Student Worksheet for Attempt to work the following practice problems after working through the sample problems in the videos. Answers are given on the last page(s). Relevant Equations Kw = 1.0*10-14 = [ - OH] [H + ] [ - OH] = 10 -poh [H + ] = 10 -ph poh = - log [ - OH] ph = - log [H + ] ph + poh = 14 Where, brackets stand for concentration/molarity. 2017 Supercharged Science www.sciencelearningspace.com 1
1. Identify the acid/base conjugate pairs in the following equation: HCl + H 2 O Cl - + H 3 O + The acid is: The base is: The conjugate acid is: The conjugate base is: 2. Identify the acid/base conjugate pairs in the following equation: HSO 4 - + H 2 O --> H 2 SO 4 + OH - The acid is: The base is: The conjugate acid is: The conjugate base is: 3. What is the poh of 1.7M hydrochloric acid (HCl) solution? 4. Find the ph of a base that has an [OH-] of 1.0 x 10-7 M. 5. What is the poh if the ph is 11.25? 6. If a solution has an [OH - ] concentration of 2.5*10-6, what is the concentration of H +? 2017 Supercharged Science www.sciencelearningspace.com 2
7. Identify the ph of the following. Tell whether it is an acid, a base or neutral substance: Substance Concentration ph Acid, base or neutral? [H 3 O+] 3.5 X 10-3 [H 3 O+] 5.8 X 10-7 [H 3 O+] 9.5 X 10-6 [OH-] 6.2 X 10-4 [OH-] 3 X 10-2 [OH-] 1 X 10-1 8. Compare and Contrast Arrhenius acids and bases to Bronsted Lowry Acids and bases. 9. Rank the following acids from weakest (being #1) to strongest (being #4). Explain your logic of ranking. 2017 Supercharged Science www.sciencelearningspace.com 3
10. Calculate the ph of a solution that has a [ - OH] of 3.4*10-7. 11. Calculate the H + concentration of a solution that has an OH concentration of 2.3*10-4. 12. Explain why C2H5OH is considered a monoprotic acid despite having 6 H in the molecule, whereas H3PO4 is considered polyprotic with only 3 H in the molecule. The structures are provided for your reference. 2017 Supercharged Science www.sciencelearningspace.com 4
13. Calculate the - OH concentration of a solution that has an H + concentration of 1.5*10-3. 14. Calculate the ph of a solution that has a [ - OH] of 3.4*10-7. 15. What product is consistently produced in every Arrhenius acid and base reaction? Why does this occur, in respect to the requirements to be an Arrhenius acid and base? 2017 Supercharged Science www.sciencelearningspace.com 5
1. Identify the acid/base conjugate pairs in the following equation: HCl + H 2 O Cl - + H 3 O + The acid is: The base is: The conjugate acid is: The conjugate base is: HCl H 2 O H 3 O + Cl - 2. Identify the acid/base conjugate pairs in the following equation: HSO 4 - + H 2 O --> H 2 SO 4 + OH - The acid is: The base is: The conjugate acid is: The conjugate base is: H 2 O HSO 4- H 2 SO 4 - OH 3. What is the poh of 1.7M hydrochloric acid (HCl) solution? poh + ph = 14 poh 0.23 = 14 ph = -log [H + ] poh = 14.23 = -log 1.7 = -0.23 4. Find the ph of a base that has an [OH-] of 1.0 x 10-7 M. poh + ph = 14 7 + ph = 14 poh = -log [ - OH] ph = 7 = -log 1.0*10-7 = 7 5. What is the poh if the ph is 11.25? poh + ph = 14 poh + 11.25 = 14 poh= 2.75 6. If a solution has an [OH - ] concentration of 2.5*10-6, what is the concentration of H +? K w = [ - OH][H + ] [H + ] = 1.0 10 14 2.5 10 6 = 4.0 * 10-9 2017 Supercharged Science www.sciencelearningspace.com 6
7. Identify the ph of the following. Tell whether it is an acid, a base or neutral substance: Substance Concentration ph Acid, base or neutral? [H 3 O+] 3.5 X 10-3 2.46 Acid [H 3 O+] 5.8 X 10-7 6.24 Acid [H 3 O+] 9.5 X 10-6 5.02 Acid [OH-] 6.2 X 10-4 10.79 Base [OH-] 3 X 10-2 12.48 Base [OH-] 1 X 10-1 13 Base Don t forget that when you are given the - OH concentration, the ph is found by subtracting the poh from 14. 8. Compare and Contrast Arrhenius acids and bases to Bronsted Lowry Acids and bases. Both acid types are required to donate an H + ion, so they are the same. An Arrhenius base is required to donate an - OH ion, but a Bronsted Lowry base is not. A Bronsted Lowry base is only required to be able to accept an H + ion. An example of each typ of Acid base reaction is shown below. Arrhenius reaction: NaOH + HCl H2O + NaCl Bronsted Lowry reaction: NH3 + HCl NH4 + + Cl - Hence, an Arrhenius acid and base are always a Bronsted Lowry acid and base, but a Bronsted Lowry acid and base is not always an Arrhenius acid and base. 9. Rank the following acids from weakest (being #1) to strongest (being #4). Explain your logic of ranking. 4 2 3 1 2017 Supercharged Science www.sciencelearningspace.com 7
Acid strength is a factor of the number of H s attached to atoms with an electronegativity difference. In this case, O is more electronegative than S, so the stronger acids will be HClO3 and H3PO4. Of the two, the phosphoric acid has more hydrogens and oxygens, so it is stronger. Thereafter, the sulfur that is less electronegative with lose its H. NaOH is a base. This is because there is a greater electronegativity difference between O and Na than O and H. 10. Calculate the ph of a solution that has a [ - OH] of 3.4*10-7. poh + ph = 14 6.47 + ph = 14 poh = -log [ - OH] ph = 7.53 = -log 3.4*10-7 = 6.47 11. Calculate the H + concentration of a solution that has an OH concentration of 2.3*10-4. K w = [ - OH][H + ] [H + ] = 1.0 10 14 2.3 10 4 = 4.35 * 10-11 12. Explain why C2H5OH is considered a monoprotic acid despite having 6 H in the molecule, whereas H3PO4 is considered polyprotic with only 3 H in the molecule. The structures are provided for your reference. The strength of an acid and ionization is based upon electronegativity differences between atoms that are attached. In this case, C and H have almost identical electronegativity values and unlikely to ionize. H and O have significant differences. When reviewing the molecules, only one O-H bond exists for C2H5OH (making it monoprotic) whereas 3 exist in H3PO4. 13. Calculate the - OH concentration of a solution that has an H + concentration of 1.5*10-3. K w = [ - OH][H + ] [ - OH]= 1.0 10 14 1.5 10 3 = 6.67 * 10-12 2017 Supercharged Science www.sciencelearningspace.com 8
14. Calculate the ph of a solution that has a [ - OH] of 3.4*10-7. poh = -log [ - OH] = -log (3.4*10-7 ) = 6.47 poh + ph = 14 6.47 + ph = 14 ph = 7.53 15. What product is consistently produced in every Arrhenius acid and base reaction? Why does this occur, in respect to the requirements to be an Arrhenius acid and base? H2O is constantly produced in every Arrhenius acid base reaction. This occurs because to be an Arrhenius acid, the molecule must donate an H +. To be an Arrhenius base, the molecule must donate an - OH. The H + and - OH join together to form H2O. 2017 Supercharged Science www.sciencelearningspace.com 9