choroid plexus papilloma 3.1.2 Standardization of Sodium Hydroxide Standard Solution

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3.1.1 Standardization of Hydrochloric Acid Standard Solution


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3.1.2 Standardization of Sodium Hydroxide Standard Solution

Reference:
Standard Solution of Sodium Hydroxide (936.16) Official Methods
of Analysis. 1990. Association of Official Analytical Chemists.
15th Edition.

Scope:
This method is applicable for the preparation and standardization
of standard sodium hydroxide solution.

Basic Principle:
A basic solution is titrated with a standardized acidic solution
to determine normality.

Equipment:
Buret, 50 mL, graduated to 0.1 mL Illuminated magnetic stirrer
Volumetric pipet, 40 mL, class A Analytical balance, sensitive to
0.1 mg Container of alkali resistant glass pH meter with glass
electrode (alternate to using phenolphthalein indicator)

Reagents:
Distilled water, carbon dioxide (CO2) free prepared either 1)
by boiling for 20 min and cooling with soda-lime protection or 2)
by bubbling air, freed from CO2 by passing through tower of soda
lime, through water for 12 hr. Sodium hydroxide solution, to 1
part reagent grade NaOH add 1 part distilled, carbon dioxide-free
water by weight. Acid potassium phthalate, NIST SRM for
Acidimetry 84, dry for 2 hr at 120oC and cool in desiccator.
Buffer solution, pH 8.6, 12.00 mL 0.2 N NaOH added to 50 mL 0.2M
boric acid/potassium chloride solution made as follows: Boric
acid-potassium chloride solution – dry boric acid (H3BO3) to
constant weight in desiccator over CaCl2. Dry potassium chloride
(KCl) 2 days in oven at 115 to 120oC. Dissolve 12.405 g H3BO3 and
14.912 g KCl in water and dilute to 1 L. Phenolphthalein
indicator, 1%, dissolve 1 g phenolphthalein in 100 mL 95%
ethanol.

Safety Precautions:

  • Alkalis can burn skin, eyes and respiratory tract
    severely. Wear heavy rubber gloves and face shield to
    protect against concentrated alkali; if spilled on skin
    wash with copius amounts of water. Use effective fume
    removal device to protect against alkali dusts or vapors.
    Always add sodium hydroxide pellets to water, not vice
    versa.

Procedure: Preparation

  • Add appropriate volume of NaOH solution (1 to 1) to
    CO2-free distilled water necessary to make 10 L of
    solution:

mLNaOH to be diluted to 10 LDesired Normality
0.015.4
0.0210.8
0.1054.0
0.20108.0
0.50270.0
1.0540.0

Standardize

  1. Accurately weigh enough dried acid potassium phthalate
    (ca. 0.4 g) to titrate about 40 mL of NaOH solution and
    transfer to 300 mL flask.
  2. Add 50 mL CO2-free water, stopper flask and swirl until
    sample dissolves.
  3. Titrate to pH 8.6 with solution being standardized,
    taking precautions to exclude CO2 and using as indicator
    either glass-electrode or phenolphthalein. If using
    indicator, add 3 drops phenolphthalein to a flask
    containing 50 mL of pH 8.6 buffer and stopper. This flask
    is used as the reference endpoint for a pH 8.6 titration.
  4. Determine volume NaOH required to produce endpoint of
    blank by matching color in another flask containing 3
    drops phenolphthalein and same volume (50 mL) CO2-free
    water.
  5. Subtract volume required to titrate blank from that used
    to titrate the potassium acid phthalate and calculate
    normality. Normality should be slightly high.
  6. Adjust to desired concentration, mix well, and recheck
    standardization.
  7. Record final standardization in logbook.

Calculations:

Normality = g KHC8H4O4 X 1000/mL NaOH X
204.229

Adjust to desired concentration by following formula: V1 =
V2 X N2 / N1

Where N2 and V2 represent normality and volume of stock solution
and V1 equals volume to which stock solution should be diluted to
obtain desired normality, N1.

 

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3.1.1 Standardization of Hydrochloric Acid Standard Solution


3.2 Nitrogen Determination by Kjeldahl (Block Digestion)
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Chemistry 104: Standardization of Acid and Base Solutions

Standardization is the process of determining the
exact concentration (molarity) of a solution. Titration is one type
of analytical procedure often used in standardization. In a titration,
an exact volume of one substance is reacted with a known amount of another
substance.

The point at which the reaction is complete in a titration
is referred to as the endpoint. A chemical substance known as an
indicator
is used to indicate (signal) the endpoint. The indicator used in this experiment
is phenolphthalein. Phenolphthalein, an organic compound, is colorless
in acidic solution and pink in basic solution.

This experiment involves two separate acid-base standardization
procedures. In the first standardization the molarity of a sodium hydroxide
solution (NaOH) will be determined by titrating a sample of potassium acid
phthalate (KHP; HKC8H4O4) with the NaOH.
In the second procedure the standardized NaOH will be used to determine
the molarity of a hydrochloric solution (HCl).

Example 1

A 0.128 g sample of KHP (HKC8H4O4)
required 28.54 mL of NaOH solution to reach a phenolphthalein endpoint.
Calculate the molarity of the NaOH.

HKC8H4O4 + NaOH —–>
NaKC8H4O4 + H2O

(0.128 g KHP)(1 mol / 204.23 g KHP ) = 6.267 x 10-4
mol KHP

(6.267 x 10-4 mol KHP)(1 mol NaOH / 1 mol KHP)
= 6.267 x 10-4 mol NaOH

6.267 x 10-4 mol NaOH / 0.02854 L NaOH = 0.0220
M NaOH

Example 2

A 20.00 mL sample of HCl was titrated with the NaOH solution
from Example1. To reach the endpoint required 23.72 mL of the NaOH. Calculate
the molarity of the HCl.

HCl + NaOH —–> NaCl + H2O

(0.02372 L NaOH)(0.0220 mol NaOH / 1 L NaOH) = 5.218 x
10-4 mol NaOH

(5.218 x 10-4 mol NaOH)(1 mol HCl / 1 mol NaOH)
= 5.218 x 10-4 mol HCl

5.218 x 10-4 mol HCl / 0.02000 L HCl = 0.0261
M HCl


Put on your CHEMICAL SPLASH-PROOF SAFETY GOGGLES!


Part I. Standardization of NaOH with KHP

1.    Clean a buret by rinsing with several
portions (about 10 mL) of tap water. (The buret is clean enough when water
droplets do not cling to the inner surface.) This rinse water can be poured
down the drain.

2.    Obtain about 150 mL of the NaOH solution
in a clean, dry 400 mL beaker. Cover with a watch glass.

3.    Rinse the buret with three portions
(about 5 mL) of the NaOH solution. Drain each NaOH rinse and discard into
the waste container located under the hood.

4.    Fill the buret with NaOH to slightly
above the zero mark and clamp the buret up vertically.

5.    Remove the air bubbles from the tip
of the buret by draining the NaOH into a small beaker. Read the NaOH level
to within + 0.02 mL and record this value in the initial base reading
on the data sheet. (It is not necessary to have the NaOH level at exactly
the 0.00 mL mark. Anywhere below 0.00 mL will suffice. What is important,
is to record this initial NaOH reading to two decimal places.)

6.    Weigh a clean 250 mL beaker to +
0.01 g. Add 0.6 to 0.7 g of KHP (potassium acid phthalate; HKC8H4O4).
Re-weigh the beaker and contents to + 0.01 g. Record the mass on
the data sheet.

7.    Dissolve all the KHP in water by
adding about 30 mL of distilled water to the beaker and stirring with a
glass rod. (If necessary, you can warm the solution to dissolve all the
solid acid.) Transfer this solution into a clean 250 mL Erlenmeyer flask.
Rinse the beaker twice with about 5 mL of distilled water to make sure
all of the acid has been transferred to the flask.

8.    Add 3 to 4 drops of phenolphthalein
indicator to the KHP solution in the Erlenmeyer flask.

9.    Place the flask containing the acid
solution and indicator under the buret. Add NaOH from the buret to the
flask with swirling until the color of the solution in the flask is a faint
pink. This faint pink color should last only 45 to 60 seconds. There should
be a one-drop difference between when the solution is colorless and when
it is pink. If too much base is added (that is, if you “over-shoot” the
endpoint), discard the solution and repeat the titration. A white piece
of paper placed under the flask will aid in the color detection.

10.    When the proper end point is reached,
read and record the final NaOH volume to within + 0.02 mL.

11.    Discard the contents of the Erlenmeyer
flask into the waste container located under the hood.

12.    Repeat the titration procedure a
second time by following steps 4 – 11.

13.    Calculate the molarity of the NaOH
from the two titrations. If the calculated base concentrations from the
first and second titration vary by more than 0.005 M, perform a third titration.

Part II. Standardization of HCl with NaOH

1.    Refill and zero the NaOH buret.
Read the NaOH level to within + 0.02 mL and record this value in
the initial base reading on the data sheet.

2.    Obtain a clean, but not necessarily
dry, 250 mL Erlenmeyer flask , and using the buret labeled “HCl” (located
at the back of the room), transfer approximately 25.00 mL of the HCl acid
solution into the flask. Read and record the initial and final acid buret
readings to + 0.02 mL. It is not necessary to deliver exactly 25.00
mL of HCl into the flask. What is important, is that the volume of HCl
delivered into the flask is known to two decimal places.

3.    Add 3 to 4 drops of phenolphthalein
indicator to the HCl solution in the Erlenmeyer flask.

4.    Place the flask containing the acid
solution and indicator under the buret and add NaOH from the buret to the
flask with swirling until a phenolphthalein endpoint is reached. There
should be a one-drop difference between when the solution is colorless
and when it is pink. If too much base is added (that is, if you “over-shoot”
the endpoint), discard the solution and repeat the titration.

5.    When the proper end point is reached,
read and record the final NaOH volume to within + 0.02 mL.

6.    Discard the contents of the Erlenmeyer
flask into the waste container located under the hood. Repeat the titration
procedure a second time by following steps 1 – 5.

7.    Calculate the molarity of the HCl
(MHCl) acid for each titration. If the calculated acid concentrations
from the first and second titrations vary by more than 0.005 M, perform
a third titration. Calculate an average acid molarity using the two closest
values.

8.    Before returning the buret
to the lab bench, please rinse it out with a couple of water rinses.

Chemistry 104: Standardization

Name________________________________________Hood No.______ Date_____________

Put on your CHEMICAL SPLASH-PROOF SAFETY GOGGLES!

Show all calculations on an attached second sheet.

Part I. Standardization of NaOH with KHP

 
Titration 1
Titration 2
Titration 3
wt. of beaker______________g______________g______________g
wt. of KHP & beaker______________g______________g______________g
wt. of KHP______________g______________g______________g
Initial NaOH buret reading______________mL______________mL______________mL
Final NaOH buret reading______________mL______________mL______________mL
mL NaOH______________mL______________mL______________mL
Molarity NaOH______________M______________M______________M

Average Molarity of NaOH _________________

 

Part II. Standardization of HCl with NaOH

 
Titration 1
Titration 2
Titration 3
Initial NaOH buret reading______________mL______________mL______________mL
Final NaOH buret reading______________mL______________mL______________mL
mL NaOH______________mL______________mL______________mL
Initial HCl buret reading______________mL______________mL______________mL
Final HCl buret reading______________mL______________mL______________mL
mL HCl______________mL______________mL______________mL
Molarity HCl______________M______________M______________M

Average Molarity of HCl _________________