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Acid-Base Titrations Experiment # 6 — Transcript

by Chemistry with Dr. Memari · 2,167 words · 469 segments · language en · Watch on YouTube

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0:00[Music]
0:07step one of the experiment i'm going to
0:10go
0:11for step one and i will also talk while
0:13i'm doing the experiment so it would
0:15give you a little bit more information
0:17for step one we have
0:20we have to prepare sodium hydroxide
0:22solution so to prepare the sodium
0:24hydroxide solution we're going to take
0:26the
0:2750 milliliter of the three 3 molar
0:29sodium hydroxide when you buy your lab
0:31manual you repeat the procedure you will
0:34get follow the procedure so those some
0:36of the numbers you find it there i don't
0:39have to write exactly for you
0:41but anything that you cannot any number
0:43you cannot find it in the lab manual i'm
0:46going to write it for you so you could
0:48have the numbers for
0:51your data sheet
0:53we are making 600 milliliters
0:55of sodium hydroxide solution and the
1:00standard that we are using is a three
1:02molar we are going to
1:04read from um experiment one that
1:07measurement with graduate cylinder is
1:10not the most accurate measurement
1:12so
1:15i'm using the graduate cylinder but i'm
1:18going to standardize this solution later
1:21so the calculation that
1:24is used downward based on the dilution
1:26is not
1:28it's not i the most accurate it's not
1:31going to give me the most accurate
1:32number
1:33but
1:35after i standardize i'm going to
1:38give you the exact number
1:40for you to calculate molarity for the
1:43base
1:44and when you have the molarity for the
1:46base then you have a
1:50standard to use for rest of the extent
1:54okay after you mix the concentrated and
1:57dilute solution you have to mix it very
2:00well because solution must be uniform
2:03but we don't want high concentration of
2:05sodium hydroxide at the bottom and low
2:07concentration on top so it has to be
2:11completely
2:12mixed next step
2:15i'm going to take the
2:17element flask
2:19measure the mass of the flask
2:26measure the mass for empty flask because
2:29i want to make sure that is going to
2:31match with what you have in the
2:34in the data sheet so
2:38for the data sheet
2:39you are going to use
2:42for part
2:43one
2:44you need the mass
2:46empty erlenmeyer flask
2:52119.632
2:57gram this is the mass
3:00for
3:02empty
3:04flask
3:08and we add about
3:111.2 grams
3:17there would be
3:18120.8 rounds
3:22120.887
3:27this is going to be the mass
3:30of
3:31flask
3:33plus
3:37earth and
3:39kh
3:40p
3:42for
3:43trial
3:44one we are going to add 50 ml of dry
3:47water
3:52this was used for sodium hydroxide
3:57clay one
4:05fifteen ruler of the year quarter just
4:07to dissolve the sample
4:12and let it stand until it's completely
4:16dissolved before we can use it
4:18so we also add
4:21three drops of three to four drops of
4:23the
4:24acid-base indicator
4:26the acid acid-base indicator of phenol
4:28fertility
4:29is colorless in acidic solution you see
4:32it's colorless
4:33when we add the base at the neutral
4:35point it will change to a light pink
4:38color
4:39but if you add too much of it it can go
4:41to dark
4:43pink or purple color which
4:45it's not desired
4:47then
4:49after we have the
4:51flats ready
4:52now you want to fill up the buret with
4:55the
4:56sodium hydroxide solution
4:58now
5:00next
5:01we have the
5:03initial buret reading
5:06i have 1.00
5:10initial
5:16view rest reading
5:21trial one
5:23when i start the titration
5:25i'm adding the base from the buret
5:29to the acid that i had in the flask
5:32until
5:34the
5:35pink color is a stable for
5:3720
5:38seconds
5:40you see the pink color appears in the
5:42center but it disappears after i mix it
5:46because the
5:47entire solution is not
5:52neutralize yet
5:54at the beginning i can add the
5:57base fast see that i'm just pouring it
6:01but
6:01after the life of this pink color gets
6:05longer basically i'm getting closer to
6:07the endpoint of the reaction and when i
6:09get close to that point of the reaction
6:11now
6:12i have to slow down and add one drop at
6:15the time
6:19so if you see there is a white paper
6:21underneath
6:22it's just to show me the color
6:25okay
6:26so i have a light pink color
6:30the color change is a light pink color
6:32if this stays for like 20 seconds
6:35that means i have added enough
6:37of the base if it doesn't then i have to
6:40add another drop finally red reading
6:45is 25.20
6:49trial one the volume of sodium hydroxide
6:53is going to be final minus initial which
6:55you have to do the calculation
6:57and then the molarity of sodium
6:59hydroxide you need to do the calculation
7:02for the molarity of sodium hydroxide i
7:04only gave you the numbers
7:06and you are going to read the image the
7:10introduction part of the experiment in
7:12order to
7:13perform the calculation so basically you
7:16find the number of moles you find the
7:18mass for khp you find the moles per kgb
7:22and then you say number of moles of khb
7:24equals moles of
7:26of sodium hydroxide
7:29and then from moles of sodium hydroxide
7:31then you have moles of sodium hydroxide
7:33you have the volume of sodium hydroxide
7:35you can calculate molarity for
7:38sodium hydroxide so i do explanation but
7:42hopefully going to rewind that couple
7:43times
7:44read it and
7:46listen to it make sure that you
7:48understand what to do
7:50with the
7:52calculation
7:55okay i'm going to refill the burette
7:59with sodium hydroxide
8:02uh because i don't want to
8:05use entire sample
8:08and if i go below 50 there's no line
8:10there and i cannot
8:13basically
8:14read the numbers below 50. there is no
8:17graduation line
8:18second trial
8:228.00
8:25is initial
8:28buret reading
8:30mass for the flask sixteen two five five
8:34one sixteen point two
8:37five five
8:39khp
8:41one point
8:44two grams about 1.2 grams
8:48so
8:49117.3 is going to be sufficient
8:54mass of
8:58flask
9:00and khb
9:02triad 2 is
9:05117.5
9:08two one one seventeen
9:11point
9:12five two one
9:15we are adding the fifty milliliter water
9:20i kind of pour it
9:22around around the flask to make sure if
9:24anything any powder it is on the wall it
9:27can go down
9:29add
9:31two drops of phenol facility
9:37trying to dissolve it
9:39the first time we added about
9:4220 milliliters right
9:43at least 20 24 milliliters that's what
9:46we added
9:48i have slightly more khp so i should be
9:50able to
9:51confidently add 24 milliliter or 25
9:55milliliter and then load down so the
9:57second trial i have better idea
9:59how much
10:00of the base is going to be
10:02used
10:04so if i start from 8 and i go to 28 that
10:08would be
10:1020.
10:15i can even go to 30 because i'm using 22
10:19milliliters or more actually we should
10:21look at the color change and not worry
10:24about the
10:25numbers up here
10:27but when the color change happens then
10:28you look at the red we record the number
10:31light pink color color change
10:34which happened with one drop addition of
10:36one last drop
10:37after
10:39that 20
10:41almost 24 milliliters so i'm recording
10:45this number as 32
10:47point
10:48one two three
10:53five
10:55thirty two point three five
10:5932.35
11:03is the
11:06final
11:09buret
11:11reading
11:12okay the two numbers they are
11:15enclosement i don't have to do trial
11:17three because try three is like if you
11:20need it
11:21uh which i don't have to use it i'm not
11:24going to use the try three at this point
11:27so
11:28we are done with part one of experiment
11:31six
11:32i'm going to move to part two of the
11:35experiment six i need to wash my flasks
11:38i need to refill the burette
11:43my sodium hydroxide
11:45is ready
11:47but i need to
11:48refuel the burette for sodium hydroxide
11:53i'm going to add more sodium hydroxide
11:5610 milliliter of this stock solution now
11:58i have my stock solution on hcl because
12:00i'm using it for different tries i'm
12:02going to pipette 10 milliliters
12:06with the pipette
12:08the
12:08number on the pipette it shows that if i
12:12fill up this pipette
12:14up to the index line is going to have 10
12:17milliliters
12:18of the solution so this is a 10
12:20milliliter pipet the number shows 10. so
12:24if i filled up to this index line again
12:26i'm looking for the meniscus and that's
12:29what we are
12:31looking for now
12:33so i'm going to fill up
12:38this is the first time you let me just
12:39pump because you do have like those
12:42fancier ones
12:44just couldn't find it
12:51and we are going to add two drops of the
12:53phenolphthalein
12:55when you're dealing with human error it
12:57doesn't matter if it's you or me or
13:00anyone
13:01you could always have the human error
13:04so
13:05looks like that a drop of it went
13:08outside of that glass
13:10and i wasn't happy with it
13:12so i said i'm going to make a new
13:16sample
13:19that i'm 100 sure is working
13:22so
13:24the volume here
13:26is exactly 10 milliliters
13:29so now
13:32what information do you need for part
13:34two
13:35to record in order to finish your
13:38sample for now is just initial buret
13:41reading
13:43part two
13:46trial one
13:50initial
13:55re-retreating
13:59is
14:010.00
14:04we're going to add enough
14:07of the
14:10sodium hydroxide
14:12until same thing like last titration
14:16the pink color appears disappears but at
14:19one point it's going to stay
14:23or be stabilized for 20 seconds that's
14:25what we are looking for
14:33why is necessary to add some water to
14:36wash the walls because sometimes the
14:37acid is on the wall inside wall
14:41and it's not being titrated
14:43so you want to make sure that everything
14:45is
14:46mixed
14:47if there's any acid on the wall it needs
14:49to be washed out
14:51adding one more drop
14:53because it's very close to it
14:56okay this is just adding one drop the
14:59pink color up here
15:01now i have a light pink color
15:03of the solution
15:06and that's the end point for the
15:08reaction i stop adding
15:12sodium hydroxide
15:14read the volume
15:17is 24.45
15:2122.45
15:27twenty two point
15:30four five
15:32is
15:34final
15:36receiving
15:39part two
15:42trial
15:43one
15:45one trial it's never enough for
15:47titration you have to have at least two
15:50trials if the numbers are within the
15:52agreement like five percent difference
15:54then you can stop otherwise you have to
15:57continue for the third try so i have to
16:00do my second try now i'm just washing
16:03one more time
16:04the flask i already watched it i was
16:06just raising with the
16:10deionized water to make sure there is
16:13nothing
16:14left over from prior experiments
16:19a major 10 milliliter of the acid
16:28exactly 10 milliliter has to be
16:39transfer
16:45okay
16:47transfer 10 milliliters of the acid
16:50add
16:52two drops of
16:57energy
17:06white sheet of paper
17:10washing down the acid to make sure that
17:12everything is down inside the
17:15flask
17:16i may not have enough i might have or
17:19may not have enough
17:21of the um
17:25of the acid so i'm going to start with
17:2923
17:33hopefully we have enough to finish the
17:35try
17:36so last time we used
17:4022
17:42if everything is the same
17:46as before if i didn't make any mistake
17:49i should be able i should also use
17:52another
17:5322 milliliters or 22.5
17:56or 32.45 milliliters
17:59so i can confidently
18:01add fast
18:04to get to the
18:0622 milliliters
18:08i'm starting with 23.
18:11so
18:12i
18:14it can go too fortified
18:18if everything is the same if it works
18:20see that pink color appears and when i
18:23mix it it disappears it's not end point
18:25of the reaction
18:26endpoint of the reaction would be
18:29when the color
18:30is
18:31maintained for 20 seconds
18:35has to stay for 20 seconds if it doesn't
18:38stay for 20 seconds
18:40we add another drop
18:49so initial reading
18:51this was for
18:53part two now part two
18:56trial two
19:00initial
19:01initial burst reading is 23.00
19:07part
19:08two try to
19:11find out
19:12your restriction
19:14final breath reading is 45.30
19:21so with the two trials being closed i
19:23don't have to do the third trial the
19:25third trial is not needed
19:28uh because the two tried they were very
19:30close
19:31luckily i was able to you know remember
19:34to add fingerprints sometimes you don't
19:36remember that fear of telling you go
19:38like 10 millimeter higher than what you
19:40use for trial one
19:42and you don't see color change then you
19:43remember you didn't add the finra
19:45facility but this one
19:47it worked out so far it's so good
19:52so we are done with part two of the
19:54experiment you are responsible for
19:56calculation though you have to do the
19:58calculation volume for acid each time
20:00was 10 milliliter
20:02so you find the molarity for the acid
20:06number of moles of hcl it comes from
20:08part two number of moles of
20:12naoh
20:14is the molarity times volume in liter
20:17for naoh that was used in the time we
20:20are using the solution molarity
20:23that we have the molarity it would be
20:26molarity
20:27times
20:29volume in liter that gives you the
20:31number of moles for
20:34for any acid or for any
20:36base or in general any solution
20:40so
20:41[Music]
20:50you

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