Finding pH

© 2011 Pearson Education, Inc. Chapter 14 – Acids and Bases 4. Which of the following metals does not react with hydrochloric acid? A. Calcium B. Copper C. Magnesium D. Zinc

Acid Properties Sour taste (grape fruit) Sour taste (grape fruit) Found in many fruits Found in many fruits Vinegar Vinegar Will burn if not diluted Will burn if not diluted Made up of Nonmetals Made up of Nonmetals Acid formulas usually start with hydrogen- ex HCl, H 2 SO 4 Acid formulas usually start with hydrogen- ex HCl, H 2 SO 4

Base Properties Bitter taste Slippery feel Most household cleaners Also dangerous if not diluted Made up of a metal and nonmetals in formulas Arrhenius bases start with metals in their formulas and end with a OH- ex NaOH, KOH, Ba(OH) 2

Arrhenius Theory Acids release hydrogen ions (H + ) Acids release hydrogen ions (H + ) HCl → H + + Cl - HCl → H + + Cl - Bases release hydroxide ions (OH - ) Bases release hydroxide ions (OH - ) NaOH → Na + + OH -

6 Know the strong acids & bases!

Brønsted-Lowry Theory D7C20 ACID: any substance that donates a proton (hydrogen ion ) ACID: any substance that donates a proton (hydrogen ion ) BASE: any substance that accepts a proton (hydrogen ion ) BASE: any substance that accepts a proton (hydrogen ion ) MUST occur together; Can not gain unless something else loses MUST occur together; Can not gain unless something else loses

Conjugate Pairs

Chemical Reactions: New products are formed Differ by ONLY H +

Hydronium ion – An ion formed when a free H + forms with water to form an H 3 O + Hydronium ion – An ion formed when a free H + forms with water to form an H 3 O +

Why is Water Neutral? When one water gains, another loses a H+ [H 3 O+ ] = [OH-] [H 3 O+ ] = [OH-]

12 Water H 2 O can function as both an ACID and a BASE. Equilibrium constant for water = K w K w = [H 3 O + ] [OH - ] = 1.00 x at 25 o C AUTOIONIZATION

13 Water K w = [H 3 O + ] [OH - ] = 1.00 x at 25 o C In a neutral solution [H 3 O + ] = [OH - ] so [H 3 O + ] = [OH - ] = 1.00 x M Autoionization K w = 1.00 x ONLY at 25 o C (depends on T)

14 [H 3 O + ], [OH - ] and pH A common way to express acidity and basicity is with pH pH = - log [H 3 O + ] In a neutral solution, [H 3 O + ] = [OH - ] = 1.00 x at 25 o C pH = -log (1.00 x ) = - (-7) = 7

The pH scale only for water solutions Basic = more OH- Acidic = more H 3 O+ Neutral H 3 O+ = OH-

Why at a pH = 7 ? Determined by concentration [ X ] of each ion Determined by concentration [ X ] of each ion [H+ ]= [OH-] = M The concentration of hydrogen ion equals the concentration of hydroxide ion equals ten to the negative seventh molar concentration Need to remember molarity and concentration

Any pX Scales In general pX = -log X pOH = - log [OH - ] pH = - log [H + ] pH = - log [H + ]

Determining pOH pH + pOH = 14 If know one can determine the other. If pH = 13, what is the pOH? 13 + pOH = 14 pOH = 14 – 13 = 1

19 [H 3 O + ], [OH - ] and pH What is the pH of M NaOH(aq)? [OH - ] = 1.0 x M [H 3 O + ] = 1.0 x M pH = - log (1.0 x ) = General conclusion — Basic solution pH > 7 Neutral pH = 7 Acidic solutionpH < 7

20 [H 3 O + ], [OH - ] and pH If the pH of Coke is 3.12, it is ________. log [H 3 O + ] = - pH = Take antilog and get [H 3 O + ] = 10 -pH [H 3 O + ] = = 7.6 x M ACID

21 Calculate pH IF [OH - ] = 4.2 x M so pOH = - log [OH - ] = 3.37 pH + pOH = 14, pH = 10.63

14.7 SAMPLE PROBLEM © 2011 Pearson Education, Inc. Calculating pH Determine the pH for a solution with [H 3 O + ] = 5  10 – 8 M. SOLUTION STEP 1 Press the log key Enter the [H 3 O + ] value. STEP 2 change the sign. STEP 3 Adjust the number of significant figures on the right of the decimal point to equal the SFs in the coefficient.

14.9 SAMPLE PROBLEM Calculating [H 3 O + ] from pH Calculate [H 3 O + ] for a solution of baking soda with a pH of STEP 1 Change the sign of pH STEP 2 enter the negative pH as the exponent : 10 -pH STEP 3 Write the display with units of concentration × 10 –9 M Adjust the significant figures in the coefficient. Because the pH value of 8.25 has two digits on the right of the decimal point, the [H 3 O + ] is written with two significant figures: [H 3 O + ] = 5.6  10 –9 M

© 2011 Pearson Education, Inc. Chapter 14 – Acids and Bases 9. What is the [H + ] of a solution at pH 3.5? A. 5.3 x B. 6.0 x C x D x 10 -3

pH = - log [H + ] = 0 pH = - log [H + ] = 2 [H 3 O + ] = 10 -pH = M [H+ ]= [HX]

27 Calculating [H 3 O + ] & [OH - ] mol of NaOH ia added to 1.0 L of pure water: Calculate [H 3 O + ] and [OH - ]. [NaOH] = [OH - ]= 5  10 –2 M NaOH → Na + + OH - pOH= -log ( 5  10 –2 M) = = 1.3 pH = 14 –1.3 = [ H 3 O + ] =  10 -pH M = 2.0  M

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29 Calculating [H 3 O + ] & [OH - ] 2[ Mg(OH) 2 ] = [OH - ]= 2x 7.5  10 –6 M Mg(OH) 2 → Mg OH - pOH= -log (1.5  10 –5 M) = = 4.8 pH = 14 –4.8= 9.2 [ H 3 O + ] =  10 -pH M = 6.3  M