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STATES OF MATTER 2: MEASURING RAM VOLATILE LIQUIDS

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Published in: Chemistry
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The presentation describes: i. The method used ii. Lattice structures iii. modern use of materials iv. Effect of structure and bonding on physical properties

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  1. MEASURING RELATIVE MOLECULAR MASS OF A VOLATILE LIQUID PREPARED BY: ATHUMANI R KAWAMBWA PHARMACIST (BPHARM)
  2. OUTLINE The methods used Lattice structures Modern uses of materials The effect of structure and bonding on physical properties
  3. The ideal gas equation is going to be used to calculate the relative molecular mass of volatile liquid. The method relies on turning liquid into a gas. Mole Is the measure of the quantity of matter in Chemistry. Number of moles (n) Is the ratio of mass of substance in grams to the relative molecular mass.
  4. QUESTIONS What is the approximately volume of: (a). 2 moles (b). 0.25 mol of carbon dioxide at room temperature and pressure? Hint mass (g) Number of moles (n) = molar mass mass (g) Number of moles (n) = molar mass volume volume at RTP volume 24 dm3
  5. METHODS USE TO MEASURE THE RAM OF VOLATILE LIQUID There are several ways of performing this experiment. Consider the apparatus shown below steam in gas syringe Steam jacket self—sealing volatile liquid hypodermic thermometer steam out
  6. The outline of this method is as follows: Take the known mass of volatile liquids Introduce the liquid into a gas syringe in an oven. Turn the liquid into vapour and measure its volume. • By knowing the volume of the as and its temperature, we can use ideal as equation to work out how many moles of gas are present.
  7. Then, because we know mass of this number of moles, we can work out the relative molecular mass of the gas and hence liquid. The nozzle of the as syringe is covered with a rubber cap called septum, and the gas syringe is put in the oven or steam jacket. Once the reading on the gas syringe shows no further changes, the initial reading on the gas syringe is taken, and the sample of the liquid is taken up into a small syringe. Here we shall assume that, we are using ethoxyethane (ether) as the liquid.
  8. The small syringe is weighed and ethoxyethane is injected into a gas syringe. Then the small syringe is immediately reweighed. Once ethoxyethane is in the gas syringe, the liquid quickly vaporizes and the plunger is driven outward. Eventually equilibrium is achieved and there is no further change in the volume recorded on the gas syringe. Provided the temperature of the steam jacket and the atmospheric pressure are known, we can calculate the relative molecular mass.
  9. SOME SAMPLE EXPERIMENTAL RESULTS Here are some sample reading: Mass of syringe and ethoxyethane Before injection into gas syringe - - 20.476 g After injection into a gas syringe - - 20.252 g 3 Initial reading on the gas syringe = 1.4 cm = 96.8 cm3 Final reading on the gas syringe
  10. DATA CONTINUES Temperature of steam jacket = 99.6 oc = (99.6+273) K = 372.6 K Atmospheric pressure = 1000kPa = 100000 Pa From the results above Mass of ethoxyethane used = 20.476 g = 0.224g mass of ethoxyethane used is 0.224 g - 20.252 g
  11. Volume of vapour = Final volume - = 96.8 - 1.4 cm3 = 95.4 cm3 Volume in metre cubic 1 cm3 = 10-6 m3 Hence 95.4 cm3 = 95.4 x 10-6 m3 Initial volume Volume of ethoxyethane used is 95.4 x 10-6 m3
  12. We use ideal gas equation to get number of moles From PV = nRT When we make number of moles ' n" subject 100000 Pa m3 x 372.6K 8.314 Kmol n = 0.003 mol
  13. Relative molecular mass From mass n molar mass Then mass molar mass — number of moles 0.224 g molar mass = 0.003 mol Molar mass is 74.7 g/mol = 74.7 g/mol
  14. EXPERIMENTAL ERROR The formula of ethoxyethane is (C2H5)20, so it is true that the relative molecular mass IS 74 g/mol. It is quite common for results in this experiment to overestimate the relative molecular mass. The most important reason for this is that, before the liquid can be injected into gas syringe some of ethoxyethane evaporates from the needle of small syringe. This means that we overestimate the mass of liquid that turns into the gas in the gas syringe.
  15. QUIZ 1 The gas syringe experiment only works with liquids that are highly volatile such that those which evaporate easily. a). Explain why the mass of liquid injected in the gas syringe is less than that given by weighing? b). How and why, does this affect calculations?
  16. QUIZ 2 The volatile liquid propanone was used in an experiment to measure its relative molecular mass like the one we have discussed in the last slides. The following data were collected: Mass of syringe and propanone before injection to the as syringe = 20.374 g after injection to the gas syringe = 20.193 g Initial reading on gas syringe = 1.6 cm3 Final reading on gas syringe = 97.1 cm3 3 Temperature of steam jacket (oven) = 99.3 cm Atmospheric pressure = 100.2 kPa Calculate the relative molecular mass of propanone.
  17. SOME LATTICE STRUCTURES Crystalline solids may be held together by variety bonds. The physical properties ot solids reflect the nature of their bonding. The following lattice structures are going to be studied: Ionic lattice Simple molecular lattice ii. iii. Hydrogen bonded lattice iv. Giant molecular lattice Metallic lattice v.
  18. l. IONIC LATTICE Ionic bonding results from the electrostatic attractions between oppositely ions which are held in giant ionic lattice. In such lattice, there is a regular arrangement of anions and cations. The exact way in which individual ions are arranged depends on their relative size and their relative charges.
  19. + Sodium chloride (NaCl) and Magnesium oxide (MgO) form cubic lattice, in which each cation is surrounded by six anions and each anion is surrounded by six cations. LATTICE STRUCTURE OF SODIUM CHLORIDE
  20. In the ionic lattice there are strong electrostatic attractions throughout the lattice. This means that the much energy is required to separate ions and the melting point is higher. The liquid formed contains ions which will be attracted to the oppositely charged ions present, thus the boiling point will be also higher. For sodium chloride (NaCl) the melting point is 808 oc and the boiling point is 1456 0 C. For magnesium oxide the melting point is 2853 oc and the boiling point is 3600 0 C.
  21. The very high melting point and boiling point of magnesium oxide (MgO) make it very suitable for use as lining of high temperature furnace. Ionic crystals are generally strong and hard, but may shatter when struck hardly. Solid ionic lattice do not conduct electricity in this form due to its ions/electrons are fixed, but they conduct electricity I molten form as ions will be free to move.
  22. ll. SIMPLE MOLECULAR LATTICE Simple molecular lattices are often held together by instantaneous dipole — induced dipole forces also called van der Waal forces. The strength of van der Waal forces increases with number of electrons present. the melting points of halogens increases down the group with increase in the relative molecular mass. This is because larger molecules have more electrons around them, which give rise to the larger instantaneous dipole — induced dipole forces.
  23. Thus Fluorine and Chlorine are gases at room temperature Bromine is liquid and Iodine is solid at room temperature. Solid Iodine (12) molecules in which there is a covalent bonds between the atoms, but between the molecules there are much weaker instantaneous dipole — induced dipole forces.
  24. STRUCTURE OF SOLID IODINE
  25. • When solid iodine is heated, the weaker instantaneous dipole — induced dipole forces are broken down and individual iodine molecules (12) are set free from lattice. Actually Iodine turns directly from solid to gases in this way producing purple vapour of Iodine molecule, the process called sublimation. Some simple molecules are held together by permanent dipole — dipole forces. Hydrogen chloride in which chlorine is more electronegative than hydrogen.
  26. THE STRUCTURE OF HYDROGEN CHLORIDE • When hydrogen chloride (HCI) is heated, the weaker permanent dipole — dipole forces breaks and hydrogen chloride leave solid lattice. Since instantaneous dipole — induced dipole forces are relatively weaker, simple molecular compounds containing them have low meting point and boiling point. Simple molecules do not conduct electricity when solid or in molten form.
  27. Ill. HYDROGEN BONDED LATTICE • Hydrogen bonding is the type of force which can exist between certain molecules such as water (H20). STRUCTURE OF AN ICE
  28. The weaker hydrogen bonds break when ice is melted, leaving covalent water molecules. Hydrogen bonds are stronger than dipole — induced dipole forces but much weaker than covalent bonds.
  29. IV. GIANT MOLECULAR LATTICES Giant molecular lattices are three dimensional arrangement of atoms held together by strong covalent bonds. Some giant molecular structures contain atoms of one element. Examples: Graphite Diamond.
  30. GIANT STRUCTURE OF GRAPHITE Graphite
  31. GIANT STRUCTURE OF DIAMOND
  32. Other lattice structures contain atoms of different elements, joined together by a strong covalent bonds. Example: Silicon (IV) oxide STRUCTURE OF SILICON (IV) OXIDE Silicon atom covalent Oxygen at
  33. When giant molecular substances are melted, large number of covalent bonds must be broken down. Therefore, they have high melting points. Silicon (IV) oxide melts at 1610 0 C. Diamond melts at 3550 0 C. 'With exception to graphite, the giant molecular structures do not conduct electricity in solid or liquid form. Giant molecular structures are usually hard.
  34. V. METALLIC LATTICES Metallic compounds are good conductor of electricity. They are ductile They are also malleable. Example: Copper is typical metal.
  35. THE CRYSTAL STRUCTURE OF COPPER
  36. EFFECTS OF STRUCTURES AND BONDING ON PHYSICAL PROPERTIES The nature of bonding of substance determine its physical properties. It is also possible to use knowledge of physical properties of substance to predict nature of bonding in unknown substance. SUBSTA MOLECULAR MELTING NCE B c MASS (g/mol) 60 74.5 86 POINT ( oc) 1610 772 -95 BOILING POINT ( oc) 2205 1402 69 ELECTRICAL CONDUCTIVI None In liquid state None
  37. INTERPRETATION Substance A and B have higher melting point, that suggest they are giant structures. Substance A does not conduct electricity at all, while substance B conducts in molten form. Substance A is a giant molecular compound. Substance B is ionic compound and The very low melting point and boiling point of substance C shows that it must be a simple molecule which agree with its lack to conduct electricity.
  38. MODERN USES OF MATERIALS Today we have enormous range of materials available. They are: Metals and their alloys ii. Ceramics iii. Glass iv. Plastics Polymers v.
  39. l. METALS The major structural metal is Iron, which has the great drawbacks. Aluminium is widely used in transportation for making the bodywork of aero plane, ship, train, buses, etc., in food packaging (Aluminium foil), and in overhead electrical power lines. 'This is because Aluminium has low density and does not readily corrode. It can be mixed with other metals, by melting them to form alloys which are light and strong.
  40. Copper has high electrical and thermal conductivity, is malleable and ductile, and is resistant to corrosion. The pure metal is therefore widely used in electrical wiring, water pipes, central heating system, roofing etc. Copper is mixed with Zinc to form an alloy called Brass which is fairly soft and easily worked into shape. Brass is used for srews, hinges and domestic objects. • A stronger alloy of Copper and Tin called Bronze. Bronze is used in bearings and ships' propellers. The coinage of many nations has used copper alloys.
  41. ll. CERAMICS The group of substances generally known as ceramics contains compounds that have giant structures. Ceramics are used in the furnace lining, electrical insulators, glass and crockery. Furnace lining needs substance that can withstand high temperature and compounds such as Aluminium oxide whose melting point is 2040 oc and Magnesium oxide whose melting point is 2800 oc are used.
  42. The strong giant covalent lattices of silicates and similar compounds such as Silicon (IV) carbide and silicon (IV) nitride give compounds that are strong, hard, and rigid and are also electrical and thermal insulators. Such compounds find use as electrical insulators, as in overhead power lines, in glass, and in crockery. Their disadvantage is that they are brittle. Tiles contain high grade silicon (IV) oxide re used in the U.S space shuttle as heat shields during re-entry to the earth atmosphere.
  43. RECYCLING Raw materials extracted from the earth surface can not last for ever. Although some materials are more abundant than others, they are all finite resources. Increasing demand for raw materials, coupled with ever growing problem of waste disposal, have led to considerable interest in recycling wastes.
  44. ADVANTAGES OF RECYCLING WASTES It leads to reduced demand for new raw materials. It leads to reduction in environmental damage It reduces demand for landfill sites to dump wastes. It reduces cost of waste disposal. It may reduce energy cost.
  45. REFERENCES •AS Level and A Level Chemistry Brian Ratcliff et el 10th Edition Online Verified Sources

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