A solution is made by dissolving 60 g of NaOH (M = 40 g-mol-1) in enough distill

Question

A solution is made by dissolving 60 g of NaOH (M = 40 g-mol-1) in enough distilled water to make 300 mL of a stock solution. What volumes of this solution and distilled water, when mixed, will result in a solution that is approximately 1 M NaOH? The definition of molarity. (2) The knowledge of vocabulary associated with solutions. (3) The procedures for preparing dilute solutions. Thinking it Through: Molarity is commonly used to express the concentration of a solution. The molarity of the solution first prepared can be calculated by substituting the given values. The volume of solution, 300 mL, should be expressed in liters, 0.300 L. This solution, called the stock solution, will now be used to prepare a solution that is approximately 1 M NaOH. The number of moles of NaOH in the diluted solution will be the same as it was in the stock solution; it will just be dispersed in a larger volume. Since we are seeking a volume in milliliters, it is more convenient to express the molarity as millimoles per milliliter (which is exactly the same as moles per liter). millimoles NaOH in stock solution = millimoles of NaOH in diluted solution Assuming 20 mL of stock solution, The total volume of the new solution is approximately equal to the volume of stock solution (20 mL) plus the water added (x mL) to produce 100 mL. That comes out to 80 mL of water added, which is intended to be the correct choice. You've probably noticed that we use the word approximately when describing the concentration and volume of the new solution. In fact, adding 80 mL of water to 20 mL of stock solution produces slightly less than 100 mL of solution. The concentration of NaOH in the diluted solution is slightly greater than 1 M. This is because the densities of NaOH solutions are greater than 1 g/mL. As the NaOH solution is diluted, the density of the solution approaches that of water, which is 1 g/mL. Nonetheless, 80 mL, choice is still the best. This is a 1:5 dilution. Choice gives a 1:6 dilution, but you may be drawn to it if you neglect to consider that it is not just the water added, but the total volume of the solution that must be used. Choice results in a 60: 90 or a 2:3 dilution, and choice results in a 2:5 dilution. None of these produce a 1 M solution.

Explanation / Answer

Option (A) is correct answer

Molarity = no. of molesVolume in Liters

Molarity of stock solution = 1.5.3 = 5M Because 60g of NaOH = 1.5moles and 300mL = 0.3L

therefore no. of moles of NaOH in 20mL of stock solution = 20 X 5 = 100mmoles = 0.1Moles

when this 20mL stock solution is diluted with 80mL distelled water total volume = 100mL

therefore molarity of new solution = No. of moles (0.1)Volume in liters (0.1) = (0.1)(0.1) = 1M Because 100mL = 0.1L

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