Science Practical 21

TRANSFER OF THERMAL ENERGY

In this practical, there were 2 parts. The first part was to compare absorption of thermal energy by different surfaces. For part two, the aim was to find out which surface was better at radiating heat energy.

Experiment part 1

Apparatus:

2 Identical Twin Cans with Lids (one painted black and the other silvery/shiny)

2 Temperature Sensors 

Bunsen Burners

MultiLog

Wire Gauze

Procedure:

Put the temperature sensors into both tins. 

Wrap a piece of wire gauze on top of the barrel of the Bunsen burner.

Place the 2 tin cans on opposite sides of the Bunsen burner, both the same distance away from the Bunsen burner.

Start the MultiLog and take note of the starting temperature of both cans.

Light the burner and observe the change in temperature of the cans.

The can that was painted black absorbed more radiant heat energy than the other can.

The wire gauze that is wrapped around the barrel of the Bunsen burner ensures that the thermal energy is evenly radiated to both of the cans.

Experiment part 2

Apparatus:

2 Identical Tins with lids (One painted black and other silvery/shiny)

2 Temperature Sensors

MultiLog

Materials:

Hot Water

Procedure:

Fill each can to the same level with hot water.

Put the sensors into the cans.

Start the MultiLog and observe the temperature changes.

The black can lost heat faster than the silvery can.

Science Practical 20

Artificial Intestines
The aim of the experiment was to investigate why food has to be digested.
Materials
Boiling Tube
Visking tube filled with a solution of starch and glucose
Iodine Solution
Benedict's Solution
The Experiment
Tie the visking tubing up with a cotton thread.
Fill the boiling tube with distilled water.
Put the visking tubing in the boiling tube.
Test the water in the boiling tube for any presence of starch and glucose after one hour.
Visking tubing is used as ut has tiny holes in it that some molecules can pass through, similar to the small intestine.
To test the water for starch, you can add iodine to the water and it should turn blue-black if there is starch present in the water.
To test for glucose, add Benedict's Solution to the water. The solution will turn brick-red if glucose is present in the water.

Science Practical 18

Bouncy Raw Egg
This experiment was to show us osmosis in living cells.
We used a quail's egg that is enclosed in a thin membrane that is protected by a shell made of calcium carbonate.
The Experiment
Place the quail's egg into a beaker and fill the beaker with dilute hydrochloric acid.
Bubbles of colourless gas and white froth was observed to have formed and hence we can infer that the egg shell was reacting to the dilute hydrochloric acid and a gas was evolved.
Soak the egg in the acid for 15 minutes, stirring occasionally.
After about 15 minutes, pour away the dilute hydrochloric acid.
Then rinse the egg with water and examine it.
Next describe how the egg feels to the touch and record your observation.
Then measure and record the length of the egg.
Next fill half a beaker with water and place the egg inside.
After 30 minutes, remove the egg from the water and describe its hardness and record the observation.
Then measure and record the length of the egg.
Put the egg back in water and leave it for 24 hours.
Observe it again after 24 hours and describe its hardness and measure it and record both observations.
The dilute hydrochloric acid dissolved the egg shell. From the observations, the egg is soft and it grew after being put in the water. Hence we can infer the egg membrane lets water pass through. 


Osmosis in living cells allows water to enter the cell but prevents the contents of the cells from escaping.
Osmosis absorbs water into the cell, which the cell needs to survive.
The egg membrane is semi-permeable.

Science Practical 14

Separating Mixtures Part 1
The task was to separate salt and sand from the mixture.
Experiment
Place the mixture into a beaker. Add 10ml of water or more if it is needed until no salt is left. Stir the mixture. Place the filter paper into the filter funnel and put an evaporating dish below it. Pour the mixture into the filter funnel. Then heat the evaporating dish over a beaker of water being boiled over the bunsen burner. Make sure the salt solution boils is evaporated to dryness.
We used Filtration and Evaporation to dryness to separate the mixture of salt and sand into just salt and sand by themselves.

Science Practical 12

Forming Compounds
In this experiment, we had to investigate the formation of compounds by reacting compounds and elements.
Experiment(1)
Hold a magnesium ribbon with a pair of tongs and place it in the Bunsen flame. When the magnesium ribbon catches fire, put it above an evaporating dish to collect the ashes.
The magnesium combined with oxygen to form a compound.
Magnesium + Oxygen ---------> Magnesium Oxide
Experiment (2)
Place half a spatula of iron filings in a test tube.
Then add dilute sulfuric acid to a depth of about 2cm.
A new substance was formed as the iron filings dissolved into the sulfuric acid.
Iron + Sulfuric Acid ----> Iron Sulfate + Hydrogen Gas
Experiment (3)
Place sodium chloride in a test tube up to a depth of 2cm.
Then add lead(II) nitrate solution slowly into the test tube using a dropper.
A white precipitate was formed.
Lead(II) Nitrate + Sodium Chloride Solution -----> Lead(II) Chloride + Sodium Nitrate

Science Practical 11

Investigating Mixtures and Compounds
In this practical, we were required to do a few experiments and learn about the properties of a mixture and a compound.
Materials
Sulfur Powder
Iron Filings
Filter Paper
A piece of paper
Magnet
Some thoughts before the start of the experiment
Both sulfur and iron are elements.
When they are mixed, a mixture of iron and sulfur is formed.
When the are heated together, a compound, iron sulfide is formed.
The Experiment
We poured the sulfur powder on the filter paper.
Then we wrapped one end of the magnet with the piece of paper, then brought it close to the sulfur powder.
Next, we put the iron filings on an evaporating dish.
We brought the magnet close to the iron filings.
Then we poured the sulfur powder into the evaporating dish of iron filings and mixed it thoroughly.
We then moved the magnet close to the mixture.
Next we heated the evaporating dish over the bunsen burner until no other changes could be observed.
Then we moved the magnet close to the compound.
What we learnt
Heat is needed for the formation of a compound but not for a mixture.
Mixtures have the properties of its congruent elements but compounds do not have the properties of their congruent elements.
Mixtures can be separated by physical means while compounds cannot.

Science Practical 19

Extracting Chlorophyll

Apparatus:

2 beakers (one 50 ml and one 250ml)

Variegated leaf (placed in sunlight for 3-4 hours)

Methylated Spirit (Alcohol)

Iodine solution

White tile

Forceps/ Tongs

Bunsen burner

Tripod stand

Wire Gauze

*Ensure that there is no heat source that could ignite the methylated spirits as it is alcohol*

Procedure:

1. Boil 150ml of water in the 250ml beaker.

2. Place a soft leaf in the boiling water for 1 to 2 minutes to break the cell structure in the leaf.

3. Turn off and remove the heat source.

4. Place the boiled leaf in 20ml of methylated spirits in the 50ml beaker. Place the 50ml beaker into the 250ml beaker which has hot water inside.

5. Jiggle or agitate the leaf using tongs/forceps till the methylated spirits is deep green and the leaf is white. (The chlorophyll is now in solution in the methylated spirits)

6. Remove the leaf and transfer it to the beaker of hot water for a while.

7. Gently place the softened leaf on a piece of white tile. Add a few drops of iodine solution to cover the leaf.

Conclusion:

The chlorophyll was successfully extracted from the leaf as there was no starch on the leaf. (The iodine did not turn blue-black)