crystallization: basic principle
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solubility of a compound usually increases with increasing temperature of
solvent; depends on concentration, polarity and temperature
spectrophotometric analysis
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- Beer's Law
- precision: semi-quantitative (+/- 5-10%)
- advantages: rapid; easy to establish quality control measures for
reliability; online monitoring
- disadvantages: have to set up chemistry so absorption of light by
chemical species of interest will have very different absorption profile than
other parts of solution
What can affect reliability?
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error/uncertainty
Every experimental measurement involves some sort of error.
first order integrated rate law
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ln[A] vs. time yields straight line with slope = -k
unknown acid: goal
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- find out precise molarity of unknown acid
- experimental Ka for unknown acid
, - determine identity
melting point: identity
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melting point confirms but does not prove identity of any given compound
since many compounds have similar melting points
choosing a good crystallization solvent
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- dissolve a large quantity of product at high temp
- not dissolve product at low temp
- dissolve the impurities at all temp
- not react with product
= high solubility at high temp; low solubility at low temp
mixed solvent system: procedures
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1) Dissolve product in better solvent (high solubility) at high temp
2) Add poorer solvent (low solubility) until soln becomes cloudy = polarity
effect
3) Heat soln to redissolve crystals
Give this one a try later!
solubility of a compound usually increases with increasing temperature of
solvent; depends on concentration, polarity and temperature
spectrophotometric analysis
,Give this one a try later!
- Beer's Law
- precision: semi-quantitative (+/- 5-10%)
- advantages: rapid; easy to establish quality control measures for
reliability; online monitoring
- disadvantages: have to set up chemistry so absorption of light by
chemical species of interest will have very different absorption profile than
other parts of solution
What can affect reliability?
Give this one a try later!
error/uncertainty
Every experimental measurement involves some sort of error.
first order integrated rate law
Give this one a try later!
ln[A] vs. time yields straight line with slope = -k
unknown acid: goal
Give this one a try later!
- find out precise molarity of unknown acid
- experimental Ka for unknown acid
, - determine identity
melting point: identity
Give this one a try later!
melting point confirms but does not prove identity of any given compound
since many compounds have similar melting points
choosing a good crystallization solvent
Give this one a try later!
- dissolve a large quantity of product at high temp
- not dissolve product at low temp
- dissolve the impurities at all temp
- not react with product
= high solubility at high temp; low solubility at low temp
mixed solvent system: procedures
Give this one a try later!
1) Dissolve product in better solvent (high solubility) at high temp
2) Add poorer solvent (low solubility) until soln becomes cloudy = polarity
effect
3) Heat soln to redissolve crystals
