Experimenting

4.0 EXPERIMENTING

4.1 IDENTIFYING VARIABLES

Activity 1.1: ANALYSING THE PROCESS OF EVAPORATION OF WATER

Constant variables: movement of air, surface area, temperature.

1. Teacher asks the students to list out all the factors that affect the rate of evaporation of water i.e. movement of air, surface area, temperature and humidity.

2. Teacher stresses that Activity 1.1 is to show that humidity affects the rate of evaporation of water.

3. Since we want to study the effect of humidity on the rate of evaporation of water, other factors such as movement of air, surface area and temperature should be kept the same and they are called constant variable.

Manipulated variables: humidity

1. Teacher asks the students to observe and compare Diagram 1.1 and Diagram 1.2 for any differences.[Is there any difference between bell jar A and bell jar B?][What is the difference between bell jar A and bell jar B?]

2. Students should be able to mention that bell jar B has anhydrous calcium chloride.

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Diagram 1.1

Diagram 1.2

3. Teacher asks the students the function of the anhydrous calcium chloride.

4. The teacher tells the students the correct answer (anhydrous calcium chloride absorbs water vapour / moisture from the air).

5. Teacher asks the students to compare the condition of the air in both bell jars. The air in bell jar B is drier than the air in bell jar A.

[Air in bell jar A contains more water vapour than the air in bell jar B.Humidity depends on the amount of water vapour in the air. The more water vapour in the air the higher the humidity]

6. Teacher stresses on the terms of “humidity ” (amount/quantity of water vapour/moisture in the air).

7. The factor that is not the same in both situations is the humidity. This factor is called manipulated variable.

Responding variables: rate of evaporation

1. Teacher asks the students to observe the volume of water in the watch glass in both bell jars before the experiment.

2. After 10 minutes, more water had evaporated from the watch glass in the bell jar B compared to bell jar A.

3. Teacher asks the students to observe the difference of volume of the water left in the watch glass in both bell jars.

4. The difference of volume of water in the watch glass in both bell jars is the responding variable.

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Activity 1.2 To show that movement of air affects the rate of evaporation of water.

Manipulated variables: movement of air

1. Activity 1.2 is carried out to show that movement of air affects the rate of evaporation of water.

2. Teacher asks the student to fill two watch glasses with 0.5 cm 3 of water.

3. Teacher asks the students to use the syringe to blow the air on one of the watch glasses.

4. Teacher asks the students which watch glass gets drier faster. (Watch glass that being blown).

5. Teacher asks the students to state the factor that affects the evaporation of the water in the watch glass that gets drier faster (movement of air/wind).

6. Factor that affects the evaporation of water is the variable that is manipulated.

7. Teacher asks the students to identify the manipulated variable.

Constant variables: temperature, humidity, surface area of water.

1. Teacher asks the students to list out all the factors that affect the rate of evaporation of water. i.e. temperature, humidity, surface area of water and movement of air.

2. Teacher stresses that Activity 2 is to show that movement of air affects the rate of evaporation of water.

3. Other factors such as humidity, surface area and temperature are kept the same and they are called constant variables.

Responding variables: rate of evaporation

1. Teacher asks the students to observe the amount of water in both watch glasses.

2. Teacher tells the students the differences of the volume of water left refers to the responding variable. The rate of evaporation is faster in one of the watch glass. The teacher stress out the terms rate of evaporation to the students.

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Activity 1.3: Analysing solution and solubility

Diagram 1.3

Manipulated variables: types of solute

1 . Teacher asks the students to observe and compare the two beakers in Diagram 1.3 for any differences.

2. Students should be able to mention that the solute in Beaker B is different from solute in Beaker A.

3. Students should be able to mention that the type of solute is manipulated variable.

Responding variables: The solubility of solute

1. Teacher asks the students to observe both beakers in Diagram 1.3.

2. Teacher asks the students to observe the maximum mass of solute (sodium chloride or sugar) that can dissolve in the certain amount of water at a specific temperature. More amount of sodium chloride dissolves in water than sugar.

3. The teacher stress out to students that different solute has different solubility in water. Student should be able to give the correct responding variable.

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Beaker BBeaker A

Constant variables: amount of distilled water , nature of solvent and temperature .

1. Teacher asks the students to list out all the factors that affect the solubility of a solute. Students will list out as many variables as they can but the teacher must make sure that these variables are included : amount of distilled water ,nature of solvent and temperature.

2. In Diagram 1.3, what are the things that are the same in both beakers ( volume of distilled water , nature of solvent and temperature).

3. The constant variables are the things that are kept the same through out the activity.

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Activity 1.4: Analysing solution and rate of dissolving

Diagram 1.4

Manipulated variables: rate of stirring

1 . Teacher asks the students to observe and compare for any differences between Beaker A and Beaker B.

2. The students should be able to mention that the stirring in the Beaker B is faster than in Beaker A.

3. The students should be able to state the manipulated variable (rate of stirring)., Constant variables: temperature, amount of water, amount of salt, type of salt

1. Teacher asks the students to list out all the factors that affect the rate of dissolving. Students will list out as many variables as they can but the teacher must make sure that these variables are included : temperature, amount of water, amount of salt, type of salt.

2. In Diagram 1.4, what are the things that are the same in both beakers (volume of distilled water, amount/quantity of solute, type of solute).

3. The constant variables are the things that are kept the same through out the activity.

Responding variables: rate of dissolving

1. Teacher asks the students to observe the fine salt in both beakers.

2. Teacher tells the students that the faster they stir the solution the faster the salt dissolves.

3. Teacher explains to the students that the rate of dissolving of salt is the responding variable. Student should be able to give the responding variable.

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Activity 1.5 : To show that the size of solute particles affect the rate of dissolving

Diagram 1.5

Manipulated variables: size of solute

1 . Teacher asks the students to observe and compare the materials given.[What is the difference between the salt in Beaker A and the salt in beaker B?(course salt and fine salt).

2. Students should be able to mention that the difference is the size of the solute.

3. The size of the solute is the manipulated variable.

Constant variables: temperature , mass of solute , volume of solvent and the rate of stirring

1. Teacher asks the students to list out all the factors that affect the rate of dissolving. Students will list out as many variables as they could but the teacher must make sure that these variables are included : temperature, mass of solute , volume of solvent and the rate of stirring.

2. In Diagram 1.5, what are the things that are the same in both beakers (rate of stirring and temperature)

3. The constant variables are the things that are kept the same through out the activity.

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1 g of fine salt

1 g of coarse salt

Beaker A Beaker B

Responding variables: rate of dissolving

1. Teacher asks the students to observe the solute in both beakers in Diagram 1.5.

2. Teacher asks the students which solute/type of salt dissolve faster (the fine salt).

3. Teacher explains to students that the rate of dissolving the solute is the responding variable.

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4.2 DEFINING OPERATIONALLY

Activity 1: Analysing acid .

Things that should be done:

1. Teacher dips the blue litmus paper into lemon juice.

2. Teacher tells the students to observe the colour changes of the litmus paper ( blue to red.)

3. Teacher ask the students what she did and what they observed.

Teacher explains that defining operationally refers to what has been done and what was observed.

4. Therefore acid is defined operationally as :

Acid is a substance that turns blue litmus paper to red when the blue litmus paper was dipped into the lemon juice.

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Activity 2: Analysing alkali.

Things that should be done:

1. Teacher dips the red litmus paper into lime water .

2. Teacher tells the students to observed the colour changes of the red litmus paper (red to blue.)

3. Teacher ask the students what she did and what they observed.

Teacher explains that defining operationally refers to what has been done and what was observed.

Based on your findings, define operationally what is alkali.

Alkali is a substance that turns red litmus paper to blue when it is dipped into the lime water.

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Activity 3: Analysing rate of dissolving

A pupil carries out an experiment to study the effect of temperature of solvent on the rate of dissolving of sugar. The time taken for sugar to dissolve completely in water is shown by stopwatch in Diagram 1.1

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100 g finesugar

50 cm3

water20 0C

Beaker A

100 g finesugar

50 cm3

water40 0C

Beaker B

100 g finesugar

50 cm3

water60 0C

Beaker C

100 g finesugar

50 cm3

water80 0C

Beaker D

DIAGRAM 3.1

( a ) Based on Diagram 3.1, complete Table 3.2 by recording the time taken on the respective temperature of water.

Temperature of water / 0C

20 40 60 8090

Time taken for sugar to dissolve completely / s

55 44 37 20 11

Table 3.2

(b) State the variables involved in this experiment.

Manipulated variable Temperature of water

Responding variable Time taken for sugar to dissolve completely

Controlled/constant variable Volume of water // quantity of sugar

(c) Based on Table 3.2, define operationally “rate of dissolving”.

Rate of dissolving is the time taken for 100 g of sugar to dissolve completely in different temperature of water,

(d) Based on the results, what will happen to the time taken to dissolve sugar in

water completely if the temperature of water is more than 100 0C?

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100 g finesugar

50 cm3

water90 0C

Beaker E

The time taken will decrease // Time taken for dissolving sugar will become shorter.

Activity 4 :Analysing the effect of temperature on air pressure

A student carries out an experiment to study the effect of temperature on air pressure. Diagram 4.1 shows the arrangement of apparatus for the experiment.

DIAGRAM 4.1

The student takes the following steps:

1. The apparatus is set up as shown in Diagram 4.1. 2. The water bath is heated until the temperature of water reaches 300C and

record the Bourdon gauge reading.

3. Repeat step 2 with temperatures of 400C, 500C, 600C and 700 C. (a) (i ) Record the Bourdon gauge reading in the space provided.

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The temperature of water = 300 C

Bourdon gauge reading = 105 kPa

DIAGRAM 4.2

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The temperature of water = 400 C

Bourdon gauge reading = …109. kPa

The temperature of water = 500 C

Bourdon gauge reading = …112.. kPa

The temperature of water = 600 C

Bourdon gauge reading = …115.. kPa

The temperature of water = 70OC

Bourdon gauge reading = ..119..kPa

(a) (ii) Based on Diagram 4.2, complete Table 4.1 by recording the Bourdon gauge reading on the respective temperature of air.

Temperature ( 0 C) 30 40 50 60 70

Bourdon gauge reading ( kPa) 105.0 109.0

…….112.0…….

115.0…….

119.0…….

TABLE 4.1

( b ) State the variables involved in this experiment..

Manipulated variable Temperature of water

Responding variable Bourdon gauge reading

Controlled variable Size of round bottom flask

(c) Based on the activity, define operationally “air pressure”?

Air pressure is the reading of Bourdon gouge when the water is heated.

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DIAGRAM 2.2

DIAGRAM 2.2

Activity 5 : Analysing the extension of spring A group of students sets up an apparatus as shown in Diagram 5.1. The pendulum bobs of different weights are used. The extension of the spring is recorded for each pendulum bob.

DIAGRAM 5.1

The pupil takes the following steps :-

Step 1 : Hang a 20 N pendulum bob to a spring.

Step 2 : Take the reading of metre rule

Step 3 : Repeat step 1 and step 2 by using pendulum bob with the weights of

40 N, 60 N, 80 N and 100 N respectively.

(a) Record the pointer reading in the space provided

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Pendulum bob

20

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The weight of pendulum bob = 20NPointer reading = 20.5 cm

Metre rule

Pointer

Spring

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20

21 The weight of pendulum bob = 40NPointer reading = …20.9. cm

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The weight of pendulum bob = 60NPointer reading = …21.3. cm

The weight of pendulum bob = 80NPointer reading = …21.7. cm

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The weight of pendulum bob = 100NPointer reading = …22.1 cm

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(b) State the variable in the experiment.

(c) Define operationally “extension of the spring”.

Manipulated variable Weight of pendulum bob

Responding variable The extension of spring

Controlled variable Type of spring

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Extension of the spring is the reading of metre rule when different mass of pendulum bob is used.

Activity 6 : Analysing frictional force

A student carried out an experiment to study the effect of different types of surfaces on frictional force. The readings of the spring balance when the wooden block is pulled along different surfaces are shown in Diagram 4.1.

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Wooden block block

5 4

Glass surface

Wooden block

4 3

Marble top

Wooden block block

6 5

Cement floor DIAGRAM 4.1

(a) State the variables involved in the experiment.

Manipulated variable: Types of surface

Responding variable:Extention of spring // Reading of spring balance

Controlled variable: Weight of wooden block // type of spring

(b) Based on Diagram 4.1, record the readings of the spring balance in Table 4.2.

Type of surface Reading of spring balance (N)

Glass surface 4.5

Marble top 3.8

Cement floor 5.2

TABLE 4.2

(c) Define operationally “frictional force”.Frictional force is the reading of spring balance when the wooden blockis pulled along different types of surfaces.

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