Honors Chemistry Unit 11 ( )

Transcription

1 Honors Chemistry Unit 11 ( ) Acids and Bases o Definitions o Indicators o ph poh calculations o Naming Molarity o Calculations o Dilution Titration o Monoprotic calculations o Polyprotic calculations We are learning to: 1. Compare and contrast the characteristics of acids and bases. 2. Name acids and bases. 3. Calculate ph, poh, [H3O + ], [OH - ] 4. Determine the molarity of an acid or base. 5. Neutralize an acid or base of unknown concentration through the titration process 1

2 Molarity Measure of the strength of a solution Strong has higher molarity Weak has lower molarity Solution has 2 parts o Solute what gets mixed in o Solvent what does the dissolving (typically water) Quantitative need accuracy Typically use volumetric flasks Include Molarity on bottles o 3M HCl (3M Hydrochloric Acid) # of moles of solute Molarity = Liters of solution Units are moles / Liter or M or M A 3M solution is read as a 3 molar solution There is a distinction between mole and molar Moles represent a quantity Molarity represents a concentration So 0.10 M NaCl is a concentration of 0.10 moles of NaCl per 1 liter of solution, it does not just mean 0.10 moles. How many ml are in a Liter? 2

3 Example: Definition says Make a 1M solution using KBr 1 mole of KBr Liter or 1000 ml H2O What units do we weigh in? grams How do we convert moles to grams?? Convert 1 mole of KBr to grams: Moles x Molar Mass K = Br = grams / mole Weigh grams of KBr Put it into a 1 Liter volumetric flask Fill to line Shake until dissolved 3

4 Making Solutions: 1) Determine the grams of solute needed to make 1.00 L of a 1.0 M solution of NaCl 2) Determine the grams of solute needed to make 1.00 L of a 0.50 M solution of NaNO3. 3) Determine the grams of solute needed to make ml of a 1.00 M solution of Al(OH)3. 4) Determine the grams of solute needed to make ml of a 0.20 M solution of KI. 4

5 Molarity Problems Work the following out on a separate sheet of paper. Show your work! 1. Determine the number of grams of H 2SO 4 needed to prepare 1.00 liter of a 2.50M solution of H 2SO Determine the number of grams of aluminum sulfate needed to prepare 1.00 liter of a 0.025M aluminum sulfate solution. 3. Determine the number of grams of phosphoric acid needed to prepare ml of a 1.00M phosphoric acid solution. 4. Determine the number of grams of calcium hydroxide needed to prepare ml of a 0.100M calcium hydroxide solution moles of nitric acid molecules are dissolved in 1.50 L of water. What is the molarity of this solution. More Molarity Problems Work the following out on a separate sheet of paper. Show your work! 1. How many grams of CaCl 2 would be required to produce a 3.50 M solution with a volume of 2.00 liters? 2. What is the molarity of a.50 Liter solution containing 249 grams of KI? 3. How many moles of LiF would be required to make a 2.50 M solution with a volume of 1.50 Liters? 4. A sample of NaNO 3 weighing 8.50 grams is placed in a ml flask. Distilled water is added to the mark on the neck. What is the molarity of this solution? 5. How many grams of NaI would be needed to produce a 2.00 M solution with a volume of 1.00 Liters? 6. How many moles of Sr(NO 3) 2 would be used in the preparation of 10.0 Liters of a 6.0 M solution? More Practice Work the following out on a separate sheet of paper. Show your work for the calculations! 1. What is the equation for Molarity? 2. What is the molarity of a solution if 5.30 g of Na 2CO 3 is dissolved in ml of water? 3. How many moles of NaCl are contained in ml of a.200m solution? 4. What mass (in grams) of H 2SO 4 would be needed to make ml of a 2.00M solution? 5. What volume (in ml) of water would be needed if you had 2.45 grams of H 2SO 4 to make a 18.0 M solution? 6. What is the molarity of a solution made by dissolving 20.0 g of H 3PO 4 in ml of water? 5

6 Dilution 1. What is the equation for dilution? 2. What volume of M KCl is needed to make ml of 0.100M KCl solution? 3. Concentrated H 2SO 4 is 18.0 M. What volume of 18.0 M solution is needed to make 2.00 L of 1.00 M H 2SO 4 solution? 4. Concentrated HCl is 12.0 M. If ml of this 12.0 M solution are diluted to ml, what is the molarity of this diluted solution? L of 0.800M KNO 3 are prepared using ml of a more concentrated KNO 3 solution. What is the molarity of this solution? 6. A M solution is to be diluted to a M solution. If the original volume is 844 ml, what is the volume after the dilution? 6

7 Show your work! More Dilution! 1. If I add 25.0 ml of water to 1.00 L of M NaOH solution, what will the molarity of the diluted solution be? 2. If I add water to ml of a M NaOH solution until the final volume is ml, what will the molarity of the diluted solution be? 3. How much M HCl solution can be made by diluting 250. ml of 10.0 M HCl? 4. I have ml of a 1.50 M NaCl solution. If I boil the water until the volume of the solution is ml, what will the molarity of the solution be? 5. How much water would I need to add to ml of a 2.40 M KCl solution to make a 1.00 M solution? 7

8 Properties of Acids Acids and Bases 1. Taste Sour 2. Itchy on skin 3. Blue Litmus turns RED Red Litmus Stays RED 4. React with Bases Examples Vinegar, Citrus Fruit Properties of Bases 1. Tastes Bitter 2. Feels slippery 3. Red Litmus turns BLUE Blue Litmus stays BLUE 4. React with Acids Examples Soaps, Milk of Magnesia (antacids, Ammonia) acids and bases can be : monoprotic (HCl, NaOH), diprotic (H2SO4, Ca(OH)2 ) or polyprotic (H3PO4, Al(OH)3 ) Neutralization: Acid + Base Salt + Water H + from the acid and OH - from the base react to form water. Name the following: Naming Acids and Bases 1. HI 7. HNO4 2. HClO3 8. H2CO 3. Pb(OH)4 9. Fe(OH)3 4. H3PO4 10. HCl 5. LiOH 11. Ca(OH)2 6. H2SO3 12. HNO Write the formula for the following: 13. Percarbonic acid 19. Mercury (II) hydroxide 14. Hydrofluoric acid 20. Acetic acid 15. Chlorous acid 21. Barium hydroxide 16. Hyposulfurous acid 22. Nitrous acid 17. Persulfuric acid 23. Hypophosphorous acid 18. Zinc hydroxide 24. Sulfuric acid 8

9 ph Measurement 1. Litmus paper Red for Acid Blue for Base Cheap but very qualitative; only can tell if acid or base 2. Chemical Indicators Color change in a small ph range Many chemical indicators to choose from o Universal Indicator ph 4 to ph 10 Various colors o Phenolphthalein Clear to Magenta at ph = 9 o Natural Indicator Cabbage anthocyanin pigment Get more information as it can be matched to a color to get an approximate ph. Universal Indicator 3. ph Meter most accurate method Get a numerical value 9

10 The ph Scale Measure or count of the hydrogen (hydronium) ion concentration, [H3O + ]. Concentration is measured by molarity (M). Scale ranges from 0 14 Substance with a ph that is: < 7 is acidic (0 is most acidic) and therefore, [H3O + ] > [OH - ] 7 is neutral and therefore, [H3O + ] = [OH - ] >7 is basic (14 is most basic), therefore, [H3O + ] < [OH - ] How to calculate ph and [H3O + ] ph = -log[h + ] or log[h3o + ] [H3O + ] = 10 ph The poh Scale Measure or count of the hydroxide ion concentration, [OH - ]. This scale is the opposite of the ph scale. Scale ranges from 0 14, but Substance with a poh that is: < 7 is basic (0 is most basic) 7 is neutral >7 is acidic (14 is most acidic) How to calculate poh and [OH - ] poh = -log[oh - ] [OH - ] = 10 -poh Important relationship: ph + poh = 14 10

11 Monoprotic Example problem: You have a 0.010M HNO3 solution, a. What is the concentration of H + ion in this solution? M b. What is the ph of this solution? ph = -log of (0.01) ph= 2.00 Diprotic Example problem: You have a 0.010M H2SO4 solution, a. What is the concentration of H + ion in this solution? M b. What is the ph of this solution? ph = -log of (0.020) ph= ) You have a M HC2H3O2 solution, a. What is the concentration of H + ion in this solution? b. What is the ph of this solution? 2) You have a M Al(OH)3 solution, a. What is the concentration of OH - ion in this solution? b. What is the poh of this solution? c. What is the ph of this solution? 3) What is the ph of solution with a hydrogen ion concentration of 2.3 x 10-6 M? 4) What is the ph of a M NaOH solution? 5) What is the poh of a M Mg(OH)2 solution? 6) What is the ph and poh of a M Fe(OH)3 solution? 11

12 Example problem: What is the [H3O + ] (same meaning as [H + ] ) of a solution if the ph = 3.20? [H3O + ] = [H3O + ]= 6.3 x10-4 M or M 7) What is the [OH - ] if the poh = 5.32? 8) What is the [H3O + ] of a solution if the poh = 3.00? Fill in the missing information in the table below. ph [ H3O 1+ ] poh [ OH 1 ] ACID or BASE? x 10 4 M What is the hydronium ion concentration of a solution whose ph is 12.40? 8. What is the [H 3O +1 ] of a M Sr(OH) 2 solution? 9. If [H 3O + ] = 8.26 x 10-5 M, what is the poh of that solution? 10. What is the hydroxide ion concentration of a solution whose ph is 12.40? 11. What is the ph of a M Al(OH) 3 solution? 12. If [H 3O +1 ] = 8.26 x 10-5 M, what is the ph of the solution? 13. If the hydroxide concentration is 3.00 x M, what is the hydronium concentration? 12

13 Review for Acids and Bases 1. Fill in the Table: Chemical Formula H2SO4 HBr HClO H2CO3 HI H2Se H2Se HBrO4 HCl Ba(OH)2 HIO2 Name Iron (III) hydroxide Phosphoric Acid Nitrous acid Hypo bromous acid Iodic acid Hydroiodic acid 2. When using litmus paper, acid is represented by what color? 3. When using litmus paper, base is represented by what color? 4. List 3 properties of acids and 3 properties of bases. 5. If the ph of a solution is 8.99 a. What is the poh? b. What is the [OH - ]? c. What is the [H3O + ]? d. acid or base? 6. If the [H3O + ] of a solution is 7.28 x 10-3 M, a. What is the ph? b. What is the poh? c. What is the [OH - ]? d. acid or base? 13

14 7. If the poh of a solution is 5.06, a. What is the ph? b. What is the [OH - ]? c. What is the [H3O + ]? d. acid or base? 8. If the [OH - ] of a solution is 6.23 x 10-7 M, a. What is the poh? b. What is the ph? c. What is the [H3O + ]? d. acid or base? 9. What is the ph of a M H 2S solution? 10. What is the poh of a M HCl solution? 11. What is the ph of a 6.5 x 10-3 M Ca(OH) 2 solution? 14

15 Titration for Acids and Bases Titration is a method used to determine the concentration of an unknown acid (hydronium ion H 3O + or H + ) or base (hydroxide OH - ). Starting with a solution of unknown concentration of acid or base, small volumes of a solution of known concentration (titrant) are added until an equivalence point or a neutralization point is reached. This is when [H 3O + ] is equal to [OH - ]. Typically, the titrant is a strong acid or base. To help determine when the equivalence point occurs, indicators are used. The indicator used will depend on the system being studied since they all change color at slightly different phs. The indicator should have its color change near the equivalence point of the reaction. Some examples: Indicator Color in Acid Color in Base Litmus paper Red Blue Methyl Orange Pink Yellow Phenolphthalein Colorless Magenta When the indicator changes color, the hydronium or hydroxide ions in the unknown solution have been neutralized. The method for determining the molarity of the unknown solution involves using what is called equivalence. Equivalence is related to the number of H 3O + and OH - ions that are available in the compound for neutralization. H 2SO 4 has 2 equivalence of H + (considered a diprotic acid) Al(OH) 3 has 3 equivalence of OH - (considered a triprotic base) Titration Technique Typically, the unknown solution and the indicator are in the flask and the known solution is put into the buret. Preparing the Buret There are a few steps used to prepare the buret for the titration. 1. Rinse the buret several times with the titrant (approximately 5 ml each time) to be used in the analysis. Use the stopcock to ensure the whole buret has been rinsed, including the tip. Discard all of this titrant into a waste beaker. 2. Drain several milliliters of titrant through the tip using the stopcock to remove any air bubbles that might be present. Again, dispose this titrant into the waste beaker. 3. Fill up the buret, but the level of the titrant must be on the buret scale. Record this initial reading (see top of next page) 15

16 In order to get accurate data, one must know how to read the level of the solution in the buret. The level of the liquid in the buret is not a straight line. It is actually a curved line called a meniscus. The meniscus should be viewed at eye level. The correct way to read a meniscus is to observe where its lowest point is and take a reading. One should always estimate the last digit of the value taken. It can be helpful to hold a white card behind the buret to make the meniscus easier to read. Always record the buret reading before starting the titration. Next, we need to put a measured amount of the unknown solution into a flask. This value will be given to us. Now, 2 or 3 drops of indicator are added to the flask containing the solution of unknown concentration. The flask is then placed under the buret that contains the titrant or known solution. Slowly, the known solution is added to the liquid in the flask remember we are looking for the equivalence point where we will see a color change based on our indicator. The flask must be swirled at all times while the titrant is being added. **It can also be helpful to place a white piece of paper underneath the flask to help identify when the color change happens. You are only looking for a slight color change for the equivalence point. A bold color change indicates that you went too far with the titration. Lighter is better!!! The color has to stay for 30 seconds. You shouldn t add the titrant too fast because it is easy to add too much, but if you add it too slowly, the titration could take a long, long time. So, you can add the titrant steadily until the color starts to hang around for a while but still disappears. At this point, it should be added drop wise until the desired color change occurs. Take an accurate buret reading of the titrant when a slight but constant color change appears. To determine the amount of titrant dispensed from the buret, subtract the initial volume reading from before titrating from the volume reading on the buret after the titration is complete. This amount of solution dispensed from the buret. Using the following equation, you can solve for the molarity of the unknown. The unknown will either the acid or the base and the titrant (substance of known concentration) will be the opposite. Molarity of acid x Equiv of acid x Volume = Molarity of base x Equiv of base x Volume (MEV) (MEV) 16

17 Name 1. What is titration? Questions on the titration reading 2. What is the titrant and what type of compounds are used as titrants usually? 3. What types of materials are used for the equivalence point and why are they used? 4. What is meant by equivalence of an acid or base? 5. Draw a sketch of a titration set up 6. Why should we rinse the buret before using it for a titration? 7. Do you need to record the initial level of titrant? 8. What is a meniscus and how should it be read? 9. How much indicator is added and where is it added? 10. Why do we put white paper under the flask? 11. Why do we swirl the flask while adding titrant? 17

18 12. What does a bold color change indicate? 13. Describe the procedure for adding the titrant. Use the following equation from the reading to solve #14 & 15. (*don t use E A nor E B to determine sig. figs.) Molarity of acid x Equiv of acid x Volume = Molarity of base x Equiv of base x Volume (MEV) (MEV) 14. It takes ml acetic acid, HC 2H 3O 2 (V a) to neutralize ml of 0.5 M cadmium hydroxide, Cd(OH) 2 (V B). What is the molarity of (M A) of the acetic acid? 15. How many ml of.020 M KOH will neutralize ml of 0.40 M H 2SO 4? 18

19 Name Titration calculations (Don t use E A nor E B to determine sig. figs.) 1. What volume of M HNO 3 will be required to react with ml of M KOH? 2. What volume of M NaOH will be required to neutralize ml of M H 2SO 4? 3. If grams of the monoprotic acid, was neutralized with ml of M NaOH, calculate the molar mass of the acid. 4. What mass, in grams, of KOH will be required to react with ml of M HCl? 5. A solution contains a monoprotic acid with a molar mass of g/mol ml of M KOH was required to neutralize a sample of this acid. Determine the mass of the acid sample that was neutralized. (Hint: MV is equal to moles. Find the moles first then multiply the moles by the molar mass). 19

20 More Titration Calculations: 1) It requires ml of potassium hydroxide solution to neutralize ml of M phosphoric acid. Type of system (circle the answer) : Phosphoric acid = mono di tri protic Potassium hydroxide = mono di tri protic Balanced equation: Calculate the concentration of the potassium hydroxide solution. What is the ph of the potassium hydroxide solution used in the titration: What is the ph of the phosphoric acid solution used in the titration: 2) ml of a citric acid (H 3C 6H 5O 7) solution is neutralized by 48.0 ml of M NaOH. Type of system (circle the answer) : Citric acid = mono di tri protic Sodium hydroxide = mono di tri protic Balanced equation: Calculate the molarity of the citric acid solution. What is the ph of the citric acid solution used in the titration? What is the ph of the sodium hydroxide solution used in the titration? 3) If.250 grams of a monoprotic acid are neutralized with ml of M NaOH solution. What is the molar mass of the monoprotic acid? Which one of these given monoprotic acids was used in this titration? Circle the answer. HF = g/mole HCl = g/mole HBr = g/mole HI = g/mole 4) A solution contains a monoprotic base with a molar mass of g/mole ml of M HCl was required to neutralize a sample of the solution. Determine the mass of the original base solution sample. 20

21 Name 1. a) How many milliliters of M HCl are required to neutralize 25.0 ml of M Ba(OH) 2? b) What are the original ph values for the HCl and the Ba(OH) 2 solutions? 2. a) What is the concentration of hydroiodic acid if ml of it is neutralized by ml of a M lithium hydroxide solution? b) What is the ph of the hydroiodic acid before the titration? 3. What is the volume of a M iron (II) hydroxide solution is needed to neutralize ml of M phosphoric acid? 4. What is the molarity of a copper (II) hydroxide solution if ml of the solution is titrated to the endpoint with ml of M carbonic acid solution. What was the ph of the copper (II) hydroxide solution? 5. In a titration of H 2SO 4 with Al(OH) 3, 60.0 ml of M Al(OH) 3 was needed to neutralize 15.0 ml of H 2SO 4. Write the neutralization reaction. What is the molarity of the acid? What is the ph of the acid? 6. Exactly 50.0 ml of Ca(OH) 2 solution of unknown concentration was titrated with moles of HClO 2. What is the concentration of the Ca(OH) 2 and its ph before titrating? 21

22 Various protic Titration Problems ml of.100 M NaOH neutralized 25.0 ml of hydrochloric acid. Determine the concentration of the acid ml of M NaOH neutralized 20.0 ml of sulfuric acid. Determine the concentration of the acid ml of M Ba(OH)2 neutralized 40.0 ml of nitric acid. Determine the concentration of the acid. 4. A ml sample of sodium hydroxide solution is titrated with a M solution of sulfuric acid. The titration requires 24.09mL of the acid solution of reach the equivalence point. What is the molarity of the base solution? H 2SO 4 (aq) + 2 NaOH (aq) Na 2SO 4 (aq) + 2H 2O (l) ml of a 1.02 M NaOH solution is added from a buret to ml of a phosphoric acid solution. Determine the molarity of the phosphoric acid. 22

23 Titration Challenge 1. What mass, in grams, of KOH will be required to react with ml of M HCl? 2. If 10.0 ml of M KOH are required to neutralize 35.0 ml of an diprotic acid, determine the ph of the acid g of an unknown monoprotic acid is titrated with 50.0 ml of M NaOH to the endpoint. Determine the molar mass (grams / mole) of the acid g of an unknown triprotic acid is titrated with 74.0 ml of M Potassium hydroxide to the endpoint. Determine the molar mass of the acid. 5. If grams of monoprotic acid was neutralized with ml of 0.400M NaOH, calculate the molar mass of the acid. 6. A solution contains a monoprotic acid with a molar mass of grams/mole ml of M KOH was required to neutralize a sample of the acid solution. Determine the mass of the original acid solution. 23

24 24

25 When Life Gives You Lemonade - Titration Purpose: To practice proper titration technique To determine molarity of citric acid (H 3 C 6 H 5 O 7 ) in Crystal Light lemonade Materials: A delicious cup full of Lemonade Phenolphthalein M NaOH dh 2 O buret 250 ml Erlenmeyer flask ml volumetric pipet and pipet pump Prelab: (IF NOT completed, you will NOT participate in the lab! You will have to complete the lab outside of school time!) 1) Write the balanced reaction for this titration 2) Use a RULER to make a data table on the back of this sheet. Read through the procedure to determine what data you will need to collect. Procedure: 1. Rinse a buret with a small amount of the titrant, M NaOH. 2. Fill the buret with M NaOH and record the initial volume. 3. Run 3 separate trials using between 10 and 50 ml of lemonade (acid) per trial (a different volume per trial). Use a pipettor to transfer the lemonade to your flask. 4. Add a few drops of phenolphthalein indicator to the lemonade that you put into your flask. 5. Add 20 ml of deionized H 2 O to the lemonade in your flask/ 6. Titrate to a faint pink endpoint then record final volume. 7. Check the level of titrant in your buret before you do your next trial to make sure you have enough for your next trial. Analysis: (complete on the back of this sheet under your data table) 1) Solve for the molarity of citric acid for each trial. 2) Calculate the average molarity of citric acid in the lemonade. 3) Using your average molarity, determine how many milliliters of M NaOH would be needed to neutralize the citric acid in a ml cup of this lemonade. 25

26 26

27 Name Experimental Determination of the Molar Mass of Monoprotic Acid Problem: Using titration, is it possible to determine the molar mass of a monoprotic acid accurately. Prelab: Read the procedure below and then answer the following questions: 1) What is the titrant for this lab? 2) What should you do to the buret prior to filling it with the liquid? 3) How much acid should you use? 4) What is the molarity of the titrant? 5) What is the indicator for this lab? 6) Where will you put the indicator? 7) Where will you put the NaOH? 8) Where will you put the acid? 9) When do you stop adding liquid from the buret? 10) What are we trying to determine in this lab? Procedure: 1. Fill the buret with.500 M NaOH. Record the initial reading on the buret in the table below. 2. Withdraw ml of acid (use 10 ml pipette 1 ½ times). Put into a 125 Erlenmeyer flask. Add 20 ml deionized H2O to the flask using a graduated cylinder. 3. Add 3 drops of phenolphthalein to the flask. 4. Put a piece of white paper under the flask. Titrate with NaOH; swirl the flask frequently. Add the NaOH drop by drop near the end point. The solution should be a light pink color at the end point. 5. Discard the solution in the flask down the drain, rinse the flask thoroughly and run a second titration. Observations: Concentration of NaOH (M) Trial One Trial Two Trial Three Volume of Base Used (NaOH) Start Value End Value Volume used Start Value End Value Volume used Start Value End Value Volume used 27

28 Calculations: (You must show your work with units for all calculations!) 1. Calculate the moles of acid that were titrated in each trial. (hint: Because both the acid and the base are monoprotic, you do not need to include the volume of acid in this calculation. Leave M AV A as unknown. instead of using M AE AV A = M B E BV B M AV A will equal the moles of acid, BUT V B must be in liters) a. Trial 1: b. Trial 2: c. Trial 3: 2. The sample of acid used contains g of the monoprotic acid. Calculate the experimental molar mass for each trial (remember molar mass is grams/moles you found the moles in #1). a. Trial 1: b. Trial 2: c. Trial 3: 3. Calculate your % error for each trial (the accepted value is 60.1 g/mole) Trial 1 Trial 2 Trial 3 28

29 Using titration. Solving for the Molarity of an Acid Prelab: Read the procedure below and then answer the following questions: 1) What is the titrant for this lab? 2) What should you do to the buret prior to filling it with the liquid? 3) How much H2SO4 should you use? 4) What is the molarity of the titrant? 5) What is the indicator for this lab? 6) Where will you put the indicator? 7) Where will you put the NaOH? 8) Where will you put the H2SO4? 9) When do you stop adding liquid from the buret? 10) What are we trying to determine in this lab? 11) Write out the balanced chemical reaction for this titration. 12) What should be the ph when you reach the endpoint? Procedure: In an Erlenmyer flask: 1. Using a pipettor, add ml of H2SO4 with an unknown molarity. 2. Add ml of deionized water using a graduated cylinder 3. Add 3 drops of phenolphthalein indicator Liquid of known concentration In a Buret: 1. Use a small amount of NaOH to rinse the buret. 2. Fill to the 0.00 line with M NaOH 3. Record the volume reading of the buret. 4. With the erlenmeyer flask under the buret, open the stopcock slowly and with constant swirling add NaOH to the acid solution. Slow down the addition of the NaOH as the color change takes longer to disappear. Liquid of unknown 5. Stop when you see a LIGHT magenta color. The color concentration must stay for at least 30 seconds. If it doesn t, keep adding titrant dropwise until it does 6. Record the new volume reading of the buret. 7. Titrations should always be done at least twice.repeat steps

30 Trial 1 Trial 2 Trial 3 Starting reading of buret Ending reading of buret Volume of NaOH used At the neutralization point, where the color changes, the concentration of Base = the concentration of Acid: [Base] = [Acid] Molarity base x Equivalence base x Volume base = Molarity acid x Equivalence acid X Volume acid Solve for Macid for each trial: (show your work!) Trial 1: Trial 2: Trial 3: Your teacher will give you the accepted value of the molarity of the acid. Using the accepted value, calculate your % error for each trial. Show your work below. Trial 1 Trial 2 Trial 3 30

31 Finding Molarity of an HCl Solution By Quantitative Analysis Introduction: In this experiment, you will find the molarity of three different hydrochloric (HCl) solutions by quantitative analysis of its reaction with Aluminum. Aluminum reacts with HCl to form 2 products. Write and balance the equation for this reaction. Caution: Hydrogen gas is highly flammable. No open flames during this part of the lab. Materials Needed: Safety goggles 10 ml volumetric pipette 3 Test tubes Pippettor Test tube rack 3 hydrochloric acid solutions 3 aluminum nails Pre-Lab:(IF NOT completed, you will NOT participate in the lab! You will have to complete the lab outside of school time!) 1) Molar mass of aluminum 2) Molar mass of aluminum chloride 3) Molar mass of hydrogen gas 4) Write the balanced chemical equation for the reaction that will occur during this lab: 5) How could you experimentally test (during the lab) to verify that the gas produced is hydrogen? 6) Use a RULER to make a data table on the back of this sheet. Read through the procedure to determine what data you will need to collect. Procedure: (goggles on for the entire lab) Day 1: 1. Label three large test tubes A, B and C and place in a test tube rack 2. Obtain 3 aluminum nails. Find the mass of each nail and record in your table. 3. Place a nail in each test tube. Be sure to indicate which nail is in each test tube. 4. Using a 10 ml pipette and a pipetter, transfer ml of each unknown molar concentration HCl solution to the appropriate test tube. Make sure there is no fluid left in the pipette to avoid contamination between transfers. 5. Observe the reaction for a few minutes. 6. Place your test tubes into a beaker in your drawer. Make sure it is stable. Lock up the drawer. Day 2: 1. Remove the test tubes from your drawer. Carefully pour off the liquid (aluminum chloride) without losing the aluminum nail. Rinse the aluminum with small amounts of distilled water. 2. Using a blue flame, gently dry the nail that remains. 3. When the nails are dry and cool, use the balance to find the mass. 4. Discard the nails into the waste beaker on my desk, NOT THE TRASH. Analysis: A) Determine the molarity of each solution (show all the work for your calculations). B) Identify the limiting reactant for each test tube and explain how you came to that conclusion. 31