Science Practical 17

Moving Waters(Teacher's Demo)

Aim: To demonstrate the process of Osmosis

Apparatus:

Beaker (400cm cube)

Capillary Tube (30cm long)

Retort Stand

Visking Tubing (15cm, knotted at one end)

String

50% Sucrose Solution

Marker Pen

Procedure:

1. Soak the visking tubing in water for 2 minutes. Remove when it becomes soft and pliable.

2. Clamp the capillary tube to the retort stand.

3. Pour the sucrose solution into the visking tubing until about 3cm from the top.

4. Place the visking tubing below the capillary tube. Move the visking tubing up so that the capillary tube is about 1cm into the sucrose solution.

5. Tie the open end of the visking tubing tightly using the string.

6. Rinse the outside of the visking tubing by dipping it into a beaker of tap water. then lower the tubing into a fresk beaker of water.

7. Mark the level of sucrose solution in the capillary tube. This is the level of sucrose solution at the start of the experiment.

8. Observe and mark the level of the sucrose solution at intervals of five minutes for about 90 minutes.

Conclusion:

Osmosis is a net movement of water molecules from a region of high water potential to a region of low water potential through a semi-permeable membrane.

Science Practical 13

Which can Dissolve More?

Aim: To find out if the solubility of different solutes differ in the same solvent.

*In experiments, we should always conduct a fair test. You should only change one factor and keep the rest constant.*

In this experiment, we want to find the solubility of different solutes, so the factor we should change is the type of solute.

Procedure:

1. Measure 20 cm cube of water into a beaker.

2. Weigh 1 gram of salt using the electronic beam balance. Put this amount of salt into the water.

3. Stir to dissolve the salt in water. If the salt dissolves completely, add another 1 gram of salt into the water.

4. Continue adding 1 gram of salt until no more will dissolve after stirring.

5. Repeat steps 1-4 twice using baking soda and iodine crystals.

From the experiment, we can infer that the salt is the most soluble in water, and iodine crystals is the least soluble in the water.

Conclusion:

Different solutes have different solubility in the same solvent.

Science Practical 10

Brownian Motion

Aim: To observe Brownian Motion of smoke particles in the air.

Apparatus:

Whiteley's Smoke Cell Set

Transformer

Microscope

Procedure:

1. Fill a smoke cell, with smoke from smouldering paper and cover it with a glass slip.

2. Illuminate the smoke particles with a bright source of light.

3. Examine through the lower-powered microscope placed at 90 degrees to the direction of the light and record what is observed.

Observation:

Against a dark background, bright spots of light are observed, and they are in continuous random motion.

Questions:

What are these bright spots actually and why do they appear to be bright?

They are smoke particles and reflect light from the light source.

What causes the 'bright spot' to move in the continuous random manner?

The air particles bombard/collide unevenly on all sides of the smoke particle, causing the continuous random motion of the smoke particle.

Do you think that there will be a difference in the motion of the smokes particles if the temperature inside the smoke cell is increased?

Yes. The smoke particles will move more quickly as the movement depends on the temperature, as the heat energy is converted to kinetic energy.

How can you tell which are the large particles and which are the small ones?

The larger particles are the ones that move slower than the rest of the particles, as the larger particles have more inertia than the smaller particles.

Suggest how you could observe brownian motion in liquids:

Suspend pollen grains/talcum powder in water and observe the movement under a light source and a powerful microscope.

Science Practical 9

Density of an Irregular Solid

Aim: To determine the density of an irregular solid.

Apparatus: 

Measuring Cylinder

A Glass Stopper

Tissue Paper

String

Electronic beam balance

Scissors

Procedure:

1. Weigh the glass stopper to determine its mass. Record its mass as M.

2. Pour water into the measuring cylinder to one-third of the cylinder's height. Note the volume as V1.

3. Tie the glass stopper to a string and lower it gently into the water. Note the volume as V2.

4. The volume of the glass stopper is V2-V1. Record the volume of the glass stopper as V.

5. Remove the glass stopper and dry it with tissue paper.

6. Repeat step 2 twice with different values of V1 and obtain the corresponding values of V2 and V2-V1.

Find the average volume of the glass stopper from the 3 readings.

Science Practical 8

Density of a Regular Object

Aim: To determine the density of a regular solid(glass marble)

Apparatus: 

Micrometer Screw Gauge

Small Plastic Bottle

Electronic Beam Balance

5 Similar Glass Marbles

Procedure:

1. Weigh the empty plastic bottle and record its mass as m1.

2. Place all 5 glass marbles into the plastic bottle and weigh again. Record the mass as m2.

3. Measure the diameter of one of the glass marbles from two different positions using the micrometer screw gauge. Record the diameter of the glass marble as d.

After finishing the experiment, we had to begin our calculations. We had to find the mass of one glass marble and record it as M.

To find the density of the glass marble, we had to take the glass marble's mass and divide it by its volume. Below is a link on how to find the volume of a sphere:

Finding the volume of a sphere

So why did we use 5 marbles instead of one?

To increase the accuracy of the result!

Science Practical 7

Measurement of Time - Pendulum

Aim of the Experiment: To determine the relationship between the period and the length of the simple pendulum.

Apparatus: 

120 cm of thread

Pendulum bob

Metre rule

Split cork

Stopwatch

Clamps retort stand

Procedure:

1. Fix one end of the thread to the pendulum bob. Clamp the other end firmly between the split cork, making pendulum of length l = 100.0cm long.

2. Give the pendulum bob a small displacement of between 0 and 10 degrees and set it into oscillation. A complete oscillation is when the bob goes from one end to the other end and back again.

3. Time the period for 10 oscillations using the stopwatch. Record the time as T1. Repeat steps 2 and 3 for another 10 oscillations and record the timing again, but this time record it as T2. Then, find the average of both readings as <t> and hence the periodic time T given by. (T = <t>/10)

4. Shorten length l of the string by pulling on its upper end, and repeat steps 2 and 3 for values of l varying from 90cm to 50cm.

5. Tabulate 6 sets of values of l. T1, T2, <t> and T.

6. Plot a graph of period T against length l.

Conclusion:

The shorter length l is, the less period T will be.

Science Practical 6

Measurement of Length

Micrometer Screw Gauge

Vernier Calipers

In this practical, we were taught how to use a vernier calipers and micrometer screw gauge(as seen from above). -We also used a metre rule but it has already been taught before-

The smallest reading for the vernier calipers(one vernier division) and the micrometer screw gauge(one thimble division) are both 0.01cm. 

In this practical, we did 3 experiments. Each experiment required to use of an apparatus that could be used to measure length. 

Experiment 1:

We had to measure the height of our seat from the floor from 4 different positions. This is very basic. The average height of the seat from the 4 readings should be taken as that would make the result more accurate.

Experiment 2:

Use the vernier calipers to measure both the internal and external diameters of a beaker at 3 different positions. Find the average of the 3 readings as then, the results would be more accurate.

Experiment 3:

Use the micrometer screw gauge to measure the diameter of the wire and ball bearings at 3 positions. Find the average of the results as it would be more accurate that way.

Here are links to show you how to use the vernier calipers and micrometer screw gauge.

Vernier Calipers

Micrometer Screw Gauge