SOP #2: MAKE UP ASSIGNMENT
For those of you who received a grade below 100% on the second SOP assignment, you
have the option of writing this make up SOP. The SOP is due any time before the last
class of the term.
Grading of the SOP. The grade you obtain on this SOP will be the average of the grade
you receive on this SOP plus the grade you received on SOP#2. For example, if the grade
on your SOP #2 was 40%, and the grade on the make up SOP is 80%, then the final grade
you will receive for SOP#2 is 60%.
Total water hardness (mg/L as CaCO3) determined by titration.
The following needs to be formatted into a SOP. There is much non-essential information
that should not be in a SOP. There is also no materials and equipment list. You are
required to find all of the materials and equipment and create a materials and equipment
list. NOTE: You must prepare all of the solutions as part of this procedure. The
instructions themselves are not presented as steps. You must format all of the instructions
into steps. NOTE: There are two titrations: a titration for a standardized solution and a
titration for the unknown water sample. All of the information you require is present in
this document. Add the following to the References section: EPA Method 130.2. The
company logo is Snow Analytics. The SOP number is ANAL.932.00. The revision or
version is NEW ISSUE. The Distribution Copy is Master Copy. You will also require a
section at the end of the procedure for Calculations for the formulae involved in titrating.
This should come after the instructions and before the Supervisor validation section.
Products that are designed to dissolve in water must be formulated to work effectively
with local water conditions; therefore, determining water hardness is a procedure useful
for Research and Development of products, and for Quality Control testing.
In this procedure a solution of EDTA will be standardized by titration against a standard
solution made from calcium carbonate, CaCO3. The EDTA solution can then be used to
determine the hardness of an unknown water sample. Since both EDTA and Ca2+ are
colorless, it is necessary to use a special indicator to detect the end point of the titration.
The indicator most often used is called Eriochrome Black T, which forms a very stable
wine-red complex, MgIn–, with the magnesium ion. A tiny amount of this complex will
be present in the solution during the titration. As EDTA is added, it will complex free
Ca2+ and Mg2+ ions, leaving the MgIn– complex alone until essentially all of the calcium
and magnesium have been converted to chelates. At this point EDTA concentration will
increase sufficiently to displace Mg2+ from the indicator complex; the indicator reverts to
its uncombined form, which is sky blue, establishing the end point of the titration.
The titration is carried out at a pH of 10, in a NH3/NH4+ buffer, which keeps the EDTA
(H4Y) mainly in the form HY3–, where it complexes the Group 2 ions very well but does
not tend to react as readily with other cations such as Fe3+ that might be present as
impurities in the water.
Procedure
Buffer solution: Dissolve 1.179 g disodium EDTA (analytical reagent grade) and 780
mg MgSO47H2O in 50 mL distilled water. Add this solution to a 250 mL volumetric
flask containing 16.9 g NH Cl and 143 mL conc. NH OH with mixing and dilute to the
mark with distilled water. Store in a tightly stoppered plastic bottle. The buffer solution
is stable for approximately one month. Dispense with bulb-operated pipet. Discard
when 1 or 2 mL added to sample fails to produce a pH of 10.0 ± 0.1 at end point of
titration.
Indicator: Mix 0.5 g Eriochrome Black T with 4.5 g hydroxylamine hydrochloride.
Dissolve in 100 mL of 95% ethanol or isopropanol.
Standard EDTA titrant 0.02 N: Place 3.723 g analytical reagent grade disodium
ethylenediamine tetraacetate dihydrate, Na2H2C1OH12O8N22H2O in a 1 litre volumetric
flask and dilute to the mark with distilled water. Check with standard calcium solution
by titration. Store in polyethylene. Check periodically because of gradual deterioration.
Standard calcium solution 0.02 N: Place 1.000 g anhydrous calcium carbonate (primary
standard low in metals) in a 500 mL flask. Add, a little at a time, 1 + 1 HCl (5) until all of
the CaCO3 has dissolved. Add 200 mL distilled water. Boil for a few minutes to expel
CO2. Cool. Add a few drops of methyl red indicator (6) and adjust to intermediate
orange color by adding 1 + 1 HCl (5) as required. Quantitatively transfer to a 1 litre
volumetric flask and dilute to mark with distilled water
Hydrochloric acid solution, 1 + 1.
Methyl red indicator: Dissolve 0.10 g methyl red in distilled water in a 100 mL
volumetric flask and dilute to the mark.
Ammonium Hydroxide, 1 N: Dilute 70 mL of conc. NH4OH to 1 liter with distilled
water.
Standardization titration procedure:
Place 10.0 mL standard calcium solution in vessel containing about 50 mL distilled water.
Add 1 mL buffer solution. Add 1-2 drops indicator. Titrate slowly with continuous
stirring until the last reddish tinge disappears, adding last few drops at 3-5 second
intervals. At end point the colour is blue. Total titration duration should be 5 minutes
from the time of buffer addition.
Titration of water sample of unknown hardness:
Since the concentration of Ca2+ is probably lower than that in the standard calcium
solution you prepared, pipet 50 mL of the water sample for each titration. Sample should
require approximately 15 mL EDTA titrant and titration should be completed within 5
minutes of buffer addition. Place 25.0 mL sample in titration vessels, neutralize with 1 N
ammonium hydroxide and dilute to about 50 mL. Add 1 to 2 mL buffer solution. Add 1
to 2 drops indicator solution. Titrate slowly with continuous stirring with standard
EDTA titrant until last reddish tint disappears. The colour change is rather slow, so
titrate slowly near the end point. Solution is blue at end point.
The colour should match that of the standardized calcium solution. Refill the buret, read
it, and titrate the second sample, then the third.