Molarity Measurement of Concentration of the Solutions (Session 18) Ciencias de la Tierra II

Concentration of solutions The concentration of a solution expresses the amount of solute present in a given amount of solution. The words concentrate and dissolved solution are just expressions, in which neither of them gives us an indication of the exact amount of solute present. Ciencias de la Tierra II

Methods to determine concentration There are many methods to give us the concentration of solutions, some of them are: Weight percentage Volume percentage Molarity Molaliity Normality In this session we will study the concentration measurement called Molarity. Ciencias de la Tierra II

Number of moles in a compound = grams We represent molarity with the letter M in caps and its solutions are known as Moles. Molarity is defined as number of solute moles in a liter of solution. M = Moles of Solute liter of solution A solution 5 M of NaOH has 5 moles of NaOH in a liter of solution. Number of moles in a compound = grams Molecular Weight Ciencias de la Tierra II

Ciencias de la Tierra II Activity 1 Prepare a watery solution 1 M of Calcium Bromine. 1 mol of CaBr2 = 200 g of CaBr2 As a result 200 g of CaBr2 are dissolved in enough water until completing 1 L of solution. Ciencias de la Tierra II

Ciencias de la Tierra II The Molar concentration is especially useful to make stoichiometric calculations in solutions… Molarity is one of the concentration measurements used more in the industry, chemical labs and doctors. Ciencias de la Tierra II

Ciencias de la Tierra II Activity 2   How many grams of NaCl do you need to prepare a 0.15M solution in 1 liter (MW 58.5) Step One: Calculate Moles of solute We know that Molarity = Moles of solute/ L In the problem above we are given M and L SO, lets solve it. .15M=x moles of solute/ 1L X= .15mol / L * 1L X = .15mol Ciencias de la Tierra II

Ciencias de la Tierra II Activity 2 continued Since we have the moles, now we can calculate the grams Use the formula # of moles in a compound = grams/MW .15mol=x grams/ 58.5 g/mol NaCl X = .15mol * 58.5 g/mol X= 8.8g Ciencias de la Tierra II

Ciencias de la Tierra II Activity Three How many grams of glucose do you need to prepare a 1.5M solution in 5 liters (MW glucose is 180g/mol) First calculate Moles of Solute Then calculate grams Ciencias de la Tierra II

Write these problems out and have your teacher check your answers How many grams do you need for a 0.400M solution in 1 liter of Copper Sulfate (MW 159.61g)? How many grams of Potassium nitrate and in a 0.800M solution in 2.5L (MW 101.10g) What mass of sucrose must be dissolved to make 460ml of a 1.10M solution (MW 342.3g) What mass of Lithium chloride must be dissolved to make a 0.194M solution that has a volume of 1L. (MW 42.4g) Ciencias de la Tierra II

Ciencias de la Tierra II Activity 4 Now, lets calculate Molarity if we are given grams…. You add 32g of Potassium Chloride (MW 74.6) to a flask and add 955ml. What is the molarity? First we must find out the moles (m=gr/MW) Then we can calculate molarity (M=m solute/L) Ciencias de la Tierra II

Ciencias de la Tierra II Activity 5 What is the molarity of a solution that contains 25.1g of KI in 4.3L of solution? (MW 166g) What is the molarity of a solution that contains 10.6g of Potasssium Nitrate in a 705ml solution? (MW 101g) Ciencias de la Tierra II

Ciencias de la Tierra II Bibliography Brown, T. et al. (1991) Chemistry: The Central Science. 5th ed. United States of America: Prentice Hall. Burns, R. (1996) Chemistry Fundaments. 2nd. ed. United States of America: Prentice Hall. Chang, R. (1992). Chemistry. 4th ed. United States of America: McGraw Hill. Ciencias de la Tierra II