Unit 4 Toxins, Section IV, L17-22
Lesson 17 Heartburn Lesson 18 Pass the Proton Lesson 19 phooey! Lesson 20 Watered Down Lesson 21 Neutral Territory Lesson 22 Drip Drop
Acids and Bases
What are the properties of acids and bases?
identify acids and bases based on general observable properties explain how an indicator is used to determine whether a solution is acidic, basic, or neutral Indicator: An indicator is a molecular substance that changes color when it comes into contact with an acid or a base.
Almonds contain Amygdalin which, under certain conditions can produce hydrogen cyanide. In fact, cyanide gas has an almond scent.
Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) Taste sour Corrode metals (react to form H 2 (g)) Electrolytes React with bases to form a salt and water ph is less than 7 Turns blue litmus paper to red
Produce OH - ions in water Taste bitter, chalky Are electrolytes Feel slippery React with acids to form salts and water (neutralize) ph greater than 7 Turns red litmus paper to blue Basic Blue
NaOH sodium hydroxide lye KOH potassium hydroxide liquid soap Mg(OH) 2 magnesium hydroxide Milk of magnesia Al(OH) 3 aluminum hydroxide Maalox (antacid)
Hydrogen bromide ACIDS start with 'H' HBr hydrobromic acid 2 elements 3 elements Hydrogen carbonate hydro- prefix -ic ending no hydro- prefix H 2 CO 3 carbonic acid Hydrogen sulfite H 2 SO 3 sulfurous acid An easy way to remember In the cafeteria, you ATE something ICky -ate ending becomes -ic ending -ite ending becomes -ous ending
The substances on the left side of the number line (from 0 to 7) are all acids. The substances on the right side of the number line (from 7 to 14) are called bases. The substances located in the middle of the number line (around 7) are called neutral substances.
What are the properties of acids and bases? Acids and bases are solutions that are classified according to their observable behavior. Acids and bases change the color of indicators. Substances that are not acids or bases are considered neutral.
Acid-Base Theories
How are acids and bases defined?
define Arrhenius and Brønsted-Lowry acids and bases explain the behavior of acids and bases on a particulate level explain the difference between strong and weak acids and bases
Acids are substances that add H+ to solution. Bases are substances that add OH- to solution.
Svante Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H 3 O + (hydronium) ions in solution. Cl H + H O H H H O H + + Cl
Arrhenius (traditional) Acids increase [H + ] in aqueous solutions (H 3 O + ) Bases produce OH - ions in solution OR react with water to remove a H leaving OH -
Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water
Acid a molecule or ion that is a proton donor Bases a molecule or ion that is a proton acceptor After all, a proton is really just a hydrogen atom that has lost it s electron!
A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor base acid The Brønsted-Lowry definition also means NH 3 is a BASE in water and water is itself acts as an!
G.N. Lewis Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair H +.. H-N-H H H H:N-H H
Formation of hydronium ion is also an excellent example. H + ACID O H H BASE H O H H Electron pair of the new O-H bond originates on the Lewis base. Lewis acid - a substance that accepts an electron pair
The heme group in hemoglobin can interact with O 2 and CO. The Fe ion in hemoglobin is a Lewis acid O 2 and CO can act as Lewis bases
conjugate acid-base pairs Cl H + H H O H O H H + + acid base conjugate acid conjugate base Cl When an acid gives up a proton, it can re-accept that proton (act as a base) and visa versa Conjugate acids and bases are found on the products side of the equation.
Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH - Cl - + H 2 O acid base conjugate base conjugate acid H 2 O + H 2 SO 4 HSO 4 - + H 3 O + base acid conjugate base conjugate acid
Acids and bases that break apart (dissociate) completely in solution are called strong acids and strong bases. Acids and bases that do not dissociate completely in solution are called weak acids and weak bases.
Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION. HNO 3, HCl, H 2 SO 4 and HClO 4 are among the only known strong acids.
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 Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) Other common strong bases include KOH and Ca(OH) 2. CaO (lime) + H 2 O --> Ca(OH) 2 (slaked lime) CaO
Strong and Weak Acids/Bases 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)
[H+] and ph
How is ph related to the acid or base concentration of a solution?
explain the mathematical relationship between the H + and OH concentrations in a solution define ph and explain the relationship between H + concentration and ph determine the H + concentration of a solution given the [OH ], and vice versa
The ph scale is a logarithmic scale that describes the concentration of H + ions in solution. ph is related to [H + ] by the formula ph = -log [H + ]
If the ph of Coke is 3.12, [H + ] =??? Because ph = - log [H + ] then - ph = log [H + ] Take antilog (10 x ) of both sides and get 10 -ph = [H + ] [H + ] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for Shift or 2 nd function and then the log button
ph = - log [H+] Example: If [H + ] = 1 x 10-10 ph = - log (1 x 10-10 ) ph = - (- 10) ph = 10 Example: If [H + ] = 6.2 x 10-9 ph = - log (6.2 X 10-9 ) ph = - (- 8.21) ph = 8.21
another way to indicate [H 3 O + ] from French pouvoir hydrogene meaning hydrogen power Defined as: the negative of the common logarithm* of the hydronium ion concentration * Common log is the power to which 10 must be raised to equal the number
[H + ] is critical in many chemical reactions. A quick method of denoting [H + ] is via ph. By definition ph = log [H 3 O + ], [H + ] = 10 -ph The ph scale describes a wide range of values The ph scale condenses possible values of [H + ] to a 14 point scale Also, it is easier to say ph = 7 vs. [H + ] = 1 x 10 7
The ph scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the negative power of 10 on the Molarity of the H + (or OH - ) ion.
There are several ways to test ph Blue litmus paper (red = acid) Red litmus paper (blue = basic) ph paper (multi-colored) ph meter (7 is neutral, <7 acid, >7 base) Universal indicator (multi-colored) Indicators like phenolphthalein Natural indicators like red cabbage, radishes
Paper tests like litmus paper and ph paper Place a drop of the solution onto a piece of the paper Read and record the color change. Note what the color indicates. You should only use a small portion of the paper. You can use one piece of paper for several tests.
Tests the voltage of the electrolyte Converts the voltage to ph Very cheap, accurate Must be calibrated with a buffer solution
Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of ph Some dyes are natural, like radish skin or red cabbage
NOTE: this is an inverse relationship: As acids get stronger, [H + ], ph. A ph of 1 is a very strong acid. As bases get stronger, [H + ], ph. A ph of 14 is a very strong base.
ph [H + ] [OH - ] poh
Pure water has an [H + ] concentration of 1.0 x 10 7 M and an [OH ] of 1.0 X 10 7 M. What does this mean?
Remember: H 2 O can function as both an ACID and a BASE. In pure water there can be AUTOIONIZATION
Let s start with water Water undergoes slight self-ionization: in H 2 O @ 25 C: [H 3 O + ] = 1.0 X 10-7 M [OH - ] = 1.0 X 10-7 M because [OH - ] = [H 3 O + ] it is considered neutral SO if [OH - ] < [H 3 O + ] you have an acid [OH - ] > [H 3 O + ] you have a base
for water [OH - ][H 3 O + ] = 1.0 X 10-14 This is known as the ionization constant (K w ) and can be used in calculations to find [OH - ] and/or [H 3 O + ] for any acid or base solution with a known molarity. one more thing to know before calculating begins
Strong acids and bases are considered completely ionized or dissociated in water. It has been determined that 1 mole of acid (or base) = 1 mole of H 3 O + (or OH - ). In other words:.01 M NaOH has 1.0 X 10-2 moles [OH - ] For example 2 X 10-4 M HCl has 2 X 10-4 M [H 3 O + ]
So, if 2 X 10-4 M HCl has a 2 X 10-4 M [H 3 O + ], what is the [OH - ]? hint: remember that K w = [OH - ][H 3 O + ] = 1.0 X 10-14 hint: use your Algebra skills to solve for the unknown [OH - ] = 1.0 X 10-14 [H 3 O + ] Luke, use the force = 1.0 X 10-14 = 5.0 X 10-10 2.0 X 10-4 2.0 X 10-4 > 5.0 X 10-10 acid
H + concentration OH concentration ph 1.0 X 10 0 M 1.0 X 10 14 M 0 More acidic 1.0 X 10 1 M 1.0 X 10 13 M 1 1.0 X 10 2 M 1.0 X 10 12 M 2 1.0 X 10 3 M 1.0 X 10 11 M 3 1.0 X 10 4 M 1.0 X 10 10 M 4 1.0 X 10 5 M 1.0 X 10 9 M 5 1.0 X 10 6 M 1.0 X 10 8 M 6 1.0 X 10 7 M 1.0 X 10 7 M 7 neutral 1.0 X 10 8 M 1.0 X 10 6 M 8 1.0 X 10 9 M 1.0 X 10 5 M 9 1.0 X 10 14 M 1.0 X 10 0 M 14 More basic
Youtube review What is the ph of a 0.0010 M NaOH solution? [OH - ] = 0.0010 (or 1.0 X 10-3 M) poh = - log 0.0010 poh = 3 ph = 14 3 = 11 OR K w = [H 3 O + ] [OH - ] [H 3 O + ] = 1.0 x 10-11 M ph = - log (1.0 x 10-11 ) = 11.00
A solution has a ph of 8.5. What is the Molarity of hydrogen ions in the solution? ph = - log [H + ] 8.5 = - log [H + ] -8.5 = log [H + ] Antilog -8.5 = antilog (log [H + ]) 10-8.5 = [H + ] 3.16 X 10-9 = [H + ]
What is the [H + ] if ph = 7.4? [H + ] = 10 ph mol/l ph = -log[h + ] -ph = log [H + ] Antilog (-ph) = [H + ] 1 x 10 -ph = [H + ] 3.98 x 10 8 M
Hank on ph Both humans and aquatic organisms depend on water. The ph of water must be within a range of 5 to 9 in order for organisms to survive. Waters with a ph less than about 5 are too acidic for humans to drink and will not allow most aquatic life to survive. Waters that are too basic can also harm humans, plants, and animals. Water with a ph of greater that 9 can dissolve materials such as animal scales and skin.
It s very important that the ph levels of water don t increase or decrease too much out of a certain range. This change could affect food chains and the survival of species.
How can ph levels change? ph can be affected by the chemicals in the water. The ph of water affects organisms living in the water. A changing ph in water can mean that there is an increase of pollution or some other environmental factor. Things such as burning fossil fuels (like with cars), mining, chemical spills, runoff (washing cars and farming), and sewage cause ph levels to change.
How is ph related to the acid or base concentration of a solution? The ph scale is a logarithmic scale that describes the concentration of hydrogen ions, H +, in solution: ph = -log [H + ]. The H + concentration is related to the OH concentration: [H + ][OH ] =10 14. So, as [H + ] increases, [OH ] decreases, and vice-versa. The ph of water is 7. In water the H + concentration is equal to the OH concentration. Thus, water is neutral.
Acid/Base Reactions
Acidic compounds react with basic compounds and neutralize each other producing a salt (and usually gas and water too!) NaHCO 3 + HCl Base Acid Salt NaCl + H 2 (g) + H 2 O Neutralization is the reaction of hydronium ions and?! Huh?! hydroxide ions to form water.
What happens when HCl and NaOH are combined in water? NaOH + H 2 O dissociates to produce Na + and OH - ions HCl completely ionizes in H 2 O to produce H 3 O + and Cl - ions The equation of the reaction: H 3 O + + Cl - + Na + + OH - Na + + Cl - + 2H 2 O Cl and Na + appear on both sides of the equation and are known as spectator ions If the solution evaporates, and additional product is formed: NaCl a salt: an ionic compound formed of a cation from a base and an anion from an acid.
We can use this knowledge to find an unknown concentration of an acid or a base by performing a procedure known as a titration
A neutralization reaction 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3. Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION.
Dilution
Add water to the 3.0 M solution to lower its concentration to 0.50 M Dilute the solution!
But how much water do we add?
How does dilution affect acids and bases?
How much water is added? The important point is that ---> moles of NaOH in ORIGINAL solution = moles of NaOH in FINAL solution
Amount of NaOH in original solution = M V = (3.0 mol/l)(0.050 L) = 0.15 mol NaOH Amount of NaOH in final solution must also = 0.15 mol NaOH Volume of final solution = (0.15 mol NaOH)(1 L/0.50 mol) = 0.30 L or 300 ml
Conclusion: add 250 ml of water to 50.0 ml of 3.0 M NaOH to make 300 ml of 0.50 M NaOH.
A shortcut M 1 V 1 = M 2 V 2
You have a stock bottle of hydrochloric acid, which is 12.1 M. You need 400 ml of 0.10 M HCl. How much of the acid and how much water will you need? M 1 V 1 =M 2 V 2 12.1(x) = (400)(0.10) 12.1x = 40 x = 3.3
complete a serial dilution of a solution explain the effect of dilution on the acidity or basicity of a solution
Adding water to an acid or a base dilutes the solution, making it less acidic or less basic. NOTE! An acid can never be turned into a base by diluting it with water, and a base can never be turned into an acid by diluting it with water.
Each time the H+ concentration is diluted tenfold, the ph number goes up 1 unit. ph H+ concentration (decimal number) H+ concentration (scientific notation) 2 0.010 mol/l 1.0 X 10 2 mol/l 3 0.0010 mol/l 1.0 X 10 3 mol/l 4 0.00010 mol/l 1.0 X 10 4 mol/l 5 0.000010 mol/l 1.0 X 10 5 mol/l 6 0.0000010 mol/l 1.0 X 10 6 mol/l 7 0.00000010 mol/l 1.0 X 10 7 mol/l
Neutralization Reactions
Excess stomach acid, HCl, can cause extreme discomfort and pain. Milk of magnesia, Mg(OH) 2, is often taken to reduce stomach acid. a. What products do you think are produced when Mg(OH) 2 and HCl are mixed? b. What products do you think are produced when HNO 3 and HCl are mixed?
What happens when acids and bases are mixed?
write a chemical equation for an acid-base neutralization reaction describe how the ph changes when acids and bases are mixed
A neutralization reaction between a strong acid and a strong base in aqueous solution produces an ionic compound (salt) and water. A neutralization reaction can be described as a double exchange reaction in which the two compounds exchange cations.
Sulfuric acid, H 2 SO 4 (aq), reacts with magnesium hydroxide, Mg(OH) 2 (aq). Write a balanced equation for the reaction that occurs. H 2 SO 4 (aq) + Mg(OH) 2 (aq) MgSO 4 + H 2 O