxygen to hydrogen ratio increases, so either oxygen atoms are being added to the compound, or hydrogen atoms removed.
• What is a ketone?


  carbonyl group bonded to 2 carbons(C=O in middle)

  ends with one eg butanone, propanone etc

  
• What is an aldehyde?


  Carbonyl group at the end of a carbon skeleton

  ends with al eg methanal, butanal etc

  
• What happens during oxidation of foods?

  When chemicals in food are exposed to oxygen in the air, their chemical composition changes and they begin to break down, peroxides form

  left unattended, foods will lose their nutritional value as they begin to discolour and break down- food becomes rancid
• What are antioxidants?


  Chemicals that are added to food to prevent food from oxidising (going off) by prevnting the formation of peroxides

  it slows down or prevents oxidation of another chemical
• How do antioxidants cancel our free radicals?

  They donate electrons to the potentially damaging free radical stabilising it therefore the antioxidant becomes oxidised

  
  

  imbalance between them can lead to disease

  free radicals attack cell membrane causing cell and tissue damage and break strands of DNA which can cause cancer

  
• What are the health benefits of antioxidants?

  They safeguard long-term health

  - by reducing the risk of chronic diseases (heart disease, a variety of cancers and disorder of the intestine)

  - By reducing damage to body cells and tissues

  
  

  They maintain a healthy immune system

  - By destroying free radicals which attacked bodies natural defence system.

  
  

  They reduce harmful oxidation of fat in the body

  - By preventing free radicals oxidising polyunsaturated fatty acid foods and in cell membranes to give a substance which causes cell damage

  - By slowing the rate at which LDL-cholesterol is deposited on artery walls, this is reducing the risk of heart disease.
• Ways to stop oxidation of food

  air-tight packaging using inert gases

  antioxidants

  refrigerating