Homework Help: Chemistry

Posted by anonymous on Tuesday, May 19, 2009 at 10:28am.

1. Ethanoic acid (acetic acid) is very soluble in water. However, naturally ocurring long-chain carboxylic acids such as palmitic acid (CH3(CH2)14COOH) are insoluble in water. Explain why.
My guess: Long-chain carboxylic acids have stronger relative strength of intermolecular forces between them, which made them unsoluble in water as they had strong intermolecular forces between their long carbon chains.

2. Why did the characteristics below apply to transition metals?
a. Ions vary in charge.
b. Many of their solids are colored.
c. Many are hard solids.
My guess:
a. It was because unpaired Delectrons can move to the outer energy level, such that they can form ions vary in charge.
b. No ideas.
c. They had more unpaired electrons in the d sublevel? This made their melting and boiling pionts higher and thus increase their hardness?

Thank you!

Chemistry - DrBob222, Tuesday, May 19, 2009 at 11:48am
1. Like dissolves like. The COOH group on the palmitic acid is an acid, it is polarized (and polarizable) and it is the water loving part. Small organic molecules containing these groups are soluble since the organic non-polar part is a small part of the molecule. As the chain length increases, however, the non-polar part increases to the point that the organic part outweighs the water soluble part and the entire molecule is not soluble. (I think you would do better to use insoluble than unsoluble.). Another point is that the COOH portion can form hydrogen bonds, both with other COOH molecules as well as water while the organic portion has only dispersion forces between molecules.
2a. Your answer is ok but it's more like this. The ionization potential difference is relatively small between s,p, and d electrons, so the atoms show variable oxidation states because of this.
2b. The fact that we see color is due almost entirely to unpaired electrons.
2c. It has been suggested that the d electrons are being used to build the crystal lattice; thus making the solid crystals harder.

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