Chemistry Tasks: All questions and core plus questions

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Test 5 Tests to dissolve polymers What are polymers? Polymers are long chain-like molecules. "Poly" means "many" and "mer" means "parts." So "polymer" means "many parts." The parts are usually the same small molecule that repeats to form a large chain-like molecule. Polymers are also referred to as plastics because they are easily molded. But polymers are not just man made. Many polymers occur in nature. Natural fibres such as cotton and wool are polymers as is wood. We usually think of polymers as plastics. http://www.chemistryland.com/CHM107/inde x.html In this test we try to dissolve two polymer materials: a Styrofoam cup, made of polystyrene (a man made polymer) and a packing material made from starch (a naturally occurring polymer). Starch packing material Polystyrene cup Polymers are made by chaining one or two smaller molecules one after another, creating a linked chain. Polymer molecules are very large, and can contain hundreds of atoms. A section of the polystyrene molecule and the starch molecule is shown below. A section of the polystyrene molecule. There is a carbon atom at each corner, but they are not shown to make it easier to view each molecule. A section of the starch molecule. Source: http://chem.chem.rochester.edu/~chem421/intro1.htm http://winnieboo.blogspot.com/2008/09/52-concepts.html Week 10 Page 2 Q 9. (a) Look at the structure of the polystyrene molecule below and explain why it is not polar. ………………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… (b) Identify which chemical bonds in the starch molecule are polar. Tests to dissolve each polymer in water Two large beakers are placed side by side. Water is poured into the each beaker until they are about half full. A Styrofoam cup is placed into one beaker. Packing material made of starch is placed in the other beaker. The polystyrene cup in water remains unchanged. Q 10. The starch packing material in water breaks down. Based on the structure of each molecule, explain the differences in solubility in water. ………………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… Week 10 Page 3 Tests to dissolve each polymer in acetone Two more large beakers are placed side by side. Acetone is poured into both beakers until they are about half full. A Styrofoam cup is placed into one beaker. Packing material made of starch is placed in the other beaker. The polystyrene cup in acetone breaks down. Q 11. The starch packing material in acetone remains unchanged. We saw in Test 3 that acetone dissolves in both water and carbon tetrachloride, showing that it has some polar properties and some nonpolar properties. Based on ‘like dissolves like’ we would expect acetone to dissolve both polar and non-polar materials. However, in this test acetone only dissolved the non-polar polymer. Suggest a reason why acetone could not dissolve the polar starch polymer. ………………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… ………………………………………………………………………… SEND Your answers to discussion questions 1 to 8 on pages 15 – 19. CORE-PLUS students also complete questions 9 to 11 on pages 20 – 22. Week 10 Page 4 Covalent network lattices LESSON 4 Go to Chapter 6 in your textbook. Read pp 129 – 132 on covalent lattices. Do Revision questions 28, 29 and 31 on page 132. Correct your answers from the back of the textbook. On the net To see 3D covalent network lattice structures online http://www.dynamicscience.com.au/tester/solutions/chemistry/bonding/bondi ng10a.htm SEND Skills question 5 on page 24 CORE-PLUS students also do Q11 on p.26 A review of chemical bonding LESSON 5 The chemical bonding we have covered includes metallic, ionic and covalent compounds. In this lesson we review these bonding models. Watch a video about intermolecular forces (forces between molecules) DVD Watch the video titled ‘Covalent molecules’ on your Chemistry DVD. Go to Chapter 6 in your textbook. • Read pages 133 to 135, including sample problem 6.8. Do Revision questions 34 and 35. Correct your answers from the back of your textbook. • Read sample problem 6.9 on page 137 of your textbook. Do Revision questions 36, 38 and 42. Correct your answers from the back of your textbook. On the net Test yourself. Take a test on the net. To test yourself on ionic and covalent compounds, do the quiz (test) classifying compounds at the site below. Go to http://antoine.frostburg.edu/chem/senese/101/compounds/compound-classifyquiz.shtml To test yourself on interpreting chemical formulas, do the quiz (test) interpreting formulas at the site below. Go to http://antoine.frostburg.edu/chem/senese/101/compounds/interpret-formulasquiz.shtml SEND Skills questions 6, 7 and 8 on pages 24 – 25 Week 10 Page 5 SEND Skills Questions 1. Use the table of electronegativities on the page 3 to help you fill in the table below. Atoms bonded Difference in electronegativity Type of bond (non-polar covalent, polar covalent, or ionic) F ⎯ Cl H⎯F N⎯N S⎯F P⎯H 2. (a) (b) Show the bond dipoles in the molecules below. Predict whether the molecules are polar and explain why. (i) CHF3 (ii) CF4 F H F C F F F 3. (a) (b) F C F Sketch the shape of ammonia, NH3 and carbon dioxide, CO2, showing the bonding and non-bonding electron pairs. At room temperature, both ammonia and carbon dioxide are gases. They are also both small molecules about the same size. However, when the temperature is lowered, ammonia forms a liquid (condenses) at a much warmer temperature more than carbon dioxide. Consider the differences in forces between molecules of ammonia compared with carbon dioxide. Explain why these differences cause ammonia to condense before carbon dioxide does. 4. CH3OH and HCl both dissolve in water, but the dissolved HCl conducts electricity, while the dissolved CH3OH doesn’t. Explain why. 5. Briefly explain why graphite can conduct electricity, but diamond cannot. 6. The electron configurations of four elements are: 2, 8, 1 (a) 2, 7 Identify the elements 2, 8, 6 2, 8 Week 10 Page 6 (b) Which pairs of elements are likely to form an ionic bond? Show the formulas of the ionic compounds. (c) Which pairs of elements are likely to form a covalent bond? Show the formulas of the covalent compounds. (d) Which element will be unreactive? Why? 7. Work out the formula of the compounds listed below. Use the flowchart on page 136 of your textbook to help you identify the type of bonding in each compound above (ionic, metallic, covalent molecule, covalent lattice). The compound Its chemical formula Its chemical bonding Magnesium chloride Sulfur dioxide Hydrogen peroxide Silicon dioxide Gold 8. The table below shows the properties of four unknown substances. Electrical conductivity Substance Melting point in solid form in liquid form when dissolved in water A 18200C High High Won’t dissolve B 8000C None High Dissolves C 280C None None Dissolves D −100C None None Won’t dissolve Use the information in the table to help you complete the following sentences: Substance ___ could have ionic bonding because__________________________________ _________________________________________________________________________ Substance ___ could have non-polar covalent bonding because___________________________ _____________________________________________________________________________ Substance ___ could have polar covalent bonding because______________________________ _____________________________________________________________________________ Substance ___ could have metallic bonding because___________________________________ _____________________________________________________________________________ Week 10 Page 7 SEND 9. Extra theory questions for CORE-PLUS students The diagram below shows the molecular structure of water and hydrogen fluoride. In each molecule the –H bond is polar, and the molecules are a similar size, but they have markedly different boiling points. The polarity of the –H bond and the boiling points are shown below. Polarity of –H bond (Differences in electronegativity) O—H 3.5 − 2.1 = 1.4 Boiling points 100 C F—H 4.0 − 2.1 = 1.9 20 C The molecule with the strongest dipole does not have the highest boiling point. Explain why this is the case, in terms of the number of Hydrogen atoms available for the lone pairs in each molecule. 10. The table shows the boiling points of group 17 hydrides, and the polarity of the –H bond. group 17 hydrides Molecular formula Polarity of —H bond (Difference in electronegativity) Boiling point HF HCl HBr HI F—H 4.0 − 2.1 = 1.9 Cl—H 3.0 − 2.1 = 0.9 Br—H 2.8 − 2.1 = 0.7 I—H 2.5 − 2.1 = 0.4 20 C −85 C −67 C −35 C (a) Rank the molecules in order of decreasing dipole-dipole strength. (b) Based on dipole strength only, what order of boiling point would you expect the molecules to follow? (c) Explain why the boiling points do not correspond to the dipole strength of the molecules. 11. The elements carbon and silicon are both group (IV) elements. They both form a dioxide (CO2 and SiO2). However CO2 is a gas at room temperature, while SiO2 is an abrasive solid (sand). Explain the different forms in terms of the different structures of each compound. Week 10 Page 8 SEND Modelling hydrocarbons …modelling propane Propane is an alkane with 3 carbon atoms. Its semi-structural formula is CH3CH2CH3. • • • • Draw the structural formula of propane (to show which atoms are bonded to which). View propane in Rasmol. Open the Rasmol folder on the chemistry CD. Open Rasmol, then open the propane molecule. Identify the geometry around each carbon atom Draw a 3D sketch of the molecule. The structural formula, geometry and the 3D sketch go in Worksheet 1 on page 22. Week 10 Page 9 Trigonal planar geometry In Week 6 we saw an example of trigonal planar geometry. The atoms lie in a flat plane at the points of a triangle. Other organic compounds also have a trigonal planar arrangement around the carbon atoms. Ethene is another example. The carbonate ion is trigonal planar. The atoms around carbon form the shape of a flat triangle. Ethene is an alkene with 2 carbon atoms and a double bond CH2==CH2 A flat diagram of ethene. H H Ethene shown as a ball and stick figure. H C H C C H H Each C atom has 4 covalent bonds. Each H atom has 1 covalent bond. Notice that Rasmol does not show double bonds. That’s why we need to draw a sketch and check that each C atom has 4 bonds and each H atom has only one bond. By checking the carbon bonds we can see where the double bonds occur. Ethene in stick form gives a better idea of its geometry. Viewed in Rasmol, ethene is a flat molecule. H C H The geometry around each carbon atom is trigonal planar. The triangles overlap. A 3D sketch of the molecule A 3D sketch of ethene H H C H C H H , the bond is flat When an atom is joined with a plain line, on the page. All of the bonds are shown as plain straight lines, showing that the molecule is flat. Week 10 Page 10 SEND Modelling hydrocarbons …modelling propene and benzene Propene is an alkene with 3 carbon atoms. It’s semi-structural formula is CH2CHCH3. H2C • • • • Draw the structural formula of propene (to show which atoms are bonded to which). View propene in Rasmol. Open the Rasmol folder on the chemistry CD. Open Rasmol, then open the propene molecule. Identify the geometry around each carbon atom. Draw a 3D sketch of propene. Close the propene molecule and open cyclohexene in Rasmol. Identify the geometry around each carbon atom and draw a 3D sketch of the cyclohexene molecule. CH2 CH2 H2C Cyclohexene is a cyclic alkene (a ring formation) with 6 carbon atoms. It’s semi-structural formula is shown in the diagram. • CH HC Cyclohexene The structural formula, geometry and the 3D sketches go in Worksheet 1 on page 22. Linear geometry Ethyne is an alkyne with 2 carbon atoms and a triple bond CHCH A flat diagram of ethyne. C H C Ethyne shown as a ball and stick figure. H Each C atom has 4 covalent bonds. Each H atom has 1 covalent bond. A 3D sketch of ethyne H C C H The molecule is flat, so all bonds are shown as straight lines. H C C H The geometry around the carbon atoms is linear. Week 10 Page 11 Notice that Rasmol does not show triple bonds. That’s why we need to draw a sketch and check that each Carbon atom has four bonds and each Hydrogen atom has only one bond. By checking the carbon bonds we can see where the triple bonds occur. SEND Modelling hydrocarbons …modelling propyne Propyne is an alkyne with 3 carbon atoms. It’s semi-structural formula is CHCCH3. • • • • Draw the structural formula of propyne (to show which atoms are bonded to which). View propyne in Rasmol. Open the Rasmol folder on the chemistry CD. Open Rasmol, then open the propene molecule. Identify the geometry around each carbon atom. Draw a 3D sketch of each molecule. The structural formula, geometry and the 3D sketch go in Worksheet 1 on page 22. Organic compounds with functional groups Many organic molecules usually contain a combination of geometries in their structure, as we see in the example below. The structural formula of diethyl ether Diethyl ether, (or just ‘ether’), was once used as a general anaesthetic. H H C C H H H H C C H H Its semi-structural formula is H CH3CH2—O—CH2CH3 Its functional group is the ether group —O— Check that: O H  Each C atom has 4 covalent bonds. Each H atom has 1 covalent bond. O has 2 covalent bonds Viewed in Rasmol we can see the geometries around each C atom. C O C C C Diethyl ether as a ball and stick figure. Diethyl ether as a stick figure gives a better idea of the geometries around each C atom. Week 10 Page 12 Week 10 Page 13 There are two different geometries in this molecule. The geometry around Oxygen is bent. The geometry around each Carbon is tetrahedral. Tetrahedral geometry around each Carbon atom. H C H C C C O H Bent geometry around Oxygen. This part of the molecule is flat. A 3D sketch of the molecule A 3D sketch of diethyl ether H H C H H C H C H C O H H H H The plain straight lines show the –C–O–C–section of the molecule is flat. The dotted and wedge lines show the –H bonds occupy 3D space around the C atoms. Remember: H, When an atom is joined with a plain line, the bond is flat on the page. H, When an atom is joined with a dotted line, the bond is directed away from you the page. H, When an atom is joined with a wedge line, the bond is directed towards you out of the page. 4 3 2 1 C H 3 C H 3 C H 2 C H C H 2 C H 2 H 3 C C H Week 10 Page 14 SEND Modelling organic compounds … ethanol, ethanamine and ethanoic acid The organic compounds ethanol, ethanamine and ethanoic acid are all derived from ethane, CH3CH3 Their semi-structural formulae are • • • • • • • Draw the structural formula of each molecule (to show which atoms are bonded to which). Identify the functional group and name it. View ethanol in Rasmol. Open the Rasmol folder on the chemistry CD. Open Rasmol, then open the ethanol molecule. Identify the geometries present in ethanol. Draw a 3D sketch of each molecule. Close ethanol and open ethyl amine in Rasmol. Identify the geometry around each carbon atom and draw a 3D sketch of the ethyl amine molecule. Close ethyl amine and open ethanoic acid in Rasmol. Identify the geometry around each carbon atom and draw a 3D sketch of the ethanoic acid molecule. SEND Methyl ethanoate, • • • • • ethanol (ethyl alcohol) CH3CH2OH ethanamine (ethyl amine) CH3CH2NH2 ethanoic acid (acetic acid) CH3COOH The structural formula, geometry and the 3D sketch go in Worksheet 2 on page 23. Modelling methyl ethanoate is an ester. Draw the structural formula of methyl ethanoate (to show which atoms are bonded to which). Identify the functional group and name it. View methyl ethanoate in Rasmol. Open Rasmol on the chemistry CD, then open the methyl ethanoate molecule. Identify the geometries present. Draw a 3D sketch of the molecule. The structural formula, geometry and the 3D sketch go in Worksheet 2 on page 23. Week 10 Page 15 SEND Worksheet 1 : Modelling hydrocarbons Use Rasmol to view each molecule in the table below. Fill in this worksheet as you investigate the 3D structure of each molecule. See pages 15 –19 for details. Molecule Propane CH3CH2CH3 Propene CH2CHCH3 Cyclohexene (CH2)4(CH)2 Propyne CHCCH3 Structural formula Identify geometry around each C atom Draw a 3D sketch Week 10 Page 16 SEND Worksheet 2: Modelling organic compounds Molecule Ethanol CH3CH2OH Ethyl amine CH3CH2NH2 Ethanoic acid CH3COOH For CORE-PLUS students only Methyl ethanoate CH3OCOCH3 Structural formula Identify functional group and name it Use Rasmol to view each molecule in the table below. Fill in this worksheet as you investigate the 3D structure of each molecule. See pages 19 – 21 for details. Show geometries present in each molecule Draw a 3D sketch Week 10 Page 17 SEND Practical exercise 1: The properties of candle wax (a hydrocarbon) This experiment can be done at home. Sources: http://images.sub-studio.com/images/2006/0922candle2.jpg Aim Background ▪ To predict some of the properties of candle wax and test them. Candle wax is a made of a group of hydrocarbon molecules called paraffin molecules. The simplest paraffin molecule is methane, CH4, a gas at room temperature. Heavier members of the series, such as that of octane C8H18, appear as liquids at room temperature. The solid forms of paraffin, called paraffin wax, are from the heaviest molecules from C20H42 to C40H82. This includes candle wax. Materials * A candle * Two glasses * A saucer * A heat source, oven mitt or tea-towel Your predictions Candle wax is a covalently bonded molecule, and it is a waxy solid at room temperature. (a) Do you think candle wax will dissolve in water? Explain why. ………………………………………………………………………… ………………………………………………………………………… (b) Do you think candle wax will need a lot of heat to be applied before it melts? Explain why. ………………………………………………………………………… ………………………………………………………………………… (c) Do you think candle wax will conduct electricity in its molten state? Explain why. ………………………………………………………………………… ………………………………………………………………………… Test your predictions Place a few flakes of candle wax in a glass of warm water. Stir to dissolve. Record your results. Place a teaspoon of candle wax flakes in a dry glass and cover with a saucer. Gently heat the glass and saucer. You may need to stand the glass in a double boiler saucepan. Week 12 Page 18 Observations Describe the changes that occur as the candle wax heats. When the changes have finished, lift the saucer (you may need t ...
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