WAYS OF EXPRESSING SOLUTION CONCENTRATION for General Chemistry 2/Grade 12-STEM Quarter 3/Week 2.c-d FOREWORD This Self Learning Kit (SLK) focuses on the discussion of the different ways of expressing solution concentration and stoichiometric calculations involving solution. Sample calculations and practice exercises are included to help you understand better on the topic. 2 OBJECTIVES: At the end of the lesson, the learners are expected to: K- Identify the different ways of expressing the concentration of a solution. S- Carry out stoichiometric calculations involving reactions in solution. A- Recognize the importance of understanding the different ways of expressing solution concentration. LEARNING COMPTENCIES: - Use different ways of expressing concentration of solutions: percent by mass, mole fraction, molarity, molality, percent by volume, ppm (STEM_GC11PPIIId-f-111). - Perform stoichiometric calculations for reactions in solution (STEM_GC11PPIIId-f-112). I. WHAT HAPPENED PRE-ACTIVITIES/PRE-TEST: Directions: Choose the best answer. Write the letter of your choice in your notebook. 1. It is a unit of concentration expressed as the number of moles of solute dissolved in a liter (L) of solution. A. molality C. percent by mass B. molarity D. percent by volume 2. It is a general term expressing the amount of solute contained in the given amount of material? A. Concentration C. Molality B. Density D. Molarity 3. It is a unit of concentration defined as the number of moles of solute per kilogram of solvent. A. molality C. percent by mass B. molarity D. percent by volume 3 4. If 10.0 g of NaCl is present in 200.0 mL of aqueous solution, what is the concentration of the solution? A. 0.02% B. 0.05% C. 5.0% D. 20.0% 5. What are the parts of solution? A. liquid and salt B. solid and salt C. solution and solute D. solvent and solute 6. Which of the following is an example of a solute-solvent combination when table salt is dissolve in water? A. gas-gas C. solid-liquid B. liquid-gas D. solid-solid 7. A solvent is _____. A. always a liquid B. always water C. the substance being dissolved D. the substance present in the greatest amount 8. A solution may contain ___________. A. many solvents and many solutes B. many solvents but only one solute C. only one solvent but many solute D. only one solvent and one solute 9. What is the concentration of solution in %(m/m) if 10.0 g solute dissolved in 90.0 g solvent? A. 0.1000% C. 10.00% B. 0.1111% D. 11.11% 10. The concentration of 0.50 mole solute in 500.00 mL solution is _. A. 0.001mol/L C. 0.100 mol/L B. 0.010 mol/L D. 1.00 mol/L II. WHAT I NEED TO KNOW DISCUSSION: Recall your previous lesson about solution. In Chemistry, solution is a homogeneous mixture composed of solute, the dissolved matter in a solution and solvent, a substance capable of dissolving other substances. The quantity of solute present in a given quantity of solvent or solution is called concentration. Several methods can be used to quantitatively express the concentration of the solution. These include percent by mass, 4 percent by volume, percent mass by volume, mole fraction, molarity, molality and parts per million (ppm). Ways of Expresing Solution Concentration 1. Percent by Mass (m/m) • It is referred as the mass of solute, in grams(g), present in 100 g of solution . Example 1. A sample of 0.446 g sodium chloride (NaCl) is dissolved in 27.3 g water (H2O). What is the percent by mass of NaCl? Given: mass of NaCl (solute)= 0.446 g mass of H2O (solvent)= 27.3 g % NaCl =? Solution: 2. Percent by Volume(v/v) • It is referred as the volume of solute present in 100 mL of solution. Example 2. A 1.75-L bottle wine contains 560 mL of ethanol. What is the v/v percent concentration of ethanol? Given: volume of ethanol (solute) = 560 mL volume of wine (solution) = 1.75 L or 1750 mL 5 % ethanol = ? Solution: 3. Percent mass by volume(m/v) • It is referred as the mass of solute, in g, present in 100 mL of solution. Example 3. If 30.0 g calcium chloride, CaCl 2, is present in 0.5000 L of aqueous solution, what is its concentration in terms of mass/volume percent? Given: mass of CaCl2 = 30.0 g volume of solution = 0.5000 L or 500.0 mL %CaCl2 =? Solution: 4. Parts Per Million, ppm • This unit of concentration is referred as the parts of a component per million parts (10 6 or 1,000,000) of the solution and is usually used if the quantity of solute present in a solution is very small. 6 Example 4. If there is 1.102 mg of silver (Ag) in 696 g of solution, what is the concentration of Ag in ppm? Given: mass of Ag= 1.102 mg or 1.102x10-3 g mass of solution=696 g concentration of Ag in ppm=? Solution: 5. Molarity • Molarity is another unit of concentration defined as moles of solute per liter of solution. Example 5. What is the molarity of a solution containing 37.4 g of NaCl in 6.8 liters solution? Given: mass of NaCl = 37.4 g (must be converted to moles) Volume of solution = 6.8 L Molarity =? Solution: moles of solute L of solution 1 mole NaCl 37.4 g NaCl 58.44 g NaCl = 6.8 L M= M = 0.094 mol/L 7 Na = 22.99 g/mol Cl = 35.45 g/mol 58.44 g/mol Moles = m/mm 6. Molality • It is the number of moles of solute dissolved in 1 kilogram of solvent. Example 6.1 Calculate the molality of a sulfuric acid solution containing 48.8 g of sulfuric acid in 396 g of water. Given: mass of sulfuric acid, H2SO4=48.8 g mass of water(solvent)=396 g molality=? Solution: Example 6.2. Calculate the molality of a 10.0 % CaCl 2 by weight. (Atomic mass: Ca=40.08 g/mol, Cl= 35.45 g/mol) Given: 10.0% CaCl2(10.0 g CaCl2 /100.0 g solution) Solution: • Calculate mole CaCl2 • Calculate Molality 8 Solution = Solute +Solvent Solvent = Solution-Solute Solvent = 100.0 g-30.0g Solvent = 70.0g (or 0.0700 kg) Mol/kg 7. Mole Fraction • It is a unitless quantity that expresses the ratio of the number of moles of one component to the total number of moles of the solution. Example 7. A solution is prepared by adding 400.8 g ethanol, C2H5OH to 287.8 g H2O. Calculate the mole fractions of these two components. (Molar masses: C2H5OH= 46.07 g/mol; H2O=18.02 g/mol) Given: mass of C2H5OH = 400.8 g Mass of H2O = 287.8 g Xethanol =? Xwater =? Solution: 9 Practice Exercise Direction: Solve the following problems and show your solutions in your notebook. 1. A 60-mL solution contains 8.6 g of ethanol and 0.042 g of antiseptic. Calculate the concentration of each component in mass/volume percent. (Ans. Ethanol = 14%; antiseptic = 0.70%) 2. What is the molarity of the solution made from 40.0 g NaOH in 500.0 mL of solution? (Atomic Mass: Na = 22.99 g/mol; O = 16.00 g/mol; H = 1.008 g/mol; Ans. M = 2.00 mol/L) 3. Calculate the molality of phosphoric acid, H3PO4, in a solution of 29.0 g H3PO4 in 250.0 g H2O. (Atomic mass: H = 1.008 g/mol; P = 30.97 g/mol; O = 16.00 g/mol; Ans. m = 1.18 mol solute/kg solvent) 4. Refer to the data given in problem # 3, calculate the mole fraction of H3PO4 and H2O. (Ans. XH3PO4 = 0.979; XH2O = 0.0209) 5. An aqueous solution has 0.0400 g of NaCl (solute) in 2.00 kg H2O (solvent). What is the concentration of the solution in parts per million? Hint: Convert mass of H2O to g. (Ans. 20.0 ppm) 10 Solution Stoichiometry Understanding solution concentration is important because it gives a concrete idea on how much solute and solvent are necessary to prepare such solution. Also, in stoichiometric calculation, solution concentration can be used as a conversion factor to determine the amount of product that can be produced in a chemical reaction. Example 1. Determine the mass, in grams, of solid Mg(OH)2 that can be produced if 90.0 mL of a 1.26 M Mg(NO3)2 solution completely reacts with excess NaOH. (Atomic mass: Mg = 24.31 g/mol; O = 16.00 g/mol; N = 14.01 g/mol; Na = 22.99 g/mol; H = 1.008 g/mol) Given: 90.0 mL of 1.26 M Mg(NO3)2 mass of Mg(OH)2 = ? Solution: • Before you will answer the problem, try to recall your previous lesson on the following: ✓ Writing chemical formula, the crisscross method. ✓ Types of chemical reaction, such as, combination, single replacement, double replacement. • To calculate the amount of magnesium hydroxide, Mg(OH)2, produced, first, we must write the balance chemical equation. • Then, calculate moles of Mg(NO3)2. 11 • Next, calculate the mass of Mg(OH)2. Example 2. Calculate the mass, in grams, of 6.00% H2O2 solution is needed to produce 132.6 g of O2 (g). Given: 6.00% H2O2 132.6 g O2 Solution: • Write the balanced chemical equation • Calculate moles O2. • Calculate mass of H2O2 solution. 12 Practice Exercise Directions: Solve the following problems and show your solutions in your notebook. 1. Calculate the volume, in mL, of 1.72 M HCl solution that will react with 2.67 mol of CaCO3? (Ans. 3.10x103 mL) 2. If 0.650% solution of Na2CO3 will be used to precipitate Ca+2 from solution, determine the amount of solution, in grams, needed to precipitate 5.00x102mL of 0.01120M Ca+2? (Atomic mass: Na=22.99 g/mol; C=12.01 g/mol; O=16.00 g/mol; Ca= 40.08 g/mol; Ans. 91.3 g) II. WHAT I HAVE LEARNED EVALUATION/POST TEST: I. Directions: Choose the best answer. Write the letter of your choice in your notebook. Show all your work if applicable! 1. It referred as a measure of the amount of solute dissolved in a specified quantity of solvent. A. concentration C. molarity B. molality D. solution 2. What is the molarity of a solution that contains 10.0 moles of solute in 2000.0 mL solution? A. 5.00x10-3 mol/L C. 5.00 mol/L B. 0.200 mol/L D. 2.00x102mol/L 3. To determine the number of solute present in a solution, which of the following operation will be used A. molality x moles of solution B. molality x volume of solution, L C. molarity x moles of solution D. molarity x volume of solution, L 13 4. The mass of sucrose(C12H22O11) needed to prepare 250.0 mL of a 0.250M solution is ________. (Atomic mass: C=12.01 g/mol; H=1.008 g/mol; O=16.00 g/mol). A. 0.0625 g B. 1.00 g C. 21.4 g D. 34.2g 5. What is the molality of 30.0% NaCl by weight? (Atomic mass: Na=22.99 g/mol; Cl=35.45 g/mol) A. 0.513 m B. 5.13 m C. 7.33 m D. 73.3 m II. Direction: Answer the following word problems in your notebook. Show your work! 1. Calculate the volume of 0.400 M H3PO4 needed to react with 200.0 mL of 0.200 M NaOH. 2. If 10.0g of glucose (C6H12O6) is present in 2.0 L of aqueous solution, what is the concentration in terms of the following: A) ppm B) mass/volume percent Atomic mass: C=12.01 g/mol; H=1.008 g/mol; O=16.00g/mol 14 C) molarity References Expressing solution concentration https://www.askiitians.com/iit-jee-solutions-colligativeproperties/expressing-concentration-of-solutions/ (accessed January 17,2021) Helmenstine, Anne Marie, Ph.D. "What Is a Mole Fraction?" ThoughtCo. https://www.thoughtco.com/mole-fraction-definitionchemistry-glossary-606379 (accessed January 25, 2021). 15 DIVISION OF NEGROS ORIENTAL SENEN PRISCILLO P. PAULIN, CESO V Schools Division Superintendent FAY C. LUAREZ, Ph.D, Ed.D, TM OIC - Assistant Schools Division Superintendent Acting CID Chief NILITA L. RAGAY OIC - Assistant Schools Division Superintendent ARNOLD R. JUNGCO PSDS – Division Science Coordinator ROSELA R. ABIERA LR Manager ELMAR L. CABRERA PDO MARICEL S. RASID Librarian AGUSTINA C. OMAGUING Writer GERALD T. UBAG Lay-Out Artist _________________________________________ ALPHA QA TEAM EUFRATES G. ANSOK JR. AGUSTINA C. OMAGUING NILO JAY A. BAYBAY BETA QA TEAM ALLAN Z. ALBERTO SEGUNDINO B. DELES JR. VERONICA A. RECTO MANASSES V. JABALDE EUFRATES G. ANSOK AGUSTINA C. OMAGUING 16 SYNOPSIS Answer Key Solution concentration is the measure of the amount of solute dissolved in a specified quantity of solvent. It can be expressed in several ways, such as, percent by mass and volume, parts per million, molality, molarity, and mole fraction. Also, in stoichiometric calculations, units of concentration can be used as the conversion factor in determining the desired quantity. . ABOUT THE AUTHOR Agustina C. Omaguing is a graduate of Bachelor of Science in Chemistry at Negros Oriental State University (NORSU). Also, she earned Education units at Foundation University, and completed her academic requirements in Master of Arts in Science Teaching at NORSU. Currently, she is a Senior High School Teacher at Valencia National High School. 17