Carbohydrates

• Carbohydrates are compounds made of Carbon, Hydrogen and Oxygen.

• They are made in PHOTOSYNTHESIS

• This process is carried out in the leaves of Green Plants.

• Green plants contain a special pigment called CHLOROPHYLL which traps sunlight. Plants use this energy along with CO2 gas and Water to make food – Glucose (sugar), Oxygen is also released.

• CO2 + H2O —>O2 + C6H12O6

• Light and Chlorophyll must be present for the reaction to take place.

Examples of Carbohydrates

• Carbohydrates contain the elements C.H. and O.• There are twice as many H in the molecules as C and O.• They can be split into 3 main groups: monosaccharides,

disaccharides and polysaccharides.( saccharide = sugar group)• Monosacharides – formula C6H12O6 e.g. glucose, fructose and

galactose. They are isomers.• Disaccharides – formula C12H22O11 e.g.. Lactose, maltose,

sucrose. They are isomers• Polysaccharides – (C6H10O5)n e.g.. Cellulose, starch, glycogen.

Respiration

• Respiration is when Carbohydrates are broken down to release energy. Oxygen must be present.

• CO2 and H2O are produced.

• C6H12O6 +O2 —>CO2 + H2O ( energy is released)

• When we eat food the energy trapped in the food is released.

• We can show that energy is contained in food in the lab.

• Example• Exploding custard tin.• When we burn sugar in the lab

we can test the products. • We use lime water and collect

the colourless liquid produced in a U tube. (CO2 + H2O)

The Carbon Cycle• These 2 reactions working

together make part of the Carbon Cycle.

• Humans can destroy the balance by: Burning – CO2 is produced.

• Chopping down trees/plants- less photosynthesis therefore too much CO2 and less O2 in the atmosphere.

• When any C compound is burned CO2 is produced

( Fossil Fuels)

• Photosynthesis and respiration are the chemical opposites of one another. When they work together without intervention they ensure the correct balance of gases in the air.

• We breathe out CO2. Plants use this in Photosynthesis. They give out O2. We require this for respiration.

• Plants go through respiration when there is no sunlight.

Testing for Carbohydrates

• Iodine test• Starch will turn Iodine

solution from brown to blue/black.

• Benedict’s Test (Fehling’s)

• Monosaccharides and disaccharides – except sucrose will turn Benedict's reagent from blue to orange.

Properties of Carbohydrates

• Mono and disaccharides are usually soluble in water. If you shine a beam of light through it, the light will pass strait through.

• They are sweet tasting.

• Starch is not sweet tasting. It forms a colloid in water – it looks as if it has dissolved but if you shine a beam of light through it you can see the particles. The molecules are too big to dissolve.

Making long chain Carbohydrates

• Disaccharides and polysaccharides are made when monosaccharides undergo condensation polymerisation. 1 water molecule is released for every two monomers joined.

• Example• Glucose +Glucose —> maltose + water• C6H12O6 + C6H12O6 —> C12H22O11 + H2O

Breaking Long Chain Carbohydrates

• Hydrolysis is the break down of Carbohydrates into smaller molecules. E.g. Starch being broken down into Glucose. This is the opposite of polymerisation. A water molecule has to be added back – hydrolysis.

• An acid or enzyme has to be present for this to happen.• Sucrose breaks down to give 1 fructose molecule and 1

glucose molecule.• Sucrose —> glucose + fructose C12H22O11

Acid/enzyme C6H12O6 + C6H12O6

Digestion

• When we eat starchy food our bodies break it down into smaller molecules so they can pass through the gut wall into the blood.

• This is another example of Hydrolysis.• It starts off in the mouth. Saliva contains an enzyme,

amylase, which starts to break down the starch.It continues in the stomach, where acid is found.

• (C6H10O5)n—>C6H12O6– Acid/enzyme

Digestion in the lab

• Place starch solution in 3 different test-tubes• To one add amylase• To another add acid• Add nothing to the third• Place all 3 in water bath at 37C ( body T)• Test each test-tube with Benedict’s solution after a few

minutes.• The test-tubes with the acid and amylase will turn orange

– proving the starch has been broken down into glucose.

Identifying the products of Digestion/Hydrolysis

• Look at how far each spot has travelled.

• Compare the spots of the mono and disaccharides with H1 and H2.

• Match up the spots at same level to identify the which type of sugar is produced in Hydrolysis.

• We can use CHROMATOGRAPHY

• Spot the paper with:the products of hydrolysis of starch(H1) and sucrose(H2) and mono and disaccharides.

• Do not mix the spots.• Let the chromatography run.• Look at results

Fermentation

• Equation• C6H12O6 →C2H5OH

+CO2

• C2H5OH is ethanol.• It is part of the Alkanols.• This is another

homologous series.

• This is the process of making Alcohol from sugar.

• Small sugar molecules can be converted to alcohol, using the enzyme Zymase, which is found in yeast.

• Carbon dioxide is also released.

Alcoholic Drinks

• Alcohol slows down our reactions.

• Too much can damage our livers.

• It can also be used as a fuel.

• You can make alcohol from any carbohydrate source.

• Source Alcohol• Barley Beer/Whiskey• ApplesCider• Grapes Wine/Sherry• Potatoes Vodka

Distillation• We place the impure alcohol in

the distillation flask with antibumping granules.

• Heat up the mixture.• Ethanol has BP of is 78C,

water is 100C.• The alcohol will boil first, pass

along delivery tube and condense back to liquid.

• WE can repeat this process to purify it even more.

• Spirits are distilled.

• WE can increase the strength of alcohol by distilling it. This removes any impurities.( normal alcohol concentration in fermentation is 15% - any stronger and the enzyme is destroyed – DENATURED)

Making Whisky

• Step 3 Fermentation• Yeast added – Glucose

brakes down into ethanol and Carbon dioxide

• Step 4 – Distilling• To purify whisky – increase

concentration.• Step 5 – Blending• Mix different whisky’s then

bottle them( malt whisky - not blended)

• Step 1 – Malting• Barley is Hydrolysed into

Maltose (uses enzyme in Barley) – Green Malt

• Step 2 – Mashing• Green Malt roasted on

peat fire and Mashed