Diffusion of Gases and Liquids (KPT) Practical.

This lab session, we investigated diffusion in Gases and Liquids.

Introduction to the experiment's aims and theories tested:

• The Kinetic Particle Theory (KPT) explains the way in which matter behaves and its physical properties in terms of the movement of the tiny particles the matter is made up of.
• Diffusion is a physical phenomenon that takes place in liquids and gases where the particles spread out and travel away in a haphazard and random way.
• Gases diffuse at different rates.
• Lighter particles travel faster than heavier ones (at the same temperature).
• Particles also move faster at higher temperatures, compared to lower temperatures.
• Diffusion takes place slower in liquids due to its lower kinetic energy.
• In liquids and gases when diffusion is taking place, a process called intimate mixing takes place.
• Intimate mixing: When collisions are taking place between these particles, the KPT states that there is sufficient space between the particles of one substance (the substance with larger particles) for the particles of another substance (the substance with smaller particles) to move into.

Aims:

• To infer and observe the properties of particles of matter
• To investigate relationships between the rate of diffusion and density(mass) of gas
• To investigate and observe the diffusion of liquid in water.

Procedure of experiment part 1:

1. Add 50 cubic cm of beans to a measuring cylinder
2. Add 50 cubic cm of sand to the same measuring cylinder.
3. Mix the 2 solids by shaking the mixture well and then, let it settle.
4. Measure the volume of the mixture.

Observations:

The volume of the mixture is 88 cubic cm although the addition of the 2 original volumes of the beans and sand is actually 100 cubic cm.

Conclusion:

When equal volumes of sand and beans are mixed, the total volume is less than the 2 volumes added together. The lesser volume is caused by the spaces in between the beans. The smaller particles of sand occupy the spaces in between the beans, causing the volume to be lesser.

Procedure of experiment part 2:

1. Fill up half the plastic tube with water.
2. Top up the remaining half of the tube with alcohol. (make sure the 2 liquids do not mix and there is an interface indicating the 2 layers of liquids)
3. Hold the tube with your thumb covering the opening of the tube fully.
4. Hold on and invert the tube a few times, taking note of the sensation the mixing creates on the thumb.
5. Hold the tube back upright.

Observations:

The final total volume of the alcohol and water became lesser than the sum of the original two volumes of the 2 liquids (the level (height) of total liquid in the tube dropped). A strange sensation (like being suctioned) was created on the thumb while the tube was inverted.

Conclusion:

When equal volumes of alcohol and water are mixed, the total volume is lesser than the 2 volumes added together. Also, the thumb used to cover the tube feels like its being suctioned. This is because when the tube is inverted, the alcohol particles, which have a lower density than water will rush upwards (towards the bottom of tube) while the water particles will rush downwards (towards the thumb) as they have a higher density. During this, the smaller water particles will collide with the alcohol particles and fill in the spaces between the alcohol particles. Thus, the total volume will decrease. Also, as the spaces in between the small water particles (which cannot be filled by alcohol particles as they are much larger) are not filled, there is vacuum between the solution and the thumb. As the pressure in a vacuum is much lower than that in normal atmosphere conditions, the thumb will feel as if its suctioned in.

Procedure of Teacher's demonstration: 

1. Two pieces of cotton wool is placed at the 2 ends of a hollow tube and held by a retort stand.
2. One cotton wool is soaked in concentrated hydrochloric acid of relative molecular mass, 36.5. (this end of the tube is called A)
3. The other is soaked with concentrated ammonia solution of relative molecular mass, 17. (this end of the tube is called B)
4. Stoppers are placed at both ends to seal the tube and then, teh set-up is observed.

Observation:

A white ring is observed nearer to end A (the Hydrochloric acid).

Conclusion:

Ammonia Gas diffuses faster than Hydrochloric acid. As Ammonia solution has a smaller mass than Hydrochloric acid, it diffused and travelled faster towards the other end (which is end A) and thus, the white ring of Ammonium Chloride (Solution formed when HCl and NH3 mix) formed nearer end A. This proves that the smaller the mass of the gas is, the faster the rate of diffusion is as well.

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Are you Good Enough for it?

In between all these lessons, a group work had to be done where we had to pit our Chemistry purification and separation method skills against other groups. We were tasked to figure out the methodology of how to separate a mixture of 6 substances using the various separation techniques we had learnt. Here are the slides:

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Crystallisation Practical.

We went to the Science laboratory to try carrying out crystallization using Copper(II)Sulfate and comparing the crystals formed in 2 types of cooling: Rapid cooling and slow cooling.

Experimental Process:

1. Boil distilled water.
2. Dissolve Copper(II)Sulfate in the boiling water until a saturated solution is created.

3. Filter the solution if there is any undissolved copper(II)sulfate or any other impure substances.
4. Heat the solution in an evaporating dish until most of the water has evaporated.

5. Transfer half of the remaining solution into a test tube and place it in a beaker filled with cold water, to carry out rapid cooling.
6. For slow cooling, jus leave the remaining solution to cool in room temperature.
7. Observe the crystals formed in the 2 types of cooling:

Crystals obtained from rapid cooling:

  

Crystals obtained from slow cooling:

 

Observation:

Rapid cooling:

• Crystals are smaller and powdery.
• Irregularly shaped

Slow cooling:

• Crystals are larger.
• Well-defined shapes

Conclusion:

Crystals obtained by rapid cooling are fine and irregularly shaped while crystals obtained by slow cooling are large and well-defined.

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Chromatography practical.

During this lab session, we were tasked to separate a green food colouring into its components through chromatography.
Aim:

• To separate the green food colouring into the individual components.
• To determine the retention value (Rf value) of the separated components.

Apparatus:

• Boiling tube
• Strip of chromatography paper
• Boiling tube rack
• Capillary tube
• Clothes peg
• Hair dryer
• Green food colouring
• Distilled water

Procedure:

 

Diagram:

Calculating the retention value:

Observations: The food colouring is composed of blue dye and yellow dye. It is not a pure substance.

Image of chromatogram:

Results & Calculation of Rf values:

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Purification & Separation

 Magnified image of the distillation process:

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Comparing Elements, Compounds & Mixtures

This was a practical session at the lab where we explored and saw the differences between compounds and mixtures ourselves by means of a few simple experiments.

Aim:

• To observe and compare the properties of mixtures and compounds that are made up of the same elements.
• To determine some common characteristics of all compounds and mixtures.

Apparatus:

• Filter Paper
• Test-tube
• Magnet
• Sulfur powder
• Iron filings
• Spatula
• Bunsen burner

Procedure:

Part A:

• Place a spatula of iron filings and a spatula of sulfur powder on a piece of filter paper.
• Mix them together and observe changes in physical appearance and the composition of both elements.

          --> Observation: The mixture has the same colour as original constituents (dark grey and yellow). The composition of the iron filings and sulfur in the mixture is not fixed and can be added in any proportion.

• Feel the temperature of the mixture. Observe whether is it has changed.

          -->Observation: The temperature remains unchanged. (room temperature)

• Move the magnet under the filter paper and observe whether the mixture is attracted to the magnet.

          --> The whole mixture is not attracted to the magnet. Instead, the iron filings, is the only element attracted and thus, separates from the sulfur powder and moves with the magnet.

• Add the mixture of iron filings and  sulfur powder to a test-tube of water.
• Stir the mixture and wait until the mixture rests.
• Observe whether the mixture is separated and whether it is floating.

          -->Observation: The mixture is separated. Sulfur powder floats on water while the iron filings sink in water, acting as two separate elements again. Heat or light isn't taken in or given out when a mixture is formed.

Concluding observations: The mixture retains the properties of its constituent elements. The mixture can be separated by physical means.

Part B:

• Mix precisely one spatula of sulfur and half a spatula of iron filings in a crucible.
• Cover the crucible with a lid and heat it using a Bunsen burner for 10 minutes over a strong non-luminous flame.
• After heating, scrap the residue onto a filter paper and move a magnet underneath.
• Observe whether the substance is attracted to the magnet.

          -->Observation: The substance is not separated and is not attracted by the magnet.

• Place the residue in a test-tube of water and observe.

          -->Observation: The residue is not separated and it sinks in water.

Concluding observations: The resulting substance formed is a compound. Iron and sulfur have gone through a chemical reaction(as heat was taken in while the substance was formed) to form the compound-Copper(II)Sulfide. It does not possess the properties of the constituent elements and is not separated by physical means (constituent element, iron was not attracted by the magnet and sulfur did not float in water alone).

Conclusion:
There are several differences between a compound and a mixture. These are:

1. A mixture does not need to go through a chemical reaction to be formed but a compound needs to go through a chemical reaction to be formed.
2. A mixture retains the properties of its constituent elements but a compound does not possess the properties of the constituents and instead, has new and different characterisitics of its own.
3. A mixture can be separated easily by physical means but a compound cannot be separated by physical means and has to go through chemical means for the chemical reaction to be reversed.

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The Bunsen Burner

The Bunsen Burner:

Functions of the parts in a Bunsen burner:

• Barrel --> To raise the flame to a suitable height for heating.

                           Where gas and air are mixed/combined.

• Air holes --> To allow air to enter the burner.

• Collar --> To control the amount of air entering the burner.

• Gas Intake Tube --> To allow the gas from gas tap to enter the burner.

• Base --> To support the burner and keep it stable

• Gas Tap --> To control the amount of gas supplied to the burner.

How to light a Bunsen burner?

1. Close the air holes.
2. Turn on the gas tap and immediately use the lighter and light it up at the barrel mouth.
3. Adjust the air holes for a non-luminous flame.

The different types of flames:

Luminous Flame:

• Produced when air holes are closed.
• Unsteady
• Orange in colour

Non-Luminous Flame:

• Produced when air holes are open.
• Steadier
• Blue in colour

 

Mini Experiment using the non-luminous flame:

Aim: To determine the hottest part of a non-luminous flame.

 

Apparatus:

• Bunsen Burner
• Lighter
• Tongs
• Metal Wires

Procedure:

1. Hold a metal wire(using a pair of tongs) in the inner dark blue zone of the flame for 30 secs and observe the change in colour of the metal wire.
2. Repeat step 1 using 2 more metal wires at the tip of the inner dark blue zone and in the outer pale blue zone.

Observations:
The metal wire glows the brightest red when held at the tip of the inner blue cone, followed by the pale blue outer cone and then, inside the inner blue one itself. Also, the metal wire starts to melt when held in the inner blue cone long enough.

Conclusion:
The hottest part of the non-luminous flame is at the tip of the inner blue cone.

Strikeback:

• Green in colour
• Dangerous; turn off immediately.

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