Transcript Slide 1

‫بنام خدا‬
‫عباس بهرامی‬
‫عضو هیات علمی گروه بهداشت حرفه ای‬
‫دانشکده بهداشت‬
‫دانشگاه علوم پزشکی کاشان‬
‫‪[email protected]‬‬
‫انتظار میرود در پایان جلسه دانشجو بتواند ‪:‬‬
‫‪-1‬روش تیتریمتری را توضیح دهد‪.‬‬‫‪ -2‬انواع تیتریمتری را بیان کند‪.‬‬
Titration
Titration •
A procedure in which one substance (titrant) is –
carefully added to another (analyte) until complete
reaction has occurred.
The quantity of titrant required for complete reaction tells how •
much analyte is present.
Volumetric Analysis •
A technique in which the volume of material needed –
to react with the analyte is measured
Titration Vocabulary
Titrant •
The substance added to the analyte in a titration –
(reagent solution)
Analyte •
The substance being analyzed –
Equivalence point •
The point in a titration at which the quantity of titrant is –
exactly sufficient for stoichiometric reaction with the
analyte.
Titration Vocabulary
End point •
The point in a titration at which there is a sudden –
change in a physical property, such as indicator color,
pH, conductivity, or absorbance. Used as a measure
of the equivalence point.
Indicator •
A compound having a physical property (usually –
color) that changes abruptly near the equivalence
point of a chemical reaction.
Titration Vocabulary
Titration error •
The difference between the observed end point and –
the true equivalence point in a titration
Blank Titration •
One in which a solution containing all reagents except –
analyte is titrated. The volume of titrant needed in the
blank titration should be subtracted from the volume
needed to titrate unknown.
Titration Vocabulary
Primary Standard •
A reagent that is pure enough and stable enough to –
be used directly after weighing. Then entire mass is
considered to be pure reagent.
Standardization •
The process whereby the concentration of a reagent –
is determined by reaction with a known quantity of a
second reagent.
Titration Vocabulary
Standard Solution •
A solution whose composition is known by virtue of –
the way it was made from a reagent of known purity
or by virtue of its reaction with a known quantity of a
standard reagent.
Direct Titration •
One in which the analyte is treated with titrant, and –
the volume of titrant required for complete reaction is
measured.
Titration Vocabulary
Back Titration •
One in which an excess of standard reagent is added –
to react with analyte. Then the excess reagent is
titrated with a second reagent or with a standard
solution of analyte.
Titration Calculations
Titration Calculations rely heavily on the •
ability to perform stoichiometric
calculations.
Examples •
NaOH + HCl
NaOH
HCl
Volume
used (mL)
Molarity (M)
NaOH + H2SO4
NaOH H2SO4
10
34.3
10
17.1
0.6
0.175
0.6
0.175
1. Neutralization
2. NaOH + HCl  H2O + NaCl
2NaOH + H2SO4  2H2O + Na2SO4
3. Twice as much HCl was required. Because it
takes twice as much HCl (one H) as H2SO4
(two Hs) to neutralize the same amount of
NaOH
4. H2SO4(aq) + 2NaOH(aq)  2H2O + Na2SO4(aq)
# L H2SO4=
0.010 L NaOHx0.60 mol NaOH 1 mol H2SO4
L H2SO4
x
x
L NaOH 2 mol NaOH 0.175 mol H2SO
= 0.01714 L = 17.1 mL
5. #H x MA x VA = #OH x MB x VB
Titration problems
What volume of 0.10 mol/L NaOH is needed
to neutralize 25.0 mL of 0.15 mol/L H3PO4?
25.0 mL of HCl(aq) was neutralized by 40.0
mL of 0.10 mol/L Ca(OH)2 solution. What
was the concentration of HCl?
A truck carrying sulfuric acid is in an accident.
A laboratory analyzes a sample of the spilled
acid and finds that 20 mL of acid is neutralized by 60 mL of 4.0 mol/L NaOH solution.
What is the concentration of the acid?
What volume of 1.50 mol/L H2S will neutralize a solution containing 32.0 g NaOH?
.1
.2
.3
.4
Titration problems
1. (3)(0.15 M)(0.0250 L) = (1)(0.10 M)(VB)
VB= (3)(0.15 M)(0.0250 L) / (1)(0.10 M) = 0.11 L
2. (1)(MA)(0.0250 L) = (2)(0.10 M)(0.040 L)
MA= (2)(0.10 M)(0.040 L) / (1)(0.0250 L) = 0.32 M
3. Sulfuric acid = H2SO4
(2)(MA)(0.020 L) = (1)(4.0 mol/L)(0.060 L)
MA = (1)(4.0 M)(0.060 L) / (2)(0.020 L) = 6.0
M
4. mol NaOH = 32.0 g x 1 mol/40.00 g = 0.800
(2)(1.50 mol/L)(VA) = (1)(0.800 mol)
V = (1)(0.800 mol) / (2)(1.50 mol/L) = 0.267 L
Titration summary
For titrations we use the formula: •
#H x MA x VA = #OH x MB x VB
Or NA x VA =
NB x VB
NA is the combination of MA and #H •
N is also known as normality •
You can think of it a neutralizing power •
We will stick with the first equation, you do not •
have to know N or what it stands for
This is a simplification of stoichiometry. We •
could get the same answer by working with
moles (n = MV) and by using the balanced
chemical equation
Titration showdown
Titration competition (best •
with a burette): find the
concentration of an H2SO4
solution – it could be
anywhere from 0-18 mol/L
You will use the NaOH that you prepared two •
weeks ago and your vast knowledge of titration
procedures and formulas.
The wining team, is the team closest to the •
correct value.
The only restriction is : don’t put base in the •
burette – only acid.
Sources of error
NaOH was not exactly 0.10 mol/L
Calculation errors (e.g. converting mL to L)
Not rinsing and drying the beaker for the acid
Over titrating (ideally, 2 titrations should be
done – one to get a rough estimate, and one to
get the exact value).
Acid or base left on the side of the flask or on
the tip of the burette (for greater precision,
water is used to rinse the tip of the burette).
Errors reading volumes.
Using pipette (10 mL is measured from 0 mL to
10 mL, not from 10 mL to empty)
Using 10 mL of base vs. 25-50 mL
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For more lessons, visit
www.chalkbored.com
ALKALINE DUSTS 7401
NaOH, KOH, LiOH, MW : 40.00
(NaOH); CAS: 1310-73-2 RTECS:
WB490000
(NaOH)
and basic salts 56.11 (KOH) 1310-58-3
TT2100000 (KOH)
23.95 (LiOH) 1310-65-2 OJ6307070
(LiOH)
METHOD: 7401, Issue 2
EVALUATION: FULL Issue 1: 15
February 1984
Issue 2: 15 August 1994
OSHA : 2 mg/m3 (NaOH)
NIOSH: C 2 mg/m3/15 min
(NaOH); Group I Pesticide
ACGIH: C 2 mg/m3 (NaOH)
PROPERTIES: basic,
hygroscopic, caustic solids and
aerosols; VP not significant
SYNONYMS: alkali; caustic soda; lye; sodium hydroxide;
potassium hydroxide
SAMPLING
SAMPLER: FILTER
(1-μm PTFE membrane)
FLOW RATE: 1 to 4 L/min
VOL-MIN: 70 L @ 2 mg/m3
-MAX: 1000 L
SHIPMENT: routine
SAMPLE
STABILITY: at least 7 days @ 25 °C [1,2]
BLANKS: 2 to 10 field blanks per set
PTFE Polytetrafluoroethylene;
polyperfluoroethylene; tetrafluoroethene
homopolymer; Teflon.
MEASUREMENT
TECHNIQUE: ACID-BASE TITRATION
ANALYTE: OH- (alkalinity)
EXTRACTION: 5.00 mL 0.01 N HCl, 15 min under
nitrogen with stirring
TITRATION: 0.01 N NaOH under nitrogen, endpoint
by pH electrode
CALIBRATION: 0.01 N NaOH standardized with
0.01 N HCl
RANGE: 0.14 to 1.9 mg (as NaOH) per sample [1]
ESTIMATED LOD: 0.03 mg per sample (as NaOH) [1]
(7 x 10-4 moles of alkalinity)
PRECISION (S r): 0.033 @ 0.38 to 1.5 mg NaOH
per sample [1]
ACCURACY
RANGE STUDIED: 0.76 to 3.9 mg/m3 [1]
(360-L samples)
BIAS: 5.6%
OVERALL PRECISION (Sˆ rT): 0.062 [1]
ACCURACY: ± 16.2%
APPLICABILITY: The working range is
0.4 to 5.4 mg/m 3 for a 360-L air sample.
The method measures total alkalinity of
alkali
hydroxides, carbonates, borates, silicates,
phosphates, and other basic salts,
expressed as equivalents of NaOH.
INTERFERENCES: Carbon dioxide in the air
may react with alkali on the filter to produce
carbonates but does not interfere when
titrated. The carbonates will produce the
equivalent amount of strong alkali that was
consumed on the filter [1]. Acid a erosols
may neutralize the sample, if present, producing
a negative interference.
OTHER METHODS: This revises Methods S381
[2] and P&CAM 241 [3].
NIOSH Manual of Analytical Methods (NMAM),
Fourth Edition, 8/15/94
REAGENTS:
1. Sodium carbonate, primary standard grade.
2. Hydrochloric acid stock solution, 0.1 N.
Standardize with sodium carbonate primary
standard.
3. Dilute hydrochloric acid, 0.01 N. Dilute 10.0
mL 0.1 N stock HCl to 100 mL in a volumetric
flask with distilled water.
4. Water, distilled, CO 2-free. Boil and cool under
N2 or bubble nitrogen through distilled water
for 30 min. Store with an Ascarite trap.
5. Nitrogen, compressed.
6. Sodium hydroxide, 50% w/v.* Dissolve 50 g
NaOH in CO 2-free distilled water and dilute to
100 mL.
7. Stock sodium hydroxide, 0.1 N. Dilute 8 mL
50% NaOH to 1.0 L with CO 2-free distilled
water. Store under Ascarite or other CO 2absorbing trap.
8. Working sodium hydroxide solution, 0.01 N.
Dilute 10 mL stock (0.1 N NaOH) to 100 mL
with CO2-free distilled water.
9. Standard buffer solutions, pH 4 and 7.
* See Special Precautions
EQUIPMENT:
1. Sampler: 37-mm diameter PTFE membrane
filter (Millipore, Fluoropore or equivalent), 1.0μm pore size, supported by a cellulose backup
pad in a cassette filter holder.
2. Personal sampling pump, 1 to 4 L/min, with
flexible connecting tubing.
3. pH meter with pH electrode and recorder.
4. Titration vessel, 150 to 200 mL beaker, flask
or jar with cover containing openings for the
pH electrode and N 2 inlet and outlet.
5. Stirrer, magnetic, and stir bar.
6. Glass rod, ca. 5-mm diameter and 10 cm long
to hold filter under liquid surface in titration
vessel.
7. Pipets, 5- and 10-mL.
8. Volumetric flasks, 100-mL and 1-L.
9. Burets, 50-mL, readable to 0.1 mL.
10. Tweezers.
SPECIAL
SPECIAL PRECAUTIONS: NaOH
solutions are corrosive to tissue [4].
Handle with care.
1. Calibrate each personal sampling
pump with a representative sampler in
line.
2. Sample at an accurately known flow
rate between 1 and 4 L/min for a sample
size of 70 to 1000
L. Do not exceed a filter loading of ca. 2
mg total dust.
SAMPLE PREPARATION:
3. Transfer the sample filter to a titration
vessel with tweezers. Place the filter face
down in the
titration vessel.
4. Place the end of a glass rod in the center
of the filter to maintain the filter below the
liquid
surface during the analysis.
5. Cover the titration vessel, add 5.00 mL
0.01 N HCl, start the magnetic stirrer and N
2 purge (ca.
0.1 L/min).
6. Allow to stand 15 min (with stirring).
CALIBRATION AND QUALITY CONTROL:
7. Calibrate the pH meter with pH 4 and pH 7 buffer
solutions.
8. Standardize aliquots of the 0.1 N HCl stock
solution with sodium carbonate in triplicate [3].
a. Dry 3 to 5 g primary standard grade Na 2CO3 at
250 °C for 4 h. Cool in a desiccator.
b. Weigh ca. 2.5 g Na 2CO3 to the nearest mg.
Dissolve and dilute to exactly 1 L with CO 2-free
distilled water. The concentration is ca. 0.05 N
Na2CO3.
c. Place 5.00 mL 0.05 N Na2CO3 solution into a
titration vessel and titrate potentiometrically to
a pH of 5.
NIOSH Manu
d. Remove electrodes, rinse them into the
titration vessel, and bubble N 2 gas through
contents
of the titration vessel for 3 to 5 min to
remove dissolved CO 2.
e. Proceed with the titration to the inflection
point.
f. Calculate the normality of the stock HCl
solution