Chemistry

Could you please give me a discriptive answer and explain what each term means? I have a hard time understanding chemistry. Thanx

q1
In a reaction between aqueous solutions of calcium chloride and sodium carbonate, a precipitate is formed. The experimental procedure which can be used to separate the solid from the solution is

A. titration
B. filtration
C. gas collection
D crystalization

q2.
Which technical procedure is similiar to the natural process which forms salt seposits?

A. titration
B. filtration
C. crystalization
D. fractional distillation

q3.
To determine the concentration of salt in ground water, the salt can be separated from the solution by

A. fractional distilling
B. filtering the solution
C. evaporating the solvent
D. lowering the temperture of the solution


Could you please give me a discriptive answer and explain what each term means? I have a hard time understanding chemistry. Thanx

q1
In a reaction between aqueous solutions of calcium chloride and sodium carbonate, a precipitate is formed. The experimental procedure which can be used to separate the solid from the solution is

A. titration
B. filtration
C. gas collection
D crystalization

Titration is when you have a known standard (such as 0.20 M HCl) and you use that, usually with an indicator, to determine the concentration of unknown solution. Usually a buret is used to add the titrant.
Filtration is a method to separate a solid phase from a liquid phase. For example, in the above example, CaCO3 is the precipitate (the solid) and you want to separate it from the liquid. The usual set up is to fold a piece of filter paper into fourths, place the folder paper into a 60 degree funnel, and pour the liquid and solid through. Gravity is what runs the system. It often takes quite some time, especially if the filter paper is not very porous. I don't know if you have been introduced to Buchner funnels or not but they are frequently used in organic chemistry to separate solids and liquids. They are much much larger than the small glass 60 degree funnels (often as much as 3-4 inches in diameter). A piece of filter paper is placed in the funnel (it has fairly large holes in the bottom (1/16 or 1/8 inch), the funnel is inserted into a flask, and the flask is connected to a water aspiration system so that a vacuum is pulled on the flask. That pulls the solvent through, usually quite quickly.
Gas collection usually entails allowing gas from a generator to flow into an inverted bottle of water. The gas displaces the water. You may remember collecting oxygen this way, or hydrogen gas, in freshman chemistry.
Crystallization is a way of purifying products that are made in some chemical reactions. It involves taking the product, a solid, and dissolving it in the minimum amount of some solvent at an elevated atemperature. Then the solution is allowed to cool and the solid will recrystallize in purer form if the right solvent was chosen.


q2.
Which technical procedure is similiar to the natural process which forms salt seposits?

A. titration
B. filtration
C. crystalization
D. fractional distillation

I have defined A, B, and C above. D of this part, fractional distillation, is performed by placing a mixture of liquids to be separated in a flask that can be heated. There is a side arm on the top part of the neck of the flask and a condenser is connected to the side arm. Finally, a thermometer is placed in the top of the flask (both to seal it off AND to allow us to know the temperature of the vapors). In practice, the flask is heated, vapors rise to the top, go through the open side arm, are condensed back to a liquid in the condenser, then drip out the bottom into a flask, beaker, or other container. The thermometer tells us the temperature at which that first product distilled. The temperature will stay at that point until all of "substance A" is distilled, then the temperature will rise until the next component vaporizes and goes through the same process. The mixture of liquids in the boiling pot is separated in this fashion into its "fractions" which is why it is called fractional distillation.

q3.
To determine the concentration of salt in ground water, the salt can be separated from the solution by

A. fractional distilling
B. filtering the solution
C. evaporating the solvent
D. lowering the temperture of the solution

I have defined A and B above.
C. evaporatiing the solvent is simple. We have a solution consisting of a solute (often a solid) dissolved in a solvent (usually a liquid). We let the solvent evaporate (just like water evaporates from a spill on the floor if we don't mop it up) and the solid is left behind in crystals.

D. Solutes are USUALLY more soluble in a solvent at elevated temperatures; therefore, lowering the temperature will often cause a solute to crystallize. This process actually is just a part of what was described in crystallization above.
I haven't given you the answers to any of these but just answered your question by giving definitions. Repost if there is something you don't understand.

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