Biochem- Amino- Acids - Lecture notes 1, Study notes of Chemistry

Download Biochem- Amino- Acids - Lecture notes 1 and more Study notes Chemistry in PDF only on Docsity! CONCENTRATION OF SOLUTION What does Tang juice tastes like if you don’t put much powder? What does Tang juice tastes like if you put too much powder? Too little? PERCENT BY MASS AND PERCENT BY VOLUME The percentage concentration of a solution may be expressed in two ways, by mass or by volume. Percent by mass= mass of solute/mass of solution x 100% Percent by volume= vol. of solute/vol of solution x 100% Examples: 1. Solve for the concentration in percent of the following solutions: a. A 10 g solution containing 1.5 g table salt b. A 250 mL solution containing 50 mL ethyl alcohol (CH3CH2OH) 2. What is the percentage by mass of a solution made by dissolving 2.0 g sugar in 150 mL water? Answers: 1. a. 9 g/ 100 g (100%) = 9 % salt b. 5 ml/ 25 ml (100 %) = 20% alcohol 2.) 0.892 g/ 55.492 (100%) = 1.61% KCl 3.) 12g/ 262g (100%) = 4.58% salt PARTS PER MILLION (ppm)  Is a unit for expressing very dilute concentrations.  It is commonly used to express the concentration of pollutants in air or in water. Components of gas mixtures present in very small amounts are usually expressed in ppm by volume as defined by the equation. ppm of component = vol of component/total vol of solution x 106 ppm Example: If 100 L of a gas mixture over a metropolitan area contains 0.006 L of CO, how many ppm of CO is present? Example: 1. What is the molar concentration of solution prepared by dissolving 1.0 g of NaOH in 500 mL of solution? (Assume that there is no change in volume.) 2. What is the molarity of a solution made by dissolving 4.00 g of glucose, C6H12O6, in 100 g of solution? Answer 1. 0.05 M 2. 0. 22 M MOLALITY  Is the number of moles of solute dissolved in 1kg of solvent. Molality = moles of solute/ mass of solvent UNIT: mole/kg or m 6. A solution is prepared by dissolving 4.00 g of NaOH in 100.00 g of water. The volume of the resulting solution is 102.00 mL. Calculate the following: a. Mole fraction of NaOH b. Molarity of the solution c. Molality of the solution d. Mass percent of NaOH e. Density of the solution Mole Fraction Mole Fraction is a way of describing solution composition. It is the ratio of the number of moles of one component of a mixture to the total number of moles of all components.  Is the ratio of the number of moles of one component (nA) to the total number of moles in the solution (nA + nB). Mole fraction = moles of component/total moles of solution XA= nA/nA + nB or XB= nB/nA + nB Example 1. A solution is prepared by dissolving 15.00 g of NaCl in 100.00 g of water. Solve for the mole fraction of salt. 2. A solution is prepared by dissolving 15.00 g of NaCl in 100.00 g of water. Solve for the mole fraction of water. 3. What is the mole fraction of the solute in a 40% by mass ethanol (C2H6O) solution in water? Exercises: 1. A 40.0 gram-sample of methanol, CH4O is mixed with 60.0 grams of ethanol, C2H6O. What is the mole fraction of the methanol? 2. Hydrogen peroxide, H2O2, is used by some water treatment systems to remove the disagreeable odor of sulfides in drinking water. An aqueous solution of H2O2 prepared in the laboratory was found to have a concentration of 20.0% by mass. What is the mole fraction of H2O2? 1. 0.49 2. 0.117 DILUTION Stock solutions in the laboratory are of known molarity. In your experiments, you may need to prepare dilute solutions from concentrated solutions. Bear in mind that the number of moles of solute does not change when a solution is diluted. Example How would you prepare a 0.1 M HCl solution from 10 mL of a 0.5 M HCl stock solution? Solution: M1V1=M2V2; therefore, V2=M1V1/M2 Substituting the values into the equation V2 = 0.5 M x 10 mL 0.1 M = 50 mL Exercises: You need 200 mL of 2 M H2SO4, but the only supply available is concentrated H2SO4 whose concentration is 18 M How will you prepare the solution? QUIZ IN CONCENTRATION OF SOLUTIONS 1.What is the molality of a solution containing 7.78 g urea (NH2)2CO in 203 g of water? 2. Calculate the molar concentration of a solution prepared by dissolving 0.5 g AgNO3 in 100mL solution. Assume that the volume is constant. 3. How many grams of CuSO4 must be dissolved in 250 mL of water to make a 0.10 M solution? 4. If 1000 g of water from Luboc River contains 0. 0075 g of Ca2+ ion, how many ppm by mass of Ca2+ is present in Luboc River?