Homework Help: science(chem)

Posted by ~christina~ on Sunday, September 2, 2007 at 9:11pm.

A few questions.

1. What is the difference btwn crystalization and precipitation?

2. What will happen if you choose a solvent whose boiling point is higher than the melting point of the compound to be crystalized?

3. Generally describe how to predict solubility.

1. just checking my thinking on this. Crystalization is the actual process of forming crystals while precipitation is actually getting a solid out of solution right?

2. No clue ..

3. To predict solubility:(my thinking)
a) determine if the molecule to be dissolved is polar or nonpolar since like dissolves like.

b)hydrocarbons = nonpolar
1. the more carbons on a compound the more hydrocarbonlike it is.

c)If it has a electronegative atom in the compound such as N and O then it is polar.
1. If the atom is a halogen thus having high electronegativity then it is polar but not alot since the halogen doesn't have a great effect on the organic compound.

2. If the molecule has a few carbons compared with alot of carbons and also has a electronegative atom in the compound then the one with fewer is more soluble in water b/c water is polar and the fewer carbons it has would make it more polar and having more carbons would make it more hydrocarbon like. (less polar)

d) Compounds that belong to the same "family" are soluble with each other but only if their size is similar. If there is a great size difference then that doesn't work.

e)dipole dipole forces of attraction btwn the hydrogens of one molecule and the electronegative atom in another molecule. (F,O,N)

Is this correct?
I'm not sure how to make my explanation for #3 in general terms (shorter abreviated form)

Thanks =)

science(chem) - bobpursley, Sunday, September 2, 2007 at 9:15pm
Your explaination for the number 3 is sufficient.

Number one, they are the same, except crystallization is very slow precipation of a solute that has strong bonds in the sold form.
Number two. Solvents do not melt solutes: solutes dissolve because of forces between the solute and solvent. Think about this with sugar dissolving in water.
science(chem) - ~christina~, Sunday, September 2, 2007 at 9:18pm
For #2 nothing would happen then right?
science(chem) - bobpursley, Sunday, September 2, 2007 at 10:22pm
Nothing. Think again about sugar, the mp of sugar is well above the bp of water.
- science(chem) - ~christina~, Sunday, September 2, 2007 at 10:40pm
  But the question asked what would happen if the solvent's boiling point was higher than the melting point not if the melting point was higher than the boiling point Bob.
  
  ex.
  Since the solvent is the water and the solute is the sugar. (Q: the solvent's boiling point higher than the melting point of the solute)

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