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Q & A: Acids and Other Materials

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Most recent answer: 10/22/2007
Q:
I know that acids are corrosive , etc they react with carbonates , base and most metals .

However , how do they destroy other materials ? Or they cant ? Is it because of their ionic charge that reacts with other elements/compounds/complex substances or its their acidic nature ?
- Bernard (age 14)
Singapore
A:
Acids are chemicals which will break apart in water (or another solvent) and yield hydrogen ions. For instance:

HCl is an acid because in water in breaks apart to form H+ and Cl- ions.

However, H+ ions react with many compounds. For example, when you put a metal (say copper) in an acid with a high concentration of H+, two H+ ions grab a couple electrons from the metal to form a hydrogen molecule (H2). A charged metal ion (say Cu++) will then go into solution, since it loses some of its electrons.

So the ’acidic nature’ is just another way of saying that acids release a particular ion (H+) that reacts with many other substances, causing them to go into solution.

Bases are compounds that produce OH- ions in water. Sodium hydroxide is a common example:

NaOH -----> Na+ + OH-

OH- and H+ react to form water.

Carbonates (CO3--) are actually weak bases. Carbonic Acid (H2CO3) breaks apart to form H+ and HCO3- or to make two H+’s and CO3--. The fractions found as H2CO3, HCO3-, and CO3-- depend on what the concentration of H+ ions is, which depends both on how much carbonate is present and on what other acids and bases are around. If there’s lot’s of H+ (acidic), it tends to recombine to make H2CO3. If there’s little (basic), then mostly CO3-- will be found.

CO3-2 and HCO3- are what chemists call "the Conjugate Base of a weak acid" since Carbonic acid is a weak acid (it doesn’t entirely break up into H+ and HCO3-; Some of the compound remains as H2CO3 in the solution)

Ions like CO3--, HCO3- as well as SO4--, PO4---, etc in water react to:

CO3-- + H20 ----> HCO3- + OH-

So a carbonate like Na2CO3 forms a weak base in water.



Jason (w mike)

(published on 10/22/2007)

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