pH of antacid (1 Viewer)

[richz]

today our class conducted an experiment and we found the pH of antacid was 5.75 using a datalogger (pH probe). Does any one have ideas why antacid is acidic when measured, my teacher told us to find this info out. Antacid is usually a drug/tablet taken to reduce the acidity in the stomach wats the use of this acid in reducing the acidity in the stomach?

 

[richz]

after spending time on investigating it i think, i have worked it out, antacid is a buffer solution so if it is mixed with a strong acid the pH will stay constant, thats why it doesnt matter if pH shows its acidic or basic,

EDITED: i think correct me if im wrong

 

[xiao1985]

5.75 is acidic tho...

antacid whould be basic as it will neutralises the hydrochloric acid in tummy when it grumbles...

 

[richz]

5.75 is acidic tho...

antacid whould be basic as it will neutralises the hydrochloric acid in tummy when it grumbles...

yes thats true but i think its a buffer solution as i said above

 

[richz]

sorry, i meant acidic 5.75 pH ................edited

 

[Slidey]

after spending time on investigating it i think, i have worked it out, antacid is a buffer solution so if it is mixed with a strong acid the pH will stay constant, thats why it doesnt matter if pH shows its acidic or basic,

EDITED: i think correct me if im wrong

That is correct. The antacid should contain a weak acid and one its salts.

 

[richz]

thnx slide for confirming that, so do u mean an antacid is a weak acid and a salt??
cuz in that post ur sentence doesnt make sense

 

[Slidey]

Uhm... it doesn't have to be an acid - bases can be buffers, too. But your antacid is an acid.

A buffer IN GENERAL is a weak acid and its salt, or a weak base and its salt.

Basically (hah, get the pun?), when you add the weak acid and its salt, you are setting up an equillibrium reaction:

HA(aq) H⁺(aq) + A^-(aq)

Where HA is the weak acid, so the equation will lean to the left. Adding the A^- anions from the salt will make it go even further left (La Chatelier's).

You've got lots of unionsed HA acid, lots of A^- anions, and enough hydrogen ions to make it acidic.

Since the acid is weak, it will supply very few A^- anions - rather, it will be the salt which supplies the bulk of them. Remember the salt is a mix of the anions of the acid HA and the cations of some base.

If you add an acid, such as stomach, new hydrogen ions will pop up - which will increase the acidity. Therefore, the buffer must remove these new hydrogen ions, and it does so by making its anions A^- attach to the hydrogen ions, making weak HA acid. This will remove most of the new hydrogen ions and the pH won't change much.

In terms of stomach acid, adding a buffer, HA will effectively turn strong stomach acid into the weak HA acid and so lower the acidity.

 

[funking_you]

today our class conducted an experiment and we found the pH of antacid was 5.75 using a datalogger (pH probe). Does any one have ideas why antacid is acidic when measured, my teacher told us to find this info out. Antacid is usually a drug/tablet taken to reduce the acidity in the stomach wats the use of this acid in reducing the acidity in the stomach?

What type of antacid did you use, i.e. what was the main active ingredient?
aluminum hydroxide, calcium carbonate, and sodium bicarbonate

Also, did you just dilute the antacid in water and test it pH or did you react it with HCl(aq)



...

 

[xiao1985]

my bad... this q is probably associated with the dp: "minimise hazard of accidental spills by the means of neutralisation ..." using a buffered soln would obviously better...

 

[funking_you]

From my understanding of antacids, i do not agree with the 'buffer' reasoning, i think that that you should re-do the experiment and check what type of antacid you are using and whether you are indeed using an antacid.
Most common antacids use calcium carbonate as the active ingredient, and this is a very basic substance.
The pH of an antacid definately >7, however if you were to mix a antacid into a solution of 0.1 M con. HCl (which is a similar concentration to that found in the stomach), your resulting solution will be acidic, possibly 5.75 (this would indicated that the antacid was very basic).

 

[Slidey]

Wikipediaantacid
An antacid is a substance that is swallowed in order to buffer gastric acid, raising the pH to reduce acid damage and relieve heartburn. Some also adsorb bile salts. Common types are:

Aluminium hydroxide (Amphojel®, AlternaGEL®)
Magnesium hydroxide (Phillips’® Milk of Magnesia)
Aluminium hydroxide and magnesium hydroxide (Maalox®, Mylanta®)
Aluminium carbonate gel (Basajel®)
Calcium carbonate (Tums®, Titralac®, Calcium Rich Rolaids®)
Sodium bicarbonate (Bicarbonate of soda)
Hydrotalcite (Mg6Al2(CO3)(OH)16 · 4(H2O); Talcid®)

I will admit that I am out of my depth, however, the buffer reason does seem to be the best one.

EDIT: It appears that the acid is neutralised by a base and then the buffer is used to ensure it doesn't become too basic.