Molarity Worksheet #1. Molarity (M) = 1.What is the molarity of a solution of 58.0 g of NaCl dissolved in 1.0 L of solution?

Transcription

1 Name: Molarity Worksheet #1 Molarity (M) = moles of solute liter of solution 1.What is the molarity of a solution of 58.0 g of NaCl dissolved in 1.0 L of solution? 2. What is the molarity of a solution of 10.0 g AgNO 3 dissolved in 500. ml of solution? 3. How many grams of KNO 3 should be used to prepare 2.00 L of a M solution? 4. To what volume should 5.0 g KCl be diluted in order to prepare 0.25 M solution? 5. How many grams of CuSO 4 *5H 2 O are needed to prepare 100. ml of a 0.10 M solution? 1

2 Dilution Acids and bases are usually acquired from chemical supply companies in concentrated form. Acids are diluted to the desired concentration by adding water. Since the total moles of acid is the same before and after dilution we can set them equal to each other. Given: moles of acid = Molarity x Volume then M 1 xv 1 = M 2 xv 2. Where M 1 xv 1 is the moles of acid before dilution and M 2 xv 2 is moles of acid after dilution. Solve the following. 1.How much concentrated 18 M sulfuric acid is needed to prepare 250 ml of a 6.0 M solution? 2. How much concentrated 12 M hydrochloric acid is needed to prepare 1.0 X 102 ml of a 2.0 M solution? 3. To what volume should 25 ml of 15 M nitric acid be diluted to prepare a 3.0 M solution? 4. To how much water should 50. Ml of 12 M hydrochloric acid be added to produce a 4.0 M solution? 5. To how much water should 100.ml of 18 M sulfuric acid be added to prepare a 1.5 M solution? 2

3 1. What does molarity mean? Molarity Worksheet #2 2. What is the molarity of a solution that contains 4.53 moles of lithium nitrate in 2.85 liters of solution? 3. What is the molarity of a solution that contains moles hydrochloric acid in 2.39 x 10-2 liters of solution? 4. A flask contains 85.5 g C 12 H 22 O 11 (sucrose) in 1.00 liters of solution. What is the molarity? 5. A beaker contains grams osmium (III) fluoride in liters of solution. What is the molarity? 6. Calculate the molarity if a flask contains 1.54 moles potassium sulfate in 125 ml of solution. 3

4 7. A chalice contains grams ammonium chlorite in 2.36 liters of solution - calculate the molarity. 8. What is the molarity of a solution that contains grams magnesium oxalate in 3.65 ml of solution? 9. What mass of lithium phosphate would you mass to make 2.5 liter of 1.06 M lithium phosphate solution? 10. If you evaporated 250. ml of a 3.5 M solution of iron (II) nitrite, what mass of iron (II) nitrite would you recover? 11. A chemist has 4.0 g of silver nitrate and needs to prepare 2.0 L of a M solution. Will there be enough silver nitrate? If so, how much silver nitrate will be left over? 4

5 12. A rabbit pours ml of a molar solution of sodium hydroxide into a liter volumetric flask and fills the flask up with water. What is the new molarity of the solution? Concentration and Molarity PhET-Chemistry Labs Introduction: Everyone likes candy. Have you ever wondered how that candy is produced? How do they get all that delicious sugar into those ny packages? Could you make hard candy like those you can buy? It s easier than you think. Web searching for rock candy will yield a number of delicious recipes you can try at home. Some handy vocabulary for you to define: Solute Solvent Moles Molarity Saturated (not fats) Unsaturated (not fats) Supersaturated Procedure: PhET Play with the Sims Chemistry Concentration Part 1: Dissolution and Saturation Take some me to play and familiarize yourself with the simula on. Click on everything. Move all the sliders. No ce what happens to the concentra on as solid solute is added and when evapora on occurs. 5

6 How does the concentra on change as solid solute is added? How does the concentra on change as addi onal water is added? How does the concentra on change as evapora on occurs? How do you know when a solu on is saturated? When a solu on is saturated, and addi onal solid solute is added, what happens? Why do you think this is? How does adding this addi onal solute change the concentra on of this saturated solu on? How does evapora on change the concentra on of a saturated solu on? Part 2: Concentrated Solutions Adding a concentrated solu on describe a way to determine the concentra on of the solu on in the spigot. Write your plan here: Using your plan how might you get that concentrated solu on to become saturated? Does your plan work for all the other solu ons too? Why? / Why Not? 6

7 Part 3: Molarity PhET Play with the Sims Chemistry Molarity Molarity is moles per Liter, that is, how many moles of solute (en re salt) is dissolved per Liter of solu on. First, determine the saturation concentration of each of the solu ons, that is, how concentrated can you get each solu on before the solu on is saturated. If you can t determine the concentra on using the simula on Molarity, try using the simula on Concentra on (You will use this informa on again in Part 5, if your instructor requires it) Satura on concentra on Satura on concentra on Part 4: Calculating Molarity Using the simula on and the formula for Molarity above, complete the table below. Moles of Compound (mol) Liters of Solu on (L) Molarity of Solu on (M) Moles of Compound (mol) Liters of Solu on (L) Molarity of Solu on (M) Part 5: (Extension Exercise) Total Ion Concentration (this will be important for Equilibrium, Kine cs, and Acid-Base ) 7

8 Just as an en re solu on has a concentra on, so does each individual ion. For instance, since there are three ions when a Calcium Chloride CaCl 2 molecule dissolves into solu on, a 3.0 M solu on of CaCl 2 is 3.0 M with respect to Ca 2+ ions and 6.0 M with respect to Cl - ions, for an overall ion concentra on (solubility) of 9.0 M (3.0 M M). Using what you know about inorganic nomenclature and common ions, complete the table below Compound Co(NO 3 ) 2 CoCl 2 K 2 Cr 2 O 7 AuCl 3 K 2 CrO 4 Saturated Concentration (from Part 3) Cation Molarity Anion Molarity Total Ion Solubility NiCl 2 CuSO 4 KMnO 4 Conclusion Questions and Calculations, Concentration and Molarity Post-Lab Exercises (please staple to your lab page) The Sims: Google: Phet PhET Play with the Sims Chemistry Concentration or Molarity 1. Adding pure water to a saturated solu on (with no solids) would cause the concentra on of that solu on to increase / decrease / remain the same. (circle) 2. Adding pure water to a saturated solu on (with some solids) would cause the concentra on of that solu on to ini ally increase / decrease / remain the same. (circle) 3. Adding a solid salt to a saturated solu on causes the concentra on of that solu on to increase / decrease / remain the same. 4. Evapora on ac ng on an unsaturated solu on causes the solu on s concentra on to increase / decrease / remain the same. 5. Evapora on ac ng on a saturated solu on causes the solu on s concentra on to increase / decrease / remain the same. 8

9 6. Using your notes, your text, or the internet discover what happens to the satura on concentra on when a solu on s temperature is increased. What happens as a solu on is heated? 7. Why does this happen? (hint think about the molecules) 8. Can you dissolve.35 moles of Potassium Permanganate (KMnO 4 ) into 500 ml of water? Why? / Why not? (please show work) 9. Can 1750 ml of water dissolve 4.6 moles of Copper Sulfate CuSO 4? Why? / Why not? (please show work) 10. What is the solu on concentra on formed from 3.6 moles NaCl dissolved into 1.3 L of water? (please show work) 11. What is the solu on concentra on formed from 2.1 moles BaCl 2 dissolved into 1.9 L of water? (please show work) 12. How many moles of solute are present in.75 L of a.89 M (molar) solu on? (please show work) 13. How many moles of solute are present in 1.4 L of a 1.9 M (molar) solu on? (please show work) 14. What volume of water would be required to dissolve.46 moles of solute to produce a.22 M solu on? (please show work) 9

10 Solve the following solutions Stoichiometry problems: 1. How many grams of silver chromate will precipitate when 150. ml of M silver nitrate are added to 100. ml of M potassium chromate? 2. How many ml of M barium nitrate are required to precipitate as barium sulfate all the sulfate ions from ml of M aluminum sulfate? ml of M NaOH are added to ml of M copper (II) sulfate. How many grams of copper (II) hydroxide will precipitate? 4. What volume of M silver nitrate will be required to precipitate as silver bromide all the bromide ion in ml of M calcium bromide? 5. What volume of M HCl is required to neutralize ml of M sodium hydroxide? 6. How many ml of M HCl is required to neutralize 1.25 grams of sodium carbonate? (producing carbonic acid) 7. How many grams of magnesium hydroxide will precipitate if ml of M magnesium nitrate are combined with ml of M potassium hydroxide? 10

11 ml of M potassium iodide are combined with ml of M lead (II) nitrate. How many grams of lead (II) iodide will precipitate? Molarity and Stoichiometry Problem Set For each of the following problems balance the given equation and then use it to find the requested information. Show all work being careful of units and significant figures. 1. Find the volume in liters of 1.00 M H 2 S needed to react completely with L of 4.00 M HNO 3. HNO 3 (aq) + H 2 S (aq) NO (g) + S (s) + H 2 O (l) 2. What volume of 0.50 M HBr is required to react with 18.0 g of zinc? HBr (aq) + Zn (s) ZnBr 2 (aq) + H 2 (g) 3. How many grams of AgCl can be produced from the reaction of 30.0 ml of 12.0 M NaCl solution with an excess of 10.0 M AgNO 3 solution? 11

12 AgNO 3 (aq) + NaCl (aq) AgCl (s) + NaNO 3 (aq) 4. What volume in liters of hydrogen gas measured at STP can be produced from reacting 500 ml of 6.0 M H2SO4 solution with an excess of nickel metal? Ni (s) + H 2 SO 4 (aq) NiSO 4 (aq) + H 2 (g) 5. What is the molarity of a 1.75 L solution of Ca(OH) 2 that would completely react with 2.00 L of CO 2 gas measured at STP according to the reaction below? CO 2 (g) + Ca(OH) 2 (aq) CaCO 3 (s) + H 2 O (l) 6. Find the molarity of KNO 3 produced if 40.0 ml of M K 3 PO 4 reacts with an excess of AgNO 3 in 250 ml of solution? AgNO 3 (aq) + K 3 PO 4 (aq) Ag 3 PO 4 (s) + KNO 3 (aq) 12

13 Concentration and Beers Law Lab White light is actually composed of a rainbow of colors of visible light. There are also other types of light (the generic term is electromagnetic radiation) such as UV, infrared, microwave, radio, etc. which differ from visible light only in frequency, wavelength, and energy. An instrument called a spectroscope has a diffraction grating that splits electromagnetic radiation into the various frequencies that make it up called a spectrum. There are two types of spectrums; emission and absorption spectrums. Emission spectrums are those produced by glowing objects (sun, stars, spectrum tubes) and show the frequencies of light emitted by the glowing object. Absorption spectrums are produced when objects absorb light and show the frequencies of light absorbed by objects. Absorption spectrums are of particular use for chemists because they can be used to determine the identity and concentrations of unknown substances in solutions. In a device called a spectrophotometer light at various frequencies is passed through a solution and the absorbance (amount of light absorbed by the solution) is measured. A plot of absorbance versus frequency or wavelength reveals a sort of unique fingerprint which can be used to identify a substance. In a device called a colorimeter light at a given frequency is passed through a solution and again the absorbance is measured. However, now the absorbance value can be used to determine the concentration of an unknown when compared to the absorbance values of a set of standard solutions. Many compounds absorb ultraviolet (UV) or visible (Vis.) light. The diagram below shows a beam of monochromatic radiation of radiant power P 0, directed at a sample solution. Absorption takes place and the beam of radiation leaving the sample has The amount of radiation absorbed may be measured in a number of ways: Transmittance, T = P / P 0 % Transmittance, %T = 100*T Absorbance, A = log 10 ( P 0 / P) A = log 10 (1 / T) 13

14 radiant power P. A = log 10 (100 / %T) A = 2 - log 10 (%T) The last equation, A = 2 - log 10 %T, is worth remembering because it allows you to easily calculate absorbance from percentage transmittance data. So, if all the light passes through a solution without any absorption, then absorbance is zero, and percent transmittance is 100%. If all the light is absorbed, then percent transmittance is zero, and absorption is infinite. The Beer-Lambert Law Now let us look at the Beer-Lambert law and explore its significance. This is important because people who use the law often don't understand it - even though the equation representing the law is so straightforward: A= ε bc Where A is absorbance (no units, since A = log 10 P 0 / P ) ε is the molar absorptivity with units of L mol -1 cm -1 b is the path length of the sample--that is, the path length of the cuvette in which the sample is contained. We will express this measurement in centimeters c is the concentration of the compound in solution, expressed in molarity (mol L-1) The Beer-Lambert Law boils down to the greater the molar absorptivity of a solution, the greater path length light must travel through, and the greater the concentration of the solution the more light is absorbed and the bigger the Absorbance. Procedure 1. Prepare ml of the CuSO 4 *5H 2 0 solution assigned by the instructor. 14

15 2. Use the spectrophotometer to obtain a spectrogram (plot of absorbance vs. wavelength). 3. Pour solution into a cuvette and use the spectrophotometer to measure the absorbance. 4. Using data from other groups, prepare a calibration curve (plot of absorbance vs. concentration). The slope of the plot is the molar absorptivity times the path length. 5. Obtain the absorbance of the unknown solution. Use the calibration curve and the Beer s law equation to calculate the concentration of the unknown solution. Concentration and Beer s Law Lab Report Objective : To determine the concentration (molarity) of an unknown copper (II) sulfate pentahydrate solution. Procedure : Describe how the standard solution was prepared and how the concentration of the unknown solution will be determined. Include glassware and equipment used. Data: 1. Record mass of CuSO 4 *5H 2 O used, volume of CuSO 4 *5H 2 O solution made, temperature, wavelength of maximum absorption, absorbance of standard solution, absorbance of unknown solution 2. Sketch the spectrogram (plot of absorbance vs wavelength) for CuSO 4 *5H 2 O 3. Record the class Absorbance vs. Concentration for class data in a neat table. 4. Prepare a calibration curve (plot of Absorbance vs. Concentration) for the class data. Calculations : 1. Show how you calculated the grams of CuSO 4 *5H 2 0 needed to prepare your standard solution. 2. Write a general Beers Law expression for the calibration curve. 3. Use the equation of best fit to calculate the concentration of the unknown solution. 15

16 4. Get the actual unknown concentration from the instructor and calculate a class percent error. Conclusion : Describe sources of error and how they affect results World of Chemistry Video: Proton in Chemistry 1. What is the #1 most manufactured chemical produced in the US? 2. Half of the top 10 chemicals are or. 3. What are some examples of strong acids and bases? 4. What are some examples of weak acids and bases? 5. Acids have a taste. 6. Bases have a taste. 7. Acids turn blue litmus paper. 8. Acids react with metals to produce gas. 9. Acids react with limestone to produce gas. 10. What happens when magnesium is put into ammonia? 16

17 11. When acids and bases come in contact they each other. 12. What is a common factor in all acid-base reactions? 13. The video referred to sulfuric acid as a catalyst. What is a catalyst? 14. How is limestone being used in coal-burning power plants? 15. The 2 major sources of acid rain are and sources. 16. What is the difference between a stationary and a mobile source? 17. Name a natural source of acid rain. 18. Rainwater during a storm in West Virginia had acidity close to acid. 19. The acidity or basicity of a solution is measured using the scale. 20. What is the ph of pure water? 21. The ph of acids is below. 17

18 22. The ph of bases is above. 23. What acid does the stomach produce? 24. Why is stomach acid necessary? 25. What is the purpose of antacids? Neutralization Reactions and Titration Problems Complete and balance the following acid-base reactions by writing a complete balanced equation in the line provided or filling in the blank spaces with the correct formulas. Remember to include appropriate states of matter. 1. H 3 PO 4 (aq) + Al(OH) 3 (s) 2. + CaI 2 (aq) + 3. hydrochloric acid + potassium hydroxide 4. nitric acid + magnesium hydroxide + 18

19 5. + Na 2 SO 4 (aq) + Using the balanced reactions from above, do the following problems. 6. What is the molarity of a solution of NaOH if 38 ml of the solution if used to neutralize 14 ml of 0.75 M H 2 SO 4? 7. A 12.4 ml solution of HNO 3 is completely neutralized by 19.8 ml of 0.25 M Mg(OH) 2. What is the concentration of the nitric acid? 8. What volume of 0.15 M KOH is needed to neutralize 12.5 ml of 0.30 M HCl? 9. How many ml of 0.45 M HI must be added to 25.0 ml of 1.00 M Ca(OH) 2 to make a neutral solution? 19

20 10. What is the molarity of H 3 PO 4 if 15.0 ml of the solution is completely neutralized by 38.5 ml of M Al(OH) 3? Chemistry ph Worksheet Calculate the ph, poh, [H + ], and [OH - ] as necessary. Identify the type of solution as acidic, basic, or neutral. ph poh [H + ] [OH - ] Classify M x 10-9 M x 10-6 M x M x 10-5 M x 10-4 M x 10-3 M x 10-6 M

21 Acid-Base Stoichiometry 1. What is the molarity of a NaOH solution if ml is titrated to the end point with 98.7 ml of 2.76 M HCl? 2. In a titration, 45.6 ml of a 2.0 X 10-2 M Al(OH) 3 solution is used to titrate a 3.4 X 10-2 M HCl solution. What is the volume of the HCl solution? 3. Suppose that 15.0 ml of 2.50 X 10-2 M H 2 SO 4 is required to neutralize 10.0 ml of an aqueous solution of KOH. What is the molarity of the KOH solution? 4. In a titration, 25.8 ml of 3.4 X 10-3 M Ba(OH) 2 is used to neutralize a 8.7 X 10-2 M HCl solution. What is the volume of the HCl solution? 5. What is the molarity of a Ca(OH) 2 solution, given that 428 ml of it is neutralized in a titration by 115 ml of 6.7 X 10-3 M HNO 3? 21

22 6. What volume of a M NaOH solution is needed to titrate 25.0 ml of M H 2 SO 4 solution to the end point? 7. Suppose that 10.1 ml of HNO 3 is neutralized by 71.4 ml of a 4.2 X 10-3 M solution of KOH in a titration. Calculate the concentration of the HNO 3 solution. 8. What volume of 1.75 X 10-2 M Ba(OH) 2 is needed to neutralize 14.5 ml of a 2.3 X 10-2 M solution of H 2 SO 4? Virtual Titration Lab Go to the following web address: Name ry/acid_base.html 1. Select reaction type. Choose strong acid vs. strong base. 2. Fill the burette with acid or base. Choose base. 3. Select the acid and the base. For trial #1 select HCl, trial #2 select HNO 3, and for trial #3 select H 2 SO 4. Choose NaOH as the base for each trial. 4. Select the indicator. Choose phenolphthalein. Record the molarity and volume of the acid in the data table. 5. Push slider or the click on the red button to add base to the phenolphthalein endpoint. 6. Record the volume of NaOH added and calculate the molarity of the NaOH. Record in the data table. Reset to start the next trial. DATA: Type of Volume of Molarity of Molarity of Volume of Acid Acid Acid NaOH NaOH Hydrochloric 22

23 Sulfuric Nitric Analysis: (Show ALL work!) 1. Write the balanced equation for the neutralization reaction between hydrochloric acid and sodium hydroxide and then find the concentration of the base using your titration data. 2. Write the balanced equation for the neutralization reaction between sulfuric acid and sodium hydroxide and then find the concentration of the base using your titration data. 23

24 3. Write the balanced equation for the neutralization reaction between nitric acid and sodium hydroxide and then find the concentration of the base using your titration data. Acid - Base Titration Lab Objective : To determine molarity of a acetic acid (aq) solution by titrating with a prepared sodium hydroxide concentration of known molarity. PROCEDURE : 1. Prepare 100 ml of a 0.15 M NaOH solution using the volumetric flasks. 2. Fill a buret with the sodium hydroxide solution. Carefully drain out 1-2 ml to see how the valve works. Make it come out drop by drop SLOWLY. Make sure that there are no bubbles in the buret. 4. Put 5.0 ml of the unknown acetic acid solution into an erlenmeyer flask and add distilled water up to a volume of 25.0 ml. Next, add 3 drops of the indicator phenolphthalein. 5. Add base from the buret into the erlenmeyer flask until the indicator just turns to a faint pink color which persists for at least 30 seconds. Record the precise volume of base added to the tenth of a milliliter. 6. RECORD DATA on the data page. When you are done with each titration you may discard all solutions down the sink with plenty of water. 7. Repeat for three trials and average results. Data Trial #1 Trial #2 Trial #3 Volume of acetic acid solution 5.0 ml 5.0 ml 5.0 ml Initial Buret Reading (ml) Final Buret Reading (ml) 24

25 Volume of 0.10 M NaOH added Analysis (Do on a separate sheet of paper!) 1. Calculate the grams of sodium hydroxide needed to prepare ml of a 0.10 M NaOH solution. 2. Write a balanced chemical equation for the reaction of acetic acid with sodium hydroxide. 3. Calculate the experimental molar concentration of the acetic acid using your prepared NaOH solution. 4. Obtain the accepted molar concentration of acetic acid from your instructor. Calculate a percent error. Conclusion (Do on a separate sheet of paper!) Describe some sources of error and how they affect results during a titration. 25

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27 Virtual Lab: Titration Introduction In chemistry laboratory, it is sometimes necessary to experimentally determine the concentration of an unknown acid or base solution. A procedure for making this kind of determination is called an acid-base titration. In this laboratory process, a solution of known concentration, called the standard solution or titrant, is carefully added to a solution of unknown concentration, the analyte, until enough titrant has been added to react exactly with the analyte. This is called the equivalence or stoichiometric point of the titration. An acid-base indicator is added which changes color near the equivalence point. The point in the titration where the indicator changes color is called the end point of the titration. If the unknown solution is acidic, then the standard solution will be basic. The opposite would be true if the unknown solution was basic. We know that the mixing of equal amounts of acid and base ions will create neutral water. At the molecular level, this reaction can be illustrated with the following net-ionic equation. H+ + OH- --> H 2 O (acid) (base) This equation states that one mole of hydrogen ions (acid) will neutralize one mole of hydroxide ions (base). Since we can calculate the moles of the standard solution by multiplying its molarity and volume, we can also calculate the moles of the solution of unknown concentration using a mole to mole ratio. Then by dividing by the volume of solution of unknown concentration we can calculate its molarity. Objective: In this experiment the unknown solution will be HCl(aq) and the standard solution will be the base sodium hydroxide. You will know the concentration of the base and the volume of the acid and base used. With this information you can calculate the concentration of the acid. The diagram below shows the set up. 27

28 Pre Lab : Define the following words: Titration- Equivalence point- Endpoint- Neutralization- Write the neutralization reaction for HCl reacting with NaOH. What is the ph of the solution at the end point of the titration for HCl and NaOH? Procedure: 1. The flask is filled with 10 ml of unknown concentration of HCl. (Click here) Record the volume of acid on your data form 2. Phenolpthalein Indicator is added to the flask. (click here) 3. Record on your data form the initial volume of base in the buret (click here) 4. You will now start adding base (0.25M NaOH) from the buret into the flask to neutralize the acid. The flask is gently swirled as the base is added. A pink color should appear as the base is added, but it will disappear as the flask is swirled. The end-point of the titration will be reached when 1 drop of base makes the solution turn and stay pink. (click here). 5. Record the final volume of base from the buret that was needed to neutralize the acid. (click here) Data: 28

29 Calculation: Determine the Molarity (concentration) of HCl using the data you collected and the titration formula. (The concentration of the NaOH used was 0.25M) Record your answer on your data form. Questions 1. State the purpose of this experiment. 2. Describe the function of the phenolphthalein in this experiment. How would this experiment be different if you had forgotten to add the phenolphthalein 3. State evidence from the lab that the endpoint was reached. 4. It takes 75ml of a 2.5M HCl solution to neutralize 55ml of a base of unknown concentration. Calculate the concentration of an unknown basic solution. 5. If the actual concentration of the HCl was 3.3 M what is your percent error? 6. Environmental studies usually involve an analysis of precipitation and its response to pollution. To quantify the degree of contamination in natural rain water or snow, titration is used. The process is quick and results are reliable. Since most titration processes do not require expensive or specialized equipment, the test can be performed often and in different areas with relatively little effort. a. A ml sample of lake water is titrated using ml of a M base solution. What is the molarity of the acid in the lake water? b. Based on the molarity of the acid calculated above, what is the ph of the lake water? 29