Download - Titrations P
Acid Base TitrationsAcid Base Titrations
Keith WarneKeith Warne
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Titration Calculations.Titration Calculations.
(COOH)(COOH)22.2H.2H22O O Unknown Unknown BaseBase (NaOH) (NaOH)OXALIC ACIDOXALIC ACID STANDARDSTANDARD SOLUTION SOLUTION
ccb b = ………….. mol.dm= ………….. mol.dm-3-3
(COOH)(COOH)22.2H.2H22O + 2NaOH --> NaO + 2NaOH --> Na22(COO)(COO)2 2 + 4H + 4H22OO
250 cm3
………..g
?
Concentration and Concentration and volume known volume known
accuratelyaccurately!!
nnvv
C =C =
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Standard SolutionA standard solution is one for which
the concentration is precisely known.
Since
c = ................/..................
= .................
Needed:• The number of moles of solute (from
...............)• The volume of solution.
These values must be accurately determined.
Mass is determined accurately using an electronic balance.
1.60gsolute
Volume is measured using a
Volumetric flask.• 250 cm3
• 100 cm3 • 200 cm3
250 cm3
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Weighing TechniqueProcedure - Weighing by difference.
1. .............. scales and clean the pan.
2. Weigh the weighing ....................
3. Add (................................) the required amount of salt. Take care not to drop any salt onto the pan.
4. Transfer the salt to a ................. beaker.
5. ................................ the weighing container.
6. ......................... the final mass of the container from the mass of salt and container to give the mass of salt transferred to the beaker.
Mass is determined accurately using an balance (electronic or triple beam).
• Possible accuracies of 0.1 - 0.0001g
2.45g
(COOH)2
Results: Mass salt + container: ………… Final Mass container: …………
Mass salt transferred:
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Making a standard solution. 1. Rinse a clean & dry 100 cm3 beaker
with a little distilled water.
2. Transfer the correctly weighed amount of salt to the beaker. ........................... .............................................................
3. Add distilled water to the salt and stir gently with a glass rod until all salt is dissolved. DO NOT REMOVE THE ROD FROM THE SOLUTION NOR ALLOW ANY DROPS OF SOLUTION
TO .........................................
4. Add ALL the solution to a volumetric flask via funnel. Ensure glass rod and beaker are thoroughly rinsed. (Include
...................................)
4. Add enough solvent to bring the level
........................................
………..g
solute
250 cm3
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Making a standard solution. 1. Use a dropper to bring the
level up to the mark.
2. The BOTTOM of the meniscus must .................. .......................... THE LINE of the flask.
3. The flask should then be ........................ at least ........ times to ensure thorough mixing.
The bottom of the meniscus must JUST touch the line!!! 250 cm3
Drag here
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Titration Proceedure.Titration Proceedure.
ACIDACID STANDARD STANDARD SOLUTIONSOLUTION
unknown BASEBASE
1. Rinse# the burette with distilled ................and then with small quantities of the ............................................solution.
2. Fill the burette with the standard ......................solution.
3. Take the ......................................reading. Does not have to be ..............
4. Rinse # a clean conical flask with .........................................
5. Rinse # a clean pipette with the .................................solution.
6. Pippette 25cm3 of the ...............................solution into the conical flask.
7. Add 3-5 drops of a suitable .......................to the conical flask.
8. Titrate the acid against the base until the FIRST ..................................................COLOUR CHANGE.
9. Note down the volume of acid and repeat this procedure with a fresh conical flask until ...................................RESULTS are obtained. ~0.1 cm3.
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Titration Calculations.Titration Calculations.
ACIDACID STANDARD SOLUTIONSTANDARD SOLUTION
a ACIDa ACID + + b BASEb BASE salt + water
AT THE END POINTAT THE END POINT
molesmoles ............ ............moles moles ........................
== ........................
unknown BASEBASE
......................
......................== ........
........
25cm3
= 0.025dm3
C(mol.dm-3)V (dm-3)
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CCaaVVaa
CCbbVVbb
==aabb
Conc of acid = ? x (trying to find)
Volume of acid –
burette = ......................
Molar ratio from ........................... reaction a = acid coefficient (2) b = base coef. (1)
(1)Na2 CO3 + 2 HCl 2NaCl + H2O + CO2
Conc of base= your
..................... soln. Worked out.
Vol. of base= ........................ (25cm3)
Solve for x
Titration Calculations
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Titration Calculations.
(COOH)2.2H2O • Unknown Base (NaOH)OXALIC ACIDOXALIC ACID STANDARDSTANDARD SOLUTION SOLUTION
ccb b = ………….. mol.dm= ………….. mol.dm-3-3
(COOH)(COOH)22.2H.2H22O + 2NaOH --> NaO + 2NaOH --> Na22(COO)(COO)2 2 + 4H + 4H22OO
250 cm3
………..g
?
Concentration and Concentration and volume known volume known
accuratelyaccurately!!
nnvv
C =C = CCaaVVaa
CCbbVVbb
== aabb
Titration Calculations.Titration Calculations.
(COO)(COO)22.2H.2H22O O
MMrr = (2(12+32+1)+2(18)= 126 = (2(12+32+1)+2(18)= 126
6.4g in 1l (1dm6.4g in 1l (1dm33))
Moles(ACID) = m/MMoles(ACID) = m/Mrr
= 6.4/(126) = 6.4/(126)
= 0.05mol/1dm= 0.05mol/1dm33
Concentration (ACID) = 0.05 MConcentration (ACID) = 0.05 M
Unknown Base (NaOH)Unknown Base (NaOH)OXALIC ACID OXALIC ACID STANDARD SOLUTIONSTANDARD SOLUTION
AT THE END POINTAT THE END POINT
(1)(1)(COO)(COO)22.2H.2H22O + O + 22NaOH --> NaNaOH --> Na22(COO)(COO)2 2 + 4H + 4H22OO
One mole of acid One mole of acid reacts withreacts with 2 moles of base. 2 moles of base..: n(acid) .: n(acid) : : n(base) n(base) 11 : : 2 2
CCaaVVaa
CCbbVVbb
==1122
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Titration ExampleTitration Example If 22.3 cmIf 22.3 cm-3 -3 of a standard hydrochloric acid solution (0.15 of a standard hydrochloric acid solution (0.15
M) was required to reach end point with 25 cmM) was required to reach end point with 25 cm-3-3 of an of an unknown sodium carbonate solution, what is the unknown sodium carbonate solution, what is the concentration of the sodium carbonate solution?concentration of the sodium carbonate solution?
2HCl + Na2HCl + Na22COCO3 3 2NaCl + CO 2NaCl + CO2 2 + H+ H22OO
CCaaVVaa
CCbbVVbb
== 1122
(0.15) (0.0223)(0.15) (0.0223)CCbb (0.025) (0.025)
1122
==
CCbb = = = = 0.268 M0.268 M2*(0.15) (0.0223)2*(0.15) (0.0223)1* (0.025)1* (0.025)
NameName
of indicator of indicator
Colour Colour acidacid
Colour Colour basebase
pH pH rangerange
Methyl OrangeMethyl Orange RedRed YellowYellow 3 - 43 - 4
Bromothymol BlueBromothymol Blue YellowYellow BlueBlue 6 - 86 - 8
PhenolphthaleinPhenolphthalein ClearClear RedRed 8 - 108 - 10
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pH
0
....
Amount of ............ added
...
The end The end point has a point has a pH lower pH lower than 7 than 7 because because the SALT the SALT of a of a STRONG STRONG acid and a acid and a weak base weak base is is ACIDIC!!ACIDIC!!
WEAK BASE
STRONG ACID
END POINT
STRONG ACID WEAK BASESTRONG ACID WEAK BASE
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STRONG BASE WEAK ACID
Strong acid/strong baseStrong acid/strong base ....................................................................
Strong acid/weak baseStrong acid/weak base ....................................................................
Weak acid/strong baseWeak acid/strong base ....................................................................
pH
0
14
Moles of base added
7
Strong acid
Weak acid
Weak base
Strong base
Blue
Bromothymol blue
Yellow
Methyl OrangeRed
Pink
PhenolphthalienColourless
STRONG BASE STRONG ACID
WEAK BASE STRONG ACID
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Keith WarneKeith Warne