Which is the correct reading to be considered while carrying out titration? State the reason for your answer. Readings :- 1) 19.82 ml 2) 19.70 ml 3) 19.62 ml
Answers
Answer:
this lab, you will determine the percent purity of two commercially available aspiring tablets using an
acid-base titration. In general, an acid and a base react to produce a salt and water by transferring a proton
(H+
):
HA (aq) + NaOH (aq) H2O (l) + NaA (aq) (1) acid base salt
The active ingredient in aspirin, and the chemical for which aspirin is the common name, is acetylsalicylic
acid. To determine the amount of aspirin (acetylsalicylic acid) in a sample, the precise volume and
concentration of the NaOH, and the overall reaction, must be known. The NaOH serves as a secondary
standard, because its concentration can change over time. To find the precise concentration of the NaOH,
it must be titrated against a primary standard, an acid that dissolves completely in water, has a high molar
mass, that remains pure upon standing, and is not hygroscopic (tending to attract water from the air).
Because sodium hydroxide is hygroscopic, it draws water from its surroundings. This mean one cannot
simply weigh out a sample of sodium hydroxide, dissolve it in water, and determine the number of moles
of sodium hydroxide present using the mass recorded, since any sample of sodium hydroxide is likely to
be a mixture of sodium hydroxide and water. Thus, the most common way to determine the concentration
of any sodium hydroxide solution is by titration. Determining the precise concentration of NaOH using a
primary standard is called standardization. You will first standardize your NaOH solution, and then use it
to analyze aspirin tablets for their aspirin content and purity.
An aspirin tablet may also include inactive ingredients that help produce a consistent product for
consumers. Think of the purpose these ingredients serve when considering whether your percent purity is
reasonable for a commercial aspirin tablet.
What is a titration?
A titration is a procedure for determining the concentration of a
solution (the analyte) by allowing a carefully measured volume of this
solution to react with another solution whose concentration is known
(the titrant). The point in the titration where enough of the titrant has
been added to react exactly with the analyte is called the equivalence
point, and occurs when moles of titrant equals moles of analyte
according to the balanced equation. For example, if a monoprotic acid
(the analyte) is titrated with a strong base like sodium hydroxide (the
titrant), the equivalence point occurs when
number of moles of OH = number of moles of HA. (2)
The equivalence point is often marked by an indicator, a substance
that changes color at (or very near) the equivalence point. 1
There are many types of titrations. In this lab you will be performing
an acid base titration.