Bonding Practical

Here is an example of two atoms bonding covalently:

Ionic – conduct electricity and when evaporated nothing is left.

Ionic with water of crystallisation – conduct electricity and when evaporated a solid is left.

Substances with Ionic bonds are usually crystalline solids, therefore usually soluble in water, conduct electricity and are very hard.

These are just some of the many properties that are affected by the bonding present inside a compound.

I am going to do a series of tests that will help me determine what type of bonding is present inside the compounds. Here is a list of the different tests and I will explain how I will perform each one.

Is it a solid

I believe this is the first test that should be done because if a substance is a liquid then it must be a small covalent compound for example substance C.

Solubility

To see whether the compound is soluble I will take a sample of it and put it into a beaker of distilled water. I will then get a stirring rod and stir the sample to see whether it will dissolve. If it is not definitely clear whether the sample has dissolved I will test the pH of the solution. If the substance has dissolved the colour of the mixture will change from the colour of distilled water. The only equipment needed for this experiment would be a beaker, a stirring rod and some universal indicator.

Conduct electricity

To test the conductivity of the compounds I will use the solution I made to test for solubility, and use two electrodes linked to a power supply to test for electrolysis in the substance. In some substances I presume that there will be clear electrolysis e.g. bubbles gathering around the cathode. If there is not clear electrolysis a multimeter will be included in the circuit so that you can clearly see whether electricity is being conducted across the mixture. For this experiment you would need to use a lab pack, crocodile clip leads, a multimeter and two electrodes.

Here is a diagram to help explain the experiment:

When evaporated is a solid left

The clearest way to see if a compound is Ionic with water of crystallisation this experiment is used. If you put some of the substance onto a nickel tray and place over a Bunsen burner, when it is melted and evaporates a solid is left behind. For this you would need exactly the same equipment as the boiling point one.

High boiling point

To test for a high boiling point I will put a small amount of the substance on a nickel dish and place it over a Bunsen burner. If the compound burns very quickly it will be clear that it does not have a high boiling point. If it does not burn straight away it will have one. To test for this you just need a nickel tray or something to put the substance on and a Bunsen burner. A stopwatch could also be used to record the time it takes to melt the substance.

Is it dense

This follows on from the previous experiment. Looking at the liquid formed when you boil the substance, if it is a dense liquid it is a Covalent Polymeric substance, but if it is not a very dense liquid it is Small Covalent. I believe this is because the Covalent Polymeric substances are long chains of atoms therefore larger molecules than the Small Covalent ones.

I have included a diagram showing the series of tests I will be doing and how they determine what bonding is present in the compound. This is the plan that I followed when I was doing the experiment.

Here are the results that I collected from doing these series of tests.

Compound A

Soluble – yes  

Conduct – no

High b.p – no

Dense – no

Compound B

Soluble – yes

Conduct – yes

Is a solid left – yes

Compound C

Did not need to be tested.

Is a liquid so must be Small Covalent.

Compound D

Soluble – yes

Conduct – yes

Is a solid left – no

Compound E

Soluble – yes

Conduct – no

High b.p – no

Dense – no

Compound F

Soluble – no

Conduct – no

High b.p – yes

Compound G

Soluble – yes

Conduct – yes

Is a solid left – no

Compound H

Soluble – no

Conduct – no

High b.p – no

Dense – yes

Now that I have discovered what type of bonding is present in each of the 8 different substances I will try and work out the intermolecular forces present in the compounds. There are several different types of intermolecular forces such as hydrogen bonding and van der Waal’s forces. Here is more about these two types of intermolecular forces.

Hydrogen Bonds

For Hydrogen bonds to exist one molecule must be a delta positive Hydrogen atom and the other must be a Fluorine, Oxygen or Nitrogen atom. To get a delta positive Hydrogen atom, you have to have the Hydrogen bonded to something that the electrons would rather spend more of their time around that, for example Oxygen in H2O. Hydrogen bonds are a kind of dipole/dipole interaction between the two atoms. Here is a diagram that shows this more clearly.

Van der Waal’s forces

This is when there is uneven distribution of the electrons across the atom. This only happens by chance but still sets up a polarity in the atom. This will then set up a similar polarity in the neighbouring atoms. Here is a diagram that will explain this well:

To test for the different intermolecular forces I will be using Cyclohexane, Ethanol and Propanone. I will add these to the solution I made to test the conductivity and use a thermometer to see whether the temperature went up, down or stayed the same. This will tell me what intermolecular forces are present in the compounds. I will only be testing the compounds that are Small Covalent because these are the only ones that have intermolecular forces.