May 28, 2023, 11:24:07 AM
Forum Rules: Read This Before Posting

### Topic: Calculating total mg of acetylsalicylic acid  (Read 2208 times)

0 Members and 1 Guest are viewing this topic.

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Calculating total mg of acetylsalicylic acid
« on: April 29, 2020, 10:31:21 AM »
So we titrated tablets containing acetylsalicylic acid in lab
Now i need to fill in this table (see attachment below)

Did i calculate mg per tablet or mg in conical flask with my formula?
Also how do i calculate the other one out of these two?

note: its divided by 2 because 1 mol ASA reacts with 2 mol NaOH

maybe i should also mention that we added 10 mL alcohol in the flask so that the tablet could fall apart properly
« Last Edit: April 29, 2020, 10:47:27 AM by 1800chisaki »

#### chenbeier

• Sr. Member
• Posts: 1348
• Mole Snacks: +102/-22
• Gender:
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #1 on: April 29, 2020, 12:39:14 PM »
No Information of the mass of tablet and also the aliquote what is used for titration.

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #2 on: April 29, 2020, 12:42:58 PM »
the mass of tablet has not been provided by our teacher so i assume its not needed and its titrated with 0,1 M HCl
this was an "online" lab due to covid-19

#### chenbeier

• Sr. Member
• Posts: 1348
• Mole Snacks: +102/-22
• Gender:
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #3 on: April 29, 2020, 12:48:57 PM »
The first row is given below in your picture. But without mass of tablet the other row cannot calculated.

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #4 on: April 29, 2020, 12:55:07 PM »
all thats mentioned in my notes is that at a temprature of 25 degrees celsius
the maximum amount of ASA that can be dissolved in 100 mL water is 0,33 grams

#### Borek

• Mr. pH
• Deity Member
• Posts: 27354
• Mole Snacks: +1775/-408
• Gender:
• I am known to be occasionally wrong.
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #5 on: April 29, 2020, 02:51:03 PM »
You don't need mass of the tablet to calculate amount of ASA that was determined by titration. However, without knowing what the procedure was, whether you titrated ASA from whole tablet, or just part of it (typical procedure often calls fro dissolving tablet, filling up to some volume - like 100 mL, and titrating aliquots - like 20 mL - measured with pipette), there is no way to say what you calculated.

What is f?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### chenbeier

• Sr. Member
• Posts: 1348
• Mole Snacks: +102/-22
• Gender:
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #6 on: April 29, 2020, 02:56:48 PM »
f is the factor of the NaOH or HCl.  Normal procedure if titration take place. 0,1 M can be higher or smaller according titration factor.

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #7 on: April 29, 2020, 02:59:14 PM »
You don't need mass of the tablet to calculate amount of ASA that was determined by titration. However, without knowing what the procedure was, whether you titrated ASA from whole tablet, or just part of it (typical procedure often calls fro dissolving tablet, filling up to some volume - like 100 mL, and titrating aliquots - like 20 mL - measured with pipette), there is no way to say what you calculated.

What is f?

Place one tablet in a conical flask of at least 250 ml. Then carefully add 20.00 mL of 0.1 M NaOH solution. Seal the conical flask and swirl regularly to disintegrate the tablet. After breaking up the tablet, add 10 mL of alcohol and let the mixture stand for 1 h (swirl regularly to dissolve the tablet). As an indicator you use phenolphthalein (2 to 3 drops). Titrate with 0.1 M HCl solution until the mixture just decolorizes. Write down the number of milliliters of HCl you have consumed. Repeat the above operations 3 times.

this is the procedure, first you had to do a blank titration and then this back titration described above

#### chenbeier

• Sr. Member
• Posts: 1348
• Mole Snacks: +102/-22
• Gender:
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #8 on: April 29, 2020, 03:03:38 PM »
You should titrate 3 times, so it means you have to use an aliqout. This is not mentioned.

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #9 on: April 29, 2020, 03:05:04 PM »
thats what i think too but then why did our teacher add two separate coloumns //:

#### chenbeier

• Sr. Member
• Posts: 1348
• Mole Snacks: +102/-22
• Gender:
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #10 on: April 29, 2020, 03:09:48 PM »
If you have the aliquot you get a value and calculated to the whole volume you will have the amount in tablet.

#### Borek

• Mr. pH
• Deity Member
• Posts: 27354
• Mole Snacks: +1775/-408
• Gender:
• I am known to be occasionally wrong.
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #11 on: April 29, 2020, 03:13:12 PM »
Place one tablet in a conical flask of at least 250 ml. Then carefully add 20.00 mL of 0.1 M NaOH solution. Seal the conical flask and swirl regularly to disintegrate the tablet. After breaking up the tablet, add 10 mL of alcohol and let the mixture stand for 1 h (swirl regularly to dissolve the tablet). As an indicator you use phenolphthalein (2 to 3 drops). Titrate with 0.1 M HCl solution until the mixture just decolorizes. Write down the number of milliliters of HCl you have consumed. Repeat the above operations 3 times.

The way I read it you do whole operation - starting with dissolving the whole tablet - three times (so you titrate whole tablets). But the wording could be better.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #12 on: April 29, 2020, 03:15:46 PM »
in total there were three titrations, each with a whole tablet. sorry if my wording is off, english isnt my first language

#### 1800chisaki

• Regular Member
• Posts: 17
• Mole Snacks: +0/-0
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #13 on: April 29, 2020, 03:17:38 PM »
If you have the aliquot you get a value and calculated to the whole volume you will have the amount in tablet.

what do you mean by aliquot?

#### chenbeier

• Sr. Member
• Posts: 1348
• Mole Snacks: +102/-22
• Gender:
##### Re: Calculating total mg of acetylsalicylic acid
« Reply #14 on: April 29, 2020, 03:40:13 PM »
A aliquot means you made up one sample let say 100 ml. From this you take then 20 ml and do the analysis.
This value would be in the first row. In the second row you have to calculate by 5 to get the whole amount.

But you saying you used 3 tablets and do titration each of them. Then there will be no difference.