Chemistry 2 - QWC's

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  • Created by: Katy **
  • Created on: 11-01-14 14:24

Water Hardness

Water is either hard or soft. To find out what type of water hardness the water is add soap solution & shake. If the water is soft a large amount of bubbles will appear called lather, if the water is hard only a few bubbles will appear on the surface called scumHard water does have its benifits, as it is good for the teeth & bones. Hard water will also decrease the risks of heart disease. Water hardness is caused by dissolved magnesium or calcium ions. There are two types of hard water, temporary hard water & permanently hard water.

Temporary hard water is caused by dissolved magnesuim hydrogen carbonate or calcium hydrogen carbonate, to remove the magnesium or calcium you have to boil the water. When boiled the compounds are decomposed, this is called a thermal decomposition reaction. Magnesium carbonate & calcium carbonate are both insoluble, so when they are boiled they created a white solid (precipiate) called limescale, which can block filters & pipes causing a problem.

Permanently hard water is caused by dissolved magnesium sulfate or calcium sulfate, & is removed by two methods (both of which work for temporary hard water as well). Firstly, you can use an Ion Exchange Resin (IER), this traps the magnsium or calcium & replaces them with Sodium that doesn't cause water hardness. Eventually the IER will run out of Sodium & stop, so wash with a Sodium chloride solution & this will replace the Sodium ions & work again. Secondly add a Sodium carbonate solution (washing soda) & this will cause a precipiate reaction.

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Reaction of Alkenes

Alkenes are unsautrated hydrocarbons & are made by cracking long chained alkanes. Unsaturated means that one pair of Carbon atoms are joined together by a double covalent bond (C=C).

The types of reactions alkenes undergo is called addition. This reaction can happen in two ways. Firstly, if the alkene is reacted with bromide water - Br2 (aq). Bromide water is orange & will change to become colourless. Alkanes do not react with Bromide water, so this test can be used to test for an alkene.

Secondly, an alkene will react with Hydrogen, but a Nickel catalyst has to be used & heat. This reaction is called a hydrogenation reaction or reduction.

An imporant reaction of an alkene is called Additional polymerisation. This is when small unsaturated molecules (C=C) called monomers join together to form in huge numbers a long chained molecule called a polymer. When an additional polymerisation is formed there is only one type of monomer.

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Testing for Ions

Testing for the Group 1 ions, use the flame test. Lithium will burn with a red flame, Sodium will burn with a yellow flame & Potassium with a lilac flame.

Testing for the Group 7 ion, just disolve in distilled water & add silver nitrate & nitric acid. This will form a precipitate of different colours. Chloride will form a white precipiate, Bromide will form a cream precipitate & Iodide a yellow precipitate.

Even if these ions are mixed with other elements, they will always burn with the same flame or form the same coloured precipitate.

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Smart Materials

Smart materials is a material whose properties will change reversibly depending on different conditions, for example heat or pH. There are four types of smart materials, thermochromic, photochromic, hydrogels or polyger gels & shape memory alloys.

Thermochromic is the change of colour reversibly depending on temperature. This is usually found in thermometre "strips" or cans to show when it is cold or in dye in clothes.

Photochromic is the change of colour reversibly depending on light. This is usually found in the lenses of some glasses.

Hyrogels or Polymer gels will absorb or expel water, causing them to swell or shrink. They are most commanly use in water hanging baskets or nappies or to "mop up" chemical spills.

Shape memory alloy will return to their original shape when heated. An example of a shape memory alloy is Nitinol - an alloy of Nickel & Titanium. Shape memory alloys are found in the frames of glasses or as a temperature control in coffee pots.

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Rate of Reaction

Rate of reaction measures a change in either reactants or products over a given time. The rate of reaction can be found by finding the gradient of the line in the graph. All chemical reactions decrease in rate in time, which means that the gradient will also decrease. This is because the particles of the reactants are getting used up, the reaction will be at its fastest at the begining.

For a chemical reaction to happen the reactants (particles) have to collide with eachother. The collision must have a certain amount of energy to the reaction to happen. This is called activation energy.

There are a number of factors that can affect the rate of reaction; temperature, concentration of a solution, surface area of the solid & adding a catalyst.

Increasing the temperature will mean that the particles will have more energy & move faster, therefore collisions are more likely to happen & have the activation energy, increasing the rate of reaction. Adding a catalyst will increase the rate of reaction without getting used up. It allows you to use a lower temperature & burn less fuel. This will save money & less Carbon dioxide will be burnt & therefore save the environment (less global warming or acid rain). When the surface area of a solid is increased, the rate of reaction increases as there is a bigger chance of collision.

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Crude Oil

Crude oil is formed by the remains of simple marine organisms over thousands of years. It is extracted using oil wells. Crude oil is a complex mixture of hydrocarbons (hydrogen & carbon) & can be separated into less complex mixture of hydrocarbons called fractions by a reaction called fractional distilation. Hydrocarbons can be separated into fractions becuase of their different boiling points.

Firstly the crude oil is heated in a fractionating column, this causes the fractions to evapourate. The vapour will rise away from the heat & then cool, when the vapour cools below its boiling point it will condense. Once condensed, the hydrocarbons are collected & the fractions are treated for impurities.

Hydrocarbons with bigger molecules will have a higher boiling point & not rise as far. The hydrocarbons with lower boiling points will riser higher. However, the hydrocarbons with very high boiling points will not evaporate & are collected at the bottom of the column as residue. And the hydrocarbons with very low boiling points do not condense & are collected as gases at the top of the column. Finally, hydrocarbons with similar boiling points do not separate & are still mixtures.

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