Chemistry Module 3

The Periodic Table - 1.1 The Early Periodic Table

The early way of organising elements in the 19th cent. was based on Atomic Mass - scientists had discovered many elements but did not know the structure. 

The Law of Octaves 

• 1863 from Newland
• Similar properties repeated every eighth element.
• 62 elements into 7 groups according to atomic weight.
• Not accepted because after Calcium, the elements did not match very well. 

Mendeleev's Periodic Table 

• 1869 from Mendeleev (Russian)
• Left gaps for undiscovered elements so that known properties matched. Left predictions for the missing elements
• Scientists accepted when some of the missing elements were discovered with propreties that matched the predictions. 
• Basis for the Periodic Table. 

The Periodic Table - 1.2 The Modern Periodic Table

Protons and Electrons discovered at start of 20th Century. Soon after models of electronic configuration were produced. This meant the Periodic Table was then arranged in Atomic Numbers rather than Atomic Mass. 

They became lined up in vertical groups.

Groups of elements have similar properties because their atoms have their atoms have the same number of electrons in the outer shell. For main groups the number of electrons in outer shell is the same as the group number. 

Reactivity Within a Group

• The more the outer shells, the least attracted to the nucleus the electrons in the outer shell are. This makes these elements more reactive
• Since each row in the Periodic Table represents a new energy shell, the further down a column you go, the more reactive an element is. 
• When non-reactive metals react they gain so the reactivity of non-metlas decreases down a group.
• When metals react they lose electrons so the reactivity of metals in a group increases going down the group. 

The Periodic Table - 1.3 Group 1 (The Alkali Metals)

• The Group 1 metals (alkalli metals) all react strongly with water and air.
• One electron in outer shell 
• Lose this electron in reactions to form Ionic Compounds in which ions have a single positive charge. 
• Soft solids at room temperature
• Low melting and boiling points (these decrease going down the group)
• Low densities (Lithium, Potassium and Sodium all float on water)
• React with water to produce hydrogen gas and a metal hydroxide that is an alkali. 

Alkali Metal + Water = Metal Hydroxide + Hydrogen
Sodium + Water = Sodium Hydroxide  + Hydrogen

• React with Halogens (Group 7) to form salts that are white or colourless crystals - 

Sodium + Chlorine = Sodium Chloride

Compounds of Alkali Metals dissolve in water forming (usually) colourless solutions. 

The Periodic Table - 1.4 The Transition Elements

• Found between Groups 2-3. 
• Metals in between. So nicknamed the 'Transition Metals' 
• Higher melting and boiling points than the alkaline metals (except for Mercury)
• Malleable
• Ductile 
• Good conductors of heat and electricity
• Only react slowly (if at all) with Oxygen and water at ordinary temperatures. 
• Most are strong and dense - useful building materials. 
• Form positive ions with various charges e.g. Fe(2+) and Fe(3+)
• Compounds of transition metals are often brightly coloured.
• Many transition metals and tehir compounds are catalysts for chemical reactions.

The Periodic Table - 1.5 Group 7 (The Halogens)

• Non-metallic elements in Group 7
• Fluorine, Chlorine, Bromine and Iodine
• Small molecules made of pairs of atoms. 
• Low melting and boiling points that increase going down the gas. 
• Seven electrons in their highest occupied shell
• Form ionic compounds with metals in which the Halide Ions have a charge of 1-. 
• Form molecules with non-metals.
• Reactivity of Halogens decreases going down the group - a more reactive halogen is able to displace a less reactive halogen from an aqueous solution of a halide ion. 

The reactivity of the Halogens decreases going down Group 7 because the attraction of the outer electrons to the nucleus decreases as the number of occupied energy levels (shells) increases. 

Water - 2.1 Hard Water

Soft Water forms a lather with soap much more effectively/quickly then hard water. This is because hard water contains dissolved compounds that react with soap to form an insoluble solid called scum. Other detergents (soapless detergents) do not react with hard water. 

• When water is in contact with rocks some compounds dissolve. If the water contains dissolved calcium or magnesium ions, these will react with soap to form scum and so the water is hard. 
• Temporary hard water when heated forms scale - an insoluble solid. This reduces the efficiency of heating systems and causes blockages. 
• Calcium compounds are good for our health , helping to develop strong bones and teeth. Calcium may reduce the risk of heart disease. 

 DO NOT CONFUSE SCUM AND SCALE THEY ARE VERY DIFFERENT EVEN THOUGH THEY ARE BOTH EFFECTS OF HARD WATER. 

Water - 2.2 Removing Hardness

Soft water may contain dissolved substances but it doesn not produce scum or scale. 

Hard water can be made soft by removing the Magnesium and Calcium ions in it. 

• Temporary Hard Water becomes soft after boiling because the heating causes the Magnesium and Calcium ions to form insoluble solid - scale - thus purifying the water. 
• Permanent Hard Water is not softened by boiling and does not produce scale when heated.

• Precipitation - Precipitate out the ions. Add washing soda (sodium carbonate). This reacts with Calcium ions and Magnesium ions in the water to form solid Calcium Carbonate and Magnesium Carbonate that cannot react with soap. 

• Ion-exchange Column - This must eb packed with resin containing Sodium/Hydrogen ions. When water is passed through the Magnesium/Calcium ions become attatched to the resin and sodium ions or hydrogen ions take their place in the water. These don't react with soap. 

Temp. Hard Water contains Hydrogencarbonate ions (HCO(3)(-). These decompose when heated to produce carbonate ions, water and CO(2). Carbonate ions react with calcium/Magnesium ions to produce precipitates of Calc. Carbonate and Mag. Carbonate that become scale - 2HCO(3)(-) aq. = CO(3)(2-) aq. + H(2)O liq. + CO(2) gas

Water - 2.3 Water Treatment

• Water for consumption should be free of harmful substances and have low levels of microbes and dissolved salts.
• Water can be treated to make it safe (often by sedimentation and filtration to remove solids), this is followed by disinfection (often Chlorine to kill microbes). 
• Water filters can be used to improve taste of water. Often contain Carbon and an ion-exchange resin that remove some soluble substances and silver or another substance  to prevent the growth of bacteria. 
• Pure water can be made by distillation. Requires a lot of energy to boil the water and so it would be very expensive to  do on a large scale. 

Three steps for drinking water - Suitable source, Removal of solids, killing of microbes

Water - 2.4 Water Issues

Hard Water + and - 

• Causes problems in heating systems and with washing
• Drinking it has health benefits (contains Calcium)
• Treatable to suit demands. 

Chlorine for Killing Microbes + and  - 

• Particularly effective
• Poisonous and can produce toxic compounds. Use must be controlled to minimise risks

Flouride Compounds + and  - 

• Added to tooth paste and to water supplies to help prevent tooth decay.
• People should be able to choose whether they want it (this is a weak argument against I know) 

Energy Calculations - 3.1

When foods or fuels react with oxygen it is an exothermic reaction - amounts of energy released depend on the food/fuel. Can be measured in Joules or calories. (1 cal = 4.2 J)

Calorimeter - Used to measure the amount of energy released when substances burn. Simplest is to buil some water with the burning fuel and calculate the change in temperature. This can then be done using this calculation - 

 Q (amount of energy transferred, J)= m (mass of water, g) x c (Spec. Heat capacity, J/g degrees C)  x (triangle sign)T (Temperature change in degrees C)

• Simple Calorimeters do not give accurate results for the energy released because much is used to heat surroundings. Results can be used in a comparison. 
• To compare the energy re;eased by burning different substances either the energy change in kJ per gram or the energy change in kJ per mole can be used. 
• The energy change in kJ/mol can be calculated by multiplying the energy change in kJ/g by the relative formula mass of the substance. 

Energy Calculations - 3.2 Energy Transfers in Solutions

When a reaction takes place in a solution, energy is transferred to or from the solution. 

We do reactions in an insulated container to reduce energy transfers to surroundings. 

We can measure the temperature change of the solution and use this to calculate the energy change using the equation Q = mc(triangle)T. For these equations we assume the solutions act like water. This means that 1 cm cubed of solution has a mass of 1 g and the specific heat capacity of the solution is 4.2 J/g degrees C. 

Rules

• When a solid is added to the solution we assume the volume of the solution does not change. We also assume that 1 cm cubed of solution has a mass of 1 g and that its specific heat capacity is 4.2 J/g degrees C. 
• If we know the number of moles involved in the reaction for which we have calculated the energy change we can calculate the energy change for the reaction. in kJ/mol. 

Energy Calculations - 3.3 Energy Level Diagrams

Energy Level Diagrams - Show the energy changes for chemical reactions. The difference between the energy levels of reactants and products is the energy change for the reaction. 

Exothermic - 

• Products will be smaller than reactants. 
• When new bonds in the products are formed energy is released. 

Endothermic - 

• Products will be larger than reactants.
• During the reaction bonds in the reactant must be broken for the reaction to take place. Breaking bonds is endothermic because energy is take in. 

Activation Energy - the minimum amount of energy needed for the reaction to happen.On an energy level diagram this is the 'peak' on the line of the graph. If a catalyst was used this peak would be smaller and the line would be dotted. This is because a catalyst increases the rate of reaction by providing a different pathway with an activation energy that is lower. 

Energy Calculations - 3.4 Calculations Using Bond Energies

Ina reaction energy is needed to break the bonds (in reactants). Energy is released when new bonds are formed in products. The difference between these two energy amounts are what make a reaction exothermic or endothermic. 

Bond energy - The energy needed to break the bond between two atoms. And equal maount is also released when the bond forms between two atoms and so we can use bond energies to calculate the overall energy change for a reaction. Bond energies are measured in kJ/mol. 

1) First the equation must be balanced

2) Calculate the total amount of energy needed to break bonds in reaction

3) Calculate the total amount of energy released in making all of the bonds in the products

4) Calculate the difference in the totals. 

Energy Calculations - 3.5 Fuel Issues

• Fossil fuels are non-renewable so alternatives must be found. 
• Hydrogen is an alternative - burns easily, releases a large amount of energy, produces no CO(2)
• Hydorgen can be burned in combustion engines or can be used in fuel cells to power vehicles. 
• Hydrogen can be produced from renewable sources.
• Disadvantages include supply, storage and safety problems.
• Vehicles that use fuel cells need to match the performance, convenience and costs of petrol/diesel vehicles. 

This is it. 

Analysis and Synthesis - 4.1 Tests for Positive Ions

Some positive (metals) ions can be identified using a flame test/by using Sodium Hydroxide. 

Lithium  - Crimson flame
Sodium - Yellow
Potassium - lilac
Calcium - Red
Barium - Green

Sodium Hydroxide Tests (Precipitate Tests)

• The Hydroxides of most metals that have ions 2+ or 3+ charges are insoluble in water. When Sodium Hydroxide is added to some of these ions the precipitate of the metal hydroxide forms. 

Aluminium, Calcium, Magnesium Hydroxides - White Precipitate (if excess is added then                                                                             Aluminium hydroxide dissolves) 
Copper (II) Hydroxide - B
Iron (II) Hydroxide - Green
Iron (III) Hydroxide - Brown 

Analysis and Synthesis - 4.2 Tests for Negative Ions

Carbonate Ions - 

• Add dilute Hydrochloric acid to the substance
• If it does effervesce and the gas produced turns limewater cloudy then it contains Carbonate ions. e.g  blah blah blah Carbonate is the name of the substance.
• 2HCl aq. + CaCO(3) s. = CaCl(2) aq. + H(2)O liq. + CO(2) g. 

Halide Ions - 

• Add dilute Nitric Acid and then silver Nitrate Solution 
• Chloride Ions - White precipitate
• Bromide Ions - Cream Precipitate
• Iodide Ions - Yellow Precipitate 
• AgNO(3) aq. + NaCl aq. = AgCl s. + NaNO(3) aq.

Sulfate Ions - 

• Add dilute Hydrochloric Acid and then Barium Chloride Solution
• If a white precipitate forms, Sulfate is present. 
• BaCl(2) aq. + MgSO(4) aq. = baSO(4) s. + MgCl(2) aq. 

Analysis and Synthesis - 4.3 Titrations

 Neutralisation Reaction - When solutions of an acid and an alkali react to form a salt and a                                                water (a neutral solution). A titration can be used to find one of these. 

Method - 

• A pipette is used to measure a precise amount of alkali to a conical flask. 
• 2-3 drops of indicator (Phenolphthalein or Universal) are added to the alkali.
• Acid is added to a burette.
• Acid is added gradually to the conical flask
• When the indicator changes colour the end point has been reached. 
• The volume of acid used is found from the start and end readings. 
• Should be repeated for security of results. 

Analysis and Synthesis - 4.4 Titration Calculations

Concentrations of solutions are measured in Grams per decimetre cubed (g/dm(3)) or moles per decimeter cubed. We can calculate the concentration of a solution if we know the mass or the number of moles of a substance dissolved in a given volume. Likewise if we know the concentration and the volume of a solution we can calculate the mass or number of moles of the substance in any volume of solution. 

Example - Look in book. 

• Titrations are used to find the volumes of solutions that react exactly.
• If concentration of one of the solutions is known and the volumes reacted together are known we can calculate the missing concentration.
• This is done using balanced symbol/mathematical equations and moles. 

Example - Look in book

Analysis and Synthesis - 4.5 Chemical Analysis

We can use chemical analysis for environmental, medical and forensic investigations.

Methods include Positive and Negative Ion Testing, Gass Chromatography and Mass Spectrometer (instrumental methods).

Some techniques (qualitative) check whether a substance is simply in a sample. 

Others (quantitative) can tell us quantities of a substance (titrations, GC-MS).

LArge databases of the results of analysis have been built up with the aid of computers. These are used to identify substances in samples, to identify individuals or to monitor changes in amounts of substances over time. 

Analysis and Synthesis - 4.6 Chemical Equilibrium

Reversible Reactions - The products can react together to make the reactants again.

In a closed system neither the products nor the reactants can escape. For a reversible reacion in a closed system equilibrium is reached when the rate of the forward reaction is equal to the rate of the revers reaction. At equilibrium both reactions continue to happen, but the amounts of reactants and products remain constant. 

Changing Concentration of a Reactant or Product

Reversible reaction amounts of products/reactants can be changed by changing the reaction conditions. This is important for controlling reactions e.g. increase the concentration of a reactant and more product will be formed as the system tries to achieve equilibrium. If a product is removed more reactants will react to try to achieve equilibrium and so more product is formed. 

Check out diagram on p91

Analysis and Synthesis - 4.7 Altering Conditions

Changing Pressure

• If the forward reaction produces more molecules of gas, an increase in pressure decreases the amount of products formed.
• If the forward reaction produces more molecules of gas, a decrease in pressure increases the amount of products formed.
• If the forward reaction produces fewer molecules of gas an increase in pressure increases the amount of products formed.
• If the forward reaction produces fewer molecules a decrease in pressure decreases the amount of products formed.  

Changing Temperature

• If the forward reaction is exothermic an increase in temperature decreases the amount of products formed.
• If the forward reaction is exothermic a decrease in temperatire increases the amount of products formed. 
• If the forward reaction is endothermic an increase in temperature increases the amount of products formed
• If the forward reaction is endothermic a decrease in temperature decreases the amount of products formed

Analysis and Synthesis - 4.8

The Haber Process - used to manufacture Ammonia - to make fertilisers and other chemicals.

Method - 

• Nitrogen (from the air) and Hydrogen (obtained from natural gas) are purified and mixed in the correct proportions
• The gases are passed over an iron catalyst at a temperature of approx. 450 degrees and a pressure of 200 atmospheres. 
• These conditions provide a fast rate of reaction and a reasonable yield of Ammonia. 
• It is a reversible reaction. 

Some of the Ammonia breaks down into Nitrogen and Hydrogen and the yield of Ammonia is only about 15%. 

The gases that come out of the reactor are coled so the Ammonia condenses. THe liquid Ammonia is separated from the unreacted gases. The unreacted gases are recycled so they aren't a waste. 

Analysis and Synthesis - 4.9 The Economics of the Haber Process

Optimum Pressure - 

• The products have fewer molecules of gas than the reactants so the higher the pressure the greater the yield of ammonia.
• However high pressure means a high amount of energy needed to compress the gas. Also need stronger reaction vessels and pipes - expensive. 200 atmospheres is a compromise.

Optimum Temperature - 

• Forward reaction is exothermic so lower the temperature the greater the yield of Ammonia.
• Reaction rate decreases as the temperature is lowered and the iron catalyst becomes ineffective so it would take longer. 450 degrees C is a compromise.  

Analysis and Synthesis - 4.9 The Economics of the Haber Process

Optimum Pressure - 

• The products have fewer molecules of gas than the reactants so the higher the pressure the greater the yield of ammonia.
• However high pressure means a high amount of energy needed to compress the gas. Also need stronger reaction vessels and pipes - expensive. 200 atmospheres is a compromise.

Optimum Temperature - 

• Forward reaction is exothermic so lower the temperature the greater the yield of Ammonia.
• Reaction rate decreases as the temperature is lowered and the iron catalyst becomes ineffective so it would take longer. 450 degrees C is a compromise.  

Organic Chemistry - 5.1 Structures of Alcohols, Carboxylic Acids and Esters

Organic Molecules - form the basis of living things. All contain Carbon atoms. 

Homologous Series - series of molecules that have a general formula e.g. Alkenes and Alkanes.

Alcohols - 

• Homologous series with the functional group -O-H. 
• Replaces one hydrogen atom in an alkane molecule with an -O-H. 
• First members are Methanol, Ethanol and Propanol.Ethanol structural formula - CH(3)CH(2)OH 

Carboxylic Acids 

• Homologous series with the functional group - COOH.
• Methanoic Acid, Ethanoic Acid and Propanoic Acid. (first three members).HCOOH (Methanoic Acid), CH(3)COOH (Ethanoic Acid) and CH(3)CH(2)COOH (Propanoic Acid) etc.

Esters 

• Functional group -COO-.If the H atom in the -COOH group of a Carboxylic Acid is replaced by a hydrocarbon group the compound is an ester. e.g. Ethyl Ethanoate

Organic Chemistry - 5.2 Properties and Uses of Alcohols

• Alcohols with smaller molecules (ethanol) mix well with water and produce neutral solutions. 
• Useful solvents - Many organic substances dissolve in them.
• Ethanol is the main alcohol in wine, beer and other alcoholic drinks. 
• Alcohols burn in air. When burned completely they produce CO(2) and H(2)O. 
• Used as fuels (because of ^^) e.g. spirit burners, combustion engines and they can be mixed with petrol. 
• Sodium reacts with alcohols to produce Hydrogen but less vigorous reaction than Sodium and water. 
• Alcohols can be oxidised by chemical oxidising agents such as potassium dichromate to produce carboxylic acids. 
• Some microbes in the air can also oxidise solutions of ethanol to produce thanoic acid which turn alcoholic drinks our and is the main acid in vinegar. 

Organic Chemistry - 5.3 Carboxylic Acids and Esters

Carboxylic Acids dissolve in water to give H(+) ions and produce solutions with a pH value of less than 7 - typical properties of acids. Or when it is added to carbonates they fizz because they react to produce carbon dioxide and a salt and water. 

However

They react with alcohols in the presence of an acid catalyst to produce Esters. e.g. ethanol and thanoic acid react togeth when mixed with sulfuric acid as a catalyst to produce Ethyl Ethanoate and water. 

Esters are volatile compounds and have distinctive smells (some are used in flavourings/perfumes)

Carboxylic Acids = Weak Acid

• Strong acids - acids that ionise completely in aqueous solutions e.g Hydrochloric acid.
• Ethanoic Acid does not ionise completely and some remain as ethanoic acid molecules in the solution. This is known as a weak acid. 
• In aqueous solutions of equal concentration weak acids have a higher pH and react more slowly than strong acids. 

Organic Chemistry - 5.4 Organic Issues

• Alcohols, Esters and Carboxylic acids can be used in foods, drinks, solvents and fuels. 

However

• Alcoholic drinks and solvents can be abused which leads to health and social problems.
• Whilst Biofuels offer and alternative to non-renewable fuels and help with global warming the land used to grow the crops for the fuel could also be used to grow food - which is more urgent. 
• Advantages and disadvantages for any use of resources may change over time or when there are new developments and so monitoring and careful research are needed. 

YOU HAVE FINISHED CHEMISTRY!!!!!