Elements, compound and mixture

This is very useful for IGCSE, ICSE, and CBSE Students

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3. Modern Classification On the basis of its physical state, matter is classified into solid, liquid and gas.(Physical Change) All these three states exist under normal temperature and pressure conditions The fourth state of matter is Plasma. on the basis of its chemical constitution, matter is classified into element, compound and mixture.( Chemical change) 6/26/2015

4. Physical and Chemical Changes Physical Change : A change of matter in size, shape or state without any change in identity is called a physical change NO new substance is formed. These changes are easily reversible or temporary. An example is dissolving salt in water. Other examples of physical change include: melting, boiling, mixing 2 solids or liquids .

5. Chemical Change : A change of matter that occurs when atoms link together in a new way, creating a new substance different from the original substance. A NEW substance is formed. These changes are irreversible or permanent . The new substance formed will have different properties compared to its original elements. (E.g. different melting and different chemical reactions from the original substance.) Physical and Chemical Changes

6. One can recognize a chemical change from 2 observations : The new substance has a different appearance , such as different color or different physical state. An example is the electrolysis of water. Reason: Electrolysis of water produces two new substances, Hydrogen gas and oxygen gas. Hydrogen and oxygen are both gases but water is a liquid. A lot of heat is given out in a chemical changes. Chemical changes are called chemical reactions. Physical and Chemical Changes

7. An Overview

8. Elements, Compounds and Mixtures “ single, attached, play play…”

9. Introducing Little Miss “Element” Hi! I am Little Miss “Element” I am PURE SUBSTANCE I cannot be broken down into any simpler substance by means of a chemical reaction* or electricity**! *Chemical process refers to chemical reaction or heat **Electricity refers to electrolysis I have got new friends

10. Elements Definition of an element: An element is a pure substance which cannot be split up into two or more simpler substances by chemical means. Sugar is not an element as it can be broken down into carbon and water.

11. Note that an element: Consists of only one kind of atom, Cannot be broken down into a simpler type of matter by either physical or chemical means Can exist as either atoms (e.g. argon) or molecules (e.g., nitrogen). Cannot possible to obtain a simpler substance chemically from these elements. Can only make more complicated substances from it. Elements

12. - They are arranged in the Periodic Table, classified as metals and non-metals. - They may consist of atoms of same element or molecules of the same element. Periodic Table

13. Elements 6/26/2015 There are 118 elements were identified. 27 of these do not occur in nature and made artificially by scientists. Eg : Curium and Unnilpentium 91 of the elements occur naturally and range from very reactive gases such as Fluorine and Chlorine, to Gold and Platinum, which are unreactive elements.

14. Examples of elements Elements are made up of tiny particles Elements can be further classified into two groups: Atoms Molecules Is the smallest particle of an element and has the same chemical properties of the element Is made up of two or more atoms that are chemically bonded together (note: these atoms are of the SAME element!!) Hi, I am from the “Noble gas” family and I work alone We same same!!

15. These are elements! Atoms of same element Cu copper element Na sodium element He helium element Molecules of same element H Hydrogen gas element O H O O ozone

16. Atoms An element is made of tiny particles called atoms . The word atom comes from the Greek word atomos meaning “ unsplittable ”. The atoms of an element is different from that of another element.

17. Elements- Atoms Microscopic view of the atoms of the element argon (gas phase). Consists of only one kind of atom

18. What is an atom? Examples of models of atoms: H Na Cl Hydrogen atom Sodium atom Chlorine atom

19. Molecules Very few elements exists as atoms besides elements such as helium and neon. Most elements exist as molecules. For example, hydrogen is H 2 . Ozone is O 3 .

20. Hydrogen (H 2 ) is a diatomic molecule. Ozone (O 3 ) is a triatomic molecule. Molecules consisting of a few atoms are called polyatomic molecules .

21. Elements-Molecules Microscopic view of the molecules of the element nitrogen (gas phase). Consists of only one kind of atom

22. Examples of molecules (elements) H H N N O O O O O S S S S S S S S

23. Chemical Symbols of Elements Chemists use symbols to represent elements. For example, O represents oxygen while Fe represents iron . Element Symbol Element Symbol Calcium Ca Mercury Hg Carbon C Neon Ne Hydrogen H Silicon Si Iron Fe Sodium Na

24. Classification of Elements – Metals and Non-metals The elements can be classified according to their various properties. There are two major groups of elements – metals and non-metals . Iron is a metal. Oxygen is a non-metal. There are some elements called metalloids which behave like both metals and non-metals. Metals and non-metals are grouped separately on the Periodic Table .

25. Physical Properties metals and non-metals Property Metals Non-metals Physical state at room temperature Usually solid (occasionally liquid) Solid, liquid or gas Malleability Good Poor – usually soft or brittle Ductility Good Appearance (Solids) Shiny (lustrous) Dull Melting point Usually high Usually low Boiling point Usually high Usually low Density Usually high Usually low Conductivity (thermal and electrical) Good Very poor

26. ELEMENTS & SYMBOLS S.No NAME SYMBOL PHYSICAL STATE NAME SYMBOL PHYSICAL STATE 1 2 3 4 5 6 7 8 9 10 Aluminium Calcium Copper Iron Magnesium Mercury Potassium Sodium Zinc Gold Al Ca Cu Fe Mg Hg K Na Zn Au Solid Solid Solid Solid Solid Liquid Solid Solid Solid Solid Argon Bromine Carbon Chlorine Silicon Sulphur Hydrogen Iodine Nitrogen oxygen Ar Br C Cl Si S H I N O Gas Liquid Solid Gas Solid Solid Gas Solid Gas Gas * Physical states are given at room temperature. METALS NON- METALS 6/26/2015

27. Introducing Little Miss “Naughty” Harlow! Hehee!!! *giggles* I am also a PURE SUBSTANCE I am made up of a fixed number of two or more elements chemically combined .

28. Atoms Everything in this world is made of billions of atoms. The smallest atom known as hydrogen. Each atom is represented as a sphere having a diameter of 7 X 10-8 mm. Different elements have different diameter and different masses. Chemists use shorthand symbols to label the elements and their atoms. The symbols consists of 1, 2 or 3 letters. For example C - Carbon Cl - Chlorine Some symbols seems to have no relations with the name of the element. For example: Na – Sodium Pb - Lead These symbols come from their Latin names. 6/26/2015

29. Molecules The atoms of same elements join together to form a molecule. The small group of atoms are called molecules. For example: when the atoms of elements hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine and iodine are each joined in pairs and are known as diatomic molecules. but in phosphorus and sulfur the atoms are joined in larger numbers, 4 and 8 respectively (P4, S8) The gaseous elements helium, neon, argon, krypton, xenon and radon are composed of separate and individual atoms. When an element exists as separate atoms, then the molecules are said to be monatomic. 6/26/2015

30. Compounds Note that a compound: can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), has properties that are different from its component elements, and always contains the same ratio of its component atoms.

31. A compound is a substance which is made up of two or more elements chemically combined together. What is a compound? Chemical reactions taking place. Cu Qn: Is this a compound? It only contains one type of element. Qn: Is this a compound? H H It only contains one type of element. H O H O O Qn: Is this a compound? It is not chemically combined.

32. So, what is a compound then? O H H Water N H H H Ammonia gas Consists of two or more elements And They are chemically combined together!

33. Compounds Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white. Hydrogen + Oxygen Water H2 + O2 2H2O

34. ELEMENTS COMPOUND hydrogen (colourless gas) oxygen ( colourless gas) lighted splint heat, light and explosion water (colourless liquid) Making compounds from their elements Example: Making water (picture) Water molecule Oxygen molecule Hydrogen molecule mixture of hydrogen and oxygen water Example: Making water (models) heat, light and explosion

35. Making compounds from their elements Example: Making Magnesium Oxide compound Magnesium + O xygen  M agnesium oxide elements compound + Silvery-White colourless gas  heat heat White + oxygen → magnesium oxide 2Mg + O 2  → 2MgO                                                                                                                                                                                                                              Magnesium + Oxygen → Magnesium oxide 2Mg + O 2  → 2MgO

36. Oxidation When the substances are combined with oxygen they are said to have been oxidised. This process is Known as oxidation. Eg : Hydrogen and Magnesium combine with Oxygen

37. Reduction It is the opposite of oxidation. In this process oxygen is removed instead of being added.

38. Redox Reactions. Oxidation Reduction

39. GCSE Oxidation : Gain of oxygen Loss of electrons Reduction : Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number

40. Redox reaction Example Removing Oxygen in the extraction of iron from iron(III)oxide This can be done in a blast furnace with carbon monoxide. The iron(III)oxide loses oxygen to the carbon monoxide and is reduced to iron. Carbon Monoxide is the reducing agent. Carbon monoxide is oxidised to carbon dioxide by the iron(III)oxide. The iron(III)oxide is the oxidising agent. iron(III)oxide + carbon iron + Carbon dioxide Both reduction and oxidation have taken place in this chemical process, and so this is known as a redox reaction. 6/26/2015

41. Reducing Agent A reducing agent is a substance that reduces another substance during a redox reaction 6/26/2015

42. Oxidising Agent An oxidising agent is a substance which oxidises another substance during redox reaction. 6/26/2015

43. Little Miss “Naughty” Property #1 I can be represented as a “ chemical formula ” The different elements present in a compound are combined in a fixed ratio General Rules: - Only write the name of the metallic element first - Write the number of atoms of any element in the compound in subscript (applies to only 2 or more atoms) - “ ide” will always be written at the end of the non metal element Special Rules: Does not apply to organic compounds (chapter 18 onwards)

44. Little Miss “Naughty” Property #2 I am formed by atoms of different elements . However, I do not have the properties as them. Examples Na + Cl 2  NaCl (s) (g) (s) H 2 + O 2  H 2 O (g) (g) (l)

45. Little Miss “Naughty” Property #3 Because of my chemical bonds , I cannot be broken down by physical means. I can only be broken down by chemical reaction or electricity. Electrolysis (breaking down of compound by electricity) 2MgCl(s)  Mg(s) +Cl 2 (g) Thermal Decomposition (breaking down of compound by heat) HgO(s)  Hg(s) + O 2 (g)

46. How do we name compounds? Rule 1 A compound made up of two elements has a name that ends in -ide . • Sodium chlor ide — made up of the elements sodium and chlorine • Zinc ox ide — made up of the elements zinc and oxygen • Carbon diox ide — made up of the elements carbon and oxygen

47. How do we name compounds? Rule 2 A compound that contains hydroxide ions , OH – (a negatively charged ion made up of oxygen and hydrogen) is named a hydroxide. • Potassium hydroxide — contains potassium ions and hydroxide ions

48. How do we name compounds? Rule 3 A compound that contains a negatively charged polyatomic ion containing oxygen usually has a name ending in –ate . • Copper(II) sulph ate — contains oxygen atoms in the sulphate ion • Sodium nitr ate — contains oxygen atoms in the nitrate ion

49. Fixed Composition of Compounds For example, water ( H 2 O ) is a compound made only by joining together two atoms of hydrogen to one atom of oxygen. That is, the ratio of hydrogen atoms to oxygen atoms in water is always 2 : 1 . A compound is made up of different elements chemically combined in a fixed ratio .

50. Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. Chemical Formula of a Compound A compound can be represented by a chemical formula . The chemical formula states • the types of atoms (i.e. elements) in the compound, • the ratio of the different atoms in the compound. Types of atoms: hydrogen, oxygen Ratio of H to O = 2:1

51. How do we write chemical formula? Rule 1 For many compounds that contain both metallic and non-metallic elements, the symbol of the metallic element is written first . • calcium oxide ( Ca O) • sodium chloride ( Na Cl) • magnesium carbonate ( Mg CO 3 )

52. How do we write chemical formula? Rule 2 The number of atoms is written as a subscript, to the right of the atom’s symbol. • water ( H 2 O , not H2O or 2HO) • magnesium carbonate ( MgCO 3 , not MgCO 3 or MgC 3 O)

53. How do we write chemical formula? Rule 3 It is not necessary to write the subscript ‘1’. • water ( H 2 O , not H 2 O 1 ) • calcium oxide ( CaO , not Ca 1 O 1 )

54. How do we write chemical formula? Rule 4 The oxygen atom is usually written at the end of the formula. • water ( H 2 O , not OH 2 ) • carbon dioxide ( CO 2 , not O 2 C) • nitric acid ( HNO 3 , not O 3 NH)

55. How do we calculate the number of atoms in a formula? Pb(NO 3 ) 2 Number of nitrogen (N) atoms = 1 x 2 = 2 Number of lead ( Pb ) atoms = 1 Number of oxygen (O) atoms = 3 x 2 = 6

56. Heat can be used to break down compounds into elements or simpler compounds. Such a chemical reaction is called thermal decomposition . Compounds can be Decomposed Mercury(II) oxide Oxygen

57. Summarizing A compound is made up of two or more elements chemically joined together A compound has a fixed composition Every compound has a unique chemical formula A compound has a completely different properties from its elements A chemical reaction (decomposition or electrolysis) is needed to separate the elements in the compound

58. Molecules- Elements or compounds? A molecule consists of two or more atoms of the same element, or different elements, that are chemically bound together. It can be a molecule of an element E.g. N 2 , O 2 , S 8 It can be molecule of a compound. H 2 O, CO 2 , NH 3 N N O O S S S S S S S S O H H O O C N H H H

59. Balancing Chemical Equations

60. Balancing chemical equations Word equations are used to represent chemical reactions. But better and more useful method is to produce a balanced chemical equation. This type of equation gives the formulae of the reactants and the products. And also it shows the relative numbers of each particle involved. 6/26/2015

61. Law of Conservation of Mass You need to remember this law! The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction . Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction. The number of atoms in the Reactants must equal the Number of atoms in the Products

62. Law of Conservation of Mass The mass of all the reactants (the substances going into a reaction) must equal the mass of the products (the substances produced by the reaction). Reactant + Reactant = Product

63. Steps to Balancing a Chemical Equation Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element 2. Use coefficients in front of each formula to balance the number of atoms on each side.

64. Steps to Balancing a Chemical Equation 3. Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side. 4 . It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

65. A simple equation, such as the synthesis of Iron (II) sulfide iron + sulfur Iron (II) sulfide Replace the words with symbols for the reactants and products. Fe + S FeS Note that in a chemical equation, by convention, we use the arrow “ " instead of the equals “ = ". There is same number of each type of atom on both sides of the equation. So this is the balanced chemical equation.

66. The last stage is to put in state of matter symbols, (s, l, g, aq ), as appropriate (solid, liquid, gas, aqueous or dissolved in water) Fe(s) + S(s) heat FeS (s) A simple equation, such as the synthesis of Iron (II) sulfide

67. Re-cap of steps from rule 4: Balance elements that appear only once on each side of the arrow. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

68. First you need an equation with the correct “formulae” ………. You’ll probably be given this in the question Just like this one Mg + O 2  MgO Then all you do is list the atoms that are involved on each side of the arrow Mg + O 2  MgO Mg O Mg O

69. [1] Just count up the atoms on each side Then start balancing: Mg + O 2  MgO Mg O 1 1 1 2 [2] The numbers aren’t balanced so then add “BIG” numbers to make up for any shortages And adjust totals Mg + O 2  MgO Mg O 1 1 1 2 2 2 2

70. Mg + O 2  MgO Mg O 1 2 2 2 2 But the numbers still aren’t equal, so add another “BIG” number 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE SAY THAT THE EQUATION IS BALANCED!! 2

71. Try to balance these equations using the same method: [1] Na + Cl 2  NaCl [2] CH 4 + O 2  CO 2 + H 2 O [4] Al + O 2  Al 2 O 3 [3] Li + HNO 3  LiNO 3 + H 2

72. How did you get on?? [1] 2 Na + Cl 2  2 NaCl [2] CH 4 + 2 O 2  CO 2 + 2 H 2 O [4] 4 Al + 3 O 2  2 Al 2 O 3 [3] 2 Li + 2 HNO 3  2 LiNO 3 + H 2 Here are the answers:

73. Instrumental techniques Modern chemists use a range of instruments to analyse and identify substances. Most produce quantitative data, which requires expert interpretation. There are many different types of machine used for analysis, each producing a different type of information, such as: whether a substance is pure or a mixture the molecular mass of a compound the types of bonds in a molecule the arrangement of atoms in a molecule the isotopes of different atoms in a substance.

74. Instrumental techniques Many instrumental methods are developed. Some methods are suited for identifying elements. 6/26/2015

75. Atomic absorption spectroscopy Atomic absorption spectroscopy (ABS) is a technique that allows elements to be identified, and their concentration measured down to just a few parts per billion. ABS has many uses: environmental chemistry – to analyse pollutant concentrations in air and water medicine – to analyse concentrations of toxic chemicals in blood and urine building – to check for impurities in concrete and steel mining – to check how much metal is in an ore.

76. Some methods are suited to the identification of compounds 6/26/2015

77. Infrared Spectroscopy This is used to identify the compounds by showing the presence of particular groupings of atoms. This is used in Pharmaceutical industries to identify and discriminate between drugs that are similar in structure. Eg : Penicillin type drugs. Used to identify both organic and inorganic molecules. Samples can be solid, liquid or gas. 6/26/2015

78. Infrared Spectroscopy This is used to monitor environmental pollution. It has biological uses in monitoring tissue physiology including Oxygenation, Respiratory status Blood flow damage 6/26/2015

79. Instrumental Techniques Forensic scientists used this methods because They are very accurate They require tiny amounts of sample 6/26/2015 Other techniques utilised are nuclear magnetic resonance spectroscopy and Ultraviolet/ Visible Spectroscopy

80. Think about this… Yummy Pickle

81. Introducing Little Mr. “Mixture” Burp!!!! I am messy! I am formed when two or more substances joined together physically ( without chemical bonds ) I have the same properties as all the substances AIR I am his best friend!

82. Mixtures Definition of a mixture: A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.

83. Mixtures Note that a mixture: consists of two or more different elements and/or compounds NOT chemically combined . Can be homogeneous or non-homogeneous can be separated into its components by physical means , and often retains many of the properties of its components .

84. Microscopic view of a gaseous mixture containing two elements (argon and nitrogen) and a compound (water). Mixtures

85. Mixtures Examples of mixtures include muddy water and air. Air is made up of gases such as nitrogen and oxygen mixed together.

86. Little Mr “Mixture” I do not have a fixed composition of the substances. A Mixture can be: element + element element + compound compound + compound (Refer to page 59, Fig 4.7) He is a “boo-boo!” He can be separated to its substances by physical methods

87. A mixture of 2 elements A mixture of two elements, e.g. neon (Ne) and hydrogen (H 2 )

88. A mixture of 1 element and 1 compound A mixture of one element and one compound, e.g. hydrogen (H 2 ) and ammonia (NH 3 )

89. A mixture of 2 compounds A mixture of two compounds, e.g. water vapour (H 2 O) and carbon dioxide (CO 2 )

90. CHARACTERISTICS OF MIXTURE It is an impure substance No formula They can be mixed in any ratio. The properties of the mixture are the properties of its constituents. Constituents can be easily seperated by physical methods e.g. heating, drying, crystallization, distillation etc. It is either homogenous or heterogenous. 90 جمعه، 10 رمضان، 1436

91. Mixtures Homogenous mixture Is the type of mixture that has a completely uniform composition throughout itself. It’s components are evenly distributed throughout the sample.

92. Homogenous or Heterogenous? Air Salt water Tea Brass Vinegar Hydrogen peroxide Steel Salad dressing Apple Sand Paint Granite Laundry detergent Cereal

93. Solutions Is the special name that scientists give to homogenous mixtures. Solutions may be gases, liquids or solids. An example: solution of sugar in water.

94. Solutions Some common types of solutions System Examples Gas-gas CO 2 and O in N (air) Liquid-gas Water vapor in air Gas-liquid CO 2 in H 2 O (Soda water) Liquid-liquid Acetic acid in H 2 O (vinegar) Solid-liquid NaCl in H 2 O (brine) Solid-solid Cu in Ag (Sterling silver)

95. Phases Any part of a system with uniform composition and properties is called a phase . On a homogenous mixture you have “one phase” only. On a heterogenous mixture you have “two or more phases”.

96. Phases in a heterogenous mixture

97. Phases in a homogenous mixture

98. Difference between Mixtures and Compounds Example A mixture of iron fillings and sulphur looks different from the individual elements. 6/26/2015 This mixture has the properties of both iron and sulfur. A magnet can be used to separate the iron fillings from the sulfur

99. Difference between Mixtures and Compounds Example This mixture has the properties of both iron and sulfur. A magnet can be used to separate the iron fillings from the sulfur. Substances in a mixture have not undergone a chemical reaction. It is possible to separate them by using their physical properties. 6/26/2015

100. If the mixture of iron and sulfur is heated a chemical reaction occurs and a new substance is formed called iron (II) sulfide. Iron + Sulfur iron (II) sulfide. iron (II) sulfide has different properties to the mixture of iron and sulfur. This iron (II) sulfide would not be attracted towards a magnet. 6/26/2015 Difference between Mixtures and Compounds Example heat t

101. Different properties of iron, sulfur, an iron/sulfur mixture and iron (II) sulfide Substance Appearance Effect of a magnet Effect of dilute HCl Iron Dark grey powder Attracted to it Very little action when cold. When warm, a gas is produced with a lot of bubbling Sulfur Yellow powder None No effect when hot or cold Iron/Sulfur mixture Dirty yellow powder Iron powder attracted to it Iron powder reacts as above iron (II) sulfide Black solid No effect A foul-smelling gas is produced 6/26/2015

102. Differences between mixtures and compounds *giggles* HeE stupid… Laugh what? I know I am a little “bushy and hairy” than you… Little Miss Compound Mr Messy VS

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107. EXTRA! Human body is made up of 28 elements? About 99% our mass is made up of the 6 main elements Oxygen (65%) Carbon (18%) Hydrogen (10%) Nitrogen (3%) Calcium (1.5%) Phosphorus (1.5%)

108. Seperating Solid Mixtures 6/26/2015 Suppose you had a mixture of iron nails , salt and water … How would you separate this mixture completely ? Based on which physical properties would you base your method on ?

109. Distillation 6/26/2015 How would you separate the components in tap water ? Distillation A liquid is boiled to produce vapor that is then condensed again to a liquid

110. Distillation Process 6/26/2015

111. Seperating Solid/Liquid mixtures Sedimentation and Decantation Sedimentation  is the process of separating an insoluble solid from a liquid in which it is suspended by allowing it to settle to the bottom of the container. If this also involves pouring off of the liquid leaving the solid behind, it is called  decantation . 6/26/2015

112. Crystallisation Crystallisation  is a sophisticated form of evaporation technique in which crystals of the solute are encouraged to develop during the process of “dissolving out” from the solution as the solvent evaporates. 6/26/2015

113. Evaporation Evaporation  is used for recovering dissolved solid substances from solutions by evaporating the solvent. The solute “dissolves out” and is left behind. 6/26/2015

114. 6/26/2015 Differential Centrifugation The simplest form of separation by centrifugation is differential centrifugation, sometimes called differential pelleting (see  Figure 1 ). Particles of different densities or sizes in a suspension will sediment at different rates, with the larger and denser particles sedimenting faster. These sedimentation rates can be increased by using centrifugal force. A suspension of cells subjected to a series of increasing centrifugal force cycles will yield a series of pellets containing cells of decreasing sedimentation rate.

115. Seperating Liquid Mixtures Liquids are divided into two: Miscible Liquids Immiscible Liquids Definition of Miscible liquids: Miscible Liquids are formed when when two substances mix together completely. For example: Apple juice and Pineapple Juice. 6/26/2015

116. Immiscible Liquids: Immiscible liquids are formed. two substances do not mix together and form a different layer for Ex: Oil and water. 6/26/2015

117. 6/26/2015 Fractional Distillation Fractional distillation  is the process of separating two or more miscible liquids by a modified distillation process, in which the distillates are collected as  fractions  having different boiling points. The separation of the liquids by this method is based on the difference in their boiling points. (Fig. 5) Fractional distillation makes use of a  fractionating column  or  distillation column , a tube which provides different temperature zones inside it during distillation, the temperature decreasing from bottom to top. It provides surfaces on which condensations (of less  volatile  liquids) and vaporizations (of more volatile liquids) can occur before the vapours enter the condenser in order to concentrate the more volatile liquid in the first fractions and the less volatile components in the later fractions. Fractional distillation is very effective is separating mixtures of volatile components, and is widely used in laboratories and industries.

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119. Filtration Filtration is used for separating insoluble solids from a liquid. 6/26/2015

120. Chromatography When we separate two or more solids that are soluble. This type of problem is encountered when you have mixtures of coloured materials such as inks and dyes.A technique called chromotography is widely used to separate these materials so that they can be identified. There are several types of chromatography, however they all follow the same basic principles the simplest kind is paper chromotography . To separate the different coloured dyes in a sample of black ink, a spot of the ink is put on to a piece of chromatography paper. This paper is then set in a suitable solvent. 6/26/2015

121. Chromotography As the solvent moves up the paper the dyes are carried with it and begin to separate. They separate because the substance have different solubilities in the solvent and are absorbed to different degrees by the chromotography paper as they result they are seperated gradually as the solvent moves up the paper. The chromotogram shows how the ink contains three dyes. 6/26/2015

122. Solvent Extraction Sugarcan be obtained from crushed sugar cane by adding water. The water dissolves the sugar from the sugarcane. This is an example of solvent extraction. In a similar way some of the green substances can be removed from ground - up grass using ethanol. The substances are extracted from the mixtures by using a solvent which dissolves only those substances required. 6/26/2015

123. Criteria for purity Drugs are manufactured to very high degree of purity. To ensure that the highest possible purity is obtained the drugs are dissolved in a suitable solvent and subjected to fractional crystallisation . It is illegal to put anything harmful into a food. Also government legislation requires that a lot of testing takes place before a new pharmaceutical is marketed. Throughout the chemical, pharmaceutical and food industries it is essential that the substance used are pure. The purity of a substance can be gauged by: 6/26/2015

124. Criteria for purity Its melting point – if it is a pure solid it will have a sharp melting point. If an impurity is present then the melting point takes over a range of temperature Its boiling point – if it is a pure liquid the temperature will remain steady at its boiling point. If the substance is pure then the mixture will boil over a temperature range. Chromotography – if it is a pure substance it will produce only one well defined spot on a chromatogram. If impurities are present then several spots will be seen the chromotogram . 6/26/2015

125. Conclusion An element is a pure substance which cannot be split up into two or more simpler substances by chemical means. A compound consist of a fixed number of different kinds of atoms chemically combined together. A mixture is not a pure substance as it contains a mixture of atoms of molecules which are not chemically combined together.

126. Well done!