Chapter 11 acids and bases - 2 different faces

Properties of acids

• Tastes sour or tart (like lemon juice)

• Are electrolytes (conduct electricity when in water)

• Causes litmus to turn red or pink 

• React with many metals to release H₂.

Properties of bases (also called Alkaline)

• Tastes bitter (ex-soap)

• Feels slippery 

• Are electrolytes

• Turns litmus paper blue

• Not found in food, but found in cleaning supplies

Arrhenius acids

• contains hydrogen that becomes an H+ ion in water

• H must be joined to a more electronegative atom (O, Cl, etc., but not C!!!)

Arrhenius bases 

• contains hydroxide that becomes an OH- ion in water

Brønsted-Lowry A and B

• Some substances don't fit the Arrhenius definition (e.g., NH₃)

• Acid - hydrogen ion - a proton donor 

• Base - hydrogen ion acceptor 

• Ex- NH3+H20 → NH4+ +OH-

  • NH3 - acceptor - basic

  • H2)- donor = acid

Bronsted Acid-

hydrogen ion, Donor

Bronsted Base-

• hydrogen ion, Acceptor 

Measuring pH

• Can be done with indicators or pH meters

• Indicators = chemicals that change color depending on pH

• Ex: phenolphthalein, litmus paper. Red cabbage juice

• Meter Electronic device that records pH

dissociates

completely breaks apart or ionizes in water,ex , A= HCl, H₂SO₄, HNO₃ (three strong acids; need to know the first three onm common acid on the back of PT)

B= NaOH, KOH, Ca(OH)₂ - need to know

Weak A or B

only practically ionized in water

Ka and Kb

• Weakness of A/B can be measured with Ka and Kb

• Kb - base dissociation constant 

• Ka - acid dissociation constant 

• The smaller K, the weaker A or B

• We will work with Ka to make it simpler

  • Ka = [H+] x [A-]/[HA]     (for weak acid, HA)

  • Ex: for HA → H+ + A-    (weak acid)

• For a 1.0 M solution to start, [H+] = 5.34x10^-2M, what is Ka

  •  (5.34x10^-2M)^2 = 0.0029

 Neutralization Reactions

• Acids and bases cancel each other out when added together (neutralize)

• Products are water and salt (not necessarily table salt)

• Need to have the right amounts of each

  • A small amount of weak base won't completely  neutralize a large amount of strong acid

  • Ex. HCL + KOH → HOH + KCL (DR 1:1:1:1) (both are strong)

  • Ex. 2HNO₃ + Ca(OH)₂ → 2HOH + Ca(NO₃) ₂

    • For the 2HOH, we don't have 2 h with OH because it is with the O

Titrations

• Used to find the unknown concentration of an acid  or base by using a certain amount and concentration

• Regardless of concentration or amount, the number of moles must be equal

• An indicator (color change) is used to determine the endpoint (neutralization) of the titration

• Ex 25.0 mL of an acid (HXL) with an unknown concentration is titrated with 16.8 mL of a 1.25M solution of NaOH. What is the concentration of the acid?

  • Since it is ml, we need to move the decimal points

1.25 m=x/0.0168

x = 0.021 mol acid

Acid = 0.021 mol/0.025 = 0.84M

Ma(va) = Mb(Vb)