Experiment 9: Volumetric Analysis Pre-Lab Guide and Questions

Experiment 9: Volumetric Analysis Pre-Lab Guide and Questions

Experiment 9: Volumetric Analysis determines an unknown solution’s concentration by measuring the precise volume of a standard reagent (titrant) required to react with it. Common techniques involve using a burette for the titrant, a pipette for the analyte, and an indicator like phenolphthalein to detect the endpoint.

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experiment 9: a volumetric analysis
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1. what is titrant for this experi-
ment ?
NaOH (base)
2. the titrant It will originally be
found in the
buret
3. The analyte for this titration is HCl (acid)
4. the analyte It will originally be
found in the
erlenmeyer flask
5. In a titration, 25.00 mL HCl re-
quired 36.15 mL of a 0.9971
M NaOH solution to reach the
endpoint.
The molar concentration of HCl
is _____ M?
Molarity of HCl = (mol of HCl) /
(L of HCl).
1) moles of NaOH = MV(l)= (0.9971 M NaOH)(0.03616 L HCl)
= 0.03606 mol/l
2) molar concentration= mol of HCl/ L HCL
(0.03606mol/L)/ 0.0250L= 1.442 mol HCl
6. What is the primary standard
used in this experiment? Define
a primary standard.
Primary Standard: accurate mass of a solid substance which is
measured, dissolved in water and then reacted. The primary
standard is PHP KHC₈H₄O₄
7. What is the secondary standard
used in this experiment. Define.
Secondary Standard: Once the molar concetration of the
titrant is measured, the remaining solution is standardized
and thus considered a secondary standard. The secondary
will be the sodium hydroxide solution.
8. Is the indicator generally added
to the titrant or analyte in a
titration.
The titrant is a standard solution of sodium hydroxide.
The indicator is phenolphtalein, and it is added to the acid,
or in this case, the analyte. This is because it is colorless in an
acid, but pink in basic solutions.
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9. Distinguish between a stochio-
metric point and an endpoint in
an acid-base titration.
Stoichiometric Point- when a reaction is complete because
the stoichiometric amounts of reactants have combined.
Endpoint- when the indicator changes colors due to the
change in pH. Indicators are selected so that the stoichiomet-
ric endpoint and the other endpoint coincide.
10. When rinsing a buret after
cleaning it with soap and water,
should the rinse be dispersed
through the tip or the opening
on the top?
In preparing the buret for titra-
tion, the final rinse is with the
NaOH titrant rather than the
deionized water. Why?
When rinsing a buret, the water and rinse should go through
the tip.
The reason you rinse with sodium hydroxide is because
whenever you clean, a small amount of water remains in the
buret and it must be cleansed before the experiment begins,
or it may alter the values-- especially since NaOH is very
hygroscopic.
11. Calculate the mass of the
KHCHO that reacts with 15 mL
of the 15 M NaOH solution.
1HCHO: 1 NaOH
15 mL--> .015 L
.015 L (.15M)= .00225 mol NaOH
.00225 NaOH x (1 mol KHCHO/1 mol NaOH)= .00225 KHCHO
.00225 HCHO x (204.23g/1 mol) =.4595 g.
12. Your Unknown Acid is HCl. The
point of the titration is to de-
termine it's unknown concen-
tration. How will you dispense
25.00 mL of the Unknown Acid
into your Erlenmeyer flask
By using a specific Unknown Acid Buret: A, B, or C.
13. What is the correct way to fill
your NaOH buret?
Pour about 100 mL of NaOH from the Storeroom Bottle into
a clean beaker. Add a funnel to the top of the buret. Carefully
pour in the NaOH using the beaker. Save the NaOH in the
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beaker to re-fill the buret for the next titration.
You can never return any unused NaOH to the Storeroom
Bottle due to contamination!
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