Questions and Answers

Your Questions About X100

July 14, 2013

David asks…

What is the percentage of water in Calcium Acetate Tetrahydrate?

Well I have this problem in a really important HW and I can’t resolve it, I know how to find the molecular masses and find the percentage but I can’t seem to find H2O anywhere, can any help me please?

Administrator answers:

The formula of calcium acetate tetra hydrate ;——Ca (CH3COO)2 .4H2O
molar mass = 40 + 2( 12+3+12 +16 +16) +4(2 +16)
=40 +2(59) +4 (18) = 40+ 118 + 72
= 230
now the % of water in( C . A. T .) = 72 x100/230 = 31.3% ans
NOTE [ TETRA HYDRATE IS NOT STABLE BUT mono hydrate is stable ]

Michael asks…

Resolution of reactant of Racemic Mixture and Polarimetry lab?

Pre-lab questions for Experiment #6: Resolution of a Racemic Mixture and Polarimetry
In this experiment, a racemic mixture of (+)- and (-)-phenylsuccinic acid is dissolved in isopropyl alcohol. (-)-Proline is then added and the mixture is heated at reflux for 30 minutes. The flask and its contents are then cooled and the resulting solid ((+)-bis salt of phenylsuccinic acid) is collected by vacuum filtration and washed with acetone. After air-drying well, the solid is added to 6M HCl and swirled for several minutes. The resulting solid ((+)-phenylsuccinic acid) is collected by vacuum filtration.

1. Which is more soluble in isopropyl alcohol, the (+)-bis salt or the (-)-bis salt?

2. What is the purpose of reacting the bis salt with aqueous hydrochloric acid?

3.If the (+)-bis salt is not dried extremely well before adding it to the HCl, no solid product forms. Explain.

4.An experimental sample of (+)-isomer (0.10g) is dissolved in 10.0 mL of acetone in a 1.0 dm polarimeter tube. The observed rotation of the sample is +1.5o. The literature value of Compound B is 173o.
a.What is the specific rotation of the experimental sample?

b. What is the enantiomeric excess of the above sample? Be sure to state whether the EE is (+) or (-).

c.What is the percentage of (+) isomer in the sample? What is the percentage of (-) isomer in the sample?

Administrator answers:

1) The (-)-bis salt is more soluble
2) to remove (-)-Proline
3) not drying thoroughly means that you’ll have the (-)-bis impurity present. Once you add HCl you will have a mixture of (-)-Proline and the phenylsuccinic acid enantiomers, which will make it harder for your desire product to crash out from solution.
4a) [?] = ?/lc = 1.5/(1.0 dm)(0.010 g/mL) = 150o mL/dmg
4b) (150/173)x100% = 86.7% (+)
4c) To answer this part of the problem you need to equations:
86.7% = %(+) – %(-)
100% = %(+) + %(-)
Adding them together gives:
186.7% = 2(+)
%(+) = 93.3%
%(-) = 6.7%

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