Chemistry Journal Entry 7

This week, we saw diffusion happening in front of our own eyes!

Basically what is diffusion?

Diffusion is the movement of substances from a region of higher concentration to a region of lower concentration 

The higher the temperature, the faster the rate of diffusion.

In the experiment, Mr Foo demonstrated diffusion by showing the spread of iodine vapor throughout the gas jar.

At the start of the experiment, the iodine vapor was at the bottom of the gas jar. There was a violet colouration at the bottom of the jar and over time, it faded. The purple colored vapor rose and spread throughout the jar.

We could then conclude that gaseous particles are in constant and random motion.

Relating it to matter...

Matter is made up of small particles which are in constant motion and random direction.

WHY DOES DIFFUSION ONLY HAPPEN IN LIQUIDS AND GASES?

The water and gas molecules are able to move freely and hence, diffusion is able to take place. In solids however, molecules are packed so tightly that a negligible amount of movement occurs and inhibits diffusion.


KINETIC PARTICLE THEORY

A solid

• cannot be compressed 
• fixed volume
• fixed shape 
• high density 

A liquid is

• cannot be easily compressed 
• no fixed shape 
• fixed volume 
• high density, but usually lower than solids

A gas 

•  can be easily compressed 
• no fixed volume
• no fixed shape - take the shape of the whole container
• low density

Solid particles vibrate about fixed positions, held together by strong intermolecular bonds between them -> fixed shape and volume 

Liquid particles are free to move about between clusters but confines within vessel containing it due to strong  attractive forces between them -> fixed volume but take the shape of container holding it 

Gas particles are always in high speed, independent motion in random manner with negligible attractive forces between them -> no fixed volume and shape, but highly compressible

BROWNIAN MOTION

We actually learnt this in physics. Pollen grains were ovine because the smaller and faster moving water particles were constantly colliding with them. 

- Random motion of visible particles (pollen grains) caused by small, invisible ones 

- Random motion of the smoke particles is caused by the bombardment of air molecules 

- When temperature increases, smoke particles gets more agitated and change direction more often. 

Boiling 

- Liquid to gas

- Gain energy

- Move faster 

- Further apart

- Completely overcome hydrogen bonding

- Far apart and away from each other

At boiling point, water molecules lose heat energy so as to bond with the molecules. 

Thank you!

 

Chemistry Blog Entry 6

SEPARATION TECHNIQUES


There were mainly 3 techniques we actually learnt about.

1. Crystallization ( most interesting!!!)
2. Simple Distillation
3. Chromatography ( 2nd interesting) 

There are actually many separation methods but those above were mainly the ones that were highly emphasized on.

CRYSTALLIZATION

To separate a dissolved solute from a solution 

Commonly used to separate the heat labile solutes from their solutions

Keywords: ** Heat-labile : substances which are easily decomposed

Experiment : Forming crystals 

We used copper sulfate which is actually a blue powdery substance to create crystals. 

My partner and I did the experiment that did not involve rapid cooling. Thus, we did not really put it into the beaker filled with ice. 

The scariest part of the experiment was the part which you had to check for the formation of crystals using the glass tube. I was really afraid to mix the bottom part ( in case somehow we actually get burnt) so we ended up saturating the mixture a LITTLE bit. Hence we had to add more water , boil it again and get the crystals. 

Before all of this, we had to use a method called FILTRATION. Basically, we had to filter all the copper sulfate chunks so that there will be no impurities. 

Filtration -> Separation of insoluble substances from liquid 

Insoluble substance- Residue

Usage of filter paper

Keywords:** Saturated solution: A solution that contains the maximum amount of solute dissolved in a given volume of a solvent at a particular temperature

DIFFERENCES BETWEEN RAPID COOLING AND SLOW EVAPORATION 

Rapid cooling of saturated solution - small and ill-shaped crystals

Slow evaporation of a cold saturated solution - Large and well defined crystals obtained

SIMPLE DISTILLATION 

Purpose: To separate the solvent from a solution of solute

Purifies liquid 

- Always use a round bottom flask 

Purpose of boiling stones: To allow the surface of the liquid to be in equilibrium with a gas 

It prevents water from being heated beyond its boiling point.

Purpose of Condenser: To cool the water vapor and condense it to form water droplets

FINAL PRODUCT: DISTILLATE

( Shown to use with the coke) 

Leftover product: Water and sugar in separate apparatus

CHROMATOGRAPHY 

To separate a mixture of solutes with different solubility and degree of absorption 

Chromatography paper 

RETENTION FACTOR: 

Rf value = Distance moved by substance 

              Distance moved by solvent 

Uses: 

Separate and identify compounds 

** A compound is a two or more elements chemically combined. 

** Locating agent: Chemical substance that will produce colored products on reaction with the colorless compounds 

**** Solvent front 

DECANTING 

Separating insoluble solids from liquids 

That's all!

Thank you!