UNIT 6 Assignment “Acid-Base TITRATIONS”
(Chap 4-pg 183-184 & Chap 16-pg 740 – 749)
6:1. TITRATION CURVES: pH changes during a titration. For (a)-(f) state (i) what is in the flask (ii) in the buretie acid or base; strong or weak and which indicator could be used ; pptl , MeO, or BTB.
13
In Flask ________________
(a)
g)
Shown is a titration curve where a strong
acid in a buret is being added to a strong base
in a flask. Superimpose the curve you would
expect if the base were more dilute
In Buret ________________
7
Indicator _______________
1
mL
13
13
pH
7
In Flask ________________
7
(b)
In Buret ________________
1
Indicator _______________
1
# mL
mL
13
7
13
Indicator _______________
pH
mL
7
In Flask ________________
(d)
7
In Buret ________________
1
Indicator _______________
1
mL
13
Shown is a titration curve where a weak
acid in a flask has a strong base added to it
from a buret. Superimpose the curve you
would expect if the base were more dilute
In Buret ________________
(c)
1
13
h)
In Flask ________________
# mL
i)
In Flask ________________
(e)
7
In Buret ________________
1
Indicator _______________
mL
Shown is a titration curve where a strong
acid in a flask has a weak base added to it
from a buret. Superimpose the curve you would
expect with a strong diprotic acid of same conc.
13
pH
7
13
In Flask ________________
(f)
7
In Buret ________________
1
Indicator _______________
1
# mL
mL
6.1. j) Sketch a titration curve depicting 10 mL of a 0.1 M tribasic base in the flask being titrated against 0.1 M HCl.
Indicate which indicator would be appropriate for this titration and how much acid would be used for the titration.
TITRATION PROBLEMS REVISITED: M*V*n (acid) = M*V*n (base) or mass / molar mass(n) = M*V *n
6:2. Attempt question # 3.120 , 3.123 , 3.124 & 3.134 on pg 146-147 , 4.82 on page 191 & 16.102 on pg 756
6:3.
40 g of NaOH pellets were dissolved in 2 L of water. 25 mL of the resulting sol'n was found to just neutralize 30 mL of sulfuric acid
sol'n. What is the molarity of the acid sol'n ?
6:4.
Calculate the molarity of a phosphoric acid sol'n, 10 mL of which requires 15.0 mL of a 0.20 M NaOH to reach an end-point.
6.5.
In order to standardize a nitric acid sol'n, 7.64 g of borax was dissolved in100 mL of water. 25 mL aliquots of this sol'n required an
average 20.13 mL of the nitric acid for neutralization. Calculate the molarity of the acid.
6.6.
Citric acid is a triprotic acid, H3Cit. 0.288 g of this acid were dissolved in water, and it was found that the sol'n req'd 45.0 mL of 0.1
M NaOH sol'n to reach an end-point with pptl. Calculate the molar mass of citric acid.
6.7.
0.60 g of a pure but unknown base (MOH ) was dissolved in water. This sol'n req'd 16.67 mL of 0.50 M phosphoric acid to be
neutralized. Identify this base.
6.8.
A certain toilet cleaner uses NaHSO4 as its active ingredient. In an analysis, 0.500 g of the cleaner was dissolved in 30.0 mL of
water and required 24.60 mL of 0.105 M NaOH for complete neutralization. What was the % by weight of NaHSO4 in the
cleaner ?
6:9.
* Back-Titration problem using mass/molar mass (n) + M*V*n = M*V*n
In an experiment to determine the molar mass of an insoluble base, M(OH)3 , 0.39 g of the base were dissolved in 40.0 mL of 0.25
M sulfuric acid. The resulting sol'n was back-titrated with 0.50 M sodium hydroxide sol'n; it was found that 10.2 mL was required.
Calculate the molar mass of the base and identify it..
Lab Questions: Hand in with your lab reports
L1:
28.7 mL of a 0.0204 M pyrophosphoric acid sol’n (H4P2O7) was titrated to an end-point with 40.30 mL of a 0.029 M NaOH sol’n.
How many of the acidic protons (H+) had been neutralized at this end-point ?
Sketch a titration curve to represent this titration. What indicator should have been used ?
L2:
A typical stomach can have 500 mL of a 0.62 M HCl sol’n in it (for whatever reason) so you swallow two - 10 g tablets containg
75% calcium carbonate to reduce the acidity (you have to belch to relieve the pressure)
a) Write the equation for the reaction that took place
b) What is the pH before you took the tablets and after
L3:
4.05 g of impure stock KOH are dissolved in 150 mL of distilled water. 15 mL samples of this base were titrated against 0.21 M
hydrochloric acid and the following data were collected and recorded
Rough titration
Titration # 1
Titration # 2
initial buret reading
4.3 mL
4.8 mL
0.4 mL
final buret reading
33.2 mL
33.2 mL
28.8 mL
Calculate the % purity of this impure KOH reagent
L4:
A tablet of the much advertised analgesic "Nopane" contains ASA as its active ingredient. 2 tablets, each weighing 3.0 g, are
dissolved in ethanol and titrated with 0.22 M Mn(OH)3 sol'n. 44.7 mL are req’d to reach an end-point. Calculate the % ASA in
Nopane
L5:
0.438 g of an unknown solid monoprotic salt of a triprotic acid was dissolved in about 52-55 mL of water. The salt dissolved easily
without heat being required. This sol’n was then titrated against 0.2145 M Ba(OH)2 until neutral and repeated for accuracy.The
following data were collected
Titration #1
Titration #2
initial buret reading
4.3 mL
14.8 mL
Identify this acidic salt.
final buret reading
11.7 mL
22.2 mL
L6:
4.34 g of an unknown solid dibasic base was dissolved in 100 mL. It was found that 6.3 mL of the resulting sol'n was required to
neutralize a 25 mL sample of 0.18 M HNO3 sol'n. Identify the base.
L7.
A new compound Louic acid is discovered at the St.Paul Laboratories Inc. It was known to be an oxy acid that contains one of the
halogens. A base solution was made by dissolving 4.65 g of Co(OH)2 in 500 mL of water.
A solution of the acid was made by dissolving 3.64 g of acid in 250 mL of water. SOME of this acidic solution (25 mL) was
titrated against the base ( Co(OH)2 ) producing the following results:
Rough titration
Titration # 1
Titration # 2
initial buret reading
0.10 mL base
20.10 mL
16.49 mL
final buret reading
20.10 mL
38.26 mL
34.56 mL
A) Calculate the concentration of the base solution you made.
B) Calculate the molar mass of the acid and identify it.
L8:
A saturated sol’n of magnesium hydroxide has 100 mL removed and titrated against 2 x10-3 M boric acid . The titration required
only 4 mL to reach neutral. Calculate the Ksp value for magnesium hydroxide
L9:
A saturated sol’n of cadmium(II) hydroxide has a pH of 9.3 @ 20 °C. Calculate the Ksp value for cadmium(II) hydroxide.
L10:
An impure sample of Ba(OH)2 with a mass of 0.60 g was added to 20 mL of a 0.12 M H3PO4 sol'n. The excess H3PO4 was
titrated with 7.5 mL of 0.28 M NaOH. What was the % of Ba(OH)2 in the original sample
L11:
A 1.35 g sample of a mixture of limestone, CaCO3 , and rock was pulverized and then treated with 50.0 mL of 0.20 M oxalic acid.
The mixture was warmed to expel the last traces of CO2 and the unreacted acid was then back-titrated with 0.05 M NaOH. The
volume of base required was 34.60 mL
a) Write the equations for the 2 reactions that occured.
b) What was the % by weight of CaCO3 in the original sample ?
L12:
Do question # 4.85 on page 191
L13:
An antacid, JackupH, consists of a suspension of Mg(OH)2 . 4.00 g of JackupH was dissolved in 30 mL of 0.5 M citric acid
(H3Cit) and then back-titrated against standard 0.06 M Ca(OH)2 sol'n. 5.2 mL were required . Calculate the % Mg(OH)2 in
JackupH.
L14:
0.68 g of a solid diprotic acid was dissolved in 30.0 mL of a 0.50 M NaOH sol'n. The resulting mixture was then back-titrated
against 0.20 M HCl; 25 mL were required. Calculate the molar mass of the acid. This acid is a solid salt of a triprotic acid, identify
this acidic salt.
Major Lab Assignment:
During the next "5" days you and your lab partner will standardize either acid or base solutions and complete the "6"
labs that follow. Each partner will hand in either set "A" or "B" including all the questions.
A) Determining the molarity of your acid sol'n using Borax as the primary standard
This is the method for standardizing your acid sol'n for subsequent use in your class experiments.
* Mass out 4.5 g of borax ( Na2B4O7·10H2O) and dissolve in 200 mL on a hot plate / stirrer then make it up to 250 mL, accurately.
*Titrate 25 mL samples of this sol'n with the HCl sol'n in the buret, using either bromthymol blue (BTB) or methyl orange (MeO).
Repeat until within 0.2 mL.. The eq'n for the rx is : Na2B4O7·10H2O + 2 HCl → 2 NaCl + 4 H3BO3 + 5 H2O
Calculate the molarity of the acid solution. Have your calculations ready for me to examine the next day
Molarity of ACID (bottle # ………..) = ……………….. M
B) Determining the molarity of your base sol'n using Oxalic acid as the primary standard
This is the method for standardizing your base sol'n for subsequent use in your class experiments.
Mass out between 2.5 and 3.0 g of oxalic acid (H2C2O4·2H2O ) and make it up to 500 mL in a volumetric flask.. Using
phenolphthalein, titrate 25 mL portions of the unknown NaOH sol'n against the acid sol'n from the buret.
The equation for the rx is:
H2C2O4·2H2O + 2 NaOH → Na2C2O4 + 4 H2O
Calculate the molarity of the base solution. Have your calculations ready for me to examine the next day
Molarity of BASE (bottle # ………..) = ……………….. M
Lab A-1: To find the % purity of "tech grade" potassium hydroxide.
* Make up stock impure KOH sol’n by dissolving 1.5 g in 250 mL. Titrate this basic sol'n against standard HCl
so you can calculate the actual concentration of the KOH then the actual mass of this active base in this product.
% purity = calculated mass / measured mass x 100
* you should discuss the concept of “% purity” and “tech grade” products that are sold.
Lab A-2. To find the % Purity of Anacin tablets ( a pain-killer containing acetylsalicylic acid-ASA)
* Find the mass of 1 tablet (use the good Mettler balance) and add it to 25 mL of ethanol (C2H5OH) in a flask ASA dissolves better in a non-polar solvent Grinding may be necessary to dissolve. Dilute to ~100 mL with distilled water.
Titrate the entire sample of this weak acid with std NaOH until neutral
* Repeat as necessary !
* Calculate the mass of ASA chemical in the original sample in mg and then the % ASA in the “ANACIN” tablet.
The formula for acetylsalycylic acid (aspirin) is HC9H7O4.
* Look on the label for the advertised mass of ASA in the tablet and calculate the theoretical % ASA in the
“ANACIN” tablet. Post discussion should include a comparison of the # of mg advertised & % purity
advertised along with a comparison of the % purity of the no-name brand.(your partner)
Hand this completed lab report in along with questions 1-4 !!!
Lab A-3: To find the molar mass and identify an unknown solid acid(2).
* Make up a sol’n of this unknown acid(2) by dissolving about 0.5 g in about 50 mL of water in an erlenmeyer
flask.
* Titrate the entire sample against standard NaOH (don't do a rough titration when using the entire sample)
* Repeat as necessary but do not use the same mass each time
* Calculate the molar mass of the unknown acid(2) (a separate calculation is required for each titration because the entire
sample of acid is used each time & you used a different mass)
* This acid is a solid monoprotic salt of the diprotic acid - phthalic acid. Identify this acidic salt & Calculate your
percent error
Lab A-4: To determine the Ksp value for potassium bitartrate (Titration technique) * see unit 4 labs
* Shake excess (1 tsp) potassium bitartrate (KHC4H4O6) with distilled water in a stoppered 250 mL erlenmeyer
flask. Fill to the neck and allow to stand at least 1 night before using.
* On lab day, carefully decant the sol'n into another flask and keep stoppered. Measure the pH of this decanted
sol’n. Now titrate 25 mL aliquots of the "clear" potassium bitartrate sol'n against standard NaOH (using pptl)
1–
to find # moles of acidic bitartrate ion and then [HC4H4O6 ]
* Calculate the Ksp value for potassium bitartrate a) using the titration data
1–
1–
b) use the pH value & the Ka value for HC4H4O6 (
) to find [HC4H4O6 ] then the Ksp value.
* Compare your 2 answers (a&b). Which do you think is more accurate? Why?
Hand this completed lab report in along with questions 5-9 !!!
Lab A-5: To find the molar mass of an insoluble carbonate(1) (XCO3 ) and attempt to "identify"it.
* Accurately mass out between 0.3 and 0.4 g of the unknown solid carbonate(1) and dissolve it in 50 mL of
standard HCl. Heat the flask gently for 1-3 minutes to drive off the CO2 that is produced. Wash the sides down
with a small amount of water and allow to cool.
* Back- titrate with standard NaOH from your buret to a neutral point. (Don't do a rough titration )
* Repeat as necessary but do not use the same mass each time!
* Now calculate the molar mass of the unknown carbonate(1) and attempt an identification(be practical) with %
error
* you should discuss the concept of a “back-titration”
Lab A-6: % of ammonia in a commercial household cleaners
* Ammonia gas is readily soluble in water forming ammonium hydroxide.
* titrate 5 mL aliquots of the ammonia cleaner with 20 mL of water against std HCl using bromcresol green
indicator. Repeat only once !
* Calculate the % ammonia →NH3 (by mass) in the commercial brand cleaner
Hand this completed lab report (A5 & A6) in along with questions 10 - 14 !!!
Lab B-1: To find the % purity of "Saniflush".
* Make up stock impure "Saniflush" sol’n by dissolving about 4.5 g in 250 mL
* Titrate this acidic sol'n against standard NaOH in the buret so you can calculate the true [ NaHSO4] in the
saniflush then the actual mass of this acid
% purity = calculated mass / measured mass x 100
* you should discuss the concept of “purity” in commercial products!
Lab B-2 To find the % Purity of a no-name brand of Aspirin (containing acetylsalicylic acid-ASA)
* Find the mass of 1 tablet (use the good Mettler balance) and add it to 25 mL of ethanol (C2H5OH) in a flask ASA dissolves better in a non-polar solvent Grinding may be necessary to dissolve. Dilute to ~100 mL with distilled water.
Titrate the entire sample of this weak acid with std NaOH until neutral
* Repeat as necessary !
* Calculate the mass of ASA chemical in the original sample in mg and then the % ASA in the “ASPIRIN” tablet.
The formula for acetylsalycylic acid (aspirin) is HC9H7O4.
* Look on the label for the advertised mass of ASA in the tablet and calculate the theoretical % ASA in the
“NO-NAME ASPIRIN” tablet. Post discussion should include a comparison of the # of mg advertised & %
purity advertised along with a comparison of the % purity of the no-name brand.(your partner)
Hand this completed lab report in along with questions 1-4 !!!
Lab B-3: To find the molar mass and identify an unknown solid acid(1).
* Make up a sol’n of this unknown acid(1) by dissolving about 0.5 g in about 50 mL of water in an erlenmeyer
flask.
* Titrate the entire sample against standard NaOH (don't do a rough titration when using the entire sample)
* Repeat as necessary but do not use the same mass each time
* Calculate the molar mass of the unknown acid(1) (a separate calculation is required for each titration because the entire
sample of acid is used each time & you used a different mass)
* Attempt an identification of acid #1 (HINT: Acid # 1 is a solid monoprotic salt of a diprotic acid )
* Calculate your percent error
Lab B-4: To determine the Ksp value for calcium hydroxide (Titration technique) ** see unit 4 labs
*
Shake excess AR calcium hydroxide (1 level tsp) with distilled water in a stoppered 250 mL erlenmeyer
flask.Fill to the neck and Allow to stand at least 2 nights before using.
* On lab day, carefully decant the sol'n into another flask and keep stoppered to prevent CO2 from reacting with
the Ca(OH)2. Measure the pH of this decanted sol’n. Now titrate aliquots of the "clear" calcium hydroxide
–
–
sol'n against standard HCl (using MeO) to find the # moles of OH in the sol’n & then [OH ]
* Calculate the Ksp value for calcium hydroxide a) using the pH
b) using the titration data.
* Compare your 2 answers (a&b). Which is more accurate? Why? How does your answer compare to the
accepted data sheet answer
NOTE: The original flask used must be rinsed with dilute HCl at the back sink after use.
Hand this completed lab report in along with questions 5-9 !!!
Lab B-5 To find the molar mass of an insoluble carbonate(2) (XCO3 ) and attempt to "identify"it.
* Accurately mass out between 0.3 and 0.4 g of the unknown solid carbonate(2) and dissolve it in 50 mL of
standard HCl. Heat the flask gently for 1-3 minutes to drive off the CO2 that is produced. Wash the sides
down with a small amount of water and allow to cool.
* Back- titrate with standard NaOH from your buret to a neutral point. (Don't do a rough titration )
* Repeat as necessary but do not use the same mass each time!
* Now calculate the molar mass of the unknown carbonate(2) and attempt an identification(be practical) with %
error
Lab B-6 : % of ammonia in a no-name household cleaners
* Ammonia gas is readily soluble in water forming ammonium hydroxide.
* titrate 5 mL aliquots of the ammonia cleaner with 20 mL of water against std HCl using bromcresol green
indicator. Repeat only once !
* Calculate the % ammonia →NH3 (by mass) in the commercial brand cleaner
Hand this completed lab report (B5 & B6) in along with questions 10 - 14 !!