Solubility and Molecular Structure laboration help

[Guest Mr Canada]

I have a slight problem with a lab report due Monday. The goal of this laboration is to determine the solubility for different substances and interpret the results in terms of intermolecular attractive forces between them. I have no idea what this means... With the laboration I've tested 6 substances in 11 different mixes to see if they solve or not. In the results I've gathered only 6 mixes have solved. Now, according to the goal set up, I need to explain why and I don't even know what the resulting solutions are called or how they are structurized. No idea then how to explain the results in terms of intermolecular attractive forces between them. Any kind of help would be greatly appreciated.

The different solved mixtures are:

Test tube 1 (Water + Methanol)

Test tube 4 (Water + Glucose)

Test tube 5 (Water + Copper Sulphate)

Test tube 6 (Methanol + Butanol)

Test tube 8 (Methanol + Copper Sulphate)

Test tube 9 (Butanol + Heptane)

[BIO-AQUA]

I have a slight problem with a lab report due Monday. The goal of this laboration is to determine the solubility for different substances and interpret the results in terms of intermolecular attractive forces between them. I have no idea what this means...

Read this to the end:

- Van der Waals forces of attraction are temporary and instantaneous forces of attraction that exist between non-polar covalent molecules. How? The unbonded pairs of electrones in the outer shells have kinetic energy and can move freely. At a certain instant and due to their random motion, the electrones assemble/accumulate on one side, making an instantaneous temporary polar molecule. This polar molecule will induce its neighboring molecule to become polar (the highly dense negative side will repel electrones of the other molecule), thus an instantaneous electrostatic force of attraction is formed. This is called the Van der Waals force of attraction.

As the molar mass, size and surface area increase, the Van der Waals forces become stronger as the valence electrones become less attracted to the nucleus and molecules are more easily polarized.

- Dipole-Dipole force of attraction is a permanent electrostatic force of attraction that exists between polar covalent molecules. It is much stronger than the Van der Waals force.

- Hydrogen Bond is the strongest bond between those and is a special case of the dipole-dipole force; it exists between the MOST polar bonds (H-O), (H-N) and (H-F).

Note (1): Don't confuse these with the covalent bond. The forces above are attraction forces between covalent molecules. The covalent bond is a bond that exists within the covalent molecule and is much stronger than the three above.

Note (2): For a molecule to be soluble in polar water, it must be polar and able to form Hydrogen bonds with polar water molecules.

With the laboration I've tested 6 substances in 11 different mixes to see if they solve or not. In the results I've gathered only 6 mixes have solved. Now, according to the goal set up, I need to explain why and I don't even know what the resulting solutions are called or how they are structurized. No idea then how to explain the results in terms of intermolecular attractive forces between them. Any kind of help would be greatly appreciated.

So from the information above, you can deduce that the 6 dissolved mixes consist of polar substances, right? What about the other 5?

The different solved mixtures are:

Test tube 1 (Water + Methanol) --> Both are polar; what is the functional group of the alcohol? What bond does it make with polar water molecules? (refer to info above).

Test tube 4 (Water + Glucose) --> Draw the structure of glucose (it's polar) and determine what forces it makes with polar water molecules.

Test tube 5 (Water + Copper Sulphate) --> Same here?

Test tube 6 (Methanol + Butanol) --> Is butanol polar? Is it able to form hydrogen bonds with water molecules? (refer to info above). (psst ) If so, then it is soluble since you proved that methanol is soluble in test tube 1 (oops! ).

Test tube 8 (Methanol + Copper Sulphate) --> You proved that methanol is soluble in water and forms hydrogen bonds with its molecules. What about Copper Sulfate?

Test tube 9 (Butanol + Heptane) --> Are these two soluble? Tackle each chemical at a time the same way you did for the ones above.

Hope this has helped. Have a nice day.

[Guest Mr Canada]

Read this to the end:

- Van der Waals forces of attraction are temporary and instantaneous forces of attraction that exist between non-polar covalent molecules. How? The unbonded pairs of electrones in the outer shells have kinetic energy and can move freely. At a certain instant and due to their random motion, the electrones assemble/accumulate on one side, making an instantaneous temporary polar molecule. This polar molecule will induce its neighboring molecule to become polar (the highly dense negative side will repel electrones of the other molecule), thus an instantaneous electrostatic force of attraction is formed. This is called the Van der Waals force of attraction.

As the molar mass, size and surface area increase, the Van der Waals forces become stronger as the valence electrones become less attracted to the nucleus and molecules are more easily polarized.

- Dipole-Dipole force of attraction is a permanent electrostatic force of attraction that exists between polar covalent molecules. It is much stronger than the Van der Waals force.

- Hydrogen Bond is the strongest bond between those and is a special case of the dipole-dipole force; it exists between the MOST polar bonds (H-O), (H-N) and (H-F).

Note (1): Don't confuse these with the covalent bond. The forces above are attraction forces between covalent molecules. The covalent bond is a bond that exists within the covalent molecule and is much stronger than the three above.

Note (2): For a molecule to be soluble in polar water, it must be polar and able to form Hydrogen bonds with polar water molecules.

So from the information above, you can deduce that the 6 dissolved mixes consist of polar substances, right? What about the other 5?

The different solved mixtures are:

Test tube 1 (Water + Methanol) --> Both are polar; what is the functional group of the alcohol? What bond does it make with polar water molecules? (refer to info above).

Test tube 4 (Water + Glucose) --> Draw the structure of glucose (it's polar) and determine what forces it makes with polar water molecules.

Test tube 5 (Water + Copper Sulphate) --> Same here?

Test tube 6 (Methanol + Butanol) --> Is butanol polar? Is it able to form hydrogen bonds with water molecules? (refer to info above). (psst ) If so, then it is soluble since you proved that methanol is soluble in test tube 1 (oops! ).

Test tube 8 (Methanol + Copper Sulphate) --> You proved that methanol is soluble in water and forms hydrogen bonds with its molecules. What about Copper Sulfate?

Test tube 9 (Butanol + Heptane) --> Are these two soluble? Tackle each chemical at a time the same way you did for the ones above.

Hope this has helped. Have a nice day.

WOW Thank you so very much for this. Really helped me to understand this a lot.

[Guest Mr Canada]

Test tube 5 (Water + Copper Sulphate) --> Same here?

One question though. What about the Copper Sulphate. You said earlier that to be able to solve with water it had to be polar and able to form hydrogen bonds, but in this case it is the Cu that makes the substance polar. This is not able to form a hydrogen bond with the water. What then?

[BIO-AQUA]

One question though. What about the Copper Sulphate. You said earlier that to be able to solve with water it had to be polar and able to form hydrogen bonds, but in this case it is the Cu that makes the substance polar. This is not able to form a hydrogen bond with the water. What then?

Copper Sulfate is quite different since it's an ionic compound. The rule about the polarity and hydrogen bonds applies only to covalent compounds. Another rule states that ALL ionic compounds are soluble in water, since they dissociate into positive and negative ions.

Edited December 10, 2007 by BIO-AQUA

[Guest Mr Canada]

Copper Sulfate is quite different since it's an ionic compound. The rule about the polarity and hydrogen bonds applies only to covalent compounds. Another rule states that ALL ionic compunds are soluble in water, since they dissociate into positive and negative ions.

Ah. Thank you so very much.