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Topic: please help ASAP!! (acidity/alkalinity/bonding)  (Read 5033 times)

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troubledinchem

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please help ASAP!! (acidity/alkalinity/bonding)
« on: September 19, 2004, 03:26:49 PM »
Can someone please explain two concepts:

1) How can one tell if something is acidic or alkaline by looking at the compound (for example,
CO2 or C6H12O6)?

2)  How is covalent, ionic, and hydrogen bonding determined?  Are CO2, C6H12O6, and C8H18 examples of covalent bonds?

one last thing:  do body fluids tend to be alkaline or acidic?

THANKS! --Mary
« Last Edit: September 19, 2004, 03:29:08 PM by troubledinchem »

Demotivator

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Re:please help ASAP!! (acidity/alkalinity/bonding)
« Reply #1 on: September 19, 2004, 05:03:34 PM »
1) You can't always tell. CO2 is acidic but you can't tell from the formula. It takes experience to know that CO2 reacts with water to form acidic H2CO3. But there are some guidelines.
Generally, mineral (as opposed to organic, carbon based) compounds with H in front are acidic (HCl, H2SO4, HF etc). But H2O is a neutral solvent and the reference point for acidity/alkalinity. Metal hydroxides (MOH) are basic.
But organic carboxylic acids have 0=C-OH where the H is acidic.
Then there are electron deficient Lewis acids like BCl3 or ALCl3 where there aren't enough valence electrons to satisfy the octet rule. On the other hand compounds with lone pair electrons on the central atom, like NH3,  act as electron donors and are considered lewis bases.
 
2) Ionic bonding (electrons not shared) mostly occurs between group 1 or group 2 metals and non metals. Covalent bonds (shared electrons) usually occur between nonmetals. In your examples, C, H, O are all nonmetals with covalent bonds between them.
NaCl (Na is a group 1 metal), CaCl2 (Ca is group 2 metal) have ionic bonds. NaNO3 is an ionic compound because it  has ionic bond between Na+ and NO3-. But the NO3- part has covalent bonds between the N and O.

Hydrogen bonding only occurs between certain molecules. It is weaker than a normal bond but still significant. Occurs Only if the molecule has hydrogen bonded to F, O or N. So HF can hydrogen bond like this:
H-F..H-F where the dots are the hydrogen bond between the hydrogen of one molecule and the fluorine of another molecule. H2O and NH3 also exhibit hydrogen bonding.

blood and cell PH is normally 7.4, so very slightly alkaline (7 is neutral, over 7 is alkaline)
« Last Edit: September 19, 2004, 05:16:38 PM by Demotivator »

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