124 Unit A: Pure Substances and Mixtures NEL

CHAPTER

3 Chapter Review

SUGGESTED ANSWERS

WHAT DO YOU REMEMBER?

1. (a) Sample answer: One method of separating sewage to produce cleaner water is to use floating andsettling to remove solids, grease, and oil.

(b) Sample answer: One method of separating wheat grains to produce white flour is to use a series of sieves.

(c) Sample answer: One method of separating petroleum to produce gasoline is to use a fractionaldistillation column.

2. (a) Sample answer: One way to separate a solution that contains two liquids is to use distillation.

(b) Sample answer: One way to reclaim a solid solute from a solution is to evaporate the liquid, whichwill leave the solid behind.

3. (a) Sample answer: A salad can be separated by sorting.

(b) Gold dust can be separated from water and other rocks by using settling.

(c) Sample answer: The iron in a pile of scrap metal can be separated from the other materials using amagnet.

(d) Sample answer: Dust and pollen can be removed from air using a filter.

(e) Sample answer: A mixture of salt and sand could be separated by dissolving the salt in water.

4. A filter separates the components of a mechanical mixture by allowing any liquids and gases to passthrough tiny holes in the filter. Solid materials cannot pass through the filter and are trapped.

5. A magnet cannot be used to separate any kind of mixture. It can be used only if one of the componentsof the mixture is attracted to magnets, but the other component is not.

6. A sample diagram is shown below.

Sample answer: To separate salt from a salt-and-water solution, I would heat the solution to a boil andevaporate the water. The salt would be left behind.

7. It is important to remove harmful materials from waste before putting waste into the environment becausethose harmful materials could damage the environment and poison plants and animals, including people.

WHAT DO YOU UNDERSTAND?

8. (a) A filter can separate dust from air. Air will move through the filter, but dust will be trapped.

(b) A magnet can be used to separate paper clips and erasers. The magnet will pick up the paper clips,but not the erasers.

(c) Settling can separate soil from water. The soil will settle to the bottom of the container of water.

(d) A sieve can be used to separate pebbles from sand. The pebbles will get caught in the sieve, but thesand will pass through.

saltwater salt

NEL Chapter 3 Separating Mixtures 125

(e) Dissolving can sort sugar from sand. The sugar will dissolve in water, leaving the sand behind.

(f) Floating can separate sawdust and sand. The sawdust will float on water, but the sand will sink.

9. Many separating techniques would be needed to separate this mixture. The waste paper would have to besorted out by hand. It has similar properties to the compost, but is more easily distinguished. Magnetscould be used to separate the steel cans from everything else. The floating and settling could be used toseparate the bottles. The plastic bottles would float and the compost would sink.

10. (a) This is a mechanical mixture.

(b) This is still a mechanical mixture.

(c) Petroleum that arrives at a refinery is a solution.

SOLVE A PROBLEM!

11. One way to separate a mixture of sand and water would be to use the settling method. The sand wouldsink to the bottom of the mixture, and the water could be poured off, leaving the sand behind. Anothermethod of separating the mixture would be to use a filter. The filter would allow the water to passthrough, but would trap the sand.

12. Sample answer: I think that Sunnydale should definitely start sewage treatment, because their untreatedwater is killing the fish and poisoning the environment. The town should at least have a primarytreatment of the water. If they don’t have enough money for both a secondary treatment and a hospital,they should probably use the money for the hospital. However, if it is possible to afford both, they shoulddefinitely get the secondary sewage treatment as well.

13. No, Chang won’t be able to remove all the salt from his juice by using a filter. When salt dissolves inwater, it breaks into particles too tiny to see. When Chang pours his drink through a filter, the tinyparticles of salt will pass through along with the juice. The filter might trap some undissolved salt if thejuice-and-salt mixture is saturated (and can’t dissolve any more salt), but it won’t trap all of the salt.

14. A sample flow chart is shown below.

15. (a) Sample answer: In my home town, we recycle newspapers, steel cans, and glass bottles and jars. We don’trecycle cardboard or plastic products.

(b) Sample answer: In addition to recycling, I could help reduce the amount of waste that goes tolandfills by re-using cardboard or plastic products. I could also donate old clothes and toys to charityinstead of throwing them out. Finally, I could start a compost pile for food. My mom could then usethe compost as fertilizer for her garden.

16. Student presentations should address all four questions, but can include other information and canpresent the information in different ways. Examples of the type of information that should be included instudents’ presentations are given below.

(a) Some places on Earth that do not have access to clean water include less developed countries such asthose in Africa, Asia, and the Middle East.

sawdust,gravel, salt

saltwateris heatedto a boil salt remains

waterevaporates

sawdust floats

gravel sinksadd water

sawdustskimmed offthe top

saltwaterpoured off

salt dissolves

stir mixture

gravel left behind

126 Unit A: Pure Substances and Mixtures NEL

(b) Clean water is not available to these places because they cannot afford the water treatment systemsthat are standard in developed countries. However, even some developed countries, such as Canada,have trouble providing clean water to all its people. This is because certain populations live in areasthat are too isolated to easily and affordably supply clean water.

(c) The water in many places is a mixture of water, bacteria, toxins, and other harmful substances. If theharmful substances are not removed from the water, the water is not good to drink.

(d) Some people are using rooftop rainwater collectors and improving access to groundwater. Othergroups provide inexpensive water filters and other sanitation methods to areas that lack them.

CREATE AND EVALUATE!

17. A sample flow chart is shown below.

Nuclear energy is a benefit to society. Like all power generation solutions, it has problems, but it providesenergy without creating CO2 emissions.

18. Sample answer: I agree that people often separate mixtures in their daily lives. We separate mixtures anytime we organize our closets, do laundry, cook pasta, or make tea.

REFLECT ON YOUR LEARNING

19. (a) Sample answer: The easiest concept to understand was how mechanical mixtures can be separated bysorting, sieving/filtration, settling, floating, and magnetism.

(b) Sample answer: The hardest concept was how certain industries separate mixtures to process rawmaterials and make new substances. Some of these separation methods were very complex.

(c) Sample answer: Drawing diagrams of these complex processes can simplify them and help me tobetter understand how they work.

(d) Sample answer: The part about how uranium generates electricity didn’t make sense to me at first.

(e) Sample answer: I asked the teacher, who explained more about how radioactive substances really workand why they can be used to generate electric power.

20. (a) Sample answer: We can separate mechanical mixtures in many different ways. Mixtures containinglarge objects can be sorted by hand. Mixtures containing smaller pieces can be separated using sievesor filtration. Certain metal substances are attracted by magnets and can be separated from mixturesusing magnetism. Other substances dissolve in water and can be separated by adding water to themixture, dissolving the substance, and then evaporating water to reclaim that substance. Water is alsoused in the floating and settling methods. Some substances are less dense than water and will float,while others are denser than water and will sink.

(b) Sample answer: Are there any other methods of sorting mechanical mixtures? How can you separatesolid solutions?

uranium ore

is crushed

ore is mixed witha solution thatdissolves uranium

solution heatedto a boil

uraniumsolutioncollected

filter removesrock

crushed oresolution filtered

mixture stored inabandoned mines

pure uraniumremains

used uraniummixed withmelted glass

uranium is used innuclear reactors torelease energy