Molarity

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  • Concentration of a solution can be expressed quantitatively using molarity.

  • Molarity is a ratio of the number of solute particles to the volume of solution.

  • Companies ensure consistency in their products by measuring the molarity of the solution.

  • Model 1 - Lemonade Mixtures:

    • Solvent: Water

    • Solute: Lemonade mix

    • Dissolved lemonade mix particles are represented by dots.

    • Lemonade Solution 1 and Solution 2 have the same volume of solution.

    • Lemonade Solution 1 has less quantity of solute compared to Solution 2.

    • Concentrated solution is darker and has more particles compared to a dilute solution.

    • The concentration of the solution in the glass is the same as the solution in the pitcher.

    • The solution in the glass does not contain the same number of solute particles as the solution in the pitcher because concentration is based on particles per unit of solution, not the total amount of solute.

    • The terms "concentrated" and "dilute" are relative and do not provide specific information about the quantities of solute or solvent in a solution.

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  • Model 2 - Chemical Solutions:

    • Beakers 3 and 4 are considered to be "concentrated."

    • The letter "M" stands for molarity in Model 2.

  • The ratio of moles of solute to liters of solution is equal to the molarity of each solution.

  • The molarity of a solution is calculated by dividing the moles of solute by the liters of solution.

  • Concentrated solutions have a larger molarity value compared to dilute solutions.

  • Beakers 3-5 with 3 M solutions have the same ratio of moles of solute to liters of solution.

  • Beaker 5 can have fewer moles of glucose but the same molarity because the ratio of moles of solute to liters of solution is the same.

  • Molarity cannot be determined by knowing either the number of moles alone or the volume of solution alone because it is a ratio of two quantities.

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  • Example calculations:

    • Molarity of a solution containing 1.5 moles of NaCl in 0.50 liters of solution is 3 M.

    • Molarity of a solution containing 0.40 moles of acetic acid in 0.250 liters of solution is 1.6 M.

    • Molarity of a solution containing 2.5 g of CuCl2 in 1 L of solution is 0.019 M.

  • The molarity of a solution can be calculated by dividing the moles of solute by the liters of solution.

  • The molarity of a KCI solution with 37.3 g of KCI dissolved in 500 mL of water is 1.00 M.

  • The student overlooked converting the mass of sucrose into moles when mixing the solution.

  • The student should convert the mass of sucrose into moles and then create the mixture to correctly prepare the 1 M solution.

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  • Extension Questions:

    • The darkness or color intensity of a solution alone cannot determine its concentration because solutes do not always darken the solution.

  • Example calculation:

    • Molarity of a KCI solution with 37.3 g of KCI dissolved in water to give a final solution volume of 500 mL is 1.00 M.

  • The student overlooked converting the mass of sucrose into moles when mixing the solution.

  • The student should convert the mass of sucrose into moles and then create the mixture to correctly prepare