human impact on air quality september 24, 2013. ph scale ph scale – measures how acidic an object...
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HUMAN IMPACT ON AIR QUALITY
September 24, 2013
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pH ScalepH scale – measures how acidic an object is. pH value is related to its hydronium ion concentration.
how many times greater is the acidity in pH 4 than pH 5
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Measuring pH with wide-range paper
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Narrow-Range pH Paper
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pH Indicators and theirranges
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Some Acid-Base Indicators
Indicator pH Range in whichColor Change Occurs
Color Changeas pH Increases
Crystal violetThymol blueOrange IVMethyl orangeBromcresol greenMethyl redChlorophenol redBromthymol bluePhenol redNeutral redThymol bluePhenolphthaleinThymolphthaleinAlizarin yellowIndigo carmine
0.0 - 1.61.2 - 2.81.4 - 2.83.2 - 4.43.8 - 5.44.8 - 6.25.2 - 6.86.0 - 7.66.6 - 8.06.8 - 8.08.0 - 9.6
8.2 - 10.09.4 - 10.610.1 - 12.011.4 - 13.0
yellow to bluered to yellowred to yellowred to yellowyellow to bluered to yellowyellow to redyellow to blueyellow to redred to amberyellow to bluecolorless to pinkcolorless to blueyellow to blueblue to yellow
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Strong vs. Concentrated
pH scale – measures how acidic an object is.pH value is related to its hydronium ion concentration.
how many times greater is the acidity in pH 4 than pH 5
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Some examples of acids and bases
Common acids: Binary acids: HF, HCl, HBr, HI
Oxyacids: HNO3, H2SO4, H2CO3
Organic acids: carboxylic acidsO4 and HClO4 are among the only known strong acids.
Common bases: Inorganic bases: metal hydroxides, ammonia Organic bases: amines
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Acid-base reactions2 definitions for acids and bases:
hydronium ion – H3O+
Arrhenius def Bronsted-Lowry def
Acid any substance that generates, H+, ions when dissolved in water
is a molecule or ion that is able to lose, or "donate," a hydrogen cation.
Base Any substance that generates OH- ions when dissolved in water.
is a molecule or ion that is able to gain, or “accept” a hydrogen cation.
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HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.
The strength of an acid (or base) is determined by the amount of IONIZATION.
The strength of an acid (or base) is determined by the amount of IONIZATION.
Strong Acids
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Weak acids are much less than 100% ionized in water.
One of the best known is acetic acid = CH3CO2H
Strong and Weak Acids/BasesStrong and Weak Acids/Bases
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Some examples of acids and bases
Common acids: Binary acids: HF, HCl, HBr, HI
Oxyacids: HNO3, H2SO4, H2CO3
Organic acids: carboxylic acids Common bases:
Inorganic bases: metal hydroxides, ammonia Organic bases: amines
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Acid-base reactions
Label the acid and the base, then complete the reaction
1)HI(aq) + KOH(aq)
2) phosphoric acid(aq) + ammonia(aq)
3) sodium bicarbonate(aq) + HBr(aq)
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Strong Base: 100% dissociated in water.
NaOH (aq) ---> Na+ (aq) + OH- (aq)
Strong and Weak Acids/Bases
Other common strong bases include KOH and
Ca(OH)2.
CaO (lime) + H2O -->
Ca(OH)2 (slaked lime)CaO
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Weak base: less than 100% ionized in water
One of the best known weak bases is ammonia
NH3 (aq) + H2O (l) NH4+ (aq) +
OH- (aq)
Strong and Weak Acids/BasesStrong and Weak Acids/Bases
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Strong vs. weak acids Strong acids (only ~6 of them):
100% ionized in water NOT treated as an equilibrium
Weak acids (all other acids): Only partially ionized in water In equilibrium with the conjugate base
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The pH scale
Every aqueous solution has both hydronium and hydroxide ions present in low concentrations. Inversely proportional If [H3O+] > [OH-] then If [OH-] > [H3O+] then
This can be translated into the pH scale:pH = -log[H3O+]
(Taking the “log” of a number means finding the exponent if the number is expressed as 10x.)
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Self-Ionization of Water
H2O + H2O H3O+ + OH-
Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”
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Ion Concentration in Solutions
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Conjugate pairs
After an acid has donated its H+, what is left over is called the conjugate base
Conjugate acid/base pair = two substances that differ by only one H+.
H2SO4 + NH3 HSO4- + NH4
+
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Water can be either an acid or a base
Water is amphiprotic (amphoteric): can donate OR accept a proton, depending on what it is reacting with
Examples:HCl(aq) + H2O(l)
NH3(aq) + H2O(l)
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The pH scale
• Every aqueous solution has both hydronium and hydroxide ions present in low concentrations.– Inversely proportional– If [H3O+] > [OH-] then
– If [OH-] > [H3O+] then
• This can be translated into the pH scale:pH = -log[H3O+]
Important Note! pH depends on acid strength (extent of ionization) BUT also concentration. So, a strong acid can have a higher pH if it is at a low molarity (ex. 0.001M HCl)
(Taking the “log” of a number means finding the exponent if the number is expressed as 10x.)
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Calculating pH, pOH
pH = -log (H3O+) pOH = -log (OH-)
Relationship between pH and pOH
pH + pOH = 14
Finding [H3O+], [OH-] from pH, pOH
[H3O+] = 10-pH
[OH-] = 10-pOH
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Practice with pH
pH pOH [H3O+] [OH-] Solution acidity
4.50
7.5
1 x 10-5 M
6.23 x 10-12 M
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acid rain simplified:
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Molarity
You are working with 4M HCl (4moles of HCl per liter) but you only have a bottle with 50mL of the 4M solution. How many moles of HCl do you have in your bottle? A. Greater than 4 moles HCl B. 4 moles of HCl C. Less than 4 moles of HCl
Calculate the exact amount of moles in the 50mL of 4M HCl bottle.
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Pre-lab
Purpose of our lab: To create acid rain and observe its effect on the
following: Plants (apple skin) Metals (magnesium) Marble (calcium carbonate)
Background: What reactants do we need to make acid rain? Why are we concerned with acid rain’s effect on the
following objects? Living things, man-made structures and natural structures.
Notes on Procedure
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Pre-lab discussion cont…
Notes on Procedure Changes
Sodium sulfite has been changed to sodium bisulfite Notes on technique
Use weigh boats to measure out sodium bisulfite Make sure bag is completely zipped up before
squeezing the pipet bulb. Safety precautions:
6M HCl SO2 gas
Disposal procedure
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Post lab discussion
What are the 2 reactions that occured in this acid rain simulation in the bag?
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Buffers
What does a buffer do?
What is the chemical composition of a buffer?
How does a buffer work?
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Buffers
What do they do? When a buffer is present it can keep the pH of
a solution almost constant when small amounts of acid or bases are added.
What are they? Buffer – is made up of a PAIR of chemicals –
1)an acid to neutralize a base and 2) a base to neutralize an added acid.
(weak acid + salt of the weak acid OR weak base + salt of weak base)
BUFFER CAPACITY – the point at which the buffer is “used-up” and no longer will stablize the pH
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Buffers in our Blood
pH of our blood = 7.35-7.45 Drops below 7.35 – acidosis Rises above 7.45 – alkalosis
Human blood has 3 buffer systems – most imp. is the hydrogen carbonate and carbonic acid.
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Re-visiting projects
Writing a scientific question: Researching your topic is important. What
about this topic do you want to find more info about – is the claim accurate? Design a test to see if it is!