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Chem 141 Lab Final

Terms in this set (42)

What is the purpose of chromatography?
to separate a mixture into its component parts, or pure substances.
What type of chromatography was used in our lab?
paper chromatography
What causes a solvent to flow up the chromatography paper?
capillary action
Explain why samples can often be separated into their components by chromatography.
Each component has a different solubility relative to the solvent chosen. Therefore, some substances are more readily dissolved and will move farther up the chromatography paper than others.
The solvent moves 3 cm in 10 minutes. Why should't the experiment be stopped at that time instead of waiting 75 minutes for the solvent to move 10 cm?
The substances may not be fully separated yet and that could mess up the Rf calculations. If given more time, the mixture could fully separate into each component part.
For experiment 3 (fractional crystallization), which component of the mixture is insoluble in water?
silicon carbide
In experiment 3 (fractional crystallization), how is most of the water removed from the mixture that remains after filtration?
boiling and a heat lamp
In experiment 3 (fractional crystallization), what caused the KNO3 to crystallize out of the solution?
cooling the solution to 0 degrees celcius
What is the catalyst used in experiment 4 (properties of oxygen)?
Cu(NH3)4^2+
Who is credited with the discovery of oxygen?
Joseph Priestly
Oxygen gas is necessary in human respiration. What product is given off by the oxygen reaction?
carbon dioxide and water
What does it mean to galvanize steel?
to apply a protective zinc coating to it to prevent rusting
What physical property of oxygen is suggested by setting the bottles of oxygen upright on the lab bench in experiment 4 (properties of oxygen)?
O2 is more dense than air
Why is the first flask of oxygen gas collected in experiment 4 (properties of oxygen) not used?
it is impure
Esterification of a fat produces
a glycerol and 3 fatty acid molecules
What ions cause hard water?
Ca^2+ and Mg^2+
Define saponification.
the hydrolysis of an ester in the presence of a base; the process of making soap
Define esterification.
the formation of an ester from glycerol and a fatty acid
How does drain cleaner (NaOH) work to remove grease from the drain?
Sodium hydroxide reacts with the grease, which is made of fat, and turns it into soap, which can then be washed down the drain.
A compound that has water as part of its formula is called a
hydrate
When the copper chloride compound is heated in experiment 6 (determination of a chemical formula), its color changes from ________ to _________.
blue-green to tan-brown
Why is the crucible covered during the cooling process in experiment 6 (determination of a chemical formula)?
so that no water will condense and re-enter the sample
What name is given to Group 17 elements?
Halogens
What color are all halide ions in water?
colorless
When hexane is mixed with bromine water, two layers are formed. Which layer is on top?
hexane
Explain how the error effects the result: All of the liquid was not vaporized when the flask was removed from the water bath.
The mass of gas would be too large, and therefore the molar mass would be too large
Explain how the error effects the result: The flask was not dried before the final weighing with the condensed liquid.
The weight of condensed liquid would be too high and therefore the molar mass would be too high
Explain how the error effects the result: The foil cap was removed while the flask was cooling and replaced before weighing.
The gas could escape or become contaminated, making the molar mass too small
Explain how the error effects the result: The flask was left in the boiling water bath for 45 minutes after the liquid vaporized.
The mass would be too small and therefore the molar mass would be too small.
Name four common methods of chromatography.
column, thin-layer, paper, and vapor
a physical process used to accomplish the resolution of a mixture; separates a substance from an impurity
fractional crystallization
Saponification produces
1 glycerol and 3 soap molecules
a synthetic soap, has the same cleaning action but can resist the effects of hard water
detergent
when used in hard water, they form a precipitate (bathtub ring)
natural soap
anhydrous compound
no water is present
Name given to Group 2 elements
Alkaline Earth metals
properties of halogens
oxidizing agents, all have an odor, only slightly soluble in water and are much more soluble in HEX where they have distinct colors
properties of halide ions
exist in solution only in water, have no color or odor, not oxidizing agent, do not dissolve in HEX
a container with insulating walls, made so that essentially no heat is exchanged between the contents and the surroundings
calorimeter
amount of heat required to raise the temperature of one gram of substance by one degree celcius
specific heat
heat is given off by the reaction mixture
exothermic
heat is absorbed by the reaction mixture from the water
endothermic
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