EXPERIMENT#4
Conductimetric Titration and Gravimetric
Determination of a precipitate
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Neutralization and Conductivity
• The conductivity of a neutralized acid-base
mixture is dependent on the salt produced!
• If the salt produced is a soluble salt, then the
neutralized acid-base mixture will be a good
conductor of electricity. Soluble salts
produce lots of free moving ions in water!
• If the salt produced is an insoluble salt, then
the neutralized acid-base mixture will be a
poor conductor of electricity. Insoluble salts
produce very few free moving ions in water!
2
Neutralization and Conductivity
Acid + Base → Water + Salt
Lots of free moving ions in the water!
H1+
Cl1H1+
Cl1-
H1+
H1+
Cl1-
Cl1-
Cl1- OH1H1+
HOH
HOH
1+
H1+
OH1- Na
Na1+ Cl1- 1+ Cl1H
HOH1OH1OH Na1+
HOH
H1+ Na1+
Cl1-
OH1Na1+
OH1Na1+
OH1-
OH1Na1+
Na1+
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Neutralization and Conductivity
Acid + Base → Water + Salt
Very few free moving ions in the water!
1-
SO42- 1+
H
H1+
21+
SO4
H
H1+
H1+
H1+ SO4
2-
SO42- OH
H1+
HOH
HOH
2+
H1+
1- Ba
OH
H1+
SO42HOH
1OH HOH
H1+
OH1OH1- Ba2+ 1- HOH
HOH
OH
H1+
2+
1+
H Ba
SO4 42BaSO4 BaSO
OH1Ba2+
OH1-
Ba2+
OH1-
OH1-
OH1-
OH1Ba2+
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Neutralization and Conductivity
4) In general, potassium hydroxide is a
______________
conductor of electricity.
good
Write the equation for the neutralization of
potassium hydroxide with hydrochloric acid.
1 KOH(aq) + 1 HCl(aq) →
__________________________
1 K Cl(aq) + 1 HOH(l)
______________________
Compared with potassium hydroxide, how
well does the resulting mixture of the neutralization of potassium hydroxide with Hydrochloric acid conduct electricity and why?
The
resulting mixture conducts as well
___________________________________
because KCl is soluble in water.
___________________________________
5
Neutralization and Conductivity
good
1) In general, sulfuric acid is a ____________
conductor of electricity.
Write the equation for the neutralization of
sulfuric acid with barium hydroxide.
1
H2SO4(aq) + 1 Ba(OH)2(aq) →
__________________________
1 Ba SO4(s) + 2 HOH(l)
______________________
Compared with sulfuric acid, how well does
the resulting mixture of the neutralization of
sulfuric acid with barium hydroxide conduct
electricity and why?
The
resulting mixture conducts less well
___________________________________
___________________________________
because
BaSO4 is insoluble in water.
6
Gravimetric Analysis
• Gravimetric Analysis – one of the most accurate
and precise methods of macro-quantitative
analysis.
• Analyte selectively converted to an insoluble
form.
• Measurement of mass of material
• Correlate with chemical composition
• Why?
• Simple
• Often required for high precision
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Gravimetric Analysis
• Precipitation Techniques
– Add precipitating reagent to sample solution
– Reacts with analyte to form insoluble material
– Precipitate has known composition or can be converted
to known composition
• Precipitate handling involves
– Quantitative collection (no losses)
– Isolation of pure product
• Measure mass of precipitate
• Calculation of original analyte content
(concentration)
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Gravimetric Analysis
• Desirable properties of analytical precipitates:
–
–
–
–
Readily filtered and purified
Low solubility, preventing losses during filtration and washing
Stable final form (unreactive)
Known composition after drying or ignition
• What steps are needed?
1. Preparation of the solution
2. Precipitation
3. Digestion
4. Filtration
5. Washing
6. Drying or igniting
7. Samples dried, triplicate portions weighed
8. Weighing
9. Calculation
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EXPERIMENT#9
Conductimetric Titration and Gravimetric analysis for Ba(OH)2
• The chemical reaction:
Ba(OH)2(aq) + H2SO4(aq)  BaSO4(s)+ H2O(l)
• Equipment:
H2SO4
•
•
•
•
•
•
•
•
•
•
Conductivity probe
Drop counter
Drop counter
250 mL Beaker
50 mL Graduated Cylinder
10 mL pipet
Magnetic stirrer and stirring bar
Ba(OH)2
Filter paper
Filter Funnel
Micro-balance
Drying Oven
Magnetic stirrer
Conductivity probe
Stirring bar
• Chemicals
• 0.1 M sulfuric acid, H2SO4, solution
• Barium Hydroxide, Ba(OH)2, solution Ba(OH)2
• Distilled Water
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Conductimetric Titration of Ba(OH)2 by H2SO4
• The chemical reaction:
Ba(OH)2(aq) + H2SO4(aq)  BaSO4(s)+ H2O(l)
• At the equivalence:
𝐞𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐜𝐞
𝐧𝐁𝐚(𝐎𝐇)𝟐 = 𝐧𝐇𝟐 𝐒𝐎𝟒
equivalence
MBa(OH)2 × VBa(OH)2 = MH2SO4 × VH2SO4
𝐞𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐜𝐞
𝐌𝐁𝐚(𝐎𝐇)𝟐 =
𝐌𝐇𝟐 𝐒𝐎𝟒 × 𝐕𝐇𝟐 𝐒𝐎𝟒
𝐕𝐁𝐚(𝐎𝐇)𝟐
• Use the conductimetric curve to
𝐞𝐪𝐮𝐢𝐯𝐚𝐥𝐞𝐧𝐜𝐞
determine 𝐕𝐇𝟐 𝐒𝐎𝟒
: Intersection
between the two slopes
• Calculate 𝐌𝐁𝐚(𝐎𝐇)𝟐
Volume H2SO4 (mL)
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Gravimetric Analysis of Ba(OH)2
Ba(OH)2(aq) + H2SO4(aq)  BaSO4(s)+ 2 H2O(l)
•
•
•
•
•
Heat the mixture
Filtration of white the precipitate
Dry the precipitate
Weigh precipitate
Calculate 𝐌𝐁𝐚(𝐎𝐇)𝟐
• 𝐧𝐁𝐚𝐒𝐎𝟒 =
𝐦𝐁𝐚𝐒𝐎𝟒
𝐌𝐌𝐁𝐚𝐒𝐎𝟒
• Based on the stoichiometry of the reaction:
𝐧𝐁𝐚𝐒𝐎𝟒 = 𝐧𝐁𝐚(𝐎𝐇)𝟐 = 𝐌𝐁𝐚(𝐎𝐇)𝟐 × 𝐕𝐁𝐚(𝐎𝐇)𝟐
𝐌𝐁𝐚(𝐎𝐇)𝟐
𝐦𝐁𝐚𝐒𝐎𝟒
=
𝐌𝐌𝐁𝐚𝐒𝐎𝟒 × 𝐕𝐁𝐚(𝐎𝐇)𝟐
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