Titration Curves

Buffers

What is a buffer? What skills do I need to answer questions about buffers?

How do I calculate the pH of a buffer solution?

Hey guys! was on stumbleupon and saw this, thought it was somewhat relevant :)

http://www.extremetech.com/extreme/165457-new-plastic-becomes-stronger-when-stressed-drop-proof-smartphones-incoming

pH Calculations

Ionic Product and the Common Ion Effect

Solubility Product and Solubility - Calculations

Solubility

Most substances are actually soluble in water; what we previously described as being insoluble may actually only be sparingly soluble. Therefore, some of the substance may be dissolving. We use a solubility product and solubility (in grams per litre, or in moles per litre) to describe the how well a solute will dissolve.

Ions in Solution

With this, we have to identify which ions are in the solutions we were given, then rank them from highest to lowest concentration.

Electrochemical Cells

Electrochemical cells involve two half-cells: one where oxidation occurs and one where reduction occurs. When connected and placed in a circuit, these chemical reactions generate an electric potential (voltage) and a current.

Electrolysis

Electrolysis is a process by which electrical energy is used to convert compounds into their elements.

More amazing science.

Scientists are on a roll this year. 

First they created the perfectly optimised bit, then were able to observe an electron cloud and now this.

Scientists directly measure Van der Waals force.

Reactions of Potassium Permanganate

The reduction of KMnO₄ is different under acidic, alkaline and neutral conditions:

Here is a wonderful summary of the reactions of KMnO₄:

Solubility

Enthalpy

What is Enthalpy? 

The following video does go further than you need, but gives a good explanation:

Enthalpy: Understanding why enthalpy can be viewed as "heat content" in a constant pressure system.

Enthalpy of Formation

Heat of Formation: Standard heat of formation or standard enthalpy change of formation.

Enthalpy of Formation values can be very useful for calculating the enthalpy change in a reaction. There are two ways to do this:

METHOD ONE

• Find the sum of the enthalpies of formation of the products.
• Find the sum of the enthalpies of formation of the reactants.
• Subtract the latter from the former.

METHOD TWO

• Write out the equations that each enthalpy of formation represents
• Use Hess' Law

Hess's Law and Reaction Enthalpy Change: Using Hess's Law and standard heats of formation to determine the enthalpy change for reactions

Enthalpy of Fusion and Enthalpy of Vaporisation

Intermolecular Forces

Last year, we learned about ionic bonds, covalent bonds, van der Waals forces and metallic bonds. We still need to know about these this year, but now need to understand hydrogen bonds and need to know more about van der Waals forces.

Lewis Structures

Here are the videos of this concept being taught to a Year 12 class:

So that is what we are expected to remember from last year. This year, things get a little more difficult; we need to know how to draw Lewis Structures which do not obey the Octet Rule and for polyatomic ions:

BEHOLD!!!

A must see use of scientific resources for fun.

World's Smallest Stop-motion movie

Ionisation Energy

We need to know a fair bit about Ionisation Energy:

1. Define 1st I.E.
2. Justify the trend in 1st I.E. down a Group
3. Justify the trend in 1st I.E. across a Period
4. Use consecutive I.E. values to infer electron configuration/number of valence electrons.

Periodic Table Trends: Ionization Energy: What an ion is. Using the periodic table to understand how difficult it is to ionize an atom.

Electronegativity

Electronegativity generally increases across a Period and generally decreases down a Group. We need to be able to justify these trends this year:

Atomic and Ionic Radius

Atomic Radius

As you move down a group, the outermost electrons are in a higher energy level, so subject to more electric shielding. Therefore, atomic radius increases down a group.

As you move across a period, the number of protons in the nucleus increases, yet the number of energy levels stays the same. Therefore, there is more effective charge on each of the outermost electrons, so the radius decreases. As we are adding more electrons to the same orbital, you would expect there to be an increase in electric repulsion between the electrons. This is true but has negligible effect compared to the increase in nuclear charge.

Ionic Radius

Electron Configurations Video

Foldit

Solve puzzles, for science!

http://fold.it/portal/

Seriously cool chemistry game/research.

Making Nylon

Today, as one of our Polymers "experiences", we made nlyon 6,10:

Sebacoyl Chloride has a -COCl group at each end; 1,6 Diaminohexane has an -NH₂ group at each end.

Thank you to Matt for being such an awesome scientist, demonstrating the experiment.

http://depts.washington.edu/mti/1999/labs/polymers/Image36.gif

Carboxylic Acids and Acyl Chlorides

Sadly the videos from today do not have wonderful sound quality, so this will primarily be a text summary of today's work:

CARBOXYLIC ACIDS

Carboxylic acids have many properties and reactions in common with mineral acids, such as hydrochloric and sulfuric acid. What is different is that they are weak acids, so react more slowly and have higher pHs (but still less than 7).

The smaller carboxylic acids are water-soluble, and ethanoic acid has a surprisingly high melting and boiling point. These features are due to their abilities to form hydrogen bonds. Ethanoic acid forms hydrogen bonds in a special way, forming dimers (di = two; mer = unit). As a dimer, ethanoic acid has a larger electron cloud, so can have a higher extent of intermolecular bonding.

ACYL CHLORIDES

The experiment on p135 was done and filmed. Sadly, it didn't go very well, so Mr Nicoll re-filmed it:

centripetal force

centripital  force !

Markovnikov's Rule

"The Rich Get Richer"

This video explains what this means when an addition reaction occurs to an alkene where the two carbons involved in the double bond are not the same:

Two products are formed, a major product and a minor product. As the names suggest, more of the major product is formed, but there is actually a mixture of both products when addition occurs to this type of alkene.

Here is another example:

http://www.chemguide.co.uk/organicprops/alkenes/propenehcl.gif

Identifying Unknown Organic Substances

Identification of Unknown Organic Substances
              Practical 10.5 - Page 140 of 3rd Edition "Continuing Chemistry" - Anne Wignall & Terry Wales

This experiment involves being given 4 unknown substances labelled W, X, Y, and Z.  Using a variety of laboratory substances to determine what functional group the organic substances contain.  Any methods could be used, and the following are only a few of what methods were used in the entire class during the experiment.

Product W

The initial smell test gave an unpleasant (open to suggestion) smell.  This gave us an indication that the substance may have been an amine or an aldehyde.
We added red litmus to the solution and the litmus turned blue.  This showed an indication of a high pH and a concentration of OH- ions, or the ability to create OH- ions.
Therefore we came to the conclusion Product W is an amine.

Product X

The initial smell test gave a vinegar smell.  This gave us an indication that the substance may have been a carboxylic acid or possibly a ketone.
We added blue litmus to the solution and the litmus turned red.  This showed an indication of a low pH and a concentration of H+ ions, or the ability to create H+ ions.
Therefore we came to the conclusion Product X is a carboxylic acid.

Product Y

The initial smell test gave a pleasant (again, open to suggestion) smell.  This gave us an indication that the substance may have been a ketone or possibly an alcohol.
To test for an aldehyde, which was for some reason thrown into the mix of possible substances, we created Tollen's reagent, which had no reaction with Product Y.  However, when tested with a known aldehyde - propanal, Tollen's reagent created a silvery mirror on the bottom inner surface of the test tube with a slightly evident black precipitate.
When adding water to the substance, we found that it was soluble.  Esters are not miscible, and therefore we came to the conclusion Product Y is a ketone.
Product Y was presented to be a secondary alcohol.  To test for this, Lucas reagent should have been used, and the solution would have turned cloudy when warmed over a long period of time.

(Unfortunately, video uploading crapped out here… I'll get onto that.)

Product Z

When water was added to this substance, two layers formed.  Therefore the substance was insoluble.  Insoluble substances include alkanes, alkenes, esters etc…
We added ammonium hydroxide to the solution to form an amine through nucleophilic substitution.  To verify, we added red litmus to the new solution and it turned blue.
Therefore we came to the conclusion that Product Z is an alkene.
Product Z was presented to be an ester.  To test for this, alcoholic ammonia can be added to form an amide and an alcohol.  If the carbon chain is long enough, the amide could be found as a white precipitate at the bottom of the tube, as well as red litmus being added to the new solution turning blue.

Optical Isomerism

Optical Isomerism (Enantiomers)

e.g 2-chloro 1-propanol

4 different groups = chiral/asymmetric carbon

            H                     Cl                     H

             |                       |                       |

H         -           C          -          C*        -          C          -           O         -           H

                         |                       |                       |

                        H                     H                     H

Similarities

•         same melting point and boiling point
•         same miscibility
•         same structural formula
•         same chemical reactions EXCEPT with other “optically active” compounds

Differences

•         mirror images
•         naturally made organic substances are selective: only ONE is made e.g. L-amino acids
•         rotate plane-polarized light in opposite directions

       

         
           http://www.youtube.com/watch?v=uD9j3nbaHsE - for the voice. #pasteur