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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: VCE_2012 on August 18, 2011, 11:02:20 pm

Title: MC Question: "A typical antacid powder..."
Post by: VCE_2012 on August 18, 2011, 11:02:20 pm

A. could contain hydrochloric acid and can be taken to lower the pH of digestion juices
B. could contain sodium hydroxide and can be taken to raise the pH of digestive juices
C. could contain sodium hydrogen carbonate and can be taken to raise the pH of digestive juices
D could contain magnesium hydroxide and can be taken to lower the pH of digestive juices

(Please explain your answer)

Title: Re: MC Question: "A typical antacid powder..."
Post by: luken93 on August 18, 2011, 11:14:32 pm

Antacid = Anti acid = Neutralises the acid in the stomach.

To neutralise acid, pH will rise towards 7 and to do this, it must be a base

As for B, C, or D, C is a common antacid.

From wikipedia "In the duodenum, gastric acid is neutralized by sodium bicarbonate. This also blocks gastric enzymes that have their optima in the acid range of pH. The secretion of sodium bicarbonate from the pancreas is stimulated by secretin. This polypeptide hormone gets activated and secreted from so-called S cells in the mucosa of the duodenum and jejunum when the pH in duodenum falls below 4.5 to 5.0. The neutralization is described by the equation:

        HCl + NaHCO3 → NaCl + H2CO3

The carbonic acid instantly decomposes into carbon dioxide and water."

Title: Re: MC Question: "A typical antacid powder..."
Post by: Vincezor on August 18, 2011, 11:17:19 pm

Well "antacid" is generally used to neutralise the acidity in the stomach (heartburn, or whatever it is called).

Therefore answers A and D would be around as the aim is to raise the pH.

Doing is quick wikipedia search yields this:

"Some well-known antacid brands"
Alka-Seltzer – NaHCO3 and/or KHCO3

So the answer would be C

EDIT: beaten by luken haha :) good work!

Title: Re: MC Question: "A typical antacid powder..."
Post by: VCE_2012 on August 18, 2011, 11:21:21 pm

How would you derive an answer if it was an actual exam (this question is from a past exam)? 

Title: Re: MC Question: "A typical antacid powder..."
Post by: Russ on August 19, 2011, 08:42:41 am

You'd have to know or conclude that an antacid will oppose the action of acid, which means you'll only have B and C left. C is probably favourable because it's more stable and will have a longer lasting action afaik.

Calcium carbonate is the most common antacid being sold OTC now, I'm pretty sure (although they're sadly being replaced by proton pump inhibitors)