Unit 11: Acids and Bases

Transcription

1 Unit 11: Acids and Bases Student Name: Class Period: _3, 5, & 10_ Page 1 of 55

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3 Unit 11 Vocabulary: 1. Acidity: The property of exhibiting the qualities of an acid. 2. Alkalinity: The property of exhibiting the qualities of a base. 3. Amphiprotic: any substance (ionic or covalent) that can both accept and donate at least one proton (H + ). 4. Amphoteric: A species that can act either as a Brönsted-Lowry acid or a Brönsted-Lowry base, depending on the other species it is reacting with. 5. Arrhenius Acid: An electrolyte that ionizes in aqueous solution to yield H + as the only cation in the solution. 6. Arrhenius Base: An electrolyte that ionizes in aqueous solution to yield OH - as the only anion in the solution. 7. Basicity: The property of exhibiting the qualities of a base. 8. Brönsted-Lowry (B-L) Acid: A species that donates H + to a B/L base in a chemical reaction. 9. Brönsted-Lowry (B-L) Base: A species that accepts H + from a B/L acid in a chemical reaction. 10. Buret: A calibrated precision (& expensive!) glass tube that precisely measures the volume of a liquid dispensed. 11. Caustic: A substance that will destroy or irreversibly damage a substance or surface that it contacts; usually used to describe bases. 12. Corrosive: A substance that will destroy or irreversibly damage a substance or surface that it contacts; usually used to describe acids. 13. Electrolyte: A compound that ionizes (dissociates) in water, allowing the solution to flow electrons freely and conduct electricity. 14. Hydrolysis: The process whereby a base reacts with a glycerol ester (a fat) to produce soap. 15. Indicator: A substance whose color is sensitive to the ph of a solution to which it is added. Page 3 of 55

4 16. Neutralization: A double-replacement reaction where an acid and a base react to form water and a salt. 17. Nonelectrolytes: A molecular compound that does not ionize (not dissociate) in water, preventing the solution from conducting electricity. 18. ph: The negative logarithm of the hydrogen ion concentration. A ph value less than 7 indicates an acidic solution, a ph value 7 is a neutral solution, and a ph value greater than 7 indicates a basic solution. The scale ranges from a hypothetical 0 (most acidic) to 14 (most basic). 19. Protonation: The addition of an acid s H + (proton) to a water molecule to form a hydronium (H 3 O + ) molecule. 20. Salt: An ionic compound formed when an acid and a base neutralize each other. The salt compound consists of both the anion of the acid and the cation of the base. 21. Titration: A process of controlled acid-base neutralization carried out using burets dispensing either an acid or a base. Page 4 of 55

5 Unit 11 Homework Assignments: Assignment: Date: Due: Page 5 of 55

6 Notes page: Page 6 of 55

7 Topic: Arrhenius Acids and Bases Objective: What is the definition of an Arrhenius Acid or Base? Arrhenius Acids: A substance that contains H + ions that ionize when dissolved in water is known as an Arrhenius Acid. Acids (and bases) are the only molecules (different from ionic crystals) that ionize (dissociate) when dissolved in water. Acids (and bases) are electrolytes, unlike other molecular substances like water (H 2 O) and sugar (C 6 H 12 O 6 ). The H + leaves the acid and bonds to the water molecule to form a hydronium ion (H 3 O + ). Arrhenius Acid examples: HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) i. The acid HCl contains one H + ion which combines with one H 2 O molecule to form one H 3 O + ion. Page 7 of 55

8 ii. iii. The acid (HCl) ionizes to form a hydrogen cation (H + ) and an anion, in this example a chloride ion (Cl - ). The hydrogen ion (H + ) bonds to the water molecule using a sneaky bonding method. The H + doesn t have an electron to share, and there are no unpaired valence electrons in the water molecule. The hydrogen ion tends to bogart two electrons from the oxygen in the water molecule. The extra hydrogen ion now has a claim on the electrons on the oxygen, forming a coordinate covalent bond. H 2 SO 4(l) + 2 H 2 O (l) 2 H 3 O + (aq) + SO 4-2 (aq) iv. The acid H 2 SO 4 contains two H + ions which combine with two H 2 O molecules to form two H 3 O + hydronium ions. H 3 PO 4(l) + 3 H 2 O (l) 3 H 3 O + (aq) + PO 4-3 (aq) v. The acid contains three H + ions which combine with three H 2 O molecules to form three H 3 O + hydronium ions. Page 8 of 55

9 Topic: Properties of Acids Objective: How are ions situated within a solution? Properties of Acids: Acids eat away (oxidize) active metals (metals above H 2 on Table J). Metals such as Li, Mg, and Zn may be oxidized by an acid to produce hydrogen gas (H 2(g) ). These are examples of metals above H 2 on Table J. We won t discuss metals below H 2 on Table J now. For these single replacement reactions: 2 Li (s) + 2 HCl (aq) 2 LiCl (aq) + H 2(g) Ca (s) + 2 HCl (aq) CaCl 2(aq) + H 2(g) i. Both of these are examples of how a more active metal (above H 2 ) will kick the hydrogen out of the acid (HCl), leaving a new aqueous ionic compound and hydrogen gas. 1. Acids have a ph value less than 7. i. The ph scale measures the relative acidity or alkalinity of a solution. A ph value 7 is neutral, and acids have a ph value less than 7. Each decrease of one whole number of ph is a tenfold increase in acid strength. An acid with a ph value 3 is ten times more acidic than a solution with a ph value 4, and an acid with a ph value 3 is 100 times more acidic than a solution with a ph value 5. Page 9 of 55

10 2. Acidic solutions may conduct electricity. i. Acids are electrolytes, because they dissociate to form ions in solution. The stronger the acid, the more it ionizes, and therefore could carry electron flow better and have better electrical conductivity. ii. Stronger electrolytes (stronger acids) include: HI, HCl, HNO 3, and H 2 SO 4. H 2 SO 4 is commonly used in lead-acid automotive batteries. iii. Weaker electrolytes (weaker acids) include: H 2 CO 3 (carbonic acid in soda) and HC 2 H 3 O 2 (acetic acid, or vinegar). 3. Dilute solutions of acids taste sour. *NOTE: this statement does NOT give you permission to taste ANY acid in lab to test this statement! i. Citric acid is found in citrus fruits like lemons and grapefruits. Citric acid is also used to give an extra sour kick to food and candies. ii. Acetic acid (5% in aqueous solution) is also known as white vinegar and is yummy on salads or French Fries! Page 10 of 55

11 4. Acids react with carbonates to form carbon dioxide gas, a salt, and water. i. Baking soda and vinegar: Spoiler Alert! - If you remember the mysterious Enzyme M from the required NYS Living Environment Relationships and Biodiversity Lab, the powder was baking soda, and the 4 plant extract solutions were food coloring and water, with three of the extracts containing vinegar. NaHCO 3(s) + HC 2 H 3 O 2(aq) CO 2(g) + H 2 O (l) + NaC 2 H 3 O 2(aq) This is the middle school (& VERY messy!) volcano reaction; the CO 2(g) forces the mixture of dry powder, liquid, and foam up and out. 5. Acids may be formed by reaction of gaseous oxides with water. i. Burning fossil fuels releases gaseous nonmetallic oxides (CO 2, * NO x, SO 2, and similar molecules) into the atmosphere. When these gaseous nonmetallic oxides react with atmospheric water vapor, they form weak aqueous acids that may form acidic precipitation. Acid precipitation can lower the ph of bodies of water, which can seriously affect aquatic ecosystems. * NO x is a generic symbol for the nitrogen oxides of NO, NO 2, & N 2 O Page 11 of 55

12 Topic: Naming of Acids Objective: How do we name acidic compounds? Naming of Binary Acids: A binary acid has a name composed of the prefix (hydro-), the nonmetallic ion name, and the last syllable (-ide) replaced with the suffix (-ic) followed by the separate word acid. Binary Acid naming examples: i. HCl (aq) : (hydro-) + (chloride - ide) + (-ic) + acid = hydrochloric acid ii. HBr (aq) : (hydro-) + (bromide - ide) + (-ic) + acid = hydrobromic acid iii. H 2 S (aq) : (hydro-) + (sulfide - ide) + (-ic) + acid = hydrosulfic acid iv. H 3 N (aq) : (hydro-) + (nitride - ide) + (-ic) + acid = hydronitric acid Writing of Binary Acid formulas: i. Write a binary acid formula just like any ionic compound, placing the H +1 first, and the anion second. 1. Hydrofluoric acid: One hydrogen (H +1 ) + one fluoride (F -1 ) HF (aq) 2. Hydrophosphoric acid: Three hydrogen (3 x H +1 ) + one phosphide (P -3 ) H 3 P (aq) ii. Ensure that you have the correct ratio of ions to equal the charges! Page 12 of 55

13 Naming of Ternary Acids: A ternary acid has a name with NO (hydro-) prefix. a) If the polyatomic ion ends in (-ide) or (-ate), replace the last syllable of the polyatomic ion with the suffix (-ic) followed by the word acid. b) If the polyatomic ion ends in (-ite), replace the last syllable of the polyatomic ion with the suffix (-ous) followed by the word acid. Ternary Acid naming examples: i. HNO 3(aq) : (nitrate - ate) + (-ic) + acid nitric acid ii. HNO 2(aq) : (nitrite -ite) + (-ous) + acid nitrous acid iii. HClO 3(aq) : (chlorate - ate) + (-ic) + acid chloric acid iv. HClO 2(aq) : (chlorite - ite) + (-ous) + acid chlorous acid v. HCN (aq) : (cyanide - ide) + (-ic) + acid cyanic acid Writing of Ternary Acid formulas: a) Remember that while there is no (hydro-) prefix, ternary acid formulas still begin with hydrogen! i. Sulfuric acid: hydrogen (2 x H +1 ) + sulfate (SO -2 4 ) H 2 SO 4(aq) ii. Sulfurous acid: hydrogen (2 x H +1 ) + sulfite (SO -2 3 ) H 2 SO 3(aq) a) Again, ensure that you have the correct ratio of ions to equal the charges! Page 13 of 55

14 Regents Practice Questions-Acids: (Ungraded) 1. The only positive ion found in an aqueous found in a aqueous solution of sulfuric acid is the a) Sulfite ion c) Hydroxide ion b) Sulfate ion d) Hydronium ion 2. An Arrhenius acid has a) Only hydrogen ions in solution b) Only hydroxide ions in solution c) Hydrogen ions as the only positive ions in solution d) Hydrogen ions as the only negative ions in solution 3. Which substance is an Arrhenius acid? a) LiF (aq) c) CH 3 CHO b) HBr (aq) d) Mg(OH) 2(aq) 4. What produces hydrogen ions as the only positive ions in aqueous solution? a) NH 3 c) KOH b) HBr d) NaCl 5. When HCl is dissolved in water, the only positive ion present in the solution is the a) Hydride ion c) Hydrogen ion b) Chloride ion d) Hydroxide ion Page 14 of 55

15 Topic: Properties of Bases Objective: How does temperature affect the solubility of a solution? Properties of Bases: Bases are substances that contain aqueous hydroxide (OH -1 (aq)) ions in solution. 1. Bases have a ph value greater than 7. i. The ph scale measures the relative acidity or alkalinity of a solution. A ph value 7 is neutral, and bases have a ph value greater than 7. Each increase of one whole number of ph is a tenfold increase in base strength. A base with a ph value 9 is ten times more basic than a solution with a ph value 8, and a base with a ph value 9 is 100 times more basic than a solution with a ph value Basic solutions may conduct electricity. i. Bases are electrolytes, because they dissociate to form ions in solution. The stronger the base, the more it ionizes, and therefore could carry electron flow better and have better conductivity. ii. Stronger electrolytes (stronger bases) include: Group 1 metal hydroxides (LiOH, NaOH, RbOH, and CsOH). iii. Weaker electrolytes (weaker bases) include: Ca(OH) 2, Mg(OH) 2, and Al(OH) 3, all of which may be found in common antacids. We Page 15 of 55

16 will learn SOON how basic antacids neutralize excess stomach acid. 3. Bases taste bitter. AGAIN, we will NOT test this statement in lab! i. However, many alkaloids are found in medicines, and are also in coffee. ii. Theobromine is an alkaloid found in chocolate, and the compound that makes chocolate dangerous to many pets. 4. Bases may be formed when Group 1 or Group 2 metals react with water, releasing hydrogen gas in the process. i. 2 Na (s) + 2 H 2 O (l) 2 NaOH (aq) + H 2(g) ii. Mg (s) + 2 H 2 O (l) Mg(OH) 2 + H 2(g) 5. Bases hydrolyze fats during saponification to form soap. i. Drain cleaners usually contain sodium hydroxide which reacts with the nonpolar molecules in grease clogging household drains. The NaOH converts the nonpolar grease molecules into ionic soap compounds, which then become soluble in water and may be washed down the drain. Page 16 of 55

17 Topic: Naming of Bases Objective: How do we name acidic compounds? Naming of Bases: (Reference Table L) 1. Most common bases are formed when a metal (especially Groups 1 and 2) bonds with a hydroxide. Naming bases is easy once you've identified them! 2. Name the metal CATION first; it keeps its name as listed in the Periodic Table. 3. The polyatomic ion "hydroxide" (OH - ) also keeps its name. Naming of Bases examples: i. LiOH is "lithium hydroxide" ii. NH 4 OH is "ammonium hydroxide" Page 17 of 55

18 Regents Practice Questions-Bases: (Ungraded) 1. According to the Arrhenius theory, when a base dissolves in water it produces a) H + as the only positive ion in solution b) NH 4 + as the only positive ion in solution c) OH - as the only negative ion in solution d) CO 3-2 as the only negative ion in solution 2. A sample of Ca(OH) 2 is considered to be an Arrhenius base because it dissolves in water to yield a) H - as the only negative ions in solution b) Ca +2 ions as the only positive ions in solution c) OH - ions as the only negative ions in solution d) H 3 O + ions as the only positive ions in solution 3. Which ion is produced when an Arrhenius base is dissolved in water? a) H + as the only positive ion in solution b) OH - ions as the only negative ion in solution c) H 3 O + ions as the only positive ion in solution d) H - as the only negative ion in solution 4. According to the Arrhenius theory, which list of compounds includes only bases? a) KOH, NaOH, and LiOH b) KOH, Ca(OH) 2, and CH 3 OH c) LiOH, Ca(OH) 2, and C 2 H 4 (OH) 2 (C 2 H 4 (OH) 2 is ethylene glycol molecule) d) NaOH, Ca(OH) 2, and CH 3 COOH 5. According to the Arrhenius theory, when a base is dissolved in water it produces a solution containing only one kind of anion. What is the name of this anion? a) Hydride ion b) Hydroxide ion c) Hydrogen sulfate ion d) Hydrogen carbonate ion Page 18 of 55

19 Al(OH) Topic: 3 is aluminum Testing hydroxide for ph Objective: How do we know if a solution is Acidic or Basic? How do we know if a solution is Acidic or Basic? Electronic ph testers: i. Electronic ph testers have probes containing electrodes that detect electrical conductivity. Once calibrated (a process comparing known standards to the probe output), the electronic signal may be interpreted to determine an ionization level, and therefore the ph value. Acid-Base Indicators: (Reference Table M) i. Indicators are chemicals that have certain color characteristics for a narrow range of ph values. Indicators may be used to determine acidity or alkalinity, or even to find a specific range of ph values. An indicator won t give an exact ph value, but a range of ph values. Page 19 of 55

20 Litmus and ph paper: i. Red litmus paper is used to test a base. When red litmus paper is immersed in a base, the red litmus paper turns blue indicating the given solution as alkaline. ii. Blue litmus paper is used to test an acid. When blue litmus paper is immersed in an acid, the blue litmus paper turns red indicating the given solution as acidic. Page 20 of 55

21 Full-range ph paper contains a mixture of indicators that will react with a solution to give an approximation of ph value for that solution. The color that the ph paper strip turns is compared to a color chart for the paper that gives a quantitative ph value based on the qualitative color. Testing for an Acid or Base example: An unknown solution gives the following results when tested with the following four indicators: Thymol Blue = yellow Methyl Orange = yellow Bromcresol Green = blue Phenolphthalein = colorless 1. Which of the following ph values could the unknown solution have? a) 2.8 b) 4.8 c) 6.5 d) 8.5 Page 21 of 55

22 Using Reference Table M, Common Acid-Base Indicators, we should be able to narrow down our possibilities. i. Thymol Blue = turned yellow Thymol Blue works between ph values of 8.0 (yellow) (blue). As it was yellow in this test, the unknown solution could be at the lower end of Thymol Blue s range, so a ph of 8.5 is a possibility, but it also could be below a ph value 8. ii. Methyl Orange = turned yellow Methyl Orange works between ph values of 3.1 (red) (yellow). As it was yellow in this test, the unknown solution has to be ABOVE a ph value of 3.1, so we may eliminate choice A. iii. Bromcresol Green = turned blue Bromcresol Green works between ph values of 3.8 (yellow) (blue). As it was not yellow in this test, the unknown solution has to be ABOVE a ph value of 3.1, so we may eliminate choice A. However, Bromcresol Green turns blue with a ph value ABOVE 5.4, so a ph of 4.8 is eliminated (along with choice B ), or it would have been green. Page 22 of 55

23 iv. Phenolphthalein = showed colorless (no change) Phenolphthalein works between ph values of 8 (colorless) - 9 (pink). As it was colorless in test, the unknown solution has to be BELOW a ph value of 8, so we may eliminate choice D. (Geesh I sound like a witty Sicilian ) v. Methyl Orange eliminated a ph value 2.8, Bromcresol Green eliminated ph value 4.8, and Phenolphthalein eliminated ph value 8.5. In this case Thymol Blue could only say that the unknown ph was below 8, so that leaves choice C with a ph value 6.5. Page 23 of 55

24 Regents Practice Questions-Indicators: (Ungraded) 1. Which solution below when mixed with a drop of bromthymol blue will cause the indicator to change from blue to yellow? a) 0.1 M HCl (aq) b) 0.1 M NH 3(aq) c) 0.1 M NaOH (aq) d) 0.1 M CH 3 OH (aq) 2. A solution with ph value 11 is first tested with phenolphthalein and then with red litmus. What will be the color of each indicator in this solution? a) Phenolphthalein is pink and red litmus is red b) Phenolphthalein is pink and red litmus is blue c) Phenolphthalein is colorless and red litmus is red d) Phenolphthalein is colorless and red litmus is blue 3. The ability of H 2 SO 4(aq) to change blue litmus paper red is mainly due to the presence of a) H 3 O + -2 (aq) ions c) SO 4 (aq) ions b) SO 2(aq) molecules d) H 2 O (l) molecules 4. Pure water containing phenolphthalein will change from colorless to pink with the addition of a) KCl (aq) c) HOH (aq) b) HCl (aq) d) KOH (aq) 5. A student records the following observations about an unknown solution: Conducts electricity Turns blue litmus red The student should conclude that the unknown solution is most likely a) A base b) An acid c) Normal d) Nonpolar Page 24 of 55

25 Student name: Class Period: _3, 5, & 10_ Please carefully remove this page from your packet to hand in. Acids & Bases Homework (1 pt. ea.) Identify each below as an acid or base based on their formulas and properties. Property Acid or Base Property Acid or Base Turns bromthymol blue Turns litmus paper red A A to yellow Tastes sour A Tastes bitter B Hydrolyzes fats into soap B Reacts with active metals forming H 2(g) A HCl (aq) A KOH (aq) B ph value 12 B Forms H 3 O + in water A Write the correct name for the following acids and bases. (Ref Table K) 1. HCl (aq) : hydrochloric acid 2. HNO 3(aq) : nitric acid 3. H 2 SO 4(aq) : sulfuric acid 4. HC 2 H 3 O 2(aq) : acetic (or ethanoic) acid 5. KOH (aq) : potassium hydroxide 6. Ca(OH) 2(aq) : calcium hydroxide Page 25 of 55

26 Write the correct formula for the following acids and bases. (As (aq) ) 7. Perchloric acid: HClO 4(aq) 8. Hypochlorous acid: HClO (aq) 9. Chromic acid: H 2 CrO 4(aq) 10. Thiosulfuric acid: H 2 S 2 O 3(aq) 11. Aluminum hydroxide: Al(OH) 3(aq) 12. Barium hydroxide : Ba(OH) 2(aq) 13. The results for of testing a colorless solution with three different indicators are shown in the table below. Indicator Red litmus paper Blue litmus paper phenolphthalein Result Blue Blue Pink Which formula could represent the solution that was tested? a) HCl (aq) b) NaOH (aq) c) C 6 H 12 O 6(aq) d) C 12 H 22 O 11(aq) Page 26 of 55

27 Topic: Acid and Base Neutralization Objective: What occurs during acid-base neutralization reactions? Neutralization: i. The combining of an acidic (H + donor) and basic (OH - supplier) forms a common molecule, HOH, or water (H 2 O). The anion from the acid and the cation from the base join to form a salt. A salt is simply an ionic compound that may be formed during acid-base neutralization. ii. Acid-base neutralization is a simple double-replacement reaction, but in this case the water molecule is the precipitate. It may be difficult to think of water as a precipitate WITHIN water, but in this case the water formed is in excess. iii. One mole of H + ions exactly neutralizes one mole of OH - ions. Completing neutralization reactions: i. Determining the products of acid-base neutralization is the SAME process as determining the products of a double-replacement reaction. Watch Crash Course Chemistry Acid & Base Reactions YouTube video - 11:17 Neutralization examples: 1. HCl (aq) + NaOH (aq) NaCl (aq) + HOH (l) Acid Base Salt Water Page 27 of 55

28 2. H 2 SO 4(aq) + 2 KOH (aq) K 2 SO 4(aq) + 2 HOH (l) Acid Base Salt Water 3. 2 HNO 3(aq) + Ca(OH) 2(aq) Ca(NO 3 ) 2(aq) + 2 HOH (l) Acid Base Salt Water Antacid neutralization: Antacids are bases used to neutralize the acid that causes heartburn. Almost all antacids act on excess stomach acid by neutralizing it with weak bases. The most common of these bases are hydroxides, carbonates, or bicarbonates. The following table contains a list of the active ingredients found in several common commercial antacids, and the reactions by which these antacids neutralize the HCl in stomach acid. Compound Formula Chemical Reaction Aluminum hydroxide Calcium carbonate Magnesium carbonate Al(OH) 3 CaCO 3 MgCO 3 Al(OH) 3(s) + 3 HCl (aq) AlCl 3(aq) + 3 H 2 O (l) CaCO 3(s) + 2 HCl (aq) CaCl 2(aq) + H 2 O (l) + CO 2(g) MgCO 3(s) + 2 HCl (aq) MgCl 2(aq) + H 2 O (l) + CO 2(g) Magnesium hydroxide Mg(OH) 2 Mg(OH) 2(s) + 2 HCl (aq) MgCl 2(aq) + 2 H 2 O (l) Sodium bicarbonate NaHCO 3 NaHCO 3(aq) + HCl (aq) NaCl (aq) + H 2 O (l) + CO 2(g) Page 28 of 55

29 Topic: Buffers Objective: How may we experimentally determine concentration? Acid-Base Buffers: Buffers are solutions consisting of a weak acid and its conjugate base; these solutions resist ph changes when either acid or base is added to it. i. A buffered solution may contain acetic acid as its weak acid and sodium acetate as its conjugate base. If we add some hydrochloric acid to this solution, the sodium acetate would react with it by the following reaction: HCl + NaC 2 H 3 O 2 C 2 H 3 O 2 H + NaCl ii. The strong HCl added to the solution has been converted to acetic acid, a weak acid. Weak acids cause a much smaller disruption in ph than strong acids, and the ph of the solution will decrease much less than if it contained no sodium acetate. iii. Likewise, if we were to add sodium hydroxide to this solution, the acetic acid would react to it by the following process: NaOH + C 2 H 3 O 2 H NaC 2 H 3 O 2 + H 2 O iv. The strong base NaOH has been converted to the weak base sodium acetate, and the ph of the solution won't rise nearly as much as if the acetic acid weren't present in the first place. Page 29 of 55

30 Topic: Titration Titration: Objective: How may we experimentally determine concentration? Titration is the controlled process of acid-base neutralization that may be used to determine the unknown molarity of an acid or base using a precisely measured volume of a base or acid of known molarity. We ll be doing a titration lab, but here are the basic steps: 1. Place a base of unknown molarity in the buret, and record the starting volume. 2. Add phenolphthalein indicator to a measured volume of a known molarity acid in a flask. 3. Add small quantities of the unknown molarity base to the acid until you start to see some semi-persistent color change. The base will cause blooms of bright pink in the solution when you start the titration. 4. Once the color begins to last longer than a few moments while gently swirling the flask, start adding the base drop-by-drop, swirling the contents of the flask after each drop. 5. Once the flask has ANY sign of a permanent light-pink tinge, STOP adding base, and record the ending volume in the buret. 6. For best results, do several trials. Usually the first trial is overtitrated, and additional trials will refine your technique to get more precise results. Page 30 of 55

31 The volume of added base (or acid if titrating acid into base instead of base into acid) can be used along with the original volume of the acid in the flask as well as the acid s molarity to determine the molarity of the unknown. The point in the titration where the color of the phenolphthalein indicator barely changes to a just noticeable pink is called the ENDPOINT of the titration. Since we are adding a base to an acid, one might think that the neutralization point would be near the neutral ph value 7. Phenolphthalein actually changes color a little higher on the ph scale, around ph value 8.2, a bit more basic than neutral. If you want to find the equivalence point, or the amount of added base that brings the solution in the flask to exactly ph value 7, the best way is with a ph probe. Of course, multiple trials are usually the best way to get closest to either an endpoint or an equivalence point in a titration. Here is an online Titration Simulation where you can practice working with titration calculations. Note that the endpoint in the simulation occurs immediately, and is NOT the way it would work in the lab. Online Titration Simulation Watch Crash Course Chemistry Buffers (w/ Titration) YouTube video - 11:40 Page 31 of 55

32 Titration Equations: i. Remember, one mole of H + neutralizes one mole of OH -. ii. Therefore, # of moles of H + = # of moles of OH - iii. Since we are dealing with solutions and molarities, use the formula: M = moles of solute L of solvent (remember this equation is Concentration on Reference Table T!) iv. Rearrange the equation to: moles = moles of solute L x liters. v. Liters are our standard unit of volume, and (M), so the equation becomes: moles = M x V. moles of solute L is molarity vi. Moles of acid = M acid x V acid and moles of base = M base x V base vii. These provide the formula: viii. We can abbreviate this to: M Acid x V Acid = M Base x V Base M A x V A = M B x V B ix. A pretty simple equation to remember, but if not, it is on Reference Table T for your use anytime as: M A V A = M B V B x. This titration equation ONLY works if the acid used has only one H + per acid molecule, and ONLY if the base used has only one OH - per base molecule. We can then modify the titration equation by adding Page 32 of 55

33 coefficients for both the number of hydrogens in an acid (# of H) and also the number of hydroxides in an acid (# of OH). # H M A V A = # OH M B V B xi. If you are only solving for moles of solute instead of molarity, the formula may be simplified to: # H Moles A = # OH Moles B Page 33 of 55

34 Topic: Titration Problem Examples Objective: How may we calculate the molarity of an unknown? Titration Problem examples: 1. If it takes 15.0 ml of 0.40 M NaOH (aq) to neutralize 5.0 ml of HCl (aq), what is the molar concentration of the HCl (aq) solution? i. Since we are given both molarity and volume of the base, and volume of the acid, use the equation: # H M A V A = # OH M B V B ii. # H M A V A = # OH M B V B rearranged to solve for the molarity of the acid is: M A = # OH M B V B / # H V A [(1)x (0.40 M)x (15.0 ml) = 1.2 M HCl (aq) [(1)x (5.0 ml) 2. If it takes 10.0 ml of 2.0 M H 2 SO 4(aq) to neutralize 30.0 ml of KOH (aq), what is the molar concentration of the KOH (aq) solution? i. Since we are given both molarity and volume of the acid, and the volume of the base, use the equation: # H M A V A = # OH M B V B ii. # H M A V A = # OH M B V B rearranged to solve for molarity of the base is: M B = # H M A V A / # OH V B [(2) x (2.0 M) x (10.0 ml)] = 1.3 M KOH (aq) [(1) x (30.0 ml)] Page 34 of 55

35 3. How many ml of 2.0 M H 2 SO 4(aq) are required to neutralize 30.0 ml of 1.0 M NaOH? i. Since we are given both molarity and volume of the base, and the molarity of the acid, use the equation: # H M A V A = # OH M B V B ii. # H M A V A = # OH M B V B rearranged to solve for volume of the acid is: V A = # OH M B V B / # H M A [(1) x (1.0 M) x (30.0 ml)] [(2) x (2.0 M)] = 7.5 ml of 2.0 M H 2 SO 4(aq) 4. How many ml of 0.10 M Ca(OH) 2(aq) are required to neutralize 25.0 ml of 0.50 M HNO 3(aq)? i. Since we are given both molarity and volume of the acid, and the molarity of the base, use the equation: # H M A V A = # OH M B V B ii. # H M A V A = # OH M B V B rearranged to solve for volume of the base is: V B = # H M A V A / # OH M B [(1) x (0.50 M) x (25.0 ml)] = 63 ml of 0.10 M Ca(OH) 2(aq) [(2) x (0.10 M)] Page 35 of 55

36 Regents Practice Questions-Titration: (Ungraded) 1. A student neutralized 16.4 ml of HCl (aq) by adding 12.7 ml of M KOH (aq). What was the original molarity of the HCl (aq)? a) M c) M b) M d) M 2. How many ml of M H 2 SO 4(aq) are required to exactly neutralize 100. ml of M Ba(OH) 2(aq)? a) 25.0 ml c) 100. ml b) 50.0 ml d) 200. ml 3. The ph of a solution that is formed by the neutralization of 1.0M H 2 SO 4(aq) and 1.0 M KOH (aq) is closest to a) 1 b) 4 c) 7 d) If equal volumes of 0.1 M NaOH (aq) and 0.1 M HCl (aq) are combined, the resulting solution will contain a salt and a) H 2 O (l) c) NaCl (aq) b) HCl (aq) d) NaOH (aq) 5. The following data were collected by a student performing an acidbase titration: Volume of aqueous acid (HCl) used: Molarity of aqueous acid (HCl) used: Volume of aqueous base (NaOH) used: 20.0 ml 0.50 M 40.0 ml From the collected data, the concentration of the base should be calculated as a) 1.0 M b) 2.0 M c) 0.25 M d) 0.50 M Page 36 of 55

37 Student name: Class Period: Please carefully remove this page from your packet to hand in. Acid and Base Neutralization Homework Write the formula of the salt formed from each reaction below. (1 pt. ea.) 1. H 2 SO 4(aq) + Mg(OH) 2(aq) 2 H 2 O (l) + MgSO 4 (aq) 2. H 2 CO 3(aq) + 2 KOH (aq) 2 H 2 O (l) + K 2 CO 3 (aq) Write the formula of the unknown used in each reaction and balance. (4 pts. ea.) 3. 3 H 2 SO 4 (aq) + _2_ Al(OH) 3(aq) _6_ H 2 O (l) + Al 2 (SO 4 ) 3(aq) 4. _2_ HCl (aq) + Ca(OH) 2 (aq) CaCl 2(aq) + _2_ H 2 O (l) Solve the following titration problems, showing ALL steps. (2 pts. ea.) 5. How many moles of KOH (aq) are needed to completely neutralize 1.5 moles of H 2 SO 4(aq)? Cont d on back: Page 37 of 55

38 6. What volume of 5.0 M NaOH (aq) is needed to neutralize 40. ml of 2.0 M HCl (aq)? 7. What is the molarity of a NaOH (aq) solution if it takes 100. ml of a NaOH to completely neutralize 50. ml of 0.10 M H 2 SO 4(aq )? Page 38 of 55

39 37 Topic: g of NaCl x 3.55 = , or about ph 130 grams of NaCl are soluble in 355 grams of water at 10 C Objective: What do we mean by the expression of ph? Power of Hydronium Ion in a Solution: The unit ph is a measure of the hydrogen ion concentration in an aqueous solution. (paired [ ] means concentration) i. Pure water is in equilibrium (remember that?) where a small amount of water molecules dissociate from HOH to form H + and OH - ions. ii. H 2 O H + + OH -, and then the free H + form a coordinate bond with another H 2 O molecule to form a H 3 O + hydronium ion. iii. This is a SMALL number; in neutral water, the concentration of H + = 1.0 x 10-7 M, so the ph of pure water is given as 7. Page 39 of 55

40 Topic: Adding Acids to Water Objective: What happens to ph when we add an acid to water? Adding Acids to Water: When adding an acid to pure water, the added acid increases the H 3 O + concentration, so that the ph increases by one with each tenfold increase in acid strength. (paired [ ] means concentration) i. If the concentration of H 3 O + = 10-1 M, the ph value is 1 (absolute value of the exponent equals the ph value for an acid) ii. If the concentration of H 3 O + = 10-3 M, the ph value is 3 iii. If the concentration of H 3 O + = 10-9 M, the ph value is 9 iv. If the concentration of H 3 O + = M, the ph value is 11 v. If the concentration of H 3 O + = 5 x 10-6 M, the ph value is 6.5 vi. If the concentration of H 3 O + = 2 x 10-2 M, the ph value is 2.2 vii. A solution with a ph value 3 is tenfold more acidic than a solution with a ph value 4. viii. A solution with a ph value 3 is a thousand fold more acidic than a solution with a ph value 6. ix. A solution with a ph value 4.4 is four times more acidic than a solution with a ph value 4. x. A solution with a ph value 4.7 is seven times more acidic than a solution with a ph value 4. Page 40 of 55

41 Topic: Adding Bases to Water Objective: What happens to ph when we add a base to water? Adding Bases to Water: When adding a base to pure water, the added base increases the OH - concentration, so that the ph increases by one with each tenfold increase in base strength. (paired [ ] means concentration) i. If the concentration of OH - = 10-1 M, the ph value is 13 (value of the exponent subtracted from 14 equals the ph value for an base) ii. If the concentration of OH - = 10-3 M, the ph value is 11 iii. If the concentration of OH - = 10-5 M, the ph value is 9 iv. If the concentration of OH - = 5 x 10-6 M, the ph value is 7.5 v. If the concentration of OH - = 7 x 10-5 M, the ph value is 8.3 vi. A solution with a ph value 9 is tenfold more basic than a solution with a ph value 8. vii. A solution with a ph value 11 is a thousand fold more basic than a solution with a ph value 8. viii. A solution with a ph value 8.8 is eight times more basic than a solution with a ph value 8. ix. A solution with a ph value 11.2 is two times more basic than a solution with a ph value 11. Page 41 of 55

42 Comparing Common examples of ph values: Watch Bozeman Chemistry Acids, Bases, & ph YouTube video - 8:53 Page 42 of 55

43 Regents Practice Questions-pH: (Ungraded) 1. Which statement below correctly describes a solution with a ph of 9? a) It has a higher concentration of H 3 O + than OH - and causes red litmus paper to turn blue b) It has a higher concentration of OH - than H 3 O + and causes red litmus paper to turn blue c) It has a higher concentration of OH - than H 3 O + and causes methyl orange to turn red d) It has a higher concentration of H 3 O + than OH - and causes methyl orange to turn yellow 2. Which ph change represents a hundredfold (100x) increase in the concentration of H 3 O +? a) ph 3 to ph 1 c) ph 5 to ph 7 b) ph 4 to ph 3 d) ph 13 to ph Given the following solutions: i. Solution A: ph of 5 ii. Solution B: ph of 7 iii. Solution C: ph of 10 Which list below has the solutions placed in order of increasing H+ concentration? a) A B C b) C A B c) B A C d) C B A 4. Which relationship is present in a solution with a ph of 7? a) [H + ] = [OH - ] c) [H + ] < [OH - ] b) [H + ] > [OH - ] d) [H + ] + [OH - ] = 7 5. What is the H 3 O + ion concentration of a solution that has an OH - ion concentration of 1.0 x 10-3 M? a) 1.0 x 10-3 M c) 1.0 x M b) 1.0 x 10-7 M d) 1.0 x M Page 43 of 55

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45 Student name: ph Homework Class Period: Please carefully remove this page from your packet to hand in. Circle the correct answer for each multiple choice question. (1 pt. ea.) 1. Which of the following ph values is the most acidic? a) 5 b) 7 c) 9 d) Which of the following ph values is the most basic? a) 5 b) 7 c) 9 d) Which of the following 1 x 10-5 M in aqueous solution could have a ph of 5? a) CH 4 b) HCl c) NaCl d) NaOH 4. What would be the ph of a solution of made from equal volumes of 0.1 M HCl (aq ) and 0.1 M NaOH (aq)? a) 0.2 c) Less than 7 b) Exactly 7 d) Greater than 7 5. Which ph value would indicate a solution as the better acidic electrolyte? a) 3 b) 5 c) 9 d) Which ph value would indicate a solution as the poorer basic electrolyte? a) 3 b) 5 c) 9 d) 12 Short answer questions. (1 pt. ea.) 7. A ph of 4 is how many times more acidic than a ph of 6? 100 x 8. A ph of 11 is how many times more acidic than a ph of 8? x 9. Neutral ph is how many times more acidic than a ph of 2? x Page 45 of 55

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47 Topic: Brönsted-Lowry Acids & Bases Objective: Describe acids and bases using only H + ions. Brönsted-Lowry Acids and Bases: The discussion we have had so far is concerning the Svante Arrhenius theory on what makes an acid and acid, and a base a base. Two other scientists, Johannes Brönsted and Thomas Lowry published separate (but almost simultaneously) alternative theories about a more general theory of acids and bases. For the Brönsted-Lowry theory of acids and bases, a specific subset of what Brönsted-Lowry call acids and bases include the Arrhenius acids and bases, so the Arrhenius classification is more restrictive as what makes an acid or a base than the Brönsted- Lowry classification. Page 47 of 55

48 Topic: Comparing Acid-Base Theory Objective: How do Arrhenius and Brönsted-Lowry theories compare? 1. According to Arrhenius: i. Arrhenius Acid: A compound that dissociates in water to produce H + that is the ONLY positive cation in the solution. ii. Arrhenius Base: A compound that dissociates in water to produce OH - as the ONLY negative anion in the solution. 2. According to Brönsted-Lowry: i. Brönsted-Lowry Acid: Any substance that donates a proton (H + ). a) A neutral hydrogen atom ( 1 1H 0 ) has only one proton and one electron to start with. Remove the e -, and all you have is the proton, which we write as H +. The Brönsted-Lowry theory states any substance that gives a H + cation (a proton) is therefore a Brönsted-Lowry acid. ii. Brönsted-Lowry Base: Any substance that accepts a proton (H + ). b) The Brönsted-Lowry theory states any substance that accepts a H + cation (a proton) is therefore a Brönsted-Lowry base. Watch The Fuse School Bronsted-Lowry Theory video - 3:55 Page 48 of 55

49 Brönsted-Lowry theory examples: 1. HCl (g) + H 2 O (l) H 3 O +1 (aq) + Cl -1 (aq) Acid Base a) The HCl donated its H + to the H 2 O forming H 3 O + b) As HCl lost (donated) an H +, it is the Brönsted-Lowry acid. As H 2 O gained (accepted) the H +, it is the Brönsted-Lowry base. 2. NH 3(g) + H 2 O (l) NH 4 +1 (aq) + OH -1 Base Acid a) The H 2 O donated an H + to the NH 3 forming NH 4 + b) As H 2 O lost (donated) an H +, it is the Brönsted-Lowry acid. As NH 3 gained (accepted) the H +, it is the Brönsted-Lowry base. Yup water may act as both acid and base. Fun, eh? Page 49 of 55

50 3. HC 2 H 3 O 2(aq) + H 2 O (l) H 3 O +1 (aq) + C 2 H 3 O 2-1 (aq) Acid Base a) The HC 2 H 3 O 2(aq) donated an H + to the H 2 O b) As HC 2 H 3 O 2 lost (donated) an H +, it is the Brönsted-Lowry acid. As H 2 O gained (accepted) the H +, it is the Brönsted-Lowry base. Page 50 of 55

51 Regents Practice - Brönsted-Lowry Acids and Bases: (Ungraded) 1. Given the reaction of NH 3(g) + H 2 O (l) NH 4 + (aq) + OH - (aq): Water acts in this reaction as the a) Acid b) Base c) Electron donor d) Proton acceptor 2. According to the alternative theory of acids and bases, an acid is any species that a) Releases oxide ions into solution b) Donates protons to another species c) Releases hydroxide ions into solution d) Accepts protons from another species 3. In the reaction NH 3 + HCl NH Cl -1 : The NH 3 acts in this reaction as a) A Brönsted-Lowry acid, only b) A Brönsted-Lowry base, only c) Both a Brönsted-Lowry acid and a Brönsted-Lowry base d) Neither a Brönsted-Lowry acid nor a Brönsted-Lowry base 4. In which forward reaction below is water acting only as a proton acceptor? a) H 2 O (l) + H 2 O (l) H 3 O + (aq) + OH - (aq) b) NH 3(g) + H 2 O (l) NH 4 + (aq) + OH - (aq) c) H 2 SO 4(aq) + H 2 O (l) HSO 4-1 (aq) + H 3 O +1 (aq) d) CH 3 COO -1 (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) Page 51 of 55

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53 Student name: Class Period: Please carefully remove this page from your packet to hand in. Brönsted-Lowry Acids and Bases Homework For each of the following equilibrium systems, identify the Brönsted-Lowry acid and the Brönsted-Lowry base on the reactant side. Place a capital A over the Brönsted-Lowry acid, and a capital B over the base. A B 1. HBr + H 2 O H 3 O + + Br - B A *Note that HERE one water acts as a base; the other water acts as an acid 2. H 2 O + H 2 O H 3 O + + OH - A B 3. NH 3 + OH - NH H 2 O B A 4. H 2 O + HPO 4-2 PO H 3 O + A B 5. H 3 PO 4 + H 2 O H 2 PO H 3 O + B A 6. CH 3 COO - + H 3 O + HCH 3 COO + H 2 O A B 7. H 2 PO CH 3 COO - HCH 3 COO + HPO 4-2 A B 8. H 2 O + S -2 HS - + OH - B A 9. CN - + HCH 3 COO HCN + CH 3 COO - B A 10. OH - + NH 4 + H 2 O + NH 3 Page 53 of 55

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