SUPPLEMENTARY CONCENTRATION PROBLEMS

Transcription

1 SUPPLEMENTARY CONCENTRATION PROBLEMS 1. Whole milk usually contains 5.0% milk fat by volume/volume. If you drink a ml glass of whole milk, how much milk fat have you consumed? (13 ml) 2. A solution contains 5.30 g of potassium chloride in g of water. Calculate the weight/weight percent of solute in this solution. Don t ignore the mass of the solute! (2.03% W/W) 3. Vinegar is sold as a 5.0% (V/V) solution of acetic acid in water. Assuming that liquid volumes are additive, what volume of water must be added to 15 ml of acetic acid to produce synthetic vinegar? (285 ml) 4. Electrician s solder is 60.0% tin and 40.0% lead by mass. What is the mole ratio of the two elements? (2.62 Sn: 1 Pb) 5. Evaporation of a g sample of slush yields a 4.58 g CaCl 2 salt residue. Calculate the weight/weight percentage of calcium chloride in the slush. (19.5% W/W) 6. The recommended W/V percentage for a TSP solution used to clean walls before wallpapering is 1.7%. What mass of TSP is needed to make 2.0 L of this solution? (34 g) 7. Ammonium nitrate, which is a major ingredient in fertilizers releases nitrate ion into the water. The World Health Organization has set an upper limit of 10.0 ppm for infants. If an infant has a mass of 4.0 kg, what is the maximum allowable mass of nitrate ions that would be permitted in the infant s body tissues? (40. mg)

2 Concentrations and Dilutions Worksheet 1. What is the molarity of a solution in which 0.45 grams of sodium nitrate are dissolved in 265 ml of solution. (0.020 M) 2. What will the volume of a 0.50 M solution be if it contains 25 grams of calcium hydroxide? (680 ml) 3. How many grams of ammonia are present in 5.0 L of a M solution? (4.3 grams) 4. How many grams of beryllium chloride are needed to make 125 ml of a M solution? (0.500 grams) 5. If 25.0 ml of water is added to 125 ml of a 0.15 M NaOH solution, what will the concentration of the diluted solution be? (0.125 M) 6. If ml of water is added to a sample of M NaOH solution until the final volume is ml, what will the molarity of the diluted solution be? ( M) 7. How much M HCl solution can be made by diluting ml of 10.0 M HCl? (50.0 L) 8. If a scientist has 345 ml of a 1.5 M NaCl solution and she boils the water until the volume of the solution is 250. ml, what will the final concentration of the solution be? (2.07 M) 9. How much water would I need to add to 500. ml of a 2.40 M KCl solution to make a 1.00 M solution? (700. ml) 10. A clear solution is made from 1.5 L of 0.40 M MgCl2 and 0.50 L of water. Calculate the resultant concentration of chloride ion. (0.60 M) 11. The density of ethanol is g/ml. How many grams of ethanol should be mixed with 225 ml of water to make a 4.5% (v/v) mixture? (8.4 g) 12. The concentration of acetic acid, CH 3 COOH, in a sample of vinegar is determined to be mol/l. If the density of the acetic acid is g/ml, calculate the volume/volume percent of acetic acid in the vinegar sample. (5.05 % v/v)

3 SOLUBILITY EXERCISE 1. State the solubility of the following substances at 30 C. (a) lead (II) nitrate (b) sodium chloride 2. State the temperature at which 56 g of solute will dissolve in 100g of water for each of the following substances. (a) ammonium chloride (b) potassium nitrate 3. What mass of potassium chlorate can be dissolved in 200 g of water at (a) 20 C (b) 80 C 4. (a) What mass of ammonium chloride can be dissolved in 100 g of water at 90 C? (b) If you were to attempt to dissolve 100 g of ammonium chloride in 100 g of water at 90 C, what mass of the ammonium chloride would remain undissolved?

4 5. (a) What mass of lead (II) nitrate can be dissolved in 200 g of water at 60 C? (b) If you were to attempt to dissolve 150 g of lead(ii) nitrate in 200 g of water at 60 C, what additional mass of the lead (II) nitrate could still be dissolved? 6. How much more lead (II) nitrate could be dissolved in 100 g of water at 50 C than sodium chloride at the same temperature? 7. (a) If 200 g of potassium nitrate is dissolved in 200 g of water at 90 C and allowed to cool, at what temperature would this solution be considered saturated? (b) If the temperature were raised from the temperature you gave to your answer in (a), would the solution now be considered, unsaturated or supersaturated? (c) If the temperature were lowered from the temperature you gave to your answer in (a), would the solution now be considered, unsaturated or supersaturated? (d) In general if a solution has a concentration of solute which is above the solubility curve on the solubility graph, will the solution will be unsaturated, saturated or supersaturated? (e) In general if a solution has a concentration of solute which is on the solubility curve on the solubility graph, will the solution will be unsaturated, saturated or supersaturated? (f) In general if a solution has a concentration of solute which is below the solubility curve on the solubility graph, will the solution will be unsaturated, saturated or supersaturated? (g) If the solution from (a) were cooled and allowed to crystallize, what mass of solute would have crystallized when the temperature reached 20 C? 8. An unsaturated solution was prepared by dissolving 30.0 g of lead nitrate in 100 g of water at 20 C. (a) What mass of lead nitrate should be added to the solution in order to saturate it at 20 C? (b) If 50 g of water is added to the saturated solution at 20 C, what is its new concentration in grams/100 g of water? 9. If a maximum of 9.0 g of calcium hydroxide will dissolve in 100 g of water at 0 C, how much calcium hydroxide could be dissolved in 84 g of water? 10. You are given a solution of potassium nitrate whose concentration is 60 g/100g (a) At what temperature will this solution be saturated? (b) What would be the total mass of this saturated solution if it were made using 100 g of water? (c)if you were given a 100 g sample of this solution, i) how much of the 100 g total mass would be potassium nitrate ii) how much of the total mass would be water? iii) how much more solute can be dissolved if the temperature of the solution is 70 C? 11. Each of the following ten test tubes contains 10 ml of water at 60 C. The following masses of an unknown solid are placed in successive tubes; 2 g, 4 g, 6 g, 8 g, etc. up to 20 g in the last test tube. After the tubes are shaken, it is observed that the entire solid has dissolved in the first five test tubes, but that there is an increasing amount of undissolved solid in each of the remaining test tubes. (a) Which of the substances in the above solubility graph could be in the test tubes? (b) If the unknown is indeed the substance you named in part "a" above, what will happen if the solution in each of the test tubes is cooled to 10 C?

5 Answers to the Solubility Exercise: 1. a) 63 g/ 100 g b) 37 g/100 g 2. a) 65 o C b) 35 o C 3. a) g b) g 4. a) 70 g b) 30 g 5. a) 180 g b) 30g = 44 g 7. a) 56 o C b) Unsaturated c) Supersaturated d) Supersaturated e) Saturated f) Unsaturated g) 138 g 8. a) 25 g b) 37g/ 100 g g 10. a) 39 o C b) 160 g c) i) 37.5 g ii) 62.5 g iii) 50 g 11. a) Potassium Nitrate b) The first test-tube would be the only one with complete dissolution.

6 Name: EXPERIMENT: The Solubility of Calcium Hydroxide Purpose: To determine the solubility of calcium hydroxide. Procedure: 1. Pipet ml of distilled water into a clean beaker 2. Carefully mass 0.25 grams of calcium hydroxide. 3. Add the calcium hydroxide powder into the distilled water and stir for 2 minutes. 4. Check for precipitate. If no precipitate has formed, add another 0.25 grams of calcium hydroxide and repeat until a precipitate forms. 5. Mass a piece of filter paper. Setup a filtering apparatus. 6. Filter the precipitate out and leave the filter paper to dry. 7. Add the solution of calcium hydroxide to the lime water jug. Observations: Quantity Mass of Weigh Boat Mass of Weigh Boat with Ca(OH)2 Mass of Ca(OH)2 Mass of Filter Paper Mass of Filter Paper with Precipitate Mass of Precipitate Mass (grams) Qualitative Observations: Calculations: Calculate the mass of Ca(OH) 2 in solution. Calculate the solubility of Ca(OH) 2 at room temperature in grams per 100 ml.

7 Evaluation: Calculate the percentage yield if the theoretical solubility of calcium hydroxide is 0.19 g/100 ml at 25.0 o C What are FOUR possible errors and TWO possible improvements to this laboratory exercise? Discussion: How well did this technique work for determining an accurate solubility? Discuss fully. Outline at least ONE factor that may affect the solubility of an ionic compound [Research may be necessary to answer this question]

8 USING THE SOLUBILITY RULES Your understanding of the solubility rules and how they govern reactions will be tested. EXERCISE A: 1. Underline which of lead (II) chloride, lead (II) sulphate or lead (II) nitrate is soluble? 2. When this solid compound is added to water write the ionic equation for this dissociation: 3. Underline which of aqueous sodium ions, aqueous sulphate ions or aqueous acetate ions, will form a precipitate with the aqueous lead (II) ions if added to the above solution. 4. Underline which of calcium ions, sodium ions or silver ions will form a soluble compound with the ion underlined in the previous step. 5. Write the chemical equation for formation of the compound in Step 4: 6. Name the precipitate you expect to obtain from Step 3: 7. Write the balanced chemical question to form the precipitate in Step Write the net ionic equation for the reaction above. EXERCISE B: 9. Write a dissociation equation for the dissolving of silver nitrate. 10. Write a dissociation equation for the dissolving of sodium bromide. 11. Name the precipitate which will form if solutions of sodium bromide and silver nitrate are mixed? 12. Write the balanced chemical equation for the precipitation reaction

9 13. Give the net ionic equation for the precipitation reaction. EXERCISE C: The objective is to find reactions that will allow one of two metal ions to form a precipitate by adding an appropriate solution to the mixture. Once the first metal ion has been made to precipitate, you will then devise a method to precipitate the other metal ion. 14. Will a solution containing both barium and copper (II) ions contain anything other than water, barium ions and copper (II) ion? If yes, explain why. 15. If it were added to a solution containing both barium and copper (II) ions, underline which of aqueous chloride ions, aqueous carbonate ions or aqueous sulphate ions will form a precipitate with one of aqueous barium ions or aqueous copper (II) ions (but not both). 16. Name the precipitate that will form if you were to carry out this addition. 17. In order to make a solution of the ion you selected in Step 15, what compound would you dissolve in water? Remember that the compound you select will introduce another positive metal ion into the chemical soup containing the barium and copper (II) ions. In order that this introduced ion not cause extraneous precipitation reactions later in the experiment, the compound you select now should contain a metal ion which will never precipitate regardless of the negative aqueous ions which may be currently present or be introduced later. 18. Write a dissociation equation for the dissolving of the compound selected in the previous step. 19. Write a balanced chemical equation for the precipitation reaction that will occur if you add a solution of the compound selected in the previous step to a solution containing a mixture of barium and copper (II) ions. 20. Circle which of Ba 2+ or Cu 2+ still remains in the solution. 21. Devise a method of precipitating this remaining positive ion from the solution, which won t cause precipitation with any of the other original positive ion that might still be present in solution? 22. Write the balanced chemical equation for this final reaction.

10 REACTIONS INVOLVING SOLUTIONS 1. Silver acetate solution may be used to precipitate the chloride ions from a sodium chloride solution. (a) Give the balanced, total ionic, net ionic equations and reaction type(s). (b) Calculate the volume of 2.50 M silver acetate solution needed to precipitate 30.0 ml of 1.5 M sodium chloride solution. 2. Zinc will displace copper from a copper(ii) nitrate solution. (a) Give the balanced, total ionic, net ionic equations and reaction type(s). (b) Calculate the volume of 4.00 M copper(ii) nitrate needed to dissolve and oxidize 5.00 g of zinc. 3. Dinitrogen monoxide will react with oxygen gas and water vapor in the atmosphere to produce nitric acid. (a) Give the balanced, total ionic, net ionic equations and reaction type(s). (b) Calculate the molarity of a nitric acid solution produced by the oxidation of 3.0 g of dinitrogen monoxide and subsequent dissolving of the product in 300. ml of water. 4. (a) Assuming that the scale formed on the bottom of a tea kettle forms only as a result of water hardness in the water supply, give the balanced, total ionic, net ionic equations and reaction type(s). (b) Kettle scale may be removed by the addition of an acid such as phosphoric acid. Give the balanced, total ionic, net ionic equations and reaction type(s). (c) Calculate the concentration of a phosphoric acid solution given that 250. ml of the solution is needed to remove 35.5 g of scale from the bottom of a tea kettle. 5. Calculate the theoretical yield of CH3OCOCH3 produced by reacting 5.0 g of CH3OH with 8.1 g of CH3CO2H. CH3OH + CH3CO2H CH3OCOCH3 + H2O

11 ACID-BASE THEORY 1. (a) Give a balanced equation for the proton transfer reaction of a typical Brönsted- Lowry base such as NH3 with water. (b) Identify the conjugate acid/base pairs in this system. (c) What is present in this system which accounts for the basicity of the solution? (d) Could the Arrhenius theory account for this basicity?. Explain. (e) Name the two Brönsted-Lowry acids present in this equilibrium system. (f) Name the two Brönsted-Lowry bases present in this equilibrium system. 2. Consider the dissolving of pure H2SO4 in pure HC2H3O2. H2SO4 + HC2H3O2 HSO -1 + H2C2H3O (a) Identify the conjugate acid/base pairs. (b) Would this reaction be considered an acid/base reaction under Arrhenius Theory? Explain. 3. Consider the following acid-base reactions. Write an equation for each of the following reactions. Identify the acids and bases. Indicate one conjugate pair by drawing boxes around their formulas and the other conjugate pair by circling them. (a) H3PO4 acting as a Brönsted acid in an aqueous solution. (b) C2H3O -1 2 acting as a Brönsted base in an aqueous solution. (c) the proton transfer reaction involving the acid HCO -1 and the base SO (d) the nonaqueous reaction in which hydrogen nitrate acts as a base and sulphuric acid acts as an acid. 4. Some acids are have more than one proton (H + ) available for donation, eg. H2SO4. These acids are called polyprotic. The loss of these protons may occur in successive steps. (a) Write the ionization equation for the Brönsted-Lowry acid H2SO4 donating one proton (H + ). (b) Identify the conjugate acid/base pairs. (c) Identify the product of the above reaction that could function as either a Brönsted- Lowry acid or base. (d) Write the ionization equation for the above product donating its remaining proton as a Brönsted-Lowry acid.

12 ph Practice Worksheet 1. What is the ph of a solution that contains 25 grams of hydrochloric acid (HCl) dissolved in 1.5 liters of water? [0.34] 2. What is the ph of a solution that contains 1.32 grams of nitric acid (HNO 3 ) dissolved in 750 ml of water? [1.55] 3. What is the ph of a solution that contains 1.2 moles of nitric acid (HNO 3 ) and 1.7 moles of hydrochloric acid (HCl) dissolved in 1000 liters of water? [2.53] 4. If a solution has a [H + ] concentration of 4.5 x 10-7 M, is this an acidic or basic solution? Explain. [6.35] 5. An acidic solution has a ph of 4. If I dilute 10 ml of this solution to a final volume of 1000 ml, what is the ph of the resulting solution? [6] 6. Determine the ph of a M HNO 3 solution. [2.47] 7. Determine the poh of a M HNO 3 solution. [11.53] 8. Determine the ph of a 4.3 x 10-4 M NaOH solution. [10.63] 9. Determine the ph of a 4.5 x M NaOH solution. [3.65] 10. Why would we say that a solution with a H + concentration of 1.00 x 10-7 M is said to be neutral. If it contains acid, shouldn t it be acidic? 11. If a solution is created by adding water to 2.3 x 10-4 moles of NaOH and 4.5 x 10-6 moles of HBr until the final volume is 1 L, what is the ph of this solution? [10.35]

13 Titration Practice Worksheet 12. Calculate the theoretical yield of CH3OCOCH3 produced by reacting 5.0 g of CH3OH with 8.1 g of CH3CO2H. CH3OH + CH3CO2H CH3OCOCH3 + H2O 13. Fully label the titration curve given below with the equivalence point and label both axes if the graph below represents a titration where ml of M HCl (aq) is being titrated with NaOH (aq). 14. Calculate the concentration of the NaOH (aq) using data from the graph given above. 15. If the titration curve below is for the titration of 15.0 ml of sulphuric acid using sodium hydroxide, calculate the concentration of the sodium hydroxide solution ph Volume of Base Added (ml)

14 SCH3U Some Solution Review Questions 1. Sugar is dissolved in water. The sugar and water are respectively the (a) solvent & solution (b) solute & solvent (c) solution & solute (d) solute & solution 2. All solutions are (a) heterogeneous (b) cloudy (c) single phased (d) colorless 3. Polar solvents will best dissolve solutes with the greater (a) London forces (b) hydrogen bonds (c) dipole-dipole force (d) ionic bond 4. Which of the following substances will have the greater solubility in water at room temperature and pressure? (a) CH3COOH (b) CH3OH (c) O2 (d) CO2 5. Evaporation of a g sample of slush yields a 4.58 g CaCl 2 salt residue. Calculate the W/W percentage of calcium chloride in the slush. (a) 5.12% (b) 51.2% (c) 0.195% (d) 19.5% 6. Vinegar is sold as a 5.0% (v/v) solution of acetic acid in water. Assuming that liquid volumes are additive, what volume of water must be added to 15 ml of acetic acid to produce synthetic vinegar? (a) 300 ml (b) 290 ml (c) 285 ml (d) 1.00 L 7. The water in a swimming pool is found to have a concentration of 3.0 mg/l of chlorine. This is the equivalent of (a) 3.0 ppm (b) 0.3 ppm (c) 0.03 ppm (d) ppm 8. Determine the molar concentration when 11.7 g of NaCl are dissolved in water to make 40 ml of solution. (a) 0.50 (b) 1.0 (c) 2.0 (d) A 0.2 M solution of HCl is prepared. The volume of a 300 ml sample is reduced to 60 ml through evaporation. The final concentration is (a) 0.2 (b) 0.4 (c) 0.8 (d) A clear solution is made from 1.5 L of 0.40 M MgCl2 and 0.50 L of water. The resultant concentration of chloride ion is (a) 0.60 M (b) 0.57 M (c) 0.45 M (d) 0.37 M 11. A crystal of sodium chloride is dropped into a beaker containing a saturated solution of sodium chloride and some undissolved sodium chloride on the bottom of the beaker. What will be observed? (a) the undissolved excess will dissolve (b) the added crystal will grow (c) no observeable change will occur (d) the added crystal will dissolve 12. A saturated solution of KNO3 may be made unsaturated by (a) raising the temperature (b) raising the pressure (c) adding a crystal of potassium nitrate (d) evaporating some of the water

15 13. For which of the following, can the metal ions be separated from one another by adding a solution of sodium hydroxide? (a) cobalt nitrate and aluminum nitrate (b) barium nitrate and potassium chlorate (c) magnesium nitrate and nickel nitrate (d) potassium nitrate and iron(ii) nitrate 14. Which of the following best represents the net ionic equation for the reaction between FeCl3 and NaOH? (a) Fe +3 (aq) + 3 OH-1 (aq) Fe(OH) 3(s) (b) Fe +3 (aq) + 3 Cl-1 (aq) + 3 Na+ (aq) + 3 OH-1 (aq) Fe(OH) 3(aq) + 3 NaCl(s) (c) Fe +3 (aq) + 3 Cl-1 (aq) + 3 Na+ (aq) + 3 OH-1 (aq) Fe(OH) 3(s) + 3 NaCl(aq) (d) Fe +3 (aq) + 3 Cl-1 (aq) + 3 NaOH (aq) Fe(OH)3(s) + 3 NaCl(aq) 15. Chemically, soap is a (a) a fat or oil (b) fatty acid (c) sodium salt of fatty acid (d) a mixture of glycerine and fat 16. "Temporarily" hard water may contain (a) MgCl 2 (b) CaCO 3 (c) CaSO 4 (d) Ca(HCO 3 ) Bubbles rise in a newly opened bottle of a carbonated beverage. This action is explained by the fact that carbon dioxide is less soluble in water when (a) pressure is increased. (b) pressure is reduced. (c) temperature is increased. (d) temperature is reduced. 18. Which solution contains the greatest mass of solute in 100 g of water? (a) A saturated solution of NaCl at 100 C (b) A saturated solution of KCl at 50 C (c) A saturated solution of NaNO3 at 25 C (d) A saturated solution of KNO3 at 25 C (e) A saturated solution of K2CrO4 at 50 C 19. Which of the following compounds would be most highly dissociated or ionized in water at room temperature and pressure (a) ammonia (b) acetic acid (c) hydrochloric acid (d) methyl alcohol 20. A solution which contains an equal number of hydrogen ions and hydroxide ions is (a) an acidic solution (b) a basic solution (c) a neutral solution (d) a solid solution

16 21. The species responsible for the acidic properties of any aqueous acid is (a) the hydroxide ion (b) the hydrogen ion (c) the negative ion (d) the oxide ion 22. Which of the following could be used to determine whether or not an acid is strong or weak? (a) effect on litmus paper (b) measurement of solubility (c) determination of concentration (d) measurement of electrical conductivity 23. Which of the following statements concerning acids and bases is true? (a) All acids are strong electrolytes. (b) All bases are strong electrolytes. (c) All acid solutions with a concentration of greater than 1mol/L are strong acids. (d) The strongest acids are those which ionize to the greatest extent when dissolved in water. (e) Water can act as either an acid or a base, and is thus one of the strongest electrolytes of all. 24. An acidic solution, such as vinegar, (a) turns litmus paper blue (b) has a salty taste (c) has a sour taste (d) feels slippery 25. If the concentration of acid in a solution is decreased, the (a) [H + ] increases and ph decreases (b) [H + ] decreases and ph increases (c) [H + ] and ph both increase (d) [H + ] and ph both decrease 26. What is the concentration of H3O + in a solution whose ph is 4? (a) 10 4 M (b) 10-4 M (c) M (d) 4 M 27. The ph of a M solution of HCl is (a) 1 (b) 2 (c) 3 (d) What is the hydrogen ion concentration, [H + ], of a M solution of sodium hydroxide, NaOH? (a) M (b) M (c) M (d) M 29. According to the Arrhenius definition, one product formed when an acid reacts with a base is (a) a salt (b) an oxide (c) a hydride (d) an anhydride 30. What role does the water play in this reaction? HCl(g) + H2O(l) H3O + (aq) + Cl (aq) (a) proton acceptor (b) electron acceptor (c) proton donor (d) elector donor 31. What is the conjugate base of the acid H3PO4? H3PO4(aq) + H2O(l) H3O + (aq) + H2PO4 (aq) (a) H3O + (aq) (b) H2O(l) (c) H2PO4 (aq) (d) OH (aq) 32. In the reaction: NH3(aq) + H2O(l) NH4 + (aq) + OH (aq) which is a conjugate acid base pair? (a) NH4 +, H2O (b) NH4 +, NH3 (c) H2O, NH3 (d) OH, NH3

17 33. How does the ph of the mixture change as hydrochloric acid, HCl, is slowly added to a solution of sodium hydroxide, NaOH? (a) The ph decreases and may go below 7 (b) The ph increases and may go above 7 (c) The ph decreases to 7 and stops (d) The ph increases to 7 and stops 34. How many grams of beryllium chloride are needed to make 125 ml of a M solution? 35. The density of ethanol is g/ml. How many grams of ethanol should be mixed with 225 ml of water to make a 4.50% (v/v) mixture? 36. To what volume will you have to dilute 30.0 ml of a 12 M HCl solution to make a 0.35 M HCl solution? 37. Indicate the solvent that will be best at dissolving the given solute in each of the following problems: Solute: LiC 2 H 3 O 2 Solvents: CS 2 or CH 2 Cl 2 Solute: PI 3 Solvents: NH 3 or H 2 O 38. An acidic solution has a ph of If I dilute ml of this solution to a final volume of ml, what is the ph of the resulting solution? 39. What is the ph of a solution that contains 1.20 moles of nitric acid (HNO 3 ) and 1.70 moles of hydrochloric acid (HCl) dissolved in liters of water? 40. If it takes 50.0 ml of 0.50 M KOH solution to completely neutralize 125 ml of sulfuric acid solution (H 2 SO 4 ), what is the concentration of the H 2 SO 4 solution? 41. If it takes 25 ml of M HCl to neutralize 345 ml of NaOH solution, what is the concentration of the NaOH solution? 42. Using your knowledge of the Brønsted-Lowry theory of acids and bases, write equations for the following acid-base reactions and indicate each conjugate acid-base pair: a) HNO 3 + OH - b) CH 3 NH 2 + H 2 O c) OH - + HPO If the titration curve below is for the titration of 5.0 ml of hydrochloric acid using aluminum hydroxide, calculate the concentration of the aluminum hydroxide solution ph Volume of Base Added (m