Amphoteric Substances: Definition and Examples in Chemistry

🧪 Quick Study Guide

• ⚖️ Amphoteric substances can act as both acids and bases.
• 💧 Water ($H_2O$) is a common example, acting as an acid by donating a proton or as a base by accepting a proton.
• ➕ Amino acids contain both an acidic carboxyl group (-COOH) and a basic amino group (-NH2), making them amphoteric.
• 🥉 Metal oxides like $Al_2O_3$ and $ZnO$ can also exhibit amphoteric behavior.
• 💡 The behavior depends on the pH of the solution they are in.

Practice Quiz

1. Which of the following best describes an amphoteric substance?
   1. A substance that only acts as an acid.
   2. A substance that only acts as a base.
   3. A substance that can act as both an acid and a base.
   4. A substance that is neither an acid nor a base.
2. Which of the following is a common example of an amphoteric substance?
   1. Hydrochloric acid (HCl)
   2. Sodium hydroxide (NaOH)
   3. Water ($H_2O$)
   4. Ammonia ($NH_3$)
3. Which functional groups in amino acids contribute to their amphoteric nature?
   1. Hydroxyl and aldehyde
   2. Carboxyl and amino
   3. Ketone and ether
   4. Ester and amide
4. What determines whether an amphoteric substance will act as an acid or a base?
   1. Its molar mass
   2. The pH of the solution
   3. Its density
   4. The temperature of the solution
5. Which of the following metal oxides is known to be amphoteric?
   1. $Na_2O$
   2. $CaO$
   3. $Al_2O_3$
   4. $MgO$
6. How does water act as an acid?
   1. By accepting a proton ($H^+$)
   2. By donating a hydroxide ion ($OH^−$)
   3. By donating a proton ($H^+$)
   4. By accepting a hydroxide ion ($OH^−$)
7. Which of the following is NOT an amphoteric substance?
   1. $H_2O$
   2. $ZnO$
   3. $HCl$
   4. Amino Acids