Posted by Donna Munir on November 05, 2000 at 17:13:28:
In Reply to: Need Help for Chemistry Report posted by Susheendran Perumal on October 24, 1996 at 08:29:03:
I am taking science prerequisite courses
for admittance into Chiropractic College.I just
don't get chemistry and unfortunately I have a
professor who is not great at explaining it
so I can get it.I haven't seen Chemistry in over 20
years.I am working on a "Volumetric Analysis"
Chemistry lab report and I need a "Conclusion".
We performed a chemical analysis of titration.
Here is the procedure:The titrating solution must
be of known concentration and contain only a
single chemically active reagent.Such a solution
is known as a standard solution.
To prepare a standard solution, a solution of
approx. the desired concentration is prepared and
then used to titrate an accurately weighed
quantity of a compund of known purity.
The compound of known purity used in this manner is
calle a primary standard. In this lab, sodium
hydroxide will be standardized against potassium
To determine % purity of KHP in an unknown sample.
Discussion on Theory:
Titration is an important technique for chemical analysis.An exact quantity of acid in an unknown mixture may be determined by measuring the quantity of a base needed to neutralize the acid.To find the exact amount of basic solution needed, a base of known concentration is added from a measuring buret until an indicator signifies the endpoint has been reached. An indicator is usually a weak organic acid or base that changes color at a certain PH range.
The titrating solution must be of known concentration and contain only a single chemically active reagent. Such a solution is known as a standard solution. To prepare a standard solution, a solution of approximately the desired concentration is prepared and then used to titrate an accurately weighed quantity of a compound of known purity.
The compound of known purity used in this manner is called a primary standard.In this lab, sodium hydroxide will be standardized against potassium hydrogen phthalate (HHC8H4O4).
We placed about 2.0 grams of sodium hydroxide pellets in a clean 500 ml volumetric flask.We then filled about half full with distilled water and swirled until the hydroxide pellets dissolved.Then we filled to the mark with distilled water and mixed well. The solution was ready to be standardized.
We obtained a 50 ml buret and buret clamp.We carefully cleaned the buret with soap and water and then we rinsed several times with water.Then we rinsed the buret twice with about 10 ml of the solution to be standardized and allowed to drain completely.We filled the buret with sodium hydroxide solution and drained to slightly below the zero mark.We made sure to check that the tip was completely full and free from air bubbles.
We obtained about 0.6 grams of potassium hydrogen phythalate accurately weighed and recorded. We placed it in a 125 ml flask and dissolve in about 40 ml of distilled water. We placed the flask under the buret (we did not have to use a white sheet to place under the flask since our buret clamp’s base was white). We then added about three drops of phenolphthalein as an indicator. We placed the flask under the buret. We recorded the initial reading of the buret. We titrated by allowing the sodium hydroxide solution to flow slowly into the flask. We constantly mixed the flask by swirling gently. When the pink color first began to linger, the sodium hydroxide needed to be added slowly, ie. drop wise.Unfortunately, we had to do this experiment several times since we must have added the solution too fast, therefore not being able to get a accurate reading. We continued the titration until the pink color persisted longer. At the time, this was the endpoint. We recorded our final buret reading. We then repeated with 1 additional sample of potassium hydrogen phthalate.
Observation & Data:
Calculations & Results:
see attached sheet
Our experiment went well despite the fact that we had to repeat it a couple of times due to allowing the.....
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