Cinnamic acid and urea melt at 133 C. The melting point of an unknown is found to be 133C. When the unknown is mixed with rea, the melting range of the mixture is 120-125 C.
Is it possible to identify the sample from this information? If not, what further tests would you perform?
I'm really kind of stumped because I have a feeling it's cinnamic acid but I don't know why it went down that much....
2007-10-09 04:56:42 · 3 answers · asked by Burnt Toast 1 in Science & Mathematics ➔ Chemistry
When the unknown was mixed with Urea, the melting point of the mixture was lower than the mp of either pure substance. That indicates that the unknown IS NOT urea.
You might mix the unknown with cinnamic acid and determine the mp of that mixture. If it is still 133, then the unknown should be cinnamic acid.
There are a number of additional tests you could do. For example, you could also run an IR spectrum of the three substances, or carry out any number of other tests. You could dissolve some of each in water and determine the pH of the solution. Urea should be neutral, but the other would form an acidic solution...
2007-10-09 05:06:28 · answer #1 · answered by hcbiochem 7 · 0⤊ 0⤋
Well N is Nitrogen... Which has a very low melting point, as it is a gas in standard temperature and pressure. It's exact melting and boiling points are: Melting: 63.15K / -210C / -346F Boiling: 77.36K / -195.79C / -320.33F Just because the other elements (Lithium, Beryllium, Boron, Carbon) have rising melting points, doesn't necessarily mean that Nitrogen's is also high. The reason for it having a low melting point is because it has WEAK INTERMOLECULAR FORCES, meaning that the attraction between each Nitrogen atom is weak, so they are more spaced out - which obviously means that it won't be solid - it will be a gas or liquid (gas obviously in this case). As John said the reason for Nitrogen having weak intermolecular forces is because it has simple covalent bonds - which are weak. Whilst Lithium, Beryllium and Boron have giant metallic lattices, which have strong bonds. And Carbon has giant covalent molecules, which have very strong bonds. Hope any of this helped!
2016-05-19 23:01:44 · answer #2 · answered by leeann 3 · 0⤊ 0⤋
The unknown sample is Cinnamic Acid since the addition of urea drove the mt. pt. down.
2007-10-09 05:01:13 · answer #3 · answered by TheMadChemist 2 · 0⤊ 1⤋