N17,N19,N20,N21 ,N22
ACIDS AND BASES
STANDARDIZATION TITRATION
N48
E
LAB N2
]
Pr.rrpose
Part
A: To standardize a hydrochloric acid solution by titration with the primary startdard sodium carbonate.
Part
B:
To use the standardized hydrochloric acid solution from Part A to determine the concentration of house-
hold ammonia.
Prelab lnlormation
The reagents most often used as acid and base of standard concentration in laboratories are HCl16q; and
ItaOHlaq).They are both quite stable, inexpensive, and easy to prepare. However, neither is a primary standard
(i.e., dnei'from which a solution of known concentration can be prepared to high accuracy). HCI is gaseous in a
pure state and commercially sold solutions vary in concentration. NaOH is a dellguescenf solid which means it
will attract and absorb moisture from the air until it becomes a solution. The absorption of water by NaOH is so
rapid that the mass of a sample of pure NaOH cannot be determined accurately.
ln this lab the concentration of solutions ol HCl16q) and NH, (aq1 witt be determined accurately by first titrating
a primary standard solution ol NarCO, with the HCI(aq) and then titrating the NH3(aq) with the standardized
HCtlaq).
Na, CO, is a primary standard because the solid can be obtained in a very pure form and overnight heating will
expel any absorbed water vapor. The pure solid NarCO, can then be used to prepare a solution ol known concen-
tration since the mass of a sample of the solid can be measured very accurately.
Materials
Part A:
Part B:
stock supply of HCIlaq)
stock bottles of Na, COs (s)
stock bottles of HCI(aq)
stock bottles of N H, (aq)
50 mL buret
wash bottle of distilled water
bu ret b rush
liquid soap
bu ret stand
50 mL buret
ret b rush
liquid soap
bu ret stand
bu
buret clamp
small short-stemmed f unnel
buret clamp
small short-stemmed funnel
ceRtig ram balance
2
2
U{
400 mL waste beaker
100 mL beaker
250 mL beaker
1 00 rn L volumetric flask with stopper
10 mL pipet with bulb
250 mL Erlenmeyer flask
100 mL beaker
250 m L beaker
400 m L waste beake r
10 mL pipet with bulb
bromthymol blue indicator
buret reader (meniscus finder)
250 mL Erlenmeyer flask
methyl orange indicator
buret reader (meniscus finder)
stirring rod
Notes.'
1.
2.
The NHr(aq)
b (or simulates)
household ammonia diluted 10 fold.
This lab could be repeated usrng pofassium hydrogen sulfate (KHSO4(s)) as a primary standard. A sodium
hydroxide solution could then be standardized and used to determine the concentration of commercial
vinegar.
!
-i
n
N17,N19,N20,N21 ,N22
ACIDS AND BASES
STANDARDIZATION TITRATION
N49
-
LAB N2
Part A
Procedu re:
1.
2.
3.
obtain about 100 mL of HCllsq; in a ctean, dry, labelled 250 mL beaker.
obtain enough dry, solid Narco. to just cover the bottom of a 100 mL beaker.
Scrub the buret using the buret brush. Rinse the buret several times with tap water and at least once with
distilled water. Note: Handle the buret carefulty as the tip is delicate and witt break very easily. Do not hold
the tip of the buret inside the sink white cleaning.
Set up the buret on its stand and set the funnel in the buret. Rinse several 5 ml portions of HCl1"o1 through
the buret into a 400 mL waste beaker. close the stopcock and fill the buret with HCt16q) usihg-a funnet.
Eliminate any air bubbles from the tip by allowing some of the HOllsq; to run through intb tiie 400 mL waste
beaker.
5.
Determine and record the mass of the second clean, dry 100 mL beaker to the nearest 0.01 g.
6
Set the balance to read exactly 1.50 g more than the mass of the beaker and add
NarCO.lr; until the beam
balances exactly.
.
Add about 50 mL of distilled water to the beaker and dissolve the Na2CO3. Using a funnel, carefully transfer
the solution into a 100 mL volumetric flask. Rinse the beaker twice using approximalely 10 mL ol distilled
water each time. Pour the rinsings through a funnel into the volumetric flask.
8.
Add distilled water to the 100 mL mark of the volumetric flask (use a meniscus finder), stopper the llask and
mix thoroughly.
9.
Rinse the pipet with a small portion of the Na2CO, solution. Pipet a 10.0 mL sample of this solution into a
clean 250 mL Erlenmeyer flask. Add 3-4 drops of methyl orange indicator. (Too much indicator gives an
orange intermediate.)
10.
Record the intialburet reading and titrate with HCllsq) until the first appearance of a red color. Swirl the
llask vigorously to expel any COr(g), rinse the sides of the flask with distilled water, and titrate until the
first permanent appearance of a red color.
7
11. Record the final buret reading. (Use a meniscus finder.)
12. Repeat Steps 9 - 13 at least two more times or until results lrom three trials are obtained that agree to plus
or minus 0.1 mL.
13.
lf Part B is not to be done in the same lab period, clean the work area. Rinse out all glassware and leave the
burel inverted with the stopcock open.
Observations:
mass of NazCOg
mass of beaker
mass of beaker + NarCOt
1.50
g
Ni7,N19,N20,N21,N22
ACIDS AND BASES
STAhIDARDIZATION TITRATIONS
N50
LAB N2
-
s
Obse rvations:
Volumes of HCI(rq) Used to Neutralize 1 0.0
m
t
of Na, CO, (aq)"
Trial #
Final Buret Reading
lnitial
Bu
ret Reading
Volume of HCI(aq; Used
Average Volume of HCI(aq; Used =
Part B:
Procedure:
'1.
2.
3.
4.
Obtain about 75 mL of HCllaq; in a clean, dry, labelled 250 mL beaker.
Obtain about 40 mL of NH.1"O; in a clean, dry, labetted 100 mL beaker.
Clean, set up and fill lhe buret with H0llsql as described in Step
4, Parl A of the lab.
Flinse the pipet with a small porlion of the NH3(aq) solution. Pipet a 10.0 mL sample of this solution into a
clean 250 mL Erlenmeyer flask. Add 3-4 drops of bromthymol blue indicator.
5.
Record the initial buret reading and titrate with the HCl1"o1 until a permanent green color is reached. (/f is
extremely easy to overshoot the green color. Try to cbri6 as c/ose as possib/e.)
6,
Record the final buret reading.
7.
:
Repeat Steps 4 to 6 at least two more times or until results f rom three trials are obtained that agree to plus
minus 0.1 mL.
8.
Clean the work area. Rinse out all glassware and leave the buret inverted with the stopcock open.
Obse rvations:
Volumes of HCllaq) Used to Neutralize 10.0 mL of NH, (aq).
Trial #
Final Buret Reading
tn
itial
Bu
ret Reading
Volume of HCI(aq) Used
A'rerage Volume of HOllaq) Used =
U
J
ACIDS AND BASES
N17 ,N22
STAN DAR DIZATION TITRATTONS
N51
-
LAB N2
Calculations
Part A:
1
2
.
Calculate the molar concentration of the NarCO, solution.
Calcuilate the concentration of the hydrochloric acid (using the volume and molar concentration of Na, CO,
solution and the average volume of HCllag) required for neutralization). Show all work.
Part B:
3.
4.
Calcufiate the concentrration of the
B).
N
H, solution (using the [HOl(aq)] from Question 2 and the data from Part
Determflne the sorrcentration of the household ammonia used to prepare the ammonia solution for this lab.
(The
hmtsffi
affinltlnla was diluted 10 fold.)
l#l
N13,N17,N18,N20,N22
ACIDS AND BASES
STANDARDIZATION TITRATION
N52
-
LAB N2
TI
Questions:
1
.
What is the pH of the hydrochloric acid solution?
2.
Find the tOX[sq1l and the pH for the household ammonia used to prepare the ammonia solution for this lab.
(Aqueous ammonia ol the concentration used reacts with water 1.4ololo produce ammonium and hydroxide
ions.)
3.
.
4.
Explain, in terms of collision orientation and collision energy, why only one proton is transferred at a time,
and why nearly all of the first protons are translerred before the second protons are transferred in a poly-
protic or polybasic reaction.
'rl
Draw a rough sketch of the tilration curve lor the continuous addition of hydrochloric acid to a sodium
carbonate solution.
it
5.
Explain why methyl orange indicator is used lor the hydrochloric acid
- sodium carbonate titration.
I;1
I