Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 7. (L25)-Acids and Bases Today’s Outline..Review of solution and solution concentrations..Our everyday-life experience with acids and bases..Acids and bases: Experimental definitions..Acids and bases: The Arrhenius acid-base theory..Acids and bases: Bronsted-Lowry acid-base theory

Chapter 7. (L25)-Acids and Bases Solutions Real solution: A homogeneous mixture of two or more substances Solute: the substance being dissolved Solvent: the substance doing the dissolving Solvent is usually much more than solute in quantity “Like dissolves like” Aqueous solutions: The solutions with water as the solvent

Chapter 7. (L25)-Acids and Bases Solution conentration: Molarity For solution concentration in the unit of molarity, we use moles to measure the quantity of solute and liter to measure the quantity of solution. Thus, molarity = moles of solute/liters of solution = mole/L

Chapter 7. (L25)-Acids and Bases Solution conentration: Percent concentrations Percent by volume (%) = (volume of solute/volume of solution)×100 (%) Percent by mass (%) = (mass of solute/mass of solution )×100 (%)

Chapter 7. (L25)-Acids and Bases Our everyday-life experience with acids and bases Out tastes: acids taste sour; bases taste bitter; compounds formed by reaction of acids with bases taste salty Common acids in our everyday life: lemons, grapefruit (citric acid) vinegar (acetic acid) Vitamin C (ascorbic acid) Battery acid (sulfuric acid) Common bases in our everyday life: oven cleaner (lye, or NaOH) baking soda (NaHCO 3 )

Chapter 7. (L25)-Acids and Bases Acids and bases: A group of chemical substances with special chemical properties and reactions..There are many many chemical substances...How can we handle them?..We try to group them based on their similar chemical properties and reactions..Acids and bases each are one group of special chemical substances with similar chemical properties and reactions...Attention: What are the similar chemical properties and reactions?

Chapter 7. (L25)-Acids and Bases Chemical properties of acids and bases Chemical properties of acids: -cause litmus indicator dye to turn red (turn blue with base) -taste sour -dissolve active metals (Zn, Fe, Cu, etc.), producing H 2 gas -react with bases to form water and ionic after the DGM loading peak, compounds called salts

Chapter 7. (L25)-Acids and Bases Chemical properties of acids and bases Chemical properties of bases: -cause litmus indicator dye to turn blue (turn red with acid) -taste bitter -feel slippery on the skin -react with acids to form water and ionic compounds called salts

Chapter 7. (L25)-Acids and Bases Acids and bases: Experimental definitions We thus can define the acids and bases based on their chemical properties. So, An acid is a compound or molecule that has all the chemical properties as listed before for the acids. An base is a compound or molecule that has all the chemical properties as listed before for the bases. Now the question: What is the definition for acids and bases in terms of chemistry or molecular composition?

Chapter 7. (L25)-Acids and Bases Acids and bases: The Arrhenius theory Question: Why do acids and bases share similar chemical properties and reactions? Svante Arrhenius (a Swedish chemist, ) developed a theory in 1887, which first successfully explained the facts about acids and bases. Arrhenius’ acid and base theory: -An acid is a molecule that will dissociate into a hydrogen cation (H +, proton) and an anion in an aqueous solution Example: HCl = H + + Cl -

Chapter 7. (L25)-Acids and Bases Acids and bases: The Arrhenius theory -A base is a molecule that will give rise to a hydroxide anion (OH - ) and a cation in an aqueous solution Example: NaOH = Na + + OH -

Chapter 7. (L25)-Acids and Bases Acids and bases: The Arrhenius theory -Neutralization reaction between an acid and a base is: acid + base = salt + water anion-H + + cation-OH - = H 2 O + anion + cation the salt is composed of the cation and anion Example: H 2 SO 4 + 2NaOH = 2H 2 O + 2Na + + SO 4 2-

Chapter 7. (L25)-Acids and Bases Acids and bases: The Arrhenius theory..the properties of an acid is caused by the proton, H + cations in a water solution -H + cations cause sour taste, turn litmus red, react with metals and bases..the properties of an base is caused by the OH - anions in a water solution -OH - anions cause bitter taste, turn litmus blue, react with acids..salt can be formed by neutralization via reaction between an acid and a base: HCl + NaOH = H 2 O + Na + + Cl -

Chapter 7. (L25)-Acids and Bases Acids and bases: The Arrhenius theory..Limitation of Arrhenius theory This theory cannot explain some chemical compounds or molecules that behave as bases. Example: NH 3, ammonia NH 3 can give rise to OH - once put into water Example: Al 3+, Al 3+ can give rise to H + once put into water (AlCl 3 dissolved in water will turn litmus red)

Chapter 7. (L25)-Acids and Bases Acids and bases: The Bronsted- Lowry acid-base theory Question: Can we have a theory that can include explanation of the new situations of acids and bases plus the old ones? The new acid/base theory was proposed independently by J.N. Bronsted in Denmark in 1923, and T.M. Lowry of Great Britain

Chapter 7. (L25)-Acids and Bases Acids and bases: The Bronsted- Lowry acid-base theory According to the Bronsted-Lowry theory: -an acid is a proton donor -a base is a proton acceptor This theory is then based solely on protons, and there is no need for OH-. This is a better theory, simpler, and can explain a broader scope of chemical facts.

Chapter 7. (L25)-Acids and Bases Acids and bases: The Bronsted-Lowry acid- base theory Hydration of proton: H + + H 2 O = H 3 O + H 3 O + is called hydronium ion..Hydrogen bond is responsible for the formation of hydronium ion..... H:O: + H + = [H:O:H] + So, water is a base now.... H H

Chapter 7. (L25)-Acids and Bases Acids and bases: The Bronsted-Lowry acid- base theory The theory to describe the ionization of HCl: HCl(aq) + H 2 O = H 3 O + + Cl - (aq) H:Cl: + H:O: = [H:O:H] + + Cl - (aq) H H General equation for acid ionization: HA(aq) + H 2 O = H 3 O + + A - (aq) H + donor

Chapter 7. (L25)-Acids and Bases Acids and bases: The Bronsted-Lowry acid- base theory The theory to describe the behavior of NH 3 : NH 3 (aq) + H 2 O = NH 4 + (aq) + OH - (aq) H H:N:H + H:O: = [H:N:H] + + OH - (aq) H H H General equation for acid ionization: A(aq) + H 2 O = AH + + OH - (aq) H + acceptor

Chapter 7. (L25)-Acids and Bases Acids and bases: The Bronsted-Lowry acid-base theory The theory to describe the behavior of NaOH: NaOH(aq) + H 2 O = Na + + H 2 O + OH - (aq) H + acceptor General equation for acid ionization: BOH(aq) + H 2 O = B - + H 2 O + OH - (aq) H + acceptor

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, an acid is a molecule that in a water solution dissociates into (a) OH - and a cation(s); (b) H + only; (c) H + and an anion(s); (d) OH - only.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, a base is a molecule that in a water solution dissociates into (a) OH - and a cation(s); (b) H + only; (c) H + and an anion(s); (d) OH - only.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, which of the following is an acid? (a) CH 4 ; (b) NaOH; (c) NaHCO 3 ; (d) H 2 SO 4.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, which of the following is an acid? (a) CH 4 ; (b) Ca(OH) 2 ; (c) NaCl; (d) H 2 CO 3.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, which of the following is a base? (a) CH 4 ; (b) KOH; (c) NaCl; (d) H 2 SO 4.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, which of the following is a base? (a) CH 4 ; (b) HCl; (c) Na 2 SO 4 ; (d) NH 4 OH.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, which of the following is a neutralization reaction? (a) 2HCl + Fe = H 2 + FeCl 2 ; (b) KOH + HCl = KCl + H 2 O; (c) Na 2 SO 3 = 2Na + + SO 3 2- ; (d) NH 3 + H 2 O = NH OH -.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Arrhenius acid/base theory, which of the following is a neutralization reaction? (a) H 2 SO 4 + Zn = H 2 + ZnSO 4 ; (b) KOH + HCl = KCl; (c) Na 2 SO 3 = 2Na + + SO 3 2- ; (d) 2NH 4 OH + H 2 SO 4 = 2H 2 O + (NH 4 ) 2 SO 4.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Bronsted-Lowry acid/base theory, which of the following is an acid? (a) FeCl 2 ; (b) KCl; (c) H 2 CO 3 ; (d) NH 4 OH.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Bronsted-Lowry acid/base theory, which of the following is an acid? (a) FeCl 3 ; (b) KCl; (c) Na 2 SO 4 ; (d) CH 4.

Chapter 7. (L25)-Acids and Bases Quiz Time According to the Bronsted-Lowry acid/base theory, which of the following is a base? (a) Cl 2 ; (b) KCl; (c) Na 2 S; (d) NH 3.