1. HUMAN IMPACT ON AIR QUALITY September 24, 2013

2. pH Scale 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

3. Measuring pH with wide-range paper

4. Narrow-Range pH Paper

5. pH Indicators and their ranges

6. Some Acid-Base Indicators Indicator pH Range in which Color Change Occurs Color Change as pH Increases Crystal violet Thymol blue Orange IV Methyl orange Bromcresol green Methyl red Chlorophenol red Bromthymol blue Phenol red Neutral red Thymol blue Phenolphthalein Thymolphthalein Alizarin yellow Indigo carmine 0.0 - 1.6 1.2 - 2.8 1.4 - 2.8 3.2 - 4.4 3.8 - 5.4 4.8 - 6.2 5.2 - 6.8 6.0 - 7.6 6.6 - 8.0 6.8 - 8.0 8.0 - 9.6 8.2 - 10.0 9.4 - 10.6 10.1 - 12.0 11.4 - 13.0 yellow to blue red to yellow red to yellow red to yellow yellow to blue red to yellow yellow to red yellow to blue yellow to red red to amber yellow to blue colorless to pink colorless to blue yellow to blue blue to yellow

7. 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

8. Some examples of acids and bases  Common acids:  Binary acids: HF, HCl, HBr, HI  Oxyacids: HNO 3, H 2 SO 4, H 2 CO 3  Organic acids: carboxylic acids O 4 and HClO 4 are among the only known strong acids.  Common bases:  Inorganic bases: metal hydroxides, ammonia  Organic bases: amines

9. Acid-base reactions 2 definitions for acids and bases: hydronium ion – H 3 O+ Arrhenius defBronsted-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.

10. HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids. The strength of an acid (or base) is determined by the amount of IONIZATION. Strong Acids

11.  Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 CO 2 H Strong and Weak Acids/Bases

12. Some examples of acids and bases  Common acids:  Binary acids: HF, HCl, HBr, HI  Oxyacids: HNO 3, H 2 SO 4, H 2 CO 3  Organic acids: carboxylic acids  Common bases:  Inorganic bases: metal hydroxides, ammonia  Organic bases: amines

14. 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) 

15.  Strong Base:100% dissociated in water.  Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Other common strong bases include KOH and Ca(OH) 2. CaO (lime) + H 2 O --> Ca(OH) 2 (slaked lime) Ca(OH) 2 (slaked lime) CaO

16.  Weak base:less than 100% ionized in water  Weak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) Strong and Weak Acids/Bases

17. 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

18. The pH scale  Every aqueous solution has both hydronium and hydroxide ions present in low concentrations.  Inversely proportional  If [H 3 O + ] > [OH - ] then  If [OH - ] > [H 3 O + ] then  This can be translated into the pH scale: pH = -log[H 3 O + ] (Taking the “log” of a number means finding the exponent if the number is expressed as 10 x.)

19. Self-Ionization of Water H 2 O + H 2 O  H 3 O + + OH - Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

21. Ion Concentration in Solutions

22. 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 +. H 2 SO 4 + NH 3  HSO 4 - + NH 4 +

23. 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) + H 2 O(l)  NH 3 (aq) + H 2 O(l) 

24. The pH scale Every aqueous solution has both hydronium and hydroxide ions present in low concentrations. – Inversely proportional – If [H 3 O + ] > [OH - ] then – If [OH - ] > [H 3 O + ] then This can be translated into the pH scale: pH = -log[H 3 O + ]  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 10 x.)

25. Calculating pH, pOH pH = -log (H 3 O + )pOH = -log (OH - ) Relationship between pH and pOH pH + pOH = 14 Finding [H 3 O + ], [OH - ] from pH, pOH [H 3 O + ] = 10 -pH [OH - ] = 10 -pOH

26. Practice with pH pHpOH[H 3 O + ][OH - ] Solution acidity 4.50 7.5 1 x 10 -5 M 6.23 x 10 -12 M

27. acid rain simplified:

32. 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.

33. 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

34. 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 SO 2 gas  Disposal procedure

35. Post lab discussion What are the 2 reactions that occured in this acid rain simulation in the bag?

38. Buffers  What does a buffer do?  What is the chemical composition of a buffer?  How does a buffer work?

39. 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

40. 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.

45. 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!