NAME ____________________________________________

FORM_____________________________________________

TEACHER__________________________________________

Read the passage below then answer the questions which follow.

* * * * * * * * * * * * * * * * * *

A solution is a special kind of mixture. A solution is formed when one chemical dissolves, or mixes evenly into another. The most common type of solution is formed when a solid, such as copper sulphate, dissolves in a liquid as water. A copper sulphate solution is formed.

In a solution no solid particles can be seen. They have all mixed evenly into the liquid. However, we can usually tell that the solid has dissolved. A copper sulphate solution, for example is blue. The colour due to the dissolved copper sulphate crystals is obvious. A sodium chloride solution looks just like water. However, if we taste it we know that salt has been dissolved in it because of the salty flavour.

We call a liquid (like water) which will dissolve another chemical (like salt) a solvent for that chemical. The salt, or any other solvent for sand because sand will not dissolve in water.

Copper sulphate and salt are both solutes in water. That is, they both dissolve in water. However, neither of them are solutes for a liquid like methylated spirits because they do not dissolve in it.

We say that copper sulphate and salt are soluble in water, but insoluble in methylated spirits.* * * * * * * * * * * * * * * * * * *

Questions

1. Use the information in the passage to write a definition of the following(a) dissolve

(b) insoluble

(c) soluble

(d) solute

(e) solution

(d) solvent

2. The passage on the previous page contains 5 paragraphs of information. Each paragraph contains a main idea as well as an example. Using one sentence only for each paragraph describe the main ideas in each paragraph.

3. For the following sentences write whether they are TRUE or FALSE.(a) Copper sulphate is a blue chemical and it is soluble in water.

(b) Sodium chloride does not dissolve in water.

(c) Water is not a solvent for sand.

(d) Salt is insoluble in methylated spirits.

(e) When Copper sulphate dissolves in water it forms a solution.

4. The following are all solutions each contains a solute dissolved in a solvent. For each solution, name the solute and the solvent.

(a) sea water

(b) swimming pool water

(c) a cup of coffee

(d) a bowl of jelly

Have you ever wondered how your clothes are cleaned and how dirt of grass, blood or coffee stains are removed? This passage will help you understand why different solvents are used in different cases.

What is a solvent

If you put sugar in drinks, like tea or coffee, the sugar dissolves in the liquid. The result is called a solution. Not all solids will dissolve in water. Sand will slowly settleto the bottom of a container filled with water. So water is not a good solvent for sand. In fact, hundreds of things willnot dissolve in water. Different solvents are needed todissolve them.

How much sugar will dissolve in water.If you put lots of sugar in your cup of tea it may not all dissolve. A solution in which there is a lot of the solute is called a concentrated solution. If the solution can dissolve no more solute then the solution is called a saturated solution.

The amount of sugar that can be dissolved in water obviously depends on how much there is. But it also depends on the temperature of the water.More sugar can be dissolved in a hot cup of tea than can be dissolved in a cold cup of tea. At room temperature ( about 18 C), 100g of water will be able to dissolve up to 200g of sugar before the solution becomes saturated. If the water is heated up to 100 C then far more sugar can be dissolved. About 500g of sugar can be dissolved in 100g of water at 100 C.

How to dissolve a solid.You should now be able to see that three things are needed for a solid to be dissolved easily.

1 A correct solvent for the solid. (Different liquids can dissolve different solids).2 Enough solvent to dissolve all the solid. ( If there is too little solvent, the solution will become

saturated before all the solid has been dissolved.)3 A high enough temperature. ( Less solvent is needed as the temperature increases, and the solid

dissolves more easily.)

Take it to the cleaners.Dirty clothes are often washed in water. The water is a solvent for the dirt. It dissolves the dirt which is then ‘washed’ away. (Soap powders help the water to dissolve the dirt.) Hot water is better for washing because it dissolves the dirt more easily. But some clothes can be damaged in hot water and, in some cases, the dyes in coloured clothes are washed out. Many of your clothes will have labels which tell you how they should be cleaned. If the clothes can be washed in water the label will tell you how hot the water should be. The numbers tell you which ‘programme’ should be used if the clothes are washed in an automatic washing machine.

When water will cause damage, or when it will not dissolve a particular stain, a different solvent must be used. Because water is not used, the process is called dry cleaning.

One common dry cleaning solvent is perchlorethylene. But it does not remove all stains and it can, in some cases, cause damage to clothing. Clothes which must be dry cleaned usually have a label which tells the cleaner which solvent is safe to use.

Questions

1 What is a saturated solution?

2. Which sugar will dissolve quickest? Why?

3. What do you think would happen if a cup of tea were saturated with sugar and then cooled down to room temperature?

4. Why are coloured clothes usually washed at lower temperatures than white clothes?

5. Why is it a good idea to tell the cleaner what particular stains you have on a piece of clothing?

6. A woman spills ink on her dress. The dress is made of nylon.Look at this table.

Liquid Nylon InkABCD

solubleinsolubleinsolublesoluble

solubleinsolublesoluble

insoluble(a) Which liquid should she use to remove the stain?(b) Explain your answer.

7. Check out some labels on your own clothes. What do they say?

8. Give the meaning and an example of each of the following:a. insoluble

b. evaporation

c. residue

d. filtration

9. For each of the following describe the separation method you would use and why it would work.a. sand and sawdust

b. gravel and sand

c. sugar and water

10. Insoluble substances can be separated from a liquid by filtering.a. What equipment would you need?

b. Why does this method work?

11. How would you separate salt from sand?Write detailed instructions and draw a diagram of the equipment you would require.

Match the descriptions in List A with a separation technique in List B.

______________________________________________________________________________LIST A LIST B_________________________________________________________________(a) One substance changes to a gas, and then crystallization

changes back to a liquid.

(b) The solute separates from the solvent, filtration

forming a solid.(c) One substance is made of iron and the evaporation

other is a non-metal(c) One substance changes to a gas more readily magnetism

than the other.

(d) The pieces of one of the substances in a mixture distillation

are larger than those of the other substance(s)

Key termssolution  solvent  solute  suspension  colloid  emulsion

SolutionA solution is made when we add something to a liquid. For example, adding sugar to water is making a solution. Solutions consist of two parts:• The first part is called the solvent. Water is a very common solvent. A

solvent is the substance that we put the second part into.• The substance that we put into the solvent is called the solute. In the

mixture of sugar and water, the sugar is the solute and the water is the solvent.

Solutions are clear.

SuspensionAnother new substance is a suspension.

When a solid is mixed into a liquid and the particles of solid can be seen in the liquid, we call it a suspension. When the suspension is allowed to stand for a long time, the solid will settle to the bottom of the container.

Orange juice is an example of a suspension. When you buy bottled orange juice, many of the solid particles of orange juice have often settled to the bottom of the bottle, so it is best to shake the bottle before drinking the juice.

ColloidColloids are another type of mixture. Examples include whipped cream, bread, jelly, shaving foam, smoke and clouds.

Colloids are made up of two or more substances spread evenly throughout another. Think about smoke from a fire. It looks like one substance, but it is really lots of different substances spread evenly through the air. Can you think of some of the substances that might be in smoke?

Colloids are not clear like solutions and the particles do not settle out like suspensions.

EmulsionEmulsions are a special type of colloid. They are made up of a liquid spread evenly throughout another liquid.

Emulsions are often used in everyday life, such as ointments and cosmetics. Foods such as homogenised milk are also emulsions.

Activity1 Use all four headings below. Each of these is a “New word”.2 Match the ‘New word’ to the ‘New substance’.3 Draw a diagram to represent the particle in each substance in the space provided.

New word New substance Your drawingIs made up of two or more substances spread evenly throughout one another.Example: shaving foam

Is made up of a liquid spread evenly throughout another liquid.Example: homogenised milk

Is made up of two parts: a solute, which is a substance dissolved in a substance; and a solvent, the substance that the solute is dissolved in.Example: sugar in waterIs a solid mixed into a liquid so that the particles of the solid can be seen. Over a long time the particles will settle to the bottom of the container.Example: orange juice

Activity1 Use words from the following box to label the diagrams below.

solute  solution  solvent  sediment  suspension

2 In the following sentences, insert the appropriate word from the box into the sentence to make it correct.

crystals  re-crystallisation dilute  dissolve  dissolved  evaporates  heated   mixed  saturated small amount soluble solute  concentrated  solution solvent suspension undissolved

a A substance that will _________ in a liquid is said to be ________ in the liquid.

b When a ________ dissolves in a _________, a _________ is formed.

c A solution that contains a lot of _________ solid is said to be _________.

d When a solution is _________ and the solvent _________, _________ of the __________

substance will form in the container.

e When an insoluble substance is _________ with water, a __________ is formed.

f A __________ solution only contains a ___________ of dissolved substance.

g A solid substance of questionable purity can be purified by _________.

3 Look at the following diagrams and the key provided with them.

Select the letter that represents:

a the most concentrated solution _____

b the most dilute solution _____

c a saturated solution _____

d pure water _____

e a solution of one liquid in another _____

f a test-tube containing a suspension _____

g a test-tube containing an insoluble solid _____

h a mixture that could be separated by filtration _____

i a test-tube containing an insoluble solid that is less dense than water _____

j a mixture that could be separated by decanting _____

k a test-tube containing an insoluble liquid that is denser than water _____

l a mixture best separated by evaporation of water _____

4 Draw a diagram similar to those in part 3 above, showing a dissolved laboratory reagent that is mainly one substance with small amounts of another dissolved substance making it impure.

Redraw your diagram showing the mixture after re-crystallisation. Show crystals of the pure substance and the impurity still dissolved.

1 For each diagram below, use words from the box to:a label the equipmentb write the method of separation under the diagram.

beaker  Bunsen burner  conical flask  crystal  crystallisation  decantingdelivery tube  evaporating dish  evaporation  filter funnel

filter paperfiltrate  filtration  sediment  sieve  sieving  test-tube

2 Complete the table below using the list of examples in the following box.

• separating sediment from old wine • separating cream from milk• separating copper from copper sulfide ore • separating sugar from sultanas• separating iron filings from sand • separating gold from sand

Separation method Example from list above Your own exampleSieving

Decanting

Gravity separation

Magnetic separation

Centrifuging

Chemical extraction

3 Each of the following words stands for a process that can be used to separate mixtures into their original components.

crystallisation  decanting  dissolving and filtering  distillation  evaporationfiltration  fractional distillation

From the list above, choose the most appropriate method or methods if you were asked to

separate:

a pure water from a sample of muddy water ____________________

b salt from sea water ____________________

c pure water from sea water ____________________

d both salt and water from sea water ____________________

e salt from a salt–sand mixture ____________________

f sand from a salt–sand mixture ____________________

g water from an oil–water mixture ____________________

h water from a water–methylated spirits mixture ____________________

ANSWER THE FOLLOWING QUESTIONS.

1. What is the difference between saturated, unsaturated, supersaturated? Draw a picture of each one to help your explanation.

2. How does an emulsifier work?

3. Give two examples of emulsifiers.

4. Explain why a bottle of soda fizzes when you first open it.

5. Replace each of the following expressions with a single word.(a) Liquid in which a substance dissolves

(b) Insoluble particles dispersed in a liquid

(c) Liquid passing through filter paper

(d) Substance which dissolves in a liquid

(e) What is formed when a solute dissolves in a solvent

(f) Material deposited on a filter

(g) An insoluble substance which sinks to the bottom

6. The air filter and oil filter in a car engine have to be replaced occasionally. Why do you think this is done?

7. To what extent do you think filtration would be helpful in purifying wastewater? Give reasons for your answer.

Imagine

You are out in the bush and the only water available to drink is in a muddy waterhole. You have an empty bottle and a cup. How would you remove the dirt from the muddy water so that you could drink the water?

Separating and Identifying Substances

When Tommy’s mother boiled vegetables she always put table salt (sodium chloride) to provide a little

extra to the taste. Tommy a new Year 8 student was interested in this, what fascinated him

particularly was that when his mother added the salt it disappeared almost immediately into the water

and their was no evidence of it being present.

Tommy decided to do a few experiments with salt and water. First he collected a cup and added to it

100 mls of boiling water. Then he added a teaspoon of salt to the water and stirred. As he expected

the salt disappeared. He added more teaspoons of salt and stirred and found that each time the salt

disappeared, until he added seventh where upon stirring most of the salt disappeared but a few grains

would not.

He was doing this at the kitchen sink and his dad asked him to move because he had to prepare tea.

As Tommy picked up the cup he slipped and spilt a few drops. Some fell on the dark grey kitchen vinyl

and some on his hand. After moving the cup out of his dad’s work space he licked the drop of water

off the back of his hand. To his surprise it was agonisingly salty!

The next when he arose he went to look at his cup. To his surprise he found not just a few grains of

salt in the bottom of the cup but instead he found about 1 cm of salt crystals. Then he also saw white

spots on the kitchen vinyl in the area where he spilt the liquid. He bent down and found the white

spots were rather powdery to the touch and came off the vinyl.

Answer the following questions.

1. What term could be applied to the salt disappearing into the water?

2. Is the salt and water mixture a solution? If so what is solute and what is the solvent?

3. When the salt disappeared there was no evidence of its presence. What two pieces of

information indicate to you that the salt was in fact present in the water.

4. On his seventh teaspoon of salt not all of the added salt dissolved. Explain this

observation.

5. Would you describe the solution made by Tommy as concentrated or dilute? What

evidence is there to support your answer?

6. Do we boil vegetables in salted water that is saturated, unsaturated or supersaturated?

Explain each term in your answer?

7. Explain why there was so much more salt present in the cup next morning?

8. What do think the white powder was on the kitchen floor? How did it appear there?

9. Fortunately Tommy did this experiment standing up! Why would this have been a

potentially dangerous experiment to do sitting down?

Tommy was interested in whether the volume of the water would increase when the salt was added.

He found in the end that if he did the experiment that with the equipment he had available there

seemed to be no increase in volume. Tommy did find however that the mass of the water increased

significantly.

10.Using your knowledge explain why there would be no (little?) increase in volume but there

would be an increase in mass?

Elvira, Tommy’s sister was in Grade 6 and she was interested in Tommy’s experimentation. Her

interest increased significantly when she was asked to do the washing up at the end of tea. She only

had to do the bowls and pans. She decided to do the glass salad bowl first. Dad had made a simple

vegetable salad but had added a mixture of cracked pepper, dark vinegar and light oil as a dressing.

Elvira was interested to see that the vinegar dissolved in the washing up water but the oil did not. The

oil seemed to hang in the water quite a while and then rise to the surface of the water. The really tiny

droplets of oil remained in the body of the water and did not rise. The pieces of cracked pepper

dropped to the bottom of the bowl.

11.With regards to solubility what term could be applied to the vinegar, the oil, and the cracked

pepper pieces.

12.Tommy told Elvira that the oil was immiscible. Explain whether Tommy was correct or not!

13.What term could be applied to the material that floated to the top and that which dropped to the

bottom of the bowl? What could you say about the density of these materials compared to that of

water?

14.Would it be accurate to call the mixture of very small oil droplets and the water as a suspension?

15.Could you go further and call it a colloid? Explain your answer.

16.What differences if any could there be between a colloid and a suspension? Could you call the

water oil mixture and emulsion?

Use the information given in the table below to answer the following questions.

Substance Reaction with waterSinks to

the bottomFloats on top Floats in

the liquidDisappears

Sand Sodium nitrate

Sulfur Copper sulfate

Salt Calcium carbonate

(a) Name two insoluble substances.

____________________________________________

(b) Name two soluble substances.

_____________________________________________

(c) Name one substance that forms a suspension.

_________________________________

(d) Name one substance that dissolves.

_________________________________________

(e) What is the name given to the mixture when copper sulfate dissolves in water.

______________________________________________________________________

State the name of the process used to separate:

(a) salt from seawater.

_________________________________________________________

(b) alcohol from red wine.

______________________________________________________

(c) the different components/colours in red pen ink. __________________________________

Oil spills—the Exxon Valdez disasterIn March 1989 the Exxon Valdez ran aground on a reef in Prince William Sound, Alaska, and immediately began spilling crude oil into the sea. It eventually spilled 20% of its cargo, which was almost 50 million litres of crude oil. This spill polluted 1770 km of the Alaskan coastline, killing an estimated 250 000 seabirds, 3000 sea otters and hundreds of seals, bald eagles, whales and other marine animals. The cleanup operation is discussed here, but more information about other aspects of oil spills is available on the Internet.

As we know, oil and water do not mix. We say they are immiscible, or that one will not dissolve in the other. We also know that oil will float on the surface of water. In the case of the Exxon Valdez spill, the biggest problem was that no-one was prepared for a spill of this size, and there was not enough equipment on hand to deal with a rapidly spreading slick (or sheen). But what sort of methods could be used to deal with the

problem? Here are several.

Because oil floats on water, it can be collected using a boom. A boom is a long, floating barrier that is towed between two boats. As the boats move, the boom is dragged through the water. Booms extend about 30 cm above the water and 60 cm below the water, and collect, or corral, the oil as they move. In the case of the Exxon Valdez spill, insufficient boom was on hand to contain the dispersing oil. Booms also require frequent cleaning because they become weighted down with oil. During the cleanup operation, a team of six men could clean about 300 m of boom per day, and about 9 km of boom was in use!

In the case of a fresh oil spill, it can be burned, because oil vapour is flammable. However, this option must be considered carefully because it has a number of nasty side effects. It creates enormous clouds of dense, noxious smoke that can harm humans and animals. It also contributes greatly to the greenhouse effect. If the environmental authorities give permission, burning can be used to reduce the sheen to a tarry residue that can be recovered by hand or scooped up.

It is possible to spray the sheen with dispersants. These are chemicals that break the oil up into smaller fragments, and allow it to disperse through the ocean. This is similar to the idea of emulsifying oil in water when you make mayonnaise. Of course, all of the oil is still there—it is just more widely spread out. It will therefore have lots of smaller environmental effects, rather than one large disaster. However, because the oil is dispersed in the water, it will not foul the coastline to the same extent. In the case of Exxon Valdez, insufficient dispersants were stockpiled to deal with a problem of this size.

Skimming is a method of sucking the oil off the surface of the water. A skimmer boat usually follows just behind a boom, so it can collect maximum oil in minimum time. Of course, the skimmers have to be able to deposit their load of collected oil somewhere and, in the case of Exxon Valdez, there was no place to put the oil–water mix.

Cleaning the shoreline was another major problem. The initial solution was blasting the shoreline with hot water under high pressure. This would be like running your greasy plate under the hot water tap to remove the grease. But hot water created a problem: it heated up the beaches, and many marine animals could not survive the changing temperature. This left about 350 km of coastline ‘dead’ before the process was stopped. Exxon, which was assisting with the cleanup operation, attempted to clean the shoreline using a solvent a bit like kerosene, which dissolved the oil. The idea was that the oil–kerosene solution would flow back into the sea, where it was immiscible with the water and could be collected using booms. Unfortunately, being thinner in consistency than oil, it easily managed to find its way around or under the booms.

Despite best efforts, only 14% of the spill was recovered. If such a spill happened today, much better resources are in place to handle the emergency. Ten years after the disaster, only 2 of the 28 wildlife species injured by the spill—bald eagles and river otters—have fully recovered. Monitoring continues, but eight species have shown little or no progress toward recovery. These are harlequin ducks, common loons, three species of cormorants, harbour seals, killer whales and pigeon guillemots.

Using the information above, answer the following questions.

1 When and where did the Exxon Valdez run aground?

2 Will oil dissolve in water? Which is heavier: oil or water?

3 Find four methods of cleaning up the spill while it was at sea.

4 Find two methods for cleaning up the spill on the coastline.

5 Using the figures in the first and last paragraphs, how many litres of oil were recovered?

6 What was the problem with burning the oil on the surface of the water?

7 Draw a map of the Alaskan coastline showing where this accident occurred.

8 Which of the methods of cleanup at sea would you call chemical methods?

9 Which of the cleanup methods on shore would you call physical methods?