HUMAN IMPACT ON AIR QUALITY

September 24, 2013

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

Measuring pH with wide-range paper

Narrow-Range pH Paper

pH Indicators and theirranges

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

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

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

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.

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

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

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

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)

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

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

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

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.)

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”

Ion Concentration in Solutions

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

+

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)

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.)

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

Practice with pH

pH pOH [H3O+] [OH-] Solution acidity

4.50

7.5

1 x 10-5 M

6.23 x 10-12 M

acid rain simplified:

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.

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

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

Post lab discussion

What are the 2 reactions that occured in this acid rain simulation in the bag?

Buffers

What does a buffer do?

What is the chemical composition of a buffer?

How does a buffer work?

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

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.

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!