Chemistry C4,5&6

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  • Created by: Lucy
  • Created on: 10-06-13 16:23

The Atom

The atomic number is the number of protons in a atom.

The mass number is the total number of protons AND neutrons in a atom.

Isotopes of a element have different amounts of neutrons.

A atom is neutral because it has an equal amount of electrons and protons so their charges cancel each other out.

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Bonding

Ionic Bonding: A metal and a non-metal

                     Transfer of electrons

                     Gained an electron-negative ion

                     Lost an electron-positive ion

Covalent Bonding: Two non-metals

                            Sharing of electrons

        

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Group 1 Metals

Lithium, Sodium & Potassium.

As you go down the group 1 metals their reactivity increases.

In a flame test:

  • Lithium produces a red flame
  • Sodium produces a orange flame
  • Potassium produces a lilac/pink flame

When they react with water the metal reacts to form a alkali solution and hydrogen gas is given off.

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The Halogens (Group 7)

Flurine, Chlorine, Bromine & Iodine.

As you move down the Halogens their reacticity decreases and the melting and boiling points increase.

At room temp: Chlorine is a green gas; Bromine is a orange liquid & Iodine is a grey solid.

They react with alkali metals to make metal halides.

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Transition Elements

If a transition metal carbonate is heated it decomposes to form a metal oxide and carbon dioxide.

  • Copper compounds are blue
  • iron (II) are pale green
  • iron (III) are orange/brown

They are often catalysts:

  • Iron is used in the Haber Process to make ammonia
  • Nickel is used in making margerine

In order to identify the presence of a transition metal in solution sodium hydroxide is used. When this is added to a solution with a transition metal in it will form a solid precipitate. 

Cu2+ ions form a blue precipitate

Fe2+ ions form a freen/grey precipitate

Fe3+ ions form a orange gelatinious precipitate.

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Equations

Number of Moles= Mass of the chemical/Molar mass (Liquid)

Number of Moles= Volume of gas in dm3/24 (Gas)

Concenrtration= Number of moles/volume of solution

Charge= Current*Time

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Water Purification

The 3 main stages:

Sedimentation- larger bits drop to the bottom

Filteration- Sand is used to filter out small particles

Chlorination- kills microbes

Seawater has may substances in it so its undrinkable. Distillation must be used to remove these dissolves substances.

Water tests; precipitate reactions (two solutions react to form a solid that doesnt dissolve)

Lead sulphate- white precipitate                                  Silver bromide- cream precipitate

Silver chloride- white precipitate                                  Silver Iodide- yellow precipitate

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Empirical Formulae

The empirical formula tells us the ratio of each atom in each compound

  • Write down the mass of each element
  • Look up the Relative Atomic Mass of each element
  • Work out how many moles of each element is present
  • Choose the element present in the lowest amount
  • Divide the moles of each element by the moles in the lowest amount
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Equilibrium

At equilibrium the rate of the forward reaction is equal ti the rate of the backwars reation. The concentration of the products do not change.

Concentration; if you add more reactant equilibrium will move to the right. If you add more product equilibrium will move to the left

Pressure; if you increase the pressure, equilibrium will shift to the side with fewer gas molecules. If you decrease the pressure equilibrium will move to the side with more gas molecules.

Temperature; if you increase the temperature in a exothermic reaction the equilibrium moves to the left reducting the temperature increase. If the forward reaction takes in heat an increase in temperature pushes the equilibrium to the right reducing the temperature increase.

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The Contact Process

The Contact Process is the process which is used to make Sulphuric Acid. During the process there is a reversible reaction like in the Haber Process.

The main stages of the Contact Process are:

  • Sulphur + Oxygen -> Sulphur Dioxide
  • Sulphur Dioxide + Oxygen -> <- Sulphur Trioxide (the reversible reaction) 
  • Sulphur Trioxide + Water -> Sulphuric Acid

For the most economic yeild the reaction is carried out at 450 degrees, at atmospheric pressure and a catalyst of venadium pentoixde is used

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Acids

What determines how storng/weak a acid is?

The concentration of H+ ions.

If there is a high concentration of H+ ions it will have a low pH number so it will be very acidic.

If there is a low concentration of H+ ions it will have a high pH number so it will be alkali.

Strong acids fully ionise when they are dissolved in water, for example HCl -> H+ + Cl-, whereas weak acids dont.

Weak acids react slower than strong acids because as strong acids have a higher concentration of H+ ions they have a higher collision frequency. 

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Titration Reactions

During a titration reaction a acid is neutralised with an alkali. The point of neutralsation occurs when the pH of the solution is 7. 

Acid + Alkali -> Salt + Water

Indicators such as Phenolphthalein, screened methyl orange and litmus give a sudden colour change at the point of neutralisation making the point of neutralisation very easy to spot.

Other indicators such as the universl indicator aren't used in a titration reaction because it has a continuous colour change.

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Electrolysis

The electrolyte used is ionic so the charge can move through the electolyte by the ions moving. If the electrolyte solidifies then the ions cannot move and current cant flow.

Positive ions move towards the negative charged cathode

Negative ions move towards the positive charged anode

In the electrolysis of copper(II) sulphate the cathode becomes plated with pure copper and the anode looses mass.

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Fuel Cells

A fuel cell converts chemical energy directly into electrical energy using no heat. 

Hydrogen + Oxygen -> Water

One of the main uses for fuel cells are in spacecraft as they: are effiecine as they waste very little energy; are lighter than normal batteries; they can be used continuiously; they don't need a special storage system and the only product prodcued is water.

Car makers are also very interested in fuel cells because cars that have fuel cells are much more efficient as so they use less fuel. The fuel does not burn therefore nitrogen oxide isn't produced causing snog; the only product made if water which isnt harmful at all.

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Redox Reactions

In a Redox reaction something is oxidised and something else is reduced.

  • Oxidation is loss of electrons
  • Reduction is gain of electrons

Rusting is a example of redox reaction,

Iron + Oxygen -> Hydrated Iron(II) Oxide

The iron looses electrons and becomes oxidised and the oxygen gains electrons and becomes reduced.

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Alcohols

Fermentation-Glucose -> Ethanol + Carbon Dioxide 

An optimum temperature4 between 25 degrees and 50 degrees is needed for fermentation to take place.

The Ethanol that is produced is dilute so the solution is distilled to get more Ethanol.

Fermentation is carried out under carefully controlled conditions:

  • if the temperature is too cold, the ezymes in the yeast will be inactive
  • if the temperature is too hot, the enxymes in the yeast will denature
  • if air is present, ethanoic acid will be produced instead of ethanol.

Ethanol can also be made by a hydration reaction.

Ethene + Water -> Ethanol (C2H5OH)

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Hardness In Water

Permenant hardness is caused my Calcium Sulphate in water. It can't be removed by boiling the water.

Tempory hardness is caused when rainwater (which has carbon dioxide in it) reacts with calcium carbonate forming Calcium Hydrogencarbonate. It can be removed by heating s the Calcium Hydrogencarbonate decomposes to insoluble Calcium Carbonate and Carbon Dioxide, this causes limescale.

Ion-exchange resins remove both premenent and temporary hardness. It does this by when the water flows over the solid resin of sodium ions which traps the calcium and magnesium ions and pushes the soidum ions into the water instead taking the calcium and magnesium ions of out the water. The sodium iond do not effect the hardness of the water.

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Fats & Oils

Fats & Oils are made from long chains of carbon atoms

  • If the carbon atoms in the chain are linked by single bonds the compound is saturated
  • If the carbon chains contain one or more double bonds the compound is unsaturated

To test if a fat or oil is saturated or unsaturated bromine water is used. When it is shaken with a unsaturated compound it will change colour from orange to colourless.

To turn a unsaturdated fat into a saturated fat hydrogen is bubbled through the oil at about 200 degrees using a nickel catalyst. The hydrogen reacts with the double bonds and turn them into single bonds.

Saponification; when fats are reacted with sodium hydroxide to make soap.

Far + Sodium Hydroxide -> Soap + Glycerol

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