1. Lifestyle Chemistry Part 2: Colloids and Surfactants HSC Questions

3. C In investigations, the control and experimental set-up should be identical except for the variable that is being tested. In this case, the insect walking across the water in a beaker containing pond water is the basic setup and the variable being tested is the effect of the detergent being added. Thus C is the answer as it is the basic setup minus the variable being tested. A, B and D are incorrect as they involve changing the basic setup rather then removing the variable.

5. C Whether detergent is biodegradable or not is unrelated to its effectiveness as a detergent, so A is incorrect. Biodegradable materials are broken down by biological agents, eg bacteria and fungi and are not needed to kill bacteria and fungi in waterways so B is incorrect. The breakdown products are nutrients for food chains in waterways but this is not in order to provide food for bacteria and fungi, so D is incorrect. The build up of non-biodegradable detergents does cause long- term environmental damage so C is correct.

7. B Compound S acts on the stain causing the dirt particles held in the stain to be released into the surrounding water. It acts on the surface of the stain so it is a surfactant (B). It does not dissolve the dirt particles so it is not a solvent as in C. A solution is a mixture of compounds and not a single compound so D is incorrect. There is insufficient information to determine whether compound S is a salt, so A is incorrect.

9. D Biodegradable materials are broken down by biological agents, eg bacteria and fungi, so D is the answer. The breakdown products are nutrients for food chains, so A is incorrect. Whether detergent is biodegradable or not is unrelated to its effectiveness or its effects on people’s skin so B and C are also incorrect.

11. D Earlier detergents were not biodegradable and so could not break down by microbes in the environment and so they persisted in the environment causing pollution. So D is the answer. Their expense was greater than soaps but their perceived advantages outweighed the additional cost so A is incorrect. They were soluble in water so B is incorrect. One advantage they had over soaps was that they did not react with chemicals in hard water so C is incorrect.

13. A Shampoos, skin cleansers and soap remove oil by forming an emulsion, so A is correct. They do not make the oil a surfactant nor do they alter the pH of the oil so B and C are incorrect. In forming an emulsion, the surface tension of the oils decreases, not increase, so D is incorrect.

15. B Water striders use the surface tension of water to walk on water so when the surface tension is lowered by the addition of detergent, they will sink. So B is correct and D is incorrect. Pure detergent is quite slippery but a dilute solution is not and this is irrelevant to the situation described so A is incorrect. The meniscus would only increase if the surface tension increased not decreased so C is incorrect.

17. C The non-polar and of substance X are dissolved in the oil, while the polar ends are dissolved in the water. This allows the oil and water mixture to form an emulsion so C is correct. The oil is still present as discrete droplets so it has not dissolved as in A, nor has it been biodegraded as in D. The description “lubricates the oil” is meaningless although oil is used as a lubricant so B is incorrect.

19. D A drop of detergent would reduce the surface tension and this would allow the water to better “wet” the glass, causing the drop to spread out as in D. Increased surface tension would be required for A so it is incorrect. The drop of detergent does not significantly affect the volume of the droplet so B is incorrect as it is considerably larger. The reduction on the surface tension by the detergent would cause noticeable effect but C shows the droplet unchanged so C is incorrect.

21. C Oil and vinegar do not react with one another, nor do either of them dissolve in the other, so both A and B are incorrect. In test 1 when initially stirred, small droplets of one liquid were homogenously distributed through the second liquid forming an emulsion that separated into the original two layers over time. In test 2, the mustard appears to have acted as an emulsifier, as in C, allowing the oil and vinegar to remain as an emulsion therefore C is correct. The musturd does not dissolve the oil or vinegar so D is incorrect.

23. C Emulsifying agents are used to stabilise various oil-water mixtures, as they allow oil to disperse in water and prevent them from separating into separate oil and water layers for long periods so C is correct.

25. A An emulsion is a stable mixture of two liquids in which one does not dissolve in the other, as the liquids stay mixed for a long time without separating into layers. So A is correct. A foam is a mixture of a gas and liquid so B is incorrect. A solution is a mixture in which one component has dissolved in the other so C is incorrect. A suspension has non-settled solid particles in a liquid or gas so D is incorrect.

26. Discuss the biodegradability of soaps and soapless detergents. 7 Marks

28. Sample Answer Compounds that are broken down by micro-organisms, such as bacteria, are biodegradable. Soaps are generally more biodegradable then soapless detergents. It is important that soaps and soapless detergents. Are biodegradable so that they do not accumulate in the environment causing harm to plant and animal life or interrupt natural balances. Soap biodegrades fairly quickly so that any scum or foam is gone within a few days. Early soapless detergents took much longer to break down, if they broke down at all, and polluted waterways with unsightly foam. Modern detergents are more biodegradable than the earlier detergents, but still take much longer to biodegrade than soaps. The carbon compounds into which biodegradable soaps and soapless detergents break down are harmless and do not have adverse effects on the environment.

31. Sample Answer AIM: To compare the solubility of oil on liquid soaps and shampoos. METHOD: 1.Obtain 3 different liquid soaps and 3 different shampoos 2.Set up 3 sets of labelled test tubes for each liquid soap and shampoo being tested. 3.Place 15 mL of water into each test tube. 4.Add 2 drops of liquid soap or shampoo being tested to a set of test tubes. 5.Set up a control test tube containing 15 mL of water only. 6.Add 5 drops of oil to each test tube and observe what happens to the oil after shaking each test tube for 1 minute. 7.Keep all test tubes under the same conditions including temperature, test tube size. 8.Record observations in a table Independent variable: The different liquid soaps and shampoos Dependent variable: Solubility of oil To ensure reliability, the experiment could be repeated several times.

37. Sample Answer Biodegradable detergents are broken down or degraded by biological agents such as bacteria or fungi. It is important that detergents are biodegradable so that they do not accumulate in the environment interrupting natural balances and causing harm to plant and animal life. The carbon compounds into which biodegradable detergents break down are harmless and do not have adverse effects on the environment and do not form unsightly foam in the water as would occur with non-biodegradable detergents.

40. Sample Answer A colloid is a uniform mixture of tiny particles dispersed through a medium. The colloid particles and the medium may be solid, liquid or gas. An emulsion is a particular type of colloid in which liquid particles are dispersed in a liquid medium, so all emulsions (milk, mayonaise) are colloids. However, not all colloids are emulsions (shaving foam which is a gas in a liquid colloid and spray deodorant is a liquid in a gas colloid) Thus the statement is correct.

43. Sample Answer Soapless detergents are used in body cleaning products because they act as a surfactant and thus allow water to mix with substances such as grease and oil. They also act as emulsifiers and keep grease and oil suspended in the water so they can be removed. Soapless detergents are more expensive then soaps, but do not deteriorate like soaps. In hard water, they lather and no scum is produced as with soaps. Modern soapless detergents are biodegradable and no longer contain phosphates that result in accumulation of these phosphates in out waterways.

46. Sample Answer Soaps and soapless detergents are both cleaning products which are used to remove dirt/oil from a variety of surfaces. They both foam in water and act by reducing surface tension. Soap and soapless detergents must be biodegradable. That is they must breakdown in the environment. Soaps tend to be made using naturally occurring oils such as olive oil, whereas soap less detergents use oils derived from crude oil. Because of this soaps tend to breakdown more quickly. Soap and soapless detergents cause similar environmental effects in that they reduce the surface tension of natural water bodies such as creeks which effect many plants and animals detrimentally. For instance, insects which normally skim on the surface will sink. Soapless detergents, in particular can be used to help clean up oil spills after a shipping disasters. This is beneficial as it helps reduce the impact of such events.

49. Sample Answer The teardrops are molecules of the emulsifier. The other two components of the mixture are immiscible liquids. One end of the emulsifier is attracted to one of the liquids and the other end is attracted to the other liquid. Agitation disperses one of the components in the other with emulsifier molecules surrounding small droplets of one component. The droplets remain dispersed because they are not attracted to each other. Answers could include: Large circles can be oil and surrounding fluid can be water. One end of the teardrop is hydrophilic and the other is hydrophobic. Labels on the diagram can show the relationships in the diagram.