Acids, Bases and Salts

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Discusses the definitions, properties and calculations associated with acid / base chemistry
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Acids, Bases and Salts

  1. 1. Copyright Sautter 2015
  2. 2. ACIDS, BASES & SALTS WHAT IS AN ACID ? WHAT IS A BASE ? WHAT ARE THE PROPERTIES OF ACIDS AND BASES ? WHAT ARE THE DIFFERENT KINDS OF ACIDS AND BASES ? HOW ARE ACIDS AND BASES NAMED?
  3. 3. PROPERTIES OF ACIDS • CONTRARY TO COMMON BELIEF ACIDS DO NOT ATTACK ALL SUBSTANCES. MANY ARE VITAL TO OUR VERY EXISTENCE ! • ALL ACIDS DO HOWEVER HAVE SEVERAL COMMON CHARACTERISTICS. • (1) ACIDS TASTE SOUR • (2) ACIDS TURN LITMUS RED (LITMUS IS A DYE THAT CHANGES COLOR DEPENDING ON ACIDITY) • (3) ACIDS REACT WITH ACTIVE METALS TO FORM HYDROGEN GAS • (4) ACIDS REACT WITH BASES TO FORM SALTS AND WATER I’VE GOT TOO MUCH HCl ! 3
  4. 4. PROPERTIES OF BASES • (1) BASES TASTE BITTER (MEDICINES ARE OFTEN BASES THUS THE TERM “BITTER MEDICINE”) • (2) BASES TURN LITMUS BLUE • (3) BASES FEEL SLIPPERY • (4) BASES REACT WITH ACIDS TO FORM SALTS AND WATER 4
  5. 5. DEFINITION OFACIDS AND BASES • ACIDS AND BASES AND THE REACTIONS WHICH RESULT CAN BE DESCRIBED USING SEVERAL DIFFERENT THEORIES. • THE THREE MOST COMMON THEORIES ARE: • (1) THE ARRENHIUS OR TRADITATIONAL THEORY • (2) THE BRONSTED – LOWRY THEORY • (3) THE LEWIS THEORY • EACH OF THE THREE THEORIES VIEW ACIDS AND BASES SLIGHTLY DIFFERENTLY BUT THEY DO NOT CONTRADICT EACHOTHER IN ANY WAY. ONE MERELY EXPANDS ON THE OTHER ! 5
  6. 6. THE ARRENHIUS OR TRADITIONAL ACID – BASE THEORY • AN ACID IS A SUBSTANCE WHICH RELEASES HYDROGEN IONS (H+) IN SOLUTION. • HNO3(aq)  H+ (aq) + NO3 - (aq) • A BASE IS A SUBSTANCE WHICH RELEASES HYDROXIDE IONS (OH-) IN SOLUTION. • NaOH(S)  Na+ (aq) + OH- (aq) • WHEN AN ACID AND BASE REACT (A REACTION CALLED NEUTRALIZATION), A SALT AND WATER ARE FORMED. • HNO3(aq) + NaOH(aq)  NaNO3(aq) + H2O(aq) (acid) (base) (salt) (water) 6
  7. 7. COMMON ACIDS & BASES • HYDROCHLORIC ACID (STOMACH ACID) – HCl • ACETIC ACID (VINEGAR) – HC2H3O2 • CARBONIC ACID (SODA WATER) – H2CO3 • SODIUM HYDROXIDE (DRAINO) – NaOH • AMMONIA WATER (CLEANING AGENT) – NH4OH • ALUMINUM HYDROXIDE (ROLAIDS) – Al(OH)3 7
  8. 8. THE BRONSTED – LOWRY ACID AND BASE THEORY • AN ACID IS A PROTON DONOR. A PROTON IN SOLUTION CONSISTS OF A HYDROGEN ION (H+). (HYDROGEN WITH AN ATOMIC NUMBER OF ONE AND A MASS NUMBER OF ONE HAS ONE PROTON, NO NEUTRONS AND AFTER LOSING ONE ELECTRON TO FORM AN ION, HAS NO ELECTRONS.) • A BASE IS A PROTON ACCEPTOR AND IT NEED NOT CONTAIN HYDROXIDE IONS. • AN ACID – BASE REACTION CONSISTS OF A PROTON TRANSFER FROM AN ACID TO A BASE. WHEN THIS OCCURS A NEW ACID AND BASE ARE FORMED. THIS IS BRONSTED- LOWRY NEUTRALIZATION. • HCl(aq) + H2O(aq)  H3O+ (aq) + Cl- (aq) (acid) (base) (new acid) (new base) 8
  9. 9. A CLOSER LOOK AT BRONSTED – LOWRY ACID – BASE REACTIONS (1) WATER CAN ACT AS A BASE. AT TIMES IT CAN EVEN ACT AS A ACID.. THE TERM IS AMPHIPROTIC MEANS THAT IT CAN BE EITHER DEPENDING ON THE SITUATON. (2) WHEN WATER ACTS AS A BASE H3O+ ION IS FORMED. THIS CALLED HYDRONIUM ION. (3) THE ORIGINAL BASE (H2O) AFTER RECEIVING THE PROTON CAN NOW FUNCTION AS AN ACID IN THE REVERSE REACTION. HYDRONIUM ION IS CALLED THE CONJUGATE ACID OF THE BASE WATER IN THIS REACTION. (4) THE ORIGINAL ACID (HCl)AFTER LOSING THE PROTON CAN NOW FUNCTION AS AN BASE IN THE REVERSE REACTION. CHLORIDE ION IS CALLED THE CONJUGATE BASE OF THE ACID HYDROCHLORIC ACID IN THIS REACTION. HCl(aq) + H2O(aq)  H3O+ (aq ) + Cl- (aq)acid base conjugate acid conjugate acid 9
  10. 10. LEWIS ACID – BASE THEORY • THE LEWIS ACID – BASE THEORY EXPANDS THE ARRENHIUS AND BRONSTED LOWRY THEORIES TO INCLUDE EVEN MORE SUBSTANCES WHICH HAVE BEEN FOUND EXPERIMENTALLY TO BE ACIDIC OR BASIC BUT NOT COMPLETELY EXPLAINED BY EITHER. • THE LEWIS THEORY DESCRIBES ACIDS AS ELECTRON PAIR ACCEPTORS AND BASES AS ELECTRON PAIR DONORS. AS A RESULT THE OBSERVED ACIDIC PROPERTIES OF METAL IONS IN SOLUTION CAN BE EXPLAINED. • ADDITIONALLY, THE BASIC PROPERTIES OF SUBSTANCES SUCH AS AMMONIA CAN AS BE EXPLAINED AS ELECTRON PAIR DONORS EVEN THOUGH AMMONIA CONTAINS NO HYDROXIDE IONS. 10
  11. 11. WHERE DO ACIDS & BASES COME FROM? • ACIDS RESULT FROM THE ADDITION OF NONMETAL OXIDES TO WATER. THESE OXIDES ARE CALLED ACID ANHYDRIDES (ACIDS WITHOUT WATER). EVEN CARBON DIOXIDE WHEN ADDED TO WATER WILL MAKE THE SOLUTION MILDLY ACIDIC. • CO2(g) + H2O(l)  H2CO3(aq) (CARBONIC ACID) • SO2(g) + H2O(l)  H2SO3(aq) (SULFUROUS ACID) • BASES ARE FORMED BY METALLIC OXIDES AND WATER. THEY ARE CALLED BASIC ANHYDRIDES. • CaO(s) + H2O(l)  Ca(OH)2(s) (CALCIUM HYDROXIDE) • Na2O(s) + H2O(l)  2 NaOH(s) (SODIUM HYDROXIDE) 11
  12. 12. ACID & BASE STRENGTH • WHEN DISSOLVED SUBSTANCES SEPARATE INTO FREE MOBILE IONS THIS IS CALLED DISSOCIATION. • THE STRENGTH OF ACIDS AND BASES DEPENDS ON THEIR ABILITY TO DISSOCIATE IN SOLUTION. • CONCENTRATION REFERS TO THE MOLARITY OF THE SOLUTION. • CONCENTRATION AND STRENGTH DO NOT MEAN THE SAME THING BUT ARE RELATED. • THERE ARE SEVERAL STRONG ACIDS AND BASES. THESE DISSOCIATE WELL (~ 100%). ALL OTHER ACIDS AND BASES ARE WEAK (DISSOCIATE POORLY) 12
  13. 13. COMMON STRONG ACIDS • STRONG ACIDS • HCLO4 PERCHLORIC ACID HI HYDROIODIC ACID HBr HYDROBROMIC ACID HCl HYDROCHLORIC ACID HNO3 NITRIC ACID H2SO4 SULFURIC ACID 13
  14. 14. COMMON STRONG BASES • STRONG BASES • LiOH LITHIUM HYDROXIDE • NaOH SODIUM HYDROXIDE • KOH POTASSIUM HYDROXIDE • RbOH RUBIDIUM HYDROXIDE • CsOH CESIUM HYDROXIDE • Ca(OH)2 CALCIUM HYDROXIDE • Sr(OH)2 STRONTIUM HYDROXIDE • Ba(OH)2 BARIUM HYDROXIDE 14
  15. 15. PH OF SOLUTIONS • PH IS A CONVENIENT SYSTEM FOR THE MEASURING THE ACIDITY OF A SOLUTION. • PH IS DEFINED AS THE NEGATIVE LOGARITHM OF THE HYDROGEN ION CONCENTRATION IN A SOLUTION. • A LOGARITHM (LOG) IS A POWER OF 10. IF A NUMBER IS WRITTEN AS 10X THEN ITS LOG IS X. • FOR EXAMPLE 100 COULD BE WRITTEN AS 102 THEREFORE THE LOG OF 100 IS 2. • IN CHEMISTRY CALCULATIONS OFTEN SMALL NUMBERS ARE USED LIKE .0001 OR 10-4. THE LOG OF .0001 IS THEREFORE –4. • FOR NUMBERS THAT ARE NOT NICE EVEN POWERS OF 10 A CALCULATOR IS USED TO FIND THE LOG VALUE. FOR EXAMPLE THE LOG OF .00345 IS –2.46 AS DETERMINED BY THE CALCULATOR. 15
  16. 16. PH OF SOLUTIONS (CONT’D) • PH = - LOG [H+] • P MEANS NEGATIVE LOG AND THE BRACKETS AROUND H+ MEANS “CONCENTRATION OF H+” SAMPLE PROBLEM: WHAT IS THE PH OF A SOLUTION WHEN ITS [H+] = 0.000001 M ? SOLUTION: 0.000001 = 10-6 PH = - LOG (10-6) = - ( -6.00) = 6.00 16
  17. 17. THE PH SCALE 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ACID RANGE BASE RANGE NEUTRAL LOW PH VALUES INDICATE HIGH ACIDITY HIGH PH VALUE INDICATE HIGH BASITY 7.00 IS THE PH OF PURE WATER PH , [H+] AND [OH-] PH , [H+] AND [OH-] [H+] = 1.00 x 10-7 M IN PURE WATER PH = - LOG (1.00 x 10-7) = 7.00 17
  18. 18. POH OF SOLUTIONS • POH = - LOG [OH-] • WHERE THE BRACKETS AROUND OH- MEANS “CONCENTRATION OF OH-” • SAMPLE PROBLEM: • WHAT IS THE POH OF A SOLUTION WHEN ITS [OH-] = 0.00001 M ? • SOLUTION: • 0.00001 = 10-5 • POH = - LOG (10-5) = - ( -5.00) = 5.00 • PH + POH = PKw = 14.0 • PH = 14.0 –5.0 = 9.0, THE SOLUTION IS BASIC 18
  19. 19. FORMATION OF A HYDROGEN ION (AN AQUEOUS PROTON) 1 P+ 0 N0 1e- A HYDROGEN ATOM LOSES ITS ELECTRON TO FORM A HYDROGEN ION Atomic number 1 Atomic mass 1 19
  20. 20. STRONG & WEAK ACID DISSOCIATION STONG ACIDS DISSOCIATE READILY (NITRIC ACID HNO3) WEAK ACIDS DISSOCIATE POORLY (HYDROFLOURIC ACID HF) FREE MOBILE IONS READILY FORM ALL MOLECULES DISSOCIATE FREE MOBILE IONS FORM BUT WITH DIFFICULTLY FEW MOLECULES DISSOCIATE 20
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