Intermolecular Forces | My Assignment Tutor

Replacement Take Home Activity: Intermolecular Forces Preparation Read the information on the following pages concerning solubility and intermolecular forces. You will also find referring to Lecture 11 and Workshop Activity 11 useful.Before attempting this worksheet, view the recommended resources associated with this exercise on Blackboard. These contain information you will need to answer the questions.This worksheet involves an optional practical component. If you do not have the ability to carry the procedure out yourself, resources will be provided on Blackboard so that you can still answer the associated questions. Goals Infer chemical concepts and predict experimental observations. Understand variations in solubility of compounds as a function of their intermolecular forces and draw some general rules about solubility based on structure and intermolecular forces.Utilise appropriate style to report your findings, including using accepted conventions to represent chemical structures, and explain concepts using appropriate terminology. Assessment Complete this worksheet using the sample data provided and submit your answers using the Turnitin submission link by 12:00 NOON Monday 24th May. Your demonstrator will assess your answers to the questions using the rubric provided on Blackboard. This worksheet should be completed individually. Academic Integrity The questions on your worksheet should be completed individually and in your own words. By submitting your work through Turnitin you are declaring that the content of the assessment is your own unassisted work. Introduction The physical properties of pure molecular substances (such as melting point, boiling point, viscosity and surface tension) depend on the strengths of intermolecular forces between molecules. The strengths of intermolecular forces are also important factors that govern whether or not one molecular substance dissolves in another. In order for one substance to dissolve in another, the following processes must occur: Solute molecules are separated from each other. Solute-solute interactions resist this.Solvent molecules are separated from each other. Solvent-solvent interactions resist this.Solute and solvent molecules mix with each other. Solute-solvent interactions assist this. The ability of two substances to dissolve completely in each other at any concentration is called miscibility. When two substances do not mix to form a homogenous (uniform) mixture, they are immiscible. Whether or not two molecular substances are miscible with each other can be accounted for as follows: There is a natural tendency for molecules of different substances to mix amongst each other.Molecular substances will be miscible in each other if the solute-solvent attractions are strong enough to overcome the resistance to mixing due to solute-solute and solvent-solvent attractions.In other words, the interactions formed between the two substances must be of equal or greater strength than the interactions each substance had by themselves. Forces between uncharged species (neutral molecules) are called van der Waals Forces. These forces can be categorised into three types: Dispersion forces (or London dispersion forces) are present in all substances. They are the weak forces that attract non-polar molecules to each other.Dipole-dipole interactions are present in substances that possess a dipole. These are stronger forces caused by the attraction of the δ+ part of one polar molecule to the δ– part of a neighbouring polar molecule.Hydrogen bonding is a particularly strong form of dipole-dipole interactions that are only present within molecules that contain a hydrogen atom directly bonded to fluorine, oxygen, or nitrogen. Many molecules can possess multiple types of intermolecular forces. In these cases, one type of intermolecular force will be predominant. In molecules that have both ‘polar’ and ‘non-polar’ groups, the group making up the larger proportion of the molecule will determine which intermolecular force is predominant. The aim of this experiment is to test a number of pairs of substances for mutual miscibility, and to explain your observations in terms of intermolecular interactions. To make these explanations you will need to examine the structure of each molecule investigated and its polarity. Introductory questions What interactions must be broken and formed in order for two substances to be miscible with each other? Identify all of the intermolecular forces that would be present between molecules in (i) water and (ii) acetic acid. (i) (ii) Based on your answer above, what intermolecular forces could form between a molecule of water and a molecule of acetic acid (hint: What intermolecular forces do they have in common)? How do these intermolecular forces compare to those existing between two molecules of acetic acid? Based on your answers above and the information provided in the introduction to this exercise, would you expect water and acetic acid to be miscible in each other? Explain your answer. Kitchen experiment In this home experiment you will be investigating the miscibility of some commonly used liquids found in your kitchen. Note: If you are not able to carry out this experiment yourself, a short video of the procedure can be found on Blackboard. Please watch the video and then fill out the following table and questions using the results. You will need: olive oil (main component is oleic acid, C18H34O2)another type of vegetable or nut oil (contains linoleic acid, C18H32O2)vinegar (acetic acid solution, CH3COOH)tap water (H2O)food colouring (any colour)3x colourless, transparent drinking glasses Pour approximately 1 cm of vinegar into a clean, dry glass. Add a similar amount of water. Swirl the glass thoroughly to mix the substances and observe whether or not they are miscible in each other. Record your observations in the table below. In new clean glasses, repeat the process with olive oil and your other chosen oil, then again with vinegar and olive oil. Record your observations in the table below. Lastly, toyourglasscontaining vinegar and olive oil,add2dropsof food colouring. Swirl the glass to ensure mixingandrecordyourobservations. On the basis of these results, fill in the remaining spaces in the table below by predicting what you would expect to observe. Complete the final row of the table with your conclusions on the polarity of each substance. Watervinegarolive oilother oil ___________watersolublevinegarsolubleolive oilsolubleother oil __________________solubleIs this substance polar or non-polar? Hint: Remember that for molecules with both polar and non-polar groups, the group with the larger proportion will determine the predominant intermolecular force. Results: Solubilities of molecular substances in molecular liquids Were the water and vinegar miscible with each other? Explain why or why not on the basis of the intermolecular forces present. Were the olive oil and other oil miscible with each other? Explain why or why not on the basis of the intermolecular forces present. Were the vinegar and olive oil miscible with each other? Explain why or why not on the basis of the intermolecular forces present. When you added olive oil to vinegar, which substance was the upper layer? On that basis, which substance is denser? When you added food colouring to the vinegar/oil mixture, which layer did the food colouring end up in? On that basis, is food colouring polar or non-polar? Conclusions: Solubilities of molecular substances in molecular liquids Make generalisations about the solubilities of:polar substances in polar substances. non-polar substances in non-polar substances. non-polar substances in polar substances. Explain the trends observed in Question 10, referring to the different interactions that may be present between solute and/or solvent molecules. (Hint: Review the information provided in the introduction.) Solubilities of alcohols in water and hexane Examine the images of mixtures of various alcohols in water and hexane. Fill in the following table with your observations and answer the questions below. AlcoholSolubility in waterSolubility in hexaneMethanolEthanol1-Propanol1-Butanol1-Pentanol On the basis of their chemical structures, do you expect water and hexane to be polar or non-polar solvents? Explain your answer. Describe the trends observed from the sample date for the solubility of methanol, ethanol, 1-propanol, 1-butanol and 1- pentanol:in water. in hexane. Compare the structures of molecules of methanol, ethanol, 1-propanol, 1-butanol and 1-pentanol with respect to:the number of hydroxyl groups in their molecules. the size of the hydrocarbon portion of their molecules. How do the solubilities in water of alcohols with one hydroxyl group in their molecules depend on the size of the hydrocarbon portion of their molecules? Account for your conclusion using arguments based on intermolecular forces. (Hint: Review the YouTube video resources provided.) Extension activity: Emulsifiers and surfactants Bonus Experiment – Make your own salad dressing! In the first kitchen experiment at the start of this activity, we created two separate layers of olive oil and vinegar. To make the perfect salad dressing however, we need the olive oil and vinegar to mix together. We can achieve this by adding an emulsifier to the mixture, such as honey or mustard. Emulsifiers contain both a hydrophilic (polar) ‘head’ that can interact with polar compounds, and a hydrophobic (non-polar) ‘tail’ that can interact with non-polar compounds. Figure: Generic emulsifier structure, with a polar ‘head’ (pink) and non-polar ‘tail’ (carbon chain). Note: If you are not able to carry out this experiment yourself, a short video of the procedure can be found on Blackboard. Please watch the video and then fill out the following questions using the results. Add equal amounts of olive oil and vinegar to a glass jar with a lid (about 1 cm depth each) and adda teaspoon of mustard or honey. Put the lid on the jar and shake the mixture for 30 seconds. Observe what happens to the olive oil and vinegar mixture and answer the questions below. When finished, add some salt and pepper and pour on some salad to enjoy! Bonus Questions – for extra credit (no marks will be lost for incorrect/incomplete answers) What happens to the olive oil and vinegar mixture after addition of the mustard/honey? Explain why, using your knowledge of intermolecular forces. Soaps and dishwashing detergents are also examples of molecules that contain both polar and non-polar components. The non-polar ‘tail’ binds to grease and dirt, while the polar ‘head’ interacts with water allowing the dirt to be washed away. Explain, in terms of intermolecular forces, why hand washing with soap is so effective at breaking down (not just removing) the viral particles that cause COVID-19. (Hint: You can research information for this question online, but make sure to cite any references you find and write the explanation in your own words). END OF WORKSHEET


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