a) To define Lewis acid/base definition and weak acid /base equilibria

     b) To introduce the auto – ionization of water, pH, pOH, Kw, -log, 10-x

Period 2/3: 

1. Complete the Lewis acid/base definition in explaining the CO2. 

2.  Review weak acid/base equilibria

Conjugate Acid Base Pairs and Complex ions new key p.pdf
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Classwork:
Acid and Bases Intro packet new.pdf
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Period 4: 

1. Complete the Lewis acid/base definition in explaining the CO2. 

2.  Review weak acid/base equilibria / homework

Notes for today:

This is the mechanism of how CO₂ acts an acid by the the Lewis Definition.

The most complete definition is the Lewis acid base definition because there are acids and bases that DO NOT HAVE protons to donate or possibly accept BUT create acidic conditions or Basic Conditions.

 

In table K they list CO₂ an acid but it had no protons to donate?  It is an acid because when we bubble CO₂ in water the conditions in water become more acidic.  

 

                    CO₂  +   H₂O             ——>              intermediate                  ——>             H₂CO₃

                                                                                                                                                                                      _then…..

                                                    H₂CO₃   +   H₂O  <——>  H₃O⁺  +   HCO₃ ^-1

 

CO₂ can accept a pair if electrons (JUST LIKE a proton!!!) so the best and most complete definition of acids and bases is the LEWIS acid base definitions! Lewis acids like CO₂ are electron acceptors while bases like water in the example are electron donators!!

 

CO₂ acts an acid by the the Lewis Definition.

Back to the pumpkin Stoichiometry from last week:

C2H2 (g)  +   5/2O2 (g)    —> 2CO2 (g)   +  H2O (g)                                                                                                               0r   2C2H2 (g)  +    5 O2 (g)    —> 4CO2 (g)   +  2H2O (g)

The chemical reaction that exploded the pumpkin was combustion or redox but the reaction the made fuel, C₂H₂ was?

What kind reaction is this?

 

                       CaC2 (s)   +   2H2O (l)           —–>                C2H2 (g)    +    Ca(OH)2

The Arrhenius definition although a good start to defining acids and bases is not complete because we have chemicals that do not have any hydroxide ions in their structure (like NaOH) but will create acidic or basic conditions in water.  In the case above,  the hydroxide ion (OH^–) was produced by the action of the  carbide ion (C₂^-2).   So the Bronsted-Lowry definition is a more complete definition because it includes those chemical species that Produce the Basic or Acidic conditions by Accepting a proton or donating a proton.                                                                                                                                                                                     

In the case above the carbide ion (C₂^-2) ion is the Bronsted-Lowry base (the carbide ion accepted the proton.) and the water is the Bronsted- Lowry acid (because water DONATED A PROTON) (

 

*Notice that acids must have electron deficient hydrogen to donate protons (H⁺).

 *Notice that Bases must have an ability to accept protons (H⁺).  Having a lone pair of electrons or having a negative           charge helps attract the protons!

 

                  The result of this acid base reaction is that acetylene C₂H₂ was produced.                                                                                                                                                                                                                                      Notes for auto – ionization of water:  

*Connections–   Stoichiometry (mole ratio) continues with Acid/Base Reactions.  The connection we need to make is that salts that are soluble and that produce a hydroxide ion (OH^–) into an aqueous solution are bases.  These are important ions because they can upset the balance of H⁺ and  OH^– in water.  Remember that these are naturally occurring ions that occur in water.  

This called auto-ionization of water.

 

                                                      H₂O (l)  →    H⁺ (aq)   +   OH^– (aq)             Kw =  1 x 10^-14

                                                             Proton               Hydroxide

 

                                                                                         or

 

                        H₂O (l)  +  H₂O (l)  →    H₃O⁺ (aq)   +   OH^– (aq)        Kw =  1 x 10^-14

                                                             Hydronium         Hydroxide

                                 

                  From 2 reactions above which are really the same you can see ONE H⁺ or H₃O⁺ for every ONE OH^–.

 

                    Acids will increase the H⁺ or the  H₃O⁺ concentration above normal* conditions.

 

                               Bases will increase the OH^– concentration above normal* conditions.

 

*Normal conditions refer to water that is NEUTRAL : (  H⁺ or the  H₃O⁺ =   OH^– )  = pH = 7

 

                                                                 H₂O (l)  →    H⁺ (aq)        +   OH^– (aq)                                                                   

                                H₂O (l)  +  H₂O (l)  →    H₃O⁺ (aq)   +   OH^– (aq)   

 

                                        Keq =   [Products]   =  Kw = [H⁺ / H₃O⁺][OH^–]

                                                     [Reactants]

 

*We can use H₃O⁺ and H+ interchangeably.  I will write H⁺ going forward but remember I can use H₃O+ at any time and it would mean the same thing.  (Whether you have a free proton or a a proton held by water does not matter)

Now the value of Kw (equilibrium constant for the auto-ionization of water) equals =  Kw = 1 x 10^-14

                                                                                      

                                                                      Kw = [ H⁺ ]    x     [ OH^–]                                                                                                                                 

                                           1 x 10^-14   = [ H⁺]     x    [ OH^–]

 

If one H⁺ dissociates for every ONE OH^– :  H₂O (l)  →    H⁺ (aq)        +   OH^– (aq)    then:                                

                                           1 x 10^-14   =  [ H⁺]     x    [ OH^–]                                                                                                                                                                             

                                          1 x 10^-14    =  [1 x 10^-7]     x    [1 x 10^-7 ]                                           

                

As you can see the concentration (molarity, M) of H⁺ and  OH^–  ARE THE SAME IN PURE WATER! 

                                                       

They must be the same concentration to equal 1 x 10^-14 !

Remember when you multiply exponents you add!

 

*THIS is WATER AT NORMAL CONDITIONS.                           

 

 Now we use a convention to measure this balance or unbalance of ions in water.  It is called pH.

 

                                     pH = – log (base 10) of the H⁺ or  H₃O⁺ concentration.

 

                            Pure water at 4 degrees Celsius the [H⁺] or  [H₃O⁺]  = 1 x 10^-7

                            if you put  -log (1 x 10-7) in your calculator you will get :  pH  = 7

 

So basically pH is a numerical system that measures “stuffs” the entire concentration (small value) into a exponent (base 10) AND MAKES IT positive for Ease  

 

                                                                            pH = – log  [H+]  

 

a)What if the [H+] = 1 x 10^-5  ?  What is the pH?   Is this an acid, basic or neutral solution?

 

b)What if the [H+] = 0.001  ?  What is the pH?  Is this an acid, basic or neutral solution?

 

c)What if we have a [HCl] = 0.1 M   What is the pH?  Is this an acid, basic or neutral solution?

 

d)What if we have a [HCl] = 5.6 x 10^-6   What is the pH?  Is this an acid, basic or neutral solution?

 

e)What if you have [NaOH] = 0.001    What is the pH?  Is this an acid, basic or neutral solution?                                                                 

e)What if you have [NaOH] = 3.34 x 10^-5   What is the pH?  Is this an acid, basic or neutral solution?

 

*Notice the above problems are strong Acids and Base, which means complete dissociation.

 

 answers on bottom of today’s homework post..   

    a) To calculate the hydronium or hydroxide concentration from pH.

    b) To calculate the pH of a strong acid or strong base from its molarity.

    b) To identify an acid/base indicator as a conjugate acid /base pair.

Period 2: 

Acid Bases Packet Intro Key 1718 p.pdf                                                                                                                                                       View Download                                                                                                      

Period 3/4: 

                                                                                                                                                

 Here are some expensive pool chemicals that change the pH.

                                  Na₂CO₃                                                                              NaHSO₄

     a) To write a net-ion reaction for an acid base reaction.

     b) To Identify ions in salts that are acidic, basic, or neutral.

     c) To perform stoichiometry calculations in acid/ base reactions.

Period 2/3: 

1.  Quick discussion in identifying acid, basic, or neutral salts using the acid/ base definitions.

2.  Take the Acid/Base RAT.

3. Review of Last nights Homework.

Stoichiometry 5a – Acid Base Reactions new Key.pdf
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Period 4: – 

1. Quick discussion in identifying acid, basic, or neutral salts using the acid/ base definitions.

2. Complete the Acid/Base RAT.

 

Notes for acid/ base salts:

Ionic compounds will dissociate into their cations (+) and anions (-) IF THEY ARE SOLUBLE and when they do they can act as either a base or an acid (or not react at all) in water.  If the ions of the salt act as an acid or base they can ionize water as either a hydronium ion (H₃O⁺) or as a hydroxide ion (OH^–) by following our acid/base definitions. 

For example if we have the following soluble salt:  NH₄Cl

                                                                    NH₄Cl    —->     NH₄⁺   +     Cl^–

NH₄⁺WILL IONIZE Water :

                                                      NH₄⁺  +   H₂O    —->    H₃O⁺ +   NH₃

Since we are increasing the hydronium ion the pH drops and ammonium chloride is an acidic salt.

For example if we have the following soluble salt:  Na₂CO₃

                                                               Na₂CO₃     —->   2Na⁺   +   CO₃^-2

CO₃^-2 will ionize water:

                                                      CO₃^-2  +   H₂O    —-> HCO₃^-1   +   OH^–

Since we are increasing the hydroxide ion the pH increases and sodium carbonate is Basic salt!

What about these expensive pool chemicals????

                                                                                                                                                

 Here are some expensive pool chemicals that change the pH.

                                  Na₂CO₃                                                                              NaHSO₄

     a) To write a net ion reaction in an acid/base reaction

     b) To calculate the volume of base or acid needed to completely neutralize.

Period 2:  – 

1.   We will start and complete the RAT 2 on acid/base basics

2.   Test 2 will be handed back. The key is posted in powerschool. There are points I want make about this test that I will on                  Monday. 

Period 3/4: –