SC STANDARD COVERED ACIDS & BASES Standard PS-3.7 Classify various solutions as acids or bases according to their physical properties, chemical properties (including neutralization and reaction with metals), generalized formulas, and ph (using ph meters, or ph paper, and litmus paper). ACIDS produce H + /H 3 O + (hydronium ion) in solution Formulas start with H (except for H 2 O and H 2 O 2 ) PROPERTIES OF ACIDS 1. Sour to taste 2. React with some metals to form H 2 gas (corrosive to metals) PROPERTIES OF ACIDS 3. Turn litmus red 4. Phenolphthalein stays colorless PROPERTIES OF ACIDS 5.Electrolytes (conduct) 6.pH < 7 7.Corrosive to body tissues 1
COMMON ACIDS COMMON ACIDS Acetic Acid (Vinegar) - HC 2 H 3 O 2 Folic acid - orange juice Phosphoric acid - H 3 PO 4 - soda Ascorbic acid - vitamin C - citrus fruits COMMON ACIDS Hydrochloric acid - HCl - stomach acid NAMING ACIDS Battery acid H 2 SO 4 sulfuric acid NAMING ACIDS HCl HI HNO 3 H 2 S H 2 SO 4 H 3 PO 4 BASES produce OH - (hydroxide ions) in solution Formulas end with OH (except for NH 3 ) H 2 SO 3 HBr H 2 CO 3 2
PROPERTIES OF BASES 1. Bitter to taste 2. Slippery to touch PROPERTIES OF BASES 3. Turn litmus blue 4. Phenolphthalein turns Magenta PROPERTIES OF BASES 5. Electrolytes 6. ph>7 7. Corrosive to skin and body tissues COMMON BASES Mg(OH) 2 Magnesium hydroxide- antacids NH 3 ammonia cleaners, fertilizers COMMON BASES NaOH Sodium hydroxide- Drano Al(OH) 3 aluminum hydroxide- deodorant NEUTRALIZATION REACTION A reaction where an acid reacts with a base. The products are water and a salt. Acid + Base water + salt HCl + NaOH H 2 O + NaCl An Acid is used to neutralize a base and vice versa. This is a double displacement reaction!!! Nothing new 3
NEUTRALIZATION REACTION IDENTIFYING ACIDS AND BASES HCl + NaOH 2 HNO 3 + Ba(OH) 2 H 2 SO 4 + 2 LiOH 2 HClO 4 + Ca(OH) 2 NaCl + H 2 O Ba(NO 3 ) 2 + 2 H 2 O Li 2 SO 4 + 2 H 2 O Ca(ClO 4 ) 2 + 2 H 2 O If a solution contains more H + (H 3 O + ) than OH - then it is acidic. If a solution contains more OH - than H + then it is basic. If a solution contains equal amounts of H + and OH - then it is neutral (HOH = H 2 O) THE ph SCALE ph - measurement of the hydrogen ion (H + ) concentration (Molarity) measures how acidic or basic a solution is. ph scale goes from 0-14. 7 is neutral. Less than 7 is acid. Lower ph, the more acidic Greater than 7 is base. Higher ph, the more basic. DETERMINING ph ph is tested for three ways: ph meter Litmus paper red paper turns blue if it is a base and blue paper turns red if it is an acid Indicator compound which turns different colors based on the ph of the solution it is in CALCULATING ph ph = measure of H 3 O +, expressed in powers of 10 ex: 10-14 to 10-1 Formula for calculating ph: ph = -log[h 3 O + ] [ ] means Molarity CALCULATING ph Example: What is the ph of a 1.8 x10-5 M acidic solution? ph = -log[h 3 O + ] ph = - log 1.8 X 10-5 ph = - (- 4.74) ph = 4.7 4
CALCULATING ph ph AND poh Find the ph of these: 1) A 0.15 M solution of Hydrochloric acid 2) A 3.00 X 10-7 M solution of Nitric acid ph = -log[h 3 O + ] ph = - log 0.15 ph = 0.82 ph = - log (3.00 x 10-7 ) ph = 6.52 ph measures [H 3 O + ] concentration, but not everything we measure is an acid poh measures [OH - ] concentration Use this formula if the substance being tested is a base. poh = -log[oh - ] poh Find the poh of a sodium hydroxide solution with a concentration of 2.5 x 10-4 M. Calculating ph from poh ph + poh = 14 poh = -log[oh - ] poh = -log[2.5 x 10-4 ] poh = 3.6 ph = 14 - poh poh = 14 - ph Calculating ph from poh What is the ph of a 0.0035 M barium hydroxide solution? Starting with a base means you have to find poh poh = -log [0.0035] poh = 2.4 ph = 14 poh ph = 14 (2) = 12 Calculating ph from poh Calculate the ph and poh for the following: a. H 3 O + = 4.25 x 10-10 M ph = 9.37 poh = 4.63 b. OH - = 8.52 x 10-7 M c. OH - = 2.79 x 10-3 M poh = 6.07 ph = 7.93 poh = 2.55 ph = 11.4 5
STRENGTH OF ACIDS AND BASES STRONG ACIDS/BASES Dissociate completely in water (break up into ions) Are strong electrolytes Higher reaction rate HCl (aq) + H 2 O (l) H 3 O + + Cl - NaOH Na + + OH - WEAK ACIDS/BASES Partially dissociates in solution Are weak electrolytes Lower reaction rate HF + H 2 O H 3 O + + F - NH 3 + H 2 O NH 4+ + OH - TITRATIONS Determine the concentration of a solution (solution 1) by reacting a known volume with another solution (solution 2) of known concentration Use Dilution Formula Slowly add acid to base or vice versa Indicator placed in the beaker will change colors as the ph changes TITRATIONS Indicator changes colors quickly known as the end point. When the indicator color changes, you have passed the equivalence point. Strong acid + strong base = neutral solution Weak acid + strong base = weak base Strong acid + weak base = weak acid 6
CALCULATIONS TITRATION PROBLEMS 50.0 ml of 4.0 M HCl were titrated with 250.0 ml of LiOH. What is the concentration of the lithium hydroxide? Where M is the molarity & V is the volume Used to determine final concentration vs original concentration M a = 4.0 M HCl V a = 50.0 ml V b = 250.0 ml LiOH M b =? 4.0 M 50.0 ml = M b (250.0 ml) 200 M ml M b = 250.0 ml M b = 0.80 M TITRATION PROBLEMS 150.0 ml of a 1.5 M NaOH solution were used to titrate 250.0 ml of acetic acid. What is the concentration of acetic acid? M b = 1.5 M NaOH V b = 150.0 ml V a = 250.0 ml HC 2 H 3 O 2 M a =? M a (250.0 ml) = 1.5 M 150.0 ml 225 M ml M a = 250.0 ml TITRATION PROBLEMS What is the concentration of 90.0 ml of KOH when it was used to titrate 50.0 ml of 2.0 M H 2 SO 4? M a = 2.0 M H 2 SO 4 V a = 50.0 ml V b = 250.0 ml KOH M b =? 2.0 M 50.0 ml = M b (90.0 ml) 100 M ml M b = 90.0 ml M a = 0.90 M M b = 1.1 M BUFFER Solution that resists changes in ph when small amounts of acid or base are added 7