Ionic compounds conduct electricity in the molten state or when dissolved in water. The charge carriers are the ions themselves.
Last year’s sixth form classes made a number of videos to help you this year. I have a great deal of misplaced confidence that you can do better than them.
Can you spot any mistakes in these presentations. Have they made any mistakes with their explanations?
Electrolysis group 1 (oscar features if you look closely)
Electrolysis group 4
Electrolysis group 3
The winning group in the Chemistry Media Awards competition get to keep Oscar this year.
….melts to form a runny yellow liquid at 113 degrees celcius
Continued heating leads to a highly viscous substance that cannot be poured from the test tube.
with further heating the deep red viscous form of sulphur becomes more fluid. At its boiling point, 445 degrees celcius, the molten sulphur can be poured out of the test tube.
Boiling sulphur quenched in cold water produces a different form (allotrope) called plastic sulphur because of its elastic nature.
Different forms of the same element are called allotropes. Diamond and graphite are allotropes of the element carbon.
Your task:
Produce a powerpoint presentation a short video or poster to explain the changes in sulphur observed as it is heated up to its boiling point. Think about the particles that are present at each stage. What are the forces between them and how does this affect their properties (in particular viscosity) Here are some key points.
Covalent bonds between atoms are strong ( water doesn’t break down into hydrogen and oxygen when you heat it to make a cup of coffee before school). It takeas a lot of energy to break covalent bonds
The forces beween molecules are comparatively weak ( they are called Van der Waals forces)
Van der Waals bonds are elcctrostatic in nature. Molecules can have a permanent dipole. All molecules have transient dipoles that are continually switching on and off
The cumulative effect of transient dipoles increases with molar mass (the size of molecules).
The blocks of the old auditorium are small and held together with mortar. The eight tonne slabs of the new building have an extended structure that is tied together tightly with steel rods.
Chemists have very specialised skills. Architects understand the materials they work with and the forces that hold them together. They can design structures that have never been built before. Architects have designed the new auditorium.
Chemists do exactly the same thing at the atomic, molecular or ionic level.
They can design new molecules with a specific purpose, to lower blood pressure, blood cholesterol or to conduct electricity like metals. Whether its quick drying paint that will protect the outside of your house for the next 10 years or an insecticide to kill the stink bugs munching happily in the vege garden a chemical architect will draw up a solution.
Chemical architects work with only three types of particle, atoms molecules and ions. The size and types of force between these particles determines many of their properties such as melting point, solubility and electrical conductivity.
In the structure and bonding topic you are constantly referring to three questions:
what are the particles (atoms ions or molecules)?
What are the forces holding these particles together (ionic covalent metallic or Van der Waals bonds)?
What are the properties (melting point, solubility and electrical conductivity)
With Van der Waals forces shapes of molecules, electronegativity and polarity are also important. Molecular shape can be predicted from Lewis diagrams and Lewis structures. That is just about everything?
Make sure that you understand everything in the video before moving on to the next section
Babylonian chemists inscribed the process on a clay tablet around 2,200 BC.
Early Egytian chemists outlined their process for making soap on papyrus about 1500 BC. Egytians liked bathing after a hard day at work building pyramids.
The Romans made soap over 2000 years ago. The term saponification is derived from Sapo, the latin word for Soap.
Ancient Britons or Celts made soap. They spent a great deal of time fighting each other and the Romans. Celts used to take all their clothes off and paint themselves blue before battle so the needed a good bath with soap afterwards.
How was early soap manufactured?
Soap was originally made by hydrolysing esters in fat. The alkali was made from the ash collected after certain hardwood trees had been burned. Hot water was poured over the wood ash to dissolve the alkali. Potassium hydroxide was originally known as potash for this reason. The alkaline solution was boiled with animal fat to make a crude soap.
How does soap remove grease and oil?
Soaps and detergents are what chemists refer to as surfactants. They are active on the surfaces between chemically different materials. Soaps have a fat soluble group (lipophilic) at one end of the molecule and a water soluble group (hydrophilic) at the other. Soap can suspend oil and the dirt it attracts and assist its removal
Surfactants are incredibly important and you should be aware of their presence as they can cause problems once they get loose in the environment, Some surfactantsare toxic to animals, ecosystems and humans, and help disperse other environmental contaminants.
Surfactants are found in emulsions, paints, adhesives, agrochemical formulations, cosmetics, food, sanitisers and spermicides. Surfactants are even produced in the lungs of unborn babies to assist breathing and prevent lung collapse.
Cold Creams
Cold creams have been used for thousands of years to clean skin and remove makeup. This is the chemical process we used.
Chemicals:
13g beeswax (contains a complex mixture of esters)
33ml water
50ml paraffin
1g borax (sodium borate, a weak alkali)
Equipment:
hotplate
thermometer
2 x 50 ml beakers
stirring rod
balance
The chemistry:
The borax and water should be heated to about 70 degrees. This will be used to hydrolyse a small amount of ester from the wax into salts of the organic acids (soap, emulsifying agent).
The wax and parfaffin should also be heated to about 70 degrees. The esters in wax are non polar and attracted to each other through weak Van der Waals forces. The paraffin molecules are non polar. They are both lipophilic and the wax dissolves in the paraffin.
Once the two solutions are at the correct temperature, mix them rapidly with stirring to form an emulsion. Put some perfume in and you have an ideal gift for mothers day. Water it all down a bit, throw some abrasives in and you have car polish for father’s day.
