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Acids and Bases

Investigation 3 – Concept Day








Acids and Bases: Investigation 3

Concept Day


  • In this Investigation, we will explore neutralization reactions.
  • A neutralization reaction is one in which an acid and a base react to form a salt and water. The free hydrogen ions (H+) of the acid react with the free hydroxide ions (OH) of the base and the solution becomes more neutral in pH.
  • We will also consider the problem of too acidic conditions in the human stomach and how a common neutralization reaction can serve to alleviate this condition.



  • This slide represents the first part of a neutralization reaction. In it, the acid hydrochloric acid (HCl) is mixed in water and produces the hydrogen ion (H+) and the chloride ion (Cl).
  • The hydrogen ion is very reactive and the mixture is acidic. When sodium hydroxide (NaOH) is added to the water, it dissociates into sodium ions (Na+) and hydroxide ions (OH).
  • The next slide will show the reaction that takes place when this mixture of dissociated ions reacts with each other.



  • In this slide, we see the effect of the neutralization reaction.
  • A solid salt may be formed through the interaction of the sodium ion (Na+) and the chloride ion (Cl).
  • Next, the hydrogen ion and hydroxide ion interact to form water. Since free hydrogen ions (H+) are consumed in water formation, the solution becomes less acidic and the pH of the solution increases and becomes “neutral”.



  • This slide shows the human digestive system on the left.
  • On the lower right, we see a surgical view of the human stomach. The function of the stomach is to promote the digestion of ingested food material in an acidic environment. Stomach acid (HCl), is secreted into the stomach by cells we will see on the next slide.
  • On the upper right of this slide, we see the normal inside of the stomach wall on the left. The stomach on the right of this pair of photographs shows a peptic ulcer. Excessive stomach acid may contribute to ulcer formation, sour stomach, acid indigestion, stomach upset, and acid reflux disorders.



  • This slide shows important cells of the human stomach lining. Both images represent thin sections of tissue that have been fixed, stain, and photographed through a light microscope.
  • As noted on the left photograph, the lumen (inside compartment) of the stomach is lined not only with cells that secrete gastric acid (HCl) but also cells that secrete mucus that acts to protect the stomach lining itself from the HCl. The parietal cells, that actually produce and secrete HCl, are stained pink in the photograph on the right.
  • The muscle layer, which is also labeled on the photograph, aids in the mechanical mashing and compaction of food materials. A combination of such mechanical digestion (caused by muscular movements) and chemical digestion (caused by the gastric acid, HCl) breaks down foodstuff before it moves on to the small intestine. As indicated in the insert on the lower right, the stomach has a pH between pH 1 and pH 2.



  • This slide simply shows the relative acidity of gastric acid compared to other familiar compounds.



  • In this slide, the actual reaction that will be conducted in Investigation 3 lab is presented.
  • Antacids are often made from various hydroxides, such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide, etc. Pure sodium hydroxide (NaOH) is too strong and reactive to be used safely as an antacid.
  • In the stomach, HCl reacts with water and forms the free and highly reactive hydrogen ion (H+). This is the acid that helps digest food material in the stomach.
  • The reaction between magnesium hydroxide Mg(OH)2 and hydrochloric acid HCl (and its associated H+)mimics the reaction that takes place in the stomach when an antacid is ingested. In this neutralization reaction, the two harmless molecules water (H2O) and the salt magnesium chloride (MgCl2) are produced from the free and potentially harmful hydrogen ions.



  • Remember to wear gloves, goggles, and lab coats when working in the lab with acids.