Chemistry C3

Newlands Law of Octaves:

Ordered in atomic mass, Newland noticed every 8th element had similar properties so listed known elements in rows of 7. However 3rd row messed up with transition metals such as titanium and iron. He left no gaps and his work was ignored. 

Work criticised because: Groups contained elements didn't have similar properties e.g. carbon and titanium. Mixed metals and non-metals e.g. oxygen and iron and no gaps left for elements not discovered.

Dmitri Mendelev

1869 50 elemtents know, Dmitri out elements in order of mass but Mendelev left gaps to keep elements with similar properties in same vertical columns -now known as groups- prepared to leave big gaps in first two rows. Gaps discovered fitted patters he predicted.

As you go down group 1

- more reactive element is                      -lower melting and boiling points

1) Lithium sodium and rubidium and caesium are less dense than water.

2) Alkali metals have one outer electron- very reactive and all have similar properties

3) Alkali metals form ionic compounds with metals- form a 1+ ion. Also produce white compounds that dissolve in water to for colourless solutions.

4) Reaction with water produces Hydrogen gas- Lithium, sodium and water react vigorously with water. Float and move around on surface, fizzing LOADS! Produce hydrogen, potassium gets hot enough to ignite it. A lighted splint indicates hydrogen by producing a squeaky popas H2 ignites. Forn hydroxides that dissolve in water to give alkaine soloutions.

2Na + 2H20 --> 2NaOH + H2

As you go down group 7

-Less reactive- harder to gain an extra electron, outer shell is further from nucleus

- Higher melting and boiling point

1) Haologens all non-metals with coloured vapours

Fluorine reactive- poisonous yellow gas              Chlorine fairly reactive- dense green gas

Bromine dense- red brown volatile liquid             Iodine dark grey solid - purple vapor

Existed as molecules, pair of atoms

2) Halogens form ionic bonds with metals- 1- ions

3) More reactive halogens displace less reactive ones- A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt (bromide or iodide.) Bromine will displace iodine because of its trend in reactivity.

Common properties

- good consuctors of heat and electricity             - dense, strong and shiny

-Less reactive than froup one- don't react with water or oxygen

-Denser, stronger and harder than group one metals and higher melting points

Transition metals, often more than one ion

e.g. Fe2+, Fe3+              also Cu+ and Cu2+          abd chromium Cr2+ snf Cr3+

Compounds are colourful

Compounds are very colourful e.g potassium chromate yellow, potassium maganate purple

Transition metals and their compounds make good catalysts

Iron catalyst used harbour process making ammonia. Magnese oxide catalyst decomposition of hyrogen peroxide. Nickel catalst used turning oils into fats.

Soft water- lather with soap.              Hard water- nasty scum

Problem hard water, dissolved calcium ions and magnesium ions in water reacting with soap to make soap, insouble. To get decent lather need more soap- more money. Also when heated hard water forms furring or scale on inside pipes, boilers and kettles. Badly scaled pipes and boilers reduce efficency of heating systems also need replacing. Scale eventually blocks pipes. Scale also thermal insulator, kettle with scale on heating element takes longer to boil than clean non-scaled kettle. So becomes less efficient.

What causes hard water?

Contains calcium ions and magnesium ions. Rainfalling on different rock yupes can dissolve compounds e.g. magnesium sulphate(insoluble) and calcium sulfate (only a bit soluble)

Is hard water good for you?

Ca2+ ions good for healthy teeth and bones, also studies say hard water area residents less risk heart disease, maybe minerals in water.

2 kinds of hardness- temp and permanent

Temporary- Hydrogencarbonate ion HCO3 causes it to be temp

Permanent- Calcium sulfate causes to be hard

Temp hardness- removed by boiling, calcium hydrogencarbonate decomposes and forns calcium carbonate. Causes limescale in kettle

Permanent hardness- removed by adding washing powder sodium carbonate to it. The carbonate ions react with the Ca2+ and Mg2+ ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. The Ca2+ and Mg2+ ions no longer dissolved in water so can't make it hard

Both water types can also be removed by running water through 'ion exchange columns' which are sold in shops. Columns have lots of sodium ions and exchange them for calcium or magnesium ions in the waer that runs through them.

Method:

1. Fill a burette with 50cm2 of soap soloution

2. Add 50cm3 of the fist water sample into a flask

3. Use a burette to add 1cm3 of soap soloution to the flask

4. Put a bung un the flask and shake for 10 seconds

5. Repeat 3 and 4 until a good lasting lather formed (bubbles cover over 30 seconds)

6. Record how much soap needed create a lasting lather

7. Repeat steps 1-6 with other water samples.

8. Boil fresh samples of each water type for 10 minutes and repeat the experiment.

Fluoride- helps reduce tooth decay

Chlorine- prevents disease.

However some studies like chlorine in water to some cancer types. Chlorine can react with other natural substances in water to produce toxins.

In high doses fluroine can cause cancer and bone problems in humans so people think there should be a choice to whether added to drinking water as it is a choice in toothpaste. 

A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants. In other words the reaction can go both ways.

Reversible reactions will reach equilibrium-  If reversible reaction occurs in a closed system a state of equilibrium will be reached, Equilibrium means the amount of reactants and products will reach a balance and stay there. A closed system means no products can escape. The reactions taking place in both directions by the overall efect is nil because the forward and reverse reaction cancel each other out. Reactions taking place at exact same rate.

Changing temperature: If raise temperature endothermicc reaction increase to use up heat.         If reduce temperature exothermic reaction give out heat.

Changing pressure: If raise pressure encourage reaction which produces less volume.                  If lower pressure it will encourage reaction which produces mass volume. 

NITROGEN + HYDROGEN needed.- Nitrogen from air and hydrogen drom natural gas/ crude oil

Industrial conditions:  Pressure 200 atmospheres     Temperature 450 degrees      Catalyst Iron

Reversible Reactions:                                                                                                     +Higher pressures favor forwawrd reaction (4 molecules gas left hand side for every 2 on the right) Pressure set as high as possible give best %yield withour plant too expensive to build, hence 200   +Forward reaction exothermic, increasing temperature move equilibrium wrong way, away ammonia towards N2+H2 so yield ammonia greater lower temperatures                                   +Howevever lower temperatues=lower rate of reaction, increase temp faster rate of reaction         +450 compromise betwwen max yield and speed of reaction better 20 seconds for 10% yield than 60 seconds 20% yield.                                                                                                +Formed as gas however as cools in condensor liquifies and is removed.                        +Unused hydrogen and nitrogen are recycled but nothing is wasted.                                 +Catalyst doesn't affect equilibirium without it though temperature would need to be raised further to get a quick enough reaction and reduce % yield even further.

Alcohols have an OH functional group and end in 'ol'         General formula is CnH2n+1OH. 

Methanol CH3OHEthanol C2H6OHPropanol C3H7OH

The first 3 alcohols have similar properties: flammable, burn air to produce carbon dioxide and water. All 3 dissolve completely in water to form neutral solotuions. React with sodium to give hydrogen and alkoxides. Ethanol is main alochol is drinks, not as toxic as methanol but still liver and brain damage.                                                                                                      Alcohols used as solvents: They can dissolve most compounds that water dissolves but also dissolve substances water can't dissolve. E.g. hydrocarbons, oils and fats. Makes solvents usegul in industry. Ethanol is solvent used perfumes and aftershave lotions, mix both oils and water.       Alcohols are used as fuels: Ethanol used spirit burners, cleanly and no smell. Ethanol mixed with petrol and used for cars, pure ethanol clean burning more ethanol less poloution. Some countries little/ no deposits buy plenty land and sunshine grow sugar cane which they ferment to form ethanol. Big advantage sugar cane renewable resource. 

Carboxylic acids have functional group '-COOH'                                                                       Their names end in 'anoic acid'

Methanoic acid             Ethanoic acid   Propanoic acid    HCOOH                                        CH3COOH                           C2H5COOH

Carboxylic acids are just like other acids- React like any other acid with carbonates to produce a salt, water and carbon dioxide.

Salts formed end in 'anoate.'

Carboxylic acids dissolve in water to produce acidic solutions, Once dissolved they ionise and release H+ions which are resoponsible for making solutions acidic. But don't ionise completely, form weak acidic acids. Means higher pH than aqueaus solotions of strong acids with the same concentration. 

Some carboxylic acids are fairly common

1) Ethanoic acid made by oxidising ethanol. Microbes like yeast cause the ethanol to ferment. Ethanol also be oxidised using oxidising agents.   Ethanol+oxygen-->ethanoic acid+water             2) Ethanoic acid dissolved in water to make vinegar, used flavorings and preserving foods.           3) Citric acid present oranges and lemons manufactured larg quantities to make fizzy drinks. Also used remove scale.

Carboxylic acids used to make soaps and esters

1) Carboxylic acids with longer chains of carbon atoms used make soaps and detergents             2) Carboxylic acids used in preparations of esters                                                                     3) Ethanoic acids good solvents for many organic molecules. But ethanoic acid isn't usually chosen as a solvent as it makes the solotuion acidic. 

Esters have a functinal group '-COO-'                                                                                    Esters formed from alcohol and a carboxylic acid, an acid catalyst usually used.                       Alcohol +Carboxylic acid---> ester + water                 end in 'oate' 

• Esters smell nice but don't mix well with water                                                                  Esters pleasant smells- often sweet and fruity, also volatile.Ideal perfumes.
• H/w very flammable. Volatility makes potentially dangerous. Esters don't mix well water but do mix well with alchols and other organic solvents.                                                        
• Esters used in flavorings and Perfumes                                                               Because many esters smell nice they're used in perfumes. Ester used flavorings and aromas e.g. esters that smell/ taste apple, banana etc. Some ester used in oitment, Others used as solvents e.g. ink, glue and in nail varnish.                                                             Things to think about:                                                                                           
• 1)Inhaling fumes and some esters irrates mucous membranes in nose and mouth              
• 2) Ester fumes heavier than air, very flammable                                                              
• 3) Some esters toxic espec. large doses. Worry health problems associated food adictives. 
• 4) But esters arent as volatile or as toxic as other organic solvents- don't release as much toxics fumes as some of them. Esters have replaced solvents e.g. tolune in paints and varnishes.