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Pre-Lab Section Case Solution & Answer

Pre-Lab Section Case Study Solution

Objective

The objective of this experiment is to measure out a sample of hydrated aluminum sulfate and dissolve it in a warm acidified aqueous solution. After this solution is mixed with an already prepared solution of barium chloride, the method of filtration will be used to collect the precipitate formed. The precipitate will be allowed to sit for a week in order to dry and the actual yield will be determined after the drying completes.

Reaction and Explanation of the Experiment

In a chemical reaction, the amount of each reactant is equally as important as what the reactants are. You will often find that it is rare that all the elements in a reaction arrive to the reaction in the perfect quantities. In a reaction with only two reactants, for example, one reactant will be present in excess, while the other will be used in its entirety throughout the reaction.

This reactant is the one considered to be the limiting reagent. This means that the reaction can only continue so long as there is more of this reactant to use. A common example to relate this too is the wheels on a car. Assume all cars produced on a line need four wheels. If you have 6 bodies and only 20 wheels, then you can only make 5 cars, leaving 1 body as excess. This means that the wheels in this example are the limiting reagent.

Just because the wheels are the limiting reagent in this specific reaction, doesn’t mean that they will always be the limiting reagent. For example, if the line only has 6 bodies, but 50 wheels, you can only make 6 cars. This means that, in this specific example, the bodies are the limiting reagent and the wheels are in excess.

The balanced chemical reaction is as follows:

Al2(SO4)3(aq) + 3BaCl2(aq)  3BaSO4(s) ¯ + 2AlCl3(aq)

 

In this experiment, we will be using the following materials to identify the limiting reagent for the given reaction.

 

Equipment Purpose Usage
50mL Beaker

 

 

 

 

 

 

 

 

Where the reaction will take place.

Will be subject to heating.

Carefully remove from hot plate and use appropriate hand protection to do so.
Graduated Cylinder

 

Used to transfer and measure aqueous barium chloride. Properly measure volume by measuring by the bottom of the meniscus. Take care when placing liquid inside of cylinder.
Eye Dropper Used to transfer liquids. Avoid splash-back by pressing bulb while tip is submerged in liquid. Use with caution when measuring with intended precision.
Funnel with Filter Paper

 

 

Used to filter final mixture. Make sure to fold the filter properly

and when pouring mixture, take care not to overflow and lose mixture.

 

Stirring Rod

 

 

Used admixture.        Take care to only stir when procedure calls for it and minimize the amount of solution that remains on the stirring rod to avoid cross-

contamination.

Hot Plate

 

Used admixture.      Take great care to handle hot items

appropriately. Only set the hot plate to a setting between 4 and 6.

 

Chemicals in Use

Compounds Melting Point Boiling Point Density

g/cm3

Safety
Hydrated aluminum sulfate 86.5ºC  

 

1.62

Can be dangerous when in contact with skin
anhydrous aluminum sulfate

(3)

770ºC 2.672 harmful if swallowed or inhaled
anhydrous barium chloride (4) 962ºC 3.865 highly toxic; handle with care

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