15
Acids and bases
• Hydronium
• Hydroxide
• Water can also self ionize, making
hydronium and hydroxide.
• Equation.
water
• Weak electrolyte
• Concentration of each ion in pure water is
1 x 10 -7 mol/L at 25 C
• .0000001 mol per liter
• Molar concentration
• [ H3O+ ]
[ H3O+] = 1x10-7 M = [OH-]
water
• The product of the concentration of [ H3O+]
and [OH- ] is a constant.
• Called ionization constant of water and it
is equal to 1x10 -14 M2
• Kw
Neutral acidic basic
• Neutral
• [H3O+] = [OH]
• Acidic when
• Basic when
How many moles?
• How any moles of each ion are in I mole of
NaOH
• If you have a 1x10-2 M solution how many
moles of each Na, and OH do you have?
– NaOH yields Na ion + OH ion
– One to one ratio therefore there are 1x10-2 M
hydroxide ions formed.
– Therefore there are 0.01 moles this is greater
than 0.0000001 so is this solution acidic or
basic?
• If [OH-]= 1x10-2 M, then what does [H3O+]
equal?
• This is based on the Kw of water. Read
page 500 and study the derivation.
1x 10 -4 M solution
• What if it’s a diaprotic or triprotic acid.
• H2SO4 yields 2H3O+ + SO4-2
• 2 moles of the hydronium ion because the
ratio is 2:1
• [OH] = 1x10-14/ [H3O] = 1x10-14 M2/2x10-4M
• = 5x10-11 M
• As the concentration of hydronium
increases, the hydroxide decreases and
visa versa.
• Practice problems page 502
• Look at pH scale page 503
pH scale
• Power of hydrogen
• The negative of the logarithm of the
hydronium ion concentration.
• pH = -log[ H3O+ ]
• pH = -log[ H3O+ ] = -log (1x10-7 ) = 7
• The pH number is the exponent of the
concentration with the opposite sign.
• If the pH is 3 then the molar concentration
of H3O+ 1x10-3 M/L and the OHconcentration is 1x10 -11 M/L
• What can you say about the exponents?
Figure 3 pg 503
• http://staff.jccc.net/pdecell/chemistry/phsc
ale.html
• http://www.purchon.com/chemistry/ph.htm
Practice problems page 505
What if concentration is not an
integral power of 10?
• Concentration is 6.7x10-4 M what is the pH?
• You must first determine the log of
6.7x10-4, which is -3.17, then take the opposite
sign, 3.17
pH = 3.17
Practice problems page 506
Concentration from pH
• What is the concentration of H3O+ if the pH
is 1.5?
• pH = -log ( 1x10-1.5 )
• pH = 1 * 10 ^(-1.5)
• 0.032M
• [H3O+ ] = 0.032M
• Practice problems page 508
pg 523
• 5,6,8-16 – due on Wed May 20
• In class on the 20th 15-1 ws
• In class on the 20th will do titration notes
Titrations
• Controlled addition and measurement of
the amount of a solution of known
concentration required to react completely
with a measured amount of a solution of
unknown concentration.
• Using a known molarity of one solution,
you can titrate to find the molarity of the
unkown solution.
• 20 mL of a 0.005 M NaOH solution is used
to reach the end point ( point where
indicator changes color) in the titration of
10mL of HCl
• Balanced equation find 1:1 ratio
• Find moles in 20mL of NaOH = .0001
moles
• Use stoich. Ratio so 0.001 moles HCl
• Find M, .001moles/.01L = 0.01M HCl
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Study sample problem F pg 520
Do the practice problems 1,2 –self check
Do #2,3 section review pg 521
In class – some problems if time
Hw due 22 – problems ½ day
24, 25, 35, 36, 37 pg 524
• 26th 15.2 review worksheet
• 27th SG
• Cats Cradle – ice nine
• 29th test