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Properties of Acids + Bases (It's that ez)

Submitted by Hertzinger on Tue, 02/09/2010 - 14:08

http://upload.wikimedia.org/math/7/3/6/736f4f31c1b23b09276c93b4c01910c7.png

Derivation
http://upload.wikimedia.org/math/4/4/b/44b8c722616b9375acc6dfa913006cf5.png

This is henderson- hasselbachs equation it's flawed tho.

I think the proper equation is pH=-log[H+]
or -log (base of ur conjunctive acid)+ (-log (base of ur conjunctive base))= pH levels. the number of zeros that come infront of ur actual number is simply the number of sig figs u have.

An arrhenius acid + an arrhenius base = water + salt

Arrhenius acid as defined by Svante Arhenius in 1884
-an arhenius acid is a substance that dissociates to produce H+ ions
IE: HCl--> H+ + CL- this is hydrochloric acid
Acetic acid = CH3COOH(aq)


[/hr] H+(aq) + CH3COO(aq)-

Arrhenius base = is a substance that dissociates to producuce OH- ions

covalent compounds with an -OH group( called alchohols) do not dissociate to OH- ions.

The oxygen is covalently bonded to something; it can not be pulled off easily. CH3OH is methanol

Arrhenius acid + arrhenius bas → water + salt

HNO3(aq) + LiOH(aq) → HOH + LiNO3

Net Ionic Equation:

H+(aq) plus OH-(aq) → H2O(L)

Bronsted- Lowry acid definition-
a substance that acts as a proton (H+) donor.
*anything with a (-) charge or a lone pair of electrons **could** be a B-L acid (some with greater ease than others)

Bronsted- Lowry base definition- a substance that acts as a proton (H+) acceptor

*anything with a (-) charge or a lone pair of electrons could be a B-L base

OH- acts as a B-L base because it can bind with H+ to make water

CO3 -2 acts as a B-L base cuz it can bind with 2H+ to make it a neutral compound

NH3 acts as a B-L base cuz it has a lone pair of electrons which can form a bond with H+

**DUMBED DOWN**
a B-L acid always needs another chemical to be a B-L base

this is and acid- base reaction

acid-base reaction= H+ transfer

In many *(but not alll)* situations WATER!!! acts as the acid or base

HCl IN water
HCl (aq) + H2O(l) --> H3O+(aq) + Cl-(aq)

H3O+ is hydronium it is equivalent to H+
H3O+ is heavy water cuz it is ozonated!!

NH3(aq) + H2O (L) --> NH4(aq) + OH-(aq)

***Hydroxide can be produced even though the base didn't contain that ion***

-log[H+] = pH

its a simple logarithm. DONT USE IF CONFUSED send me a msg i'll help u out

Remember its high school equations I am only 17

If you closely at the reactants in these examples:

HCl(aq) + H2O (l) --> H30+(aq)  +  Cl-(aq)

and

NH3 (aq) + H2O (l) --> NH4+(aq) + OH-(aq)

you may ask yourself "How do you know which reactant is the acid and which is the base?"

1. The acid must have an H to donate
2. The base must be able to accept an H
3. If both are amphiprotic* then the stronger acid gets to be the acid

* an adjective describing a chemical that can act as an acid or a base

HCl + H2O --> H3O++ Cl-

HCl has an H so it could act as an acid... It can't be a base(neutral and not nitrogen-based) must act as an acid. HAHA funny that it's hydrochloric acid.

H2O can be both (its amphiprotic) but because the HCl can only be an acid the water must act as a base.

NH3+ H2O -->  NH4+ + OH-

NH3 has an "H" so it could act as an acid... It could act as a base as well!

H2O is a stronger acid (?!?!) than NH3, so it forces its H+ onto the NH3.


Well, the H-H equation is in a correct form, it's just that you can write it in multiple ways, depending if it's for acids or bases. Also, the equation :

pH= -log[H+

is the sorensen equation, or also called the hydrogen potential and is not the H-H equation.

The H-H equation for an acid is derived from the equation of the dissociation of an acid, HA, which i'll show you here:

1- The dissociation of a general acid in water is :

HA + H2O H3O+ + A-

2- which can also be written as :
     
      Ka
HA H+ + A-

3- where Ka is the acidity constant (Here i'll use the concentrations to save some time, but the real acidity constant is used with the activity instead of concentration) :

Ka = [H+] [A-] / [HA]

4- Now, lets take the logarithm on each side of the equation :

log Ka = log ([H+]) + log([A-]/[HA])

5- which can be rewritten as (knowing that pH = -log[H+] (here again, the form H+ doesn't exist, and is found as H3O+ in water, but to make it faster ti write, i used H+)) :

pKa = pH - log([A-]/[HA])

and it gives the H-H equation for weak acids :

pH = pKa + log([A-]/[HA])

and the equivalent for the weak bases :

pH = 14.00 - pKb + log([B]/[BH+])

I hope i helped you make it clear for the Henderson-Hasselbalch equation :)

Ps: English isn't my first langage, so it might not be as clear as other persons on this forum, but i tried to make it as clear as i could :)

Source : D'Amboise, M. Chimie analytique et traitement de données, Université de Montréal, 2009, p.35,36,40


Dragonbreath wrote:

Well, the H-H equation is in a correct form, it's just that you can write it in multiple ways, depending if it's for acids or bases. Also, the equation :

pH= -log[H+

is the sorensen equation, or also called the hydrogen potential and is not the H-H equation.

The H-H equation for an acid is derived from the equation of the dissociation of an acid, HA, which i'll show you here:

1- The dissociation of a general acid in water is :

HA + H2O H3O+ + A-

2- which can also be written as :
       
       Ka
HA H+ + A-

3- where Ka is the acidity constant (Here i'll use the concentrations to save some time, but the real acidity constant is used with the activity instead of concentration) :

Ka = [H+] [A-] / [HA]

4- Now, lets take the logarithm on each side of the equation :

log Ka = log ([H+]) + log([A-]/[HA])

5- which can be rewritten as (knowing that pH = -log[H+] (here again, the form H+ doesn't exist, and is found as H3O+ in water, but to make it faster ti write, i used H+)) :

pKa = pH - log([A-]/[HA])

and it gives the H-H equation for weak acids :

pH = pKa + log([A-]/[HA])

and the equivalent for the weak bases :

pH = 14.00 - pKb + log([B]/[BH+])

I hope i helped you make it clear for the Henderson-Hasselbalch equation :)

Ps: English isn't my first langage, so it might not be as clear as other persons on this forum, but i tried to make it as clear as i could :)

Source : D'Amboise, M. Chimie analytique et traitement de données, Université de Montréal, 2009, p.35,36,40


Thanks Wasn't able to get that.


oops, just saw that i made an error in the last formula, there's a [ B] missing on the /[BH+]


Salt redifined by Hertzinger
a salt is any ionic compound that doesn't fall under the Arrhenius category (acid or base)

*We often think of these compounds as being 'neutral' because they wouldn't appear to have acidic or basic properties on first inspection.

**However, when they are dissolved in water the individual ions (or the compound itself) can create a pH other than 7.0 based on how it (they) react with water.

Take NaCl for example NaCl(s)Na+(aq)+Cl-(aq)

The Anion will be the conjugate base of some acid, or it could be an amphiprotic species.

The Cation may form an acidic complex ion or could be an acid itself.

The Compound may react with water to produce an acid or base molecule


Here are some Practice Problems

Holla if you need some help.

1. H2O + CN--->
2. F- + H2 SO4-->
3.* OH- + H2O-->
4. HCO3-+ O-2-->
5. HI + H2O -->
Leave #3. Till I post further lessons

*The chemical acting as the acid loses one Hydrogen and its charge drops by one

*The chemical acting as the base gains one hydrogen and its charge goes up by one


If you mix two things which are amphiprotic, how do you know which is the stronger acid?

The Table of Relative Strengths of acids- being the Ka

The higher the acid on the table the stronger it is....
Write the products of each acid-base reaction :
1. HC2O4-+ HCO3_-->

2.HCO3- + H2O-->

3. NH3+ HSO4- -->

Take a look at every acid-base reaction that has been written down so far. Every reactant acid becomes a chemical that looks like a base and every reactan base becomes a chemical that looks like an acid!

These partners are called Conjugates to each other.

Its My conjugate acid + base theorem. Perhaps its wrong? tell me if it is.

-logA+ -logB=pH

Both A and B both have to be the concentrated values of the chemical with the number of sig figs infront of the number sig figs have to be a 0 though.
This only works with the Bronsted-Lowry theorem.


Lets take a brake from chemistry and read some poetry
Let Bye Gone's Be Bye Gone's
Let Truth Be Truth
May Democracy Never Lead To An
Autocracy
Or Has Spirituality Become Less of a Reality
Let the Condemnable Be Redeemable
My Sedation Lead To Redemption


There's no way you can understand an "acidic" or "basic" solution without knowing what "neutral" means first.

Pure,distilled water is neutral; meaning it has a value of 7 on a pH scale

Where does the 7 come from? Lets look at water first.

THE DISSOCIATION OF WATER

The water molecule naturally dissociates (much like a low soluble compound) to produce H+ and OH- ions. The equilibrium sonstant is quite low at 1.0 x 10-14. This value is know as Kww:

Kw= 1.O x 10 -14 Note: this value of Kw is @ 25oC...... If the water is warmer Kw increases; if it is colder Kw decreases.

[glow=red,2,300]Kw is derived from the equation:
H2OL--> H+(aq)+ OH-(aq)

Kw= [H+][OH-]

Kw= [H3O+][OH-]

In pure water the H+ + OH- are in a 1:1 ratio and
[H+]=[OH-]= square root of Kw= 1.0 x 10-7