2A Chemistry - Classification of Substances

Transcription

1 CHEMISTRY The world is made up of a variety of substances. Some of these occur naturally in our environment, others are made through the combination of naturally occurring substances to form new materials. The study of chemistry can lead us to a better understanding of our material world and the processes by which materials can change and be changed. Matter is anything that occupies space and has mass There are three states of matter Solids, Liquids and Gases Characteristics of the States of Matter Solid Liquid Gas Fixed Shape Shape of Container Shape of Container Fixed Volume Fixed Volume Shape of Container Cannot flow Can flow Can flow e.g. iron, copper, sulphur e.g. water, mercury e.g. hydrogen. oxygen, methane Changes of State Elements, Compounds and Mixtures Elements: Cannot be broken down into anything simpler using chemical means or Substance made up of one type of atom All the known elements are listed in the Periodic Table Invented by Dmitri Mendeleev Vertical columns are called Groups Horizontal rows are called Periods Metals are to the left of the red line and Non-metals are to the right of the red line Periodic Table Solid H 1 Li 3 Na 11 K 19 Rb 37 Cs 55 Fr 87 Be 4 Mg 12 Ca 20 Sr 38 Ba 56 Ra 88 Sc 21 Y 39 La Ac Ti 22 Zr 40 Hf 72 Rf 104 Liquid Gas V 23 Nb 41 Ta 73 Db 105 Cr 24 Mn 42 W 74 Sg 106 Mn 25 Tc 43 Re 75 Bh 107 Fe 26 Ru 44 Os 76 Hs 108 Cu 27 Rh 45 Ir 77 Mt 109 Metals Ni 28 Pd 46 Pt 78 Ds 110 Cu 29 Ag 47 Au 79 Rg 111 Zn 30 Cd 48 Hg 80 Uub 112 B 5 Al 13 Ga 31 In 49 Tl 81 Uut 113 C 6 Si 14 Ge 32 Sn 50 Pb 82 Uuq 114 Non-metals N 7 P 15 Se 33 Sb 51 Bi 83 Uup 115 O 8 S 16 Sc 34 Te 52 Po 84 Uuh 116 F 9 Cl 17 Br 35 I 53 At 85 Uus 117 He 2 Ne 10 Ar 18 Kr 36 Xe 54 Rn 87 Uuo 118 Physical Properties of two metals and two Non-metals Element Metal or Non-metal State Colour Hydrogen (H) Non-metal Gas Colourless Carbon (C) Non-metal Solid Black Copper (Cu) Metal Solid Salmon pink Mercury (Hg) Metal Liquid Silvery 1

2 Compounds: Substance made up of more than one type of atom chemically joined Elements combine chemically to form compounds When elements combine they lose their individual properties o Sodium is a very reactive silvery metal o Chlorine is a poisonous green-yellow gas o Sodium chloride (table salt) formed when they react is a white crystalline solid + = Sodium Chlorine Gas Table Salt Crystals Properties of Simple Compounds and their Constituent Elements Compound Properties Elements Properties H 2 O Colourless liquid Hydrogen Colourless gas burns Water Does not burn Oxygen Colourless gas, supports combustion CO 2 Colourless gas Carbon Black solid Carbon dioxide Does not burn Oxygen Colourless gas, supports combustion MgO White powder Magnesium Silvery metal, burns Magnesium oxide Does not burn Oxygen Colourless gas, supports combustion FeS Grey solid Iron Grey shiny metal, burns if powdered Iron sulphide Does not burn Sulphur Yellow solid, burns Mixtures: Substance made up of more than one type of atom NOT chemically joined e.g. salt and sand, salt and water Separating Sand and Water by Filtration Filtration is used to separate an insoluble solid from a liquid e.g. salt and sand Set up the apparatus as in the diagram Fold the filter paper twice and place it opened in the filter funnel Pour the mixture of sand and water into the filter paper The sand particles are trapped in the filter paper and are called the residue. Water passes through and is called the filtrate Conclusion: Filtration can be used to separate an insoluble solid from a liquid Separating Salt and Water by Evaporation Evaporation is used to separate a soluble solid from a liquid e.g. salt and water Set up the apparatus as in the diagram Pour the salt water solution into the evaporating basin Place the evaporating basin on top of the boiling water bath The water evaporates leaving the salt behind Conclusion: Evaporation can be used to separate a soluble solid from a liquid 2

3 Separating Salt and Water by Distillation Distillation separates a liquid from a soluble solid or another liquid, and collects the liquid separated Set up the apparatus as shown Connect the bottom lug to the tap so that water enters the bottom of the condenser The pipe from the top lug should go to the sink Heat the flask Collect the distillate in a beaker Water evaporates from the flask and is condensed (turned back to water) in the Liebig condenser. Conclusion: distillation can be used to separate and collect a liquid from a soluble solid Separating a Mixture of Inks using Paper Chromatography Place a spot of black ink near the bottom of a strip of chromatography paper Place the paper in water so that the black ink spot is above the water as shown in diagram Leave for a time and observe the solvent moving up the paper the different inks are carried up the paper by the solvent at different rates and so are separated. Conclusion: Paper chromatography can be used to separate a mixture of inks Metals are shiny (have a lustre) e.g. silver and fresh copper in new coins can be stretched into wires (ductile) e.g. copper can be hammered into sheets (malleable) e.g. gold leaf conduct heat conduct electricity are used to make tins, cars, ships, bridges, knives, gold rings and bracelets etc. Good examples of metallic elements are copper (Cu), zinc (Zn), aluminium (Al), iron (Fe), silver (Ag) and gold (Au) [Learn these symbols] Alloys are mixtures of metals (carbon is considered as a metal in this case) Alloy Constituents Uses Bronze Copper (Cu) and Zinc (Zn) Ornaments, coins and statues Brass Copper (Cu) and Tin (Sn) Door knobs, hinges and musical instruments Steel Iron (Fe) and Carbon (C) Ships, bridges and car bodies Solder Lead (Pb) and Tin (Sn) Joining metals in electrical circuits Non-metals Are not shiny Are brittle Do not conduct heat Don not conduct electricity (carbon is a notable exception) Many are gases You need to know the following non-metals and their symbols: Carbon (C), Oxygen (O), Sulfur (S), Hydrogen (H) and Nitrogen (N) 3

4 Mixtures and Compounds Compare a Mixture and a Compound made from the same Constituents Take some iron filings (14.0g) and powdered sulfur (8g) Note their colours (Iron grey and sulfur yellow) Mix fully Hold a magnet (wrapped in polythene) near the mixture iron filings stick to the magnet as mixture separates Remix the elements and place the mixture in a test tube Heat strongly in a Bunsen flame Note what happens Allow to cool and test once more with a magnet Mixture glows as they react and iron sulphide forms Iron sulphide is NOT magnetic Conclusion: The constituents of the mixture retain their original properties The compound formed (iron sulphide) does NOT keep the properties of the original substances Water and Solutions Solution: a mixture of a liquid (solvent) and a solid dissolved in it (solute) e.g. water and sugar Water is a very good solvent Dilute Solution: contains a small amount of solute (salt) in a lot of solvent (water) Concentrated Solution: contains a large amount of solute (salt) in a small amount of solvent (water) Saturated Solution: contains as much solute dissolved in it as is possible at a particular temperature The Effect of Temperature on Solubility Set up the apparatus as shown Place 10 cm 3 of water in the test tube Place some copper sulfate (50g) on a filter paper Weigh it Heat the water bath to 20 o C Add a small amount of copper sulfate to the test tube and stir Keep adding copper sulfate and stirring till no more dissolves Calculate the amount of copper sulfate added by the change in weight of the crystals on the filter paper Increase the temperature of the water bath to 40 o C and repeat Increase the temperature of the water bath to 60 o C and repeat Plot a graph of the amount of copper sulfate dissolved against temperature as the temperature increases the amount of copper sulfate that dissolves increases Conclusion: Solubility increases with temperature Test for Water Take some dry cobalt chloride paper (it should be blue) Put a piece of cobalt chloride paper in (i) a test tube of water and (ii) a test tube of pure alcohol Water turns the cobalt chloride paper blue Alcohol has no effect on the cobalt chloride paper Conclusion: Cobalt chloride paper can be used as a test for water 4

5 Examine the difference between a Dilute, Concentrated and Saturated Solution Make up three copper sulphate solutions (i) Dilute (ii) Concentrated (iii) Saturated Compare the solutions Result If the solution is coloured the colour gets deeper as the concentration increases Note: Copper sulfate solution is clear and blue while water is clear and colourless. Growing Copper Sulfate Crystals Dissolve copper sulfate crystals is hot water until you have a saturated solution Divide the solution equally between two evaporating basins (leave any undissolved crystals in the container) Place one evaporating basin on the bench to cool slowly Place the other on ice to cool it quickly Compare the two sets of crystals o the crystals formed slowly on the bench are large o the crystals formed quickly on the ice are smaller Conclusion: The faster crystals are formed the smaller they are Acids and Bases An Acid is a substance that turns Blue Litmus Red A Base is a substance that turns Red Litmus Blue The ph Scale is a scale from 0 to 14 that tells how strong an acid or a base is Substances with a ph of 7 are Neutral Substances with a ph of less than 7 are Acidic Substances with a ph of more than 7 are Basic An Indicator is a substance used to show how acidic or basic a substance is Litmus Indicator is red in acids and blue in bases Universtal Indicator tells us how acidic or basic a substance is by turning a variety of colours Investigate the ph of a Variety of Materials using the ph Scale Take a sample of the substance to be tested Disolve it in a small amount of water Add a few drops of universal indicator and mix Note the colour against the supplied chart (see above) Record the ph Results: See table below Strong Acids Weak Acids Neutral Weak Bases Strong Bases Sulfuric Acid Vinegar Pure Water Toothpaste Sodium hydroxide Hydrochloric Acid Lemon Juice Alcohol Baking Soda Potassium hydroxide Nitric Acid Rainwater Sugar solution Soap Ammonia solution Nettle sting Salt Solution 5