Chemistry

2. All parts of a homogeneous mixture look the same, as in a solution. A heterogeneous mixture has two or more distinguishable parts, as in a mechanical mixture, or tiny particles of one substance held within another, as in a suspension.

3. Cohesion refers to the attraction of a substance to itself, and adhesion refers to the attraction between different substances.

4. (a) physical

(b) physical

(c) chemical

(d) physical

(e) chemical

5. Boiling refers to the process of changing state from liquid to gas, while condensing refers to the process of changing state from gas to liquid.

6. As a solid is heated, its particles begin to vibrate more quickly. If enough heat is added, the motion of the particles will break the attractions between them, and they will move farther apart. When this occurs, the solid melts.

7. Students’ answers may vary but could include the following.

• Water has a boiling point of 100ºC and a melting point of 0ºC. It is a clear, colourless liquid at room temperature. It is not combustible. Its density is 1 g/mL. As a solid, it is somewhat hard but not ductile. It is not lustrous, nor is it malleable. It is non-reactive with most substances, but reacts  violently with Group I and II elements. It is often a solute and is not viscous.

• Gold is a metal element with a yellow lustre. It is a relatively soft solid at room temperature and is very malleable. Its density is 19 g/mL, and it is conductive. It is not very reactive.

8. John Dalton’s atomic model is different from the current atomic model in that he viewed atoms as small solid spheres and did not know about the subatomic particles.

9. J.J. Thomson used cathode ray tubes to show that all elements he tested could produce cathode rays, which are streams of negatively charged particles. He concluded that there were subatomic particles inside an atom, some negatively charged and some positively charged.

10. Ernest Rutherford discovered the nucleus of an atom through an experiment in which he directed streams of positively charged particles at gold foil. Because the particles bounced back or changed paths as they were directed at the gold foil, he concluded that there was a dense, positively charged mass at the centre of an atom, which he called the nucleus.

11. Niels Bohr developed an early version of what is now known as a Bohr diagram. He thought that electrons exist in energy levels or shells around the atomic nucleus and discovered that electrons can jump from one shell to another.

12. Groups (or chemical families) in the periodic table are organized in columns, and periods are organized in rows. A group is an assortment of elements with similar properties. A period is a single row on the periodic table in which each successive element has one more proton per atom than the element to its left.

13. Metals are found on the left side and middle of the period table, non-metals on the right, and metalloids in a staircase pattern between metals and non-metals.

14. Halogens are very reactive non-metals, each with a distinctive colour. At room temperature or slightly higher, they are all gases.

15. Students’ answers may vary but could include sodium or any other alkali metal.

16. (a) 1

(b) 3

(c) 4

(d) 6

(e) 7

17. (a) calcium

(b) Group 2, alkaline earth metals

(c) 2+.

(d) 2

18. Students’ answers may vary but could include the following examples:

(a) carbon or sodium

(b) silicon or arsenic

(c) sodium or lithium

(d) chlorine or bromine

19. (a) An ion charge is the charge on an atom after it gains or loses electrons to form an ion. If an atom loses an electron, it will have more protons and, as a result, a positive charge. If an atom gains an electron, it will have fewer protons and, as a result, a negative charge.

(b) By balancing opposite ion charges, the ratio of elements and thus the chemical formula of an ionic compound can be determined.

20. A metal element is most likely to form an ion by losing electrons; it will form a positive ion.

21. (a) lithium and chlorine, 1:1

(b) aluminum and sulphur, 2:3

(c) silver and fluorine, 1:1

(d) zinc and oxygen, 1:1

(e) nitrogen and sulphur, 2:3

(f) bromine

22. (a) ionic compound

(b) ionic compound

(c) ionic compound

(d) ionic compound

(e) molecular compound

(f) neither (element)

23. Students’ answers may vary but could include symptoms of mercury poisoning such as impaired speech or memory loss.

24. Students’ answers may vary but could include some of the following ideas.

(a) Polyethylene plastic is inert, flexible, fairly strong, heat resistant, ductile, and lightweight, all of which make it useful.

(b) Some concerns about the use of polyethylene include the length of time it takes to decompose and the amount of volume it takes in landfills, improper disposal of plastic bags (littering), and the potential for chemicals to leach from containers into foods or water.

25. Students’ answers may vary but could include any three of the following: People can benefit from water as a solid (ice rinks), a liquid (drinking water), and a gas (steam engines). Water is nontoxic, so you can wash in it without harming yourself. It is vital to the survival of all living things on Earth. Water is also useful because it dissolves many substances.

26. Aluminum foam would be a good choice for a car bumper because it maintains much of aluminum’s properties, such as strength, but the gas contained within the foam creates a cushion in case of an accident without adding more mass to the car.

27. You could alter the viscosity of honey by heating or cooling it.

28. (a) Sugar is only one white substance. While other substances may be white, their other properties, such as solubility in water, may differ from those of sugar.

(b) Sugar solutions will not conduct electricity. Sugar is a molecular compound and does not form ions when dissolved in water.

29. Diamond is made of carbon only and so is considered an element.

30. We cannot dispose of all household waste in the same way because some substances may have harmful chemical properties. Examples may vary but could include car batteries, which need to be taken to special waste depots because they contain dangerously strong acids, and vinegar, which is also an acid but weak enough to pour down the sink.

31. Water is made up of two types of atoms, hydrogen and oxygen, which makes it a compound. Elements are pure substances made up of one type of atom.

32. (a) Students’ answers may vary but could include the fact that Groups 17 and 18 are both groups of non-metals or that both are gases at room temperature or slightly above room temperature.

(b) Group 17 elements are highly reactive, while Group 18 elements are inert.

33. (a) does not normally form ions

(b) Ba2+

(c) Be2+

(d) does not normally form ions

(e) Pb2+ or Pb4+

(f) Se2

34. Students’ answers may vary but could include:

• Density can vary throughout a mixture. For example, salad dressing contains vinegar and oil. The densities of these two substances are very different, which is why they separate into different layers after a while.

• Density can vary throughout a mixture because a mixture is made of different pure substances. The pure substances in a mechanical mixture may have different densities.

35. Students’ answers may vary but could include these patterns:

Within the periodic table, the number of protons increases from left to right across a period and top to bottom down a group; in general, the same is true of atomic mass.

36. (a) mechanical mixture

(b) solution

(c) suspension

37. (a) White represents hydrogen and black represents carbon.

(b) The lines in the diagram represent the chemical bonds between the atoms.

(c) molecular compound

38. (a) potassium chloride and (d) MgO

39. The formula for a molecule indicates the type (element) and number of atoms in it.

40. Neon is not likely to be part of a compound as it has a full valence shell, making it virtually inert. It does not react or bond readily with other substances.

41. No, not all substances containing hydrogen and oxygen have the same properties. Examples may vary but could include hydrogen peroxide and water, which both contain hydrogen and oxygen but have very different chemical properties. You can wash your hair with water without chemically changing your hair, while hydrogen peroxide bleaches your hair.

42. Students’ answers may vary but could include the dust rising up behind a truck as it moves along a dirt road (the truck being the nucleus and the dust cloud the electrons), or a swarm of bees (electrons) around a hive (nucleus).

43. (a) Atoms of elements in the same period have the same number of electron shells.

(b) From left to right across the periodic table, each consecutive atom in a period contains one more proton than the previous atom.

44. (a) The non-metal is X. (It has the properties of a halogen.)

(b) The alkali metal is Z. (It is a reactive solid.)

(c) The noble gas is Y. (It is an non-reactive gas.)

45. The ball-and-stick model is a useful representation of a molecule because it shows exactly how the atoms are bonded.

46. Students’ answers may vary but could include the use of toxic chemicals to make ultimately non-toxic products, such as food grade plastics, or the use of chemicals that are toxic when wet but not when dry, such as some paints.

47. Students’ answers may vary but could include heavy metals, such as mercury and lead, which can cause brain damage and other effects of heavy metal poisoning, and hydrogen, which could catch fire if a spark were to get near it.

48. It would be safer to eat the fish at the bottom of the food chain, as the concentration of pollutants that bioaccumulate and biomagnify would be less than in a fish at the top of the food chain. This way, you would consume a smaller amount of dangerous pollutants such as heavy metals.

49. Dish soap would be useful for cleaning a bird caught in an oil spill, as it would dissolve the oil and wash it off with the water.

50. Students’ answers may vary but could include:

• Sodium is Nasty, silicon is Silly, and sulphur Smells.

• Sodium is Natrium, silicon is Silex, and sulphur is Sulphur!

51. The sample shown is a purple-pink, somewhat dull, crystalline solid, with a lumpy texture. Students may add that cobalt(II) chloride is a salt and so has properties of an ionic compound, such as the ability to conduct electricity when dissolved in water.

52. If the test tube contained oxygen gas, the splint would relight when the glowing splint was inserted into it.

54.(a) You could test the conductivity of a soft drink by dipping the two ends of a conductivity tester in it.

(b) You could test the conductivity of a strip of copper by attaching the leads from a conductivity tester to opposite ends of the strip.

55. (a) neon (A) and fluorine (B)

(b) Fluorine gained an electron.

(c) No, the atom formed in A would not be found in an ionic compound. Neon has a full valence shell, making it quite inert and unlikely to form chemical bonds.

(d) A fluoride ion is negatively charged and so would be more likely to bond with Ca2+ to form an ionic compound than to bond with O2to form a molecular compound.

57.(a) magnesium bromide

(b) barium nitride

(c) calcium phosphide

(d) aluminum oxide

(e) sodium iodide

(f) calcium chloride

 

58.(a) ionic, Mg3P2

(b) ionic, Li3N

(c) molecular, PCl5

(d) ionic, AlBr3

(e) ionic, CaS

(f) molecular, SO2

(g) ionic, KI

(h) ionic, Na2O

(i) ionic, Ca(OH) 2

(j) ionic, Al(HCO3) 3

(k) molecular, NCl3

60. You would know that the lemon juice reacted with copper if there were bubbles (gas produced), if the copper changed colour, or if heat was released or absorbed.

61. It would be better to use the number of protons than the number of neutrons to find out what element an atom belongs to: the number of neutrons may vary for atoms of the same element.

62. Table salt is intended for human consumption, whereas road salt is intended for spreading on roads and sidewalks. Table salt is mostly made of sodium chloride (NaCl), while road salt is often made ofcalcium chloride (CaCl2).

63. Students’ answers may vary but should include a reference to atoms and/or molecules as particles. For example, an element is a pure substance made up of only one type of atom (a particle), and an atom’s properties depend on its subatomic particles. A compound is a pure substance composed of ions (another type of particle) or molecules (particles made up of two or more atoms). A mixture contains two or more pure substances.

64. The development of the atomic model made it easier for people to explain chemical reactions because it became easier to visualize what was occurring during a reaction, particularly the transfer or sharing of valence electrons between atoms.

65. Elements are pure substances composed of only one type of atom. Each atom, and thus each element, has a specific set of physical and chemical properties. When atoms of different elements combine chemically, they form new substances known as compounds. Compounds are pure substances (have the same composition throughout) and are always composed of the same ratio of atoms of different elements. Compounds therefore have characteristic properties but ones that may be different from the properties of their component elements.

66. Students’ answers may vary but could include the following.

(a) The plastic is clear, so it is easy to see how full it is, and will not break easily. However, it may add harmful chemicals to my drinking water.

(b) The plastic will not break easily, but it may be contaminated by bacteria. Also, the plastic may have started to degrade and could leach harmful chemicals into my drinking water.

(c) Aluminum is lightweight and will not break, which are useful properties. It is metallic, so I need to be careful not to use it to carry any drinks that will react with metal.

(d) Glass is heavier than other materials and can break if dropped, but it will not leach harmful chemicals into my drinking water. I would choose aluminum because it is lightweight, sturdy, and fairly non-reactive. An aluminum bottle is re-usable and so won’t add to landfill. It can be cleaned fairly easily, and it won't add harmful chemicals to my drinking water as some plastic bottles can, old or new.

67. Since benzene can dissolve in fat, it can be readily absorbed by the body. It is combustible, which means that it can burst into flames easily. The fact that it can easily change state from liquid to gas makes it even more likely to catch fire, challenging to contain, and easy to breathe in by accident.

68. Students’ answers may vary but could include examples such as chemicals from batteries, lead paint, and motor oil. All three may leach into the water system from landfill, thus polluting the soil, water, and organisms that live in the area.

69. Table salt and road salt are both ionic compounds. They form solid crystals at room temperature. Table salt is mainly sodium chloride, which is non-toxic when used as a food supplement. Types of road salts vary, but a common kind is calcium chloride. Calcium chloride lowers the melting temperature of water. It is also toxic if ingested. Students’ opinions may vary but could include the view that sand should be used instead of salt to melt the ice patches at the school entrance because sand would not harm the school garden, and if someone slipped, the sand would do much less damage to that person’s clothes. Another view is that sand is messy, so it would be better to use road salt at the entrance to the school.

70. The energy to light, heat, and cool our homes, use appliances, and heat water comes from various sources. Sources such as coalburning power plants or natural gas produce pollution. Therefore, the more energy efficient a home is, the less pollution the people who live there will contribute.

71. Students’ answers may vary but could include setting up light-bulb collection depots at hardware stores and/or making public service announcements about the dangers of mercury and how to handle fluorescent bulbs.

72. Students’ answers may vary but could include the pollution of water supplies when industrial  companies have dumped chemicals or waste straight into the water system, or when a company has removed water from a water source, used it, and then returned it contaminated by chemicals. In addition, smoke released from industrial activities contaminates precipitation, which ends up as pollution in water systems.

73. Keeping drinking water safe is not the only reason for preventing water pollution. Water sources are used for many purposes.  Examples may vary but could include watering crops, habitats for plants and animals, and water activities for humans.

74. Students’ answers may vary but could include water, which is used for cleaning and cooking, or chalk (calcium carbonate), which is used as an antacid.

75. Students’ answers may vary but could include the following.

(a) Changes of state are physical changes that people can use to alter matter. Cooking food by heating it is a chemical change that people can use to alter matter.

(b) Sometimes when we alter matter, there is waste, and often this waste pollutes the environment. The polluted environment can affect our health. At the same time, it can be very useful to alter matter.

(c) We can alter matter to meet our needs while improving the condition of the environment. For example, we can use sand instead of salt to deal with icy winter conditions. The sand will not hurt the environment in the spring as the salt would as it enters the water system, but the roads are still made safer for winter drivers. Another example is using alternatives to chlorine to bleach paper.

76. Even if the area is completely uncontaminated and unaffected by human activity, this lake is going to contain chemicals that are naturally occurring in the environment. All matter is composed of chemicals, including water.

77. Students’ answers may vary but could include:

• After studying this unit, I am more aware that everything is considered a chemical, not just the stuff in a lab or in a cleaning product.

• Before completing this unit I thought that all chemicals were harmful; now I know that all things are chemicals.

78. Students’ answers may vary but include issues such as mercury contamination of fish, environmental damage due to diamond mining, or the effects on the ozone layer of banning CFCs. Students’ letters may discuss the useful properties of a substance, its harmful effects, and the proper disposal of it.

79. Students’ answers may vary but could include using bacteria to decompose existing polyethylene bags or using corn-based solvents.