I understand how to get #1-3. Can someone please explain #4 to me? A scientist n
ID: 485142 • Letter: I
Question
I understand how to get #1-3. Can someone please explain #4 to me?
A scientist needs 10 milliliters (ml) of a 1 M NaCl solution. The first task is to prepare a stock NaCl solution. In this ease, concentration is expressed as molarity (M). Molarity is the number of motes of a specified substance dissolved in one liter of liquid. Molarity is used to describe solutions in which components are specified in proportion to the number of molecules of each component, rather than by weight or volume. Larger amounts (weights) of heavy molecules and smaller amounts (weights) of light molecules are required. One mole of any substance is equal to the gram molecular weight of that substance, he gram molecular weight Of NaCl is 58.44 (the sum of the atom weights of one atom of Na and one atom of Cl). Thus, one mole NaCl is equal to 58.44 g of NaCl. To prepare a 1 M solution of' NaCl, 58.44 g of NaCl can be dissolved in approximately 800 ml of water and the final volume brought up to 1000 ml with more water. To determine the amount of NaCl that would be used to prepare any volume under or over one liter, one mole (or 58.44 g) is multiplied by the desired volume (in ml) and divided by 1000 ml. For example: to prepare 400 ml of a 1 M NaCl solution: 58.44 g times (400 ml/1000 ml). (Here, this amount is dissolved in 360 ml of water, and the final volume brought to 400 ml.) The chemical formula for sucrose is C_12H_22O_11. The following exercise will help you practice the concept of preparing molar solutions. Calculate the gram molecular weight of sucrose. Use this value to calculate the number of grams of sucrose you will need to prepare 1 liter of a 0.33 M sucrose solution. Remember that M (molarity) represents moles of a dissolved substance/liter. How would you make 20 ml (and only 20 ml) of 0.33 M sucrose? Use the concentration (in g/1) determined in step 2 to calculate the amount of dry sucrose you will need to prepare 20 ml of 0.33 M sucrose (show your calculations). To prepare this solution, dissolve the calculated amount of sucrose in deionizer water (the volume to equal approximately 80% of the desired final volume). When the sucrose is completely dissolved, bring the solution to the desired final volume. Mix thoroughly before using.Explanation / Answer
If I understand your question correctly, your question is why we have to make solution 80 percent initially?
Because it is to make sure that the amount of solute we are taking dissolves completely.
To do that it is suggested to do with 80 percent of volume. If the solute dissolves in 80 percent of volume, we can believe completely that it will dissolve in 100 percent volume.