CHEM 343 Quiz 1 Questions and Answers Fully Solved Graded A+
How can you tell if a compound is pure or impure? - AnswersPure substances tend to be uniform and
homogenous, they also have a sharp melting and boiling point.
What are the characteristics considered when taking a melting point? - AnswersDetermination of purity
and how close it is to a known unknown.
What is recrystallization? - AnswersSpreads molecules of impurity and purity apart, Then allows for the
purity to recrystallize while keeping the impurities in solution.
How are solvents chosen for recrystallization? - AnswersUse micro samples of your unknown in test
tubes and use each solvent til you find one that does not dissolve the unknown at room temp.
How are crystals collected? - AnswersUse a vaccuum filtration system to filter out the impurities (liquid)
from the crystals.
Rinse off the crystals with cold solvent, and vacuum to dry
Remove crystals, invert and scrape onto filter paper
What do you do if a solid impurity remains after compound is dissolved by solvent? - AnswersUse gravity
filtration ( Filter paper, stemless funnel, and Beaker) onto a hot plate
What do you do if your solid contains a colored impurity? - AnswersGet rid of the dye before crystals
form, To do this add activated charcoal to the solution to absorb the dye. and filter it out via hot
filtration
What are all the equipment used? - AnswersScale - for mass of unknown
Hot Plate - for melting point and heating
Beaker - for heating
Test tubes - for solvent and testing
Stem less funnel - for seperation of unknown and impurities
Ice - for cooling
Filtration paper - for funnel
How does the melting point change if solid sample is pure vs impure? - AnswersImpurities weaken IMFs
and decrease the melting point
When first heating your sample what should the ramp rate be and starting temperature? - AnswersYou
should start at 35 degree and rap at 10 degrees (C) per minute
How can you tell if a compound is pure or impure? - AnswersPure substances tend to be uniform and
homogenous, they also have a sharp melting and boiling point.
What are the characteristics considered when taking a melting point? - AnswersDetermination of purity
and how close it is to a known unknown.
What is recrystallization? - AnswersSpreads molecules of impurity and purity apart, Then allows for the
purity to recrystallize while keeping the impurities in solution.
How are solvents chosen for recrystallization? - AnswersUse micro samples of your unknown in test
tubes and use each solvent til you find one that does not dissolve the unknown at room temp.
How are crystals collected? - AnswersUse a vaccuum filtration system to filter out the impurities (liquid)
from the crystals.
Rinse off the crystals with cold solvent, and vacuum to dry
Remove crystals, invert and scrape onto filter paper
What do you do if a solid impurity remains after compound is dissolved by solvent? - AnswersUse gravity
filtration ( Filter paper, stemless funnel, and Beaker) onto a hot plate
What do you do if your solid contains a colored impurity? - AnswersGet rid of the dye before crystals
form, To do this add activated charcoal to the solution to absorb the dye. and filter it out via hot
filtration
What are all the equipment used? - AnswersScale - for mass of unknown
Hot Plate - for melting point and heating
Beaker - for heating
Test tubes - for solvent and testing
Stem less funnel - for seperation of unknown and impurities
Ice - for cooling
Filtration paper - for funnel
How does the melting point change if solid sample is pure vs impure? - AnswersImpurities weaken IMFs
and decrease the melting point
When first heating your sample what should the ramp rate be and starting temperature? - AnswersYou
should start at 35 degree and rap at 10 degrees (C) per minute
