Intermediate Topic 515 of 1102 Acids, Bases & Electrochemistry
Amphoteric Substances
Species that can act as either acid or base, such as water and bicarbonate.
Practise Acids, Bases & Electrochemistry All Acids, Bases & Electrochemistry topics
In-depth explanation of Amphoteric Substances
An amphoteric substance can behave as either an acid or a base depending on the partner it reacts with, while an amphiprotic species specifically can both donate and accept protons. Water, bicarbonate and amino acids are typical examples because each has a proton it can give away and a site that can take one up. Amphoteric oxides and hydroxides, such as aluminium hydroxide and zinc hydroxide, dissolve in strong acids as bases and also in strong bases as acids. This dual nature means the chemistry of these species depends strongly on what else is present in the solution. Recognizing amphoteric behaviour explains many buffer systems and the pH dependence of metal hydroxide solubility.
Going deeper: Amphoteric Substances
Key ideas: Amphoteric species react as both acid and base. Amphiprotic ones (H2O, HCO3-, H2PO4-, HS-) can donate or accept a proton; amphoteric oxides and hydroxides such as Al2O3, ZnO, Al(OH)3 dissolve in both strong acid and strong base, forming Al3+ or Al(OH)4-. The pH of an amphiprotic salt solution is about the average of the two relevant pKa values.
Common mistakes and connections: Amphoteric is not the same as neutral or a buffer. Students also expect all oxides of metals to be basic; oxides near the metalloid line (Al, Zn, Sn, Pb, Be) are amphoteric. Remember the average-pKa shortcut: pH of NaHCO3 is about (6.35 + 10.33)/2 = 8.3.
Visualization of Amphoteric Substances
Glycine carries both an acidic carboxyl group and a basic amino group, so it can donate or accept a proton and is a model amphiprotic molecule. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Aluminium hydroxide dissolves in hydrochloric acid, where it acts as a base, and also dissolves in sodium hydroxide, where it acts as an acid.
Frequently asked questions about Amphoteric Substances
What is Amphoteric Substances?
Species that can act as either acid or base, such as water and bicarbonate.
Is Amphoteric Substances a beginner, intermediate or advanced topic?
Amphoteric Substances is a intermediate topic in Acids, Bases & Electrochemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Amphoteric Substances?
Study these earlier topics in Acids, Bases & Electrochemistry first: Bronsted-Lowry Theory, Lewis Acids and Bases, Conjugate Acid-Base Pairs.
What comes after Amphoteric Substances?
The next topics in Acids, Bases & Electrochemistry are Autoionization of Water and pH Scale.
Can I practise Amphoteric Substances with quizzes?
Yes. The interactive lesson includes a self-check question on Amphoteric Substances, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Where Amphoteric Substances fits in Acids, Bases & Electrochemistry
Amphoteric Substances is topic 5 of 105 in Acids, Bases & Electrochemistry.