Chemistry C1

Nota:

• Some foods have to be cooked. Reasons why: >Better taste and texture >Easier digestion >to kill microbes >some foods are poisionous when raw (e.g raw kidney beans)

1. Chemical change

   Nota:

   • Cooking food produces new substances, i also creates an IRREVERSIBLE change. This means a chemical change has taken place.
   • NB: Not all chemical changes are irreversible (e.g melted chocolate) however, if it's irreversible you know a chemical change has happened.
   1. Protein

      Nota:

      • Protein molecules change shape when heated. The energy from cooking BREAKS some of the chemical bonds in protein, allowing it to be a different shape.
      • This change is called denaturing.
      • The change makes the food have a more edible texture.
      • The change is irreversable. (E.g you can't UNCOOK an egg.)
   2. Carbohydrate

      Nota:

      • E.g Potatoes Because potatoes are plants, they are surrounded by a ridgid cell wall made of cellulose.
      • When cooking the potato the cell walls rupture (break down) We cook them because we can't digest the cellulose surrounding the cell.
      • Cooking also makes the STARCH grains inside the cells swell and spread. This makes the potatoe softer and more digestible.
2. Baking Powder

   Nota:

   • When heated baking powder undergoes THERMAL DECOMPOSIUTION.
   • Thermal decompositon is when ONE substance breaks down into lots of other simpler substances when heated. Usually  catalyst is used to help the process.
   • baking powder>other substances sodium hydrogencarbonate> sodium carbonate + carbon dioxide + water 2NaHCO_3>Na_2CO_3+CO_2+H_2O
   • The carbon dioxide (CO_2) produced causes cakes to rise. [CO_2 test= cloudy limewater]
3. Emulsifiers

   Nota:

   • These help water and oil mix. Oil and water would otherise seperate.  
   • One part of an emulsifier is a part which is attracted to water this is called the HYDROPHYLIC end. The other part is attracted to oil this is called the HYDROPHOBIC end. 
   • The hydrophilic part bonds to the water molecule. The hydrophobic part bonds to the oil molecule.  When you shake the oil and water together with the emulsifier, the oil forms droplets, surrounded by the emulsiphier wich bonds to the water forcing them together.
   • Other oil droplets are repelled by the water surrounding each other so they don't attactch to each other and mix.
4. Additives

   Nota:

   • Additives are added to foods to make them look better, taste better and keep for longer.
   • 1) Food colours- make the food look more appealing
   • 2) Flavour enhancers- bring out the taste and smell of food without ading taste of their own
   • 3) Antioxidants- help preserve food
   • 4) Emulsiphiers- help oil and water join together

Nota:

• Esters are naturally occuring chemicals which smell sweet and fruity.

1. Perfumes

   Nota:

   • Chemicals that smell nice are used as perfumes. Esters are often used as perfumes.
   • You need a substance with certain properties to make it a perfume: 1) Easily evaporating- or the particles won;t reach your nose and you won't smell it
   • 2) Non-toxic- it mustn't seep through skin and poison.
   • 3) Doesn't react with water- or it will react with the water in sweat.
   • 4) Doesn't irritate the skin- So it can be applied straight to the neck/wrists, without the risk of burning.
   • 5) Insoluble in water- so it doesn't wash off everytime the skin gets wet.
   1. Natural

      Nota:

      • Esters are natural perfumes. Lots of fruity smells-like apple- and flowers- like jasmine- contain natural esters.
   2. Artificial

      Nota:

      • Esters can be manufactured synthetically to be used as perfume. E.g there are esters that smell of lavender, orange, cinamon etc.
2. Esterification

   Nota:

   • You can make an ester by heating a carbolic acid [an acid built around one or more carbon atoms] with alcohol.
   • An acid catalyst is usually used. (E.g concentrated sulphuric acid)
   • Acid + Alcohol -> Ester + Water
3. Volatility

   Nota:

   • Volatility's how we smell stuff.
   • When a liquid is heated the heat energy makes the particles move really fast.
   • Some particles move faster than others.
   • Fast moving particles AT THE SURFACE will overcome the forces of attraction from the other  particles and escape. This is EVAPORATION.
   • How easily a a liquid evaporates is called it's volatility.
   • When the particles have escaped they travel through the air. When they are detected by the smell detectors in your nose you smell it.
   • Perfumes have to have a high volatility so they can evaporate enough to smell them.
   • The particles in a liquid perfume have very week forces so it's easy to over come the force and escape-so you only need little heat energy to make the particles escape. (This happens when perfume is put onto skin.)

1. Atoms, their nucleus and electrons

   Nota:

   • Within atoms there is a centre nucleus (positively charged) surrounded by electrons on shells (with a negatice charge). 
   • Atoms can from bonds to make molecules and compounds. The electrons are involved in making bonds NOT the nucleus. The electrons loose or gain electrons to other atoms to make the bonds. This exchange changes the atom's overall charge.
   • Charged atoms are known as IONS. A positive ion has LOST electrons, a negative ions had GAINED ions. If a positive ion meets a negative one then the join together. This is called their ionic bond.
   • Another form of bond is a covalent bond. These are atoms which share their electrons.
2. Displayed and Molecular formulas.

   Nota:

   • CH_4 (Small 4) This is the molecular formula of Methane. It contains 1 carbon aton (C) and 4 Hydrogen atoms (H_4). 
   •     H H-C-H     H This is a dispayed formula. It shows the Methane atom as a picture (1 carbon and 4 hydrogen)
3. Formulas to remember

   Nota:

   • Carbon dioxide CO_2 Hydrogen H Water H_2O Oxygen O_2 Carbon Monoxide CO Hydrochloric acid HCl Calcium chloride CaCl_2 Magnesium Chloride MgCl_2 Sodium Carbonate Na_2CO_3 Calcium Carbonate CaCO_3 Sulphuric acid H_2SO_4 Magnesium sulfate MgSO_4

1. Solids

   Nota:

   • There are strong forces of attraction between particles which holds them in fixed positions in a LATTICE arrangement.
   • The particles don't move from their positions, so all solids keep a definate shape and volume- unlike liquids.
   • The particles vibrate in their positions- the hotter the solid becomes the more they vibrate. This causes solids to expand slightly when they get hot.
2. Liquids

   Nota:

   • There is some force of attraction between the particles. They're free to move past each other but they do tend to stick to each other.
   • Lioquids don't keep a definate shape and will flow to fill the bottom of a container. But they do keep the same volume.
   • The partices contantly move wih random motion. The hotter the liquid the faster they move. This causes liquids to expand slightly when heated (boiling).
3. Gases

   Nota:

   • There's next to no force between bag particles- they're free to move. They travle in straight lines and only interact when they collide.
   • Gases don't keep a definate shape or volum and will always fill any container. When particles bounce off the wals of a container they exert a presure on the walls.
   • The particles move contantly with random motion. The hotter a gas gets, th faster they move. Gases either expand when heated, or their pressure increases.