lab 4 procedure

lab 4 procedure - Part I. Preparing your Solutions You will...

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Part I. Preparing your Solutions You will prepare about 1 L of approximately 0.15 M sodium hydroxide solution by diluting the stock solution of 6 M NaOH. You will need to calculate the volume of 6M NaOH required in this dilution. 1. Begin by pouring about 200 mL of deionized water into your (clean) plastic bottle. Calculate the appropriate volume of stock solution, use a polyethylene dropper to dispense it into a 25 mL graduated cylinder, and then pour the contents of the graduated cylinder into the partially filled plastic bottle. Rinse the graduated cylinder out with fresh water at least twice, adding the rinsing to the contents of the plastic bottle. Screw the cap on the plastic bottle and mix the contents thoroughly by inverting the bottle and swirling it repeatedly. Then add the remaining volume of water to bring the total volume to about 1 L, mixing the bottle contents thoroughly. The bottle should be shaken at least 30 times after the last addition. Label this bottle 0.15 M NaOH. 2. Take the second 1 L plastic bottle and label it as 0.2 M HCl. Fill it with about 200 mL of deionized water. You will need to calculate and accurately measure out the volume of 6.0 M HCl needed to make 1 L of 0.2 M HCl. Clean your graduated cylinder before using it to measure the HCl. Add the necessary amount of acid to the plastic bottle, rinse the graduated cylinder several times with deionized water, adding each rinsing to the plastic bottle. Cap and shake the bottle to mix thoroughly and then fill the remainder of the bottle with water. Cap the plastic bottle and shake well. Again, invert the bottle at least 30 times in order to completely mix the solution. Part II. Standardizing the base against Potassium Acid Phthalate In this step of the experiment you will standardize your sodium hydroxide solution against the primary standard, potassium acid phthalate, KHP. You will also use a technique called weighing by difference . This is a very important technique to use because it eliminates systematic errors from the balance. Weighing by difference is quite simple. First, mass the container and the material from which you are going to draw your sample. Then remove some of the material and place it in a separate container. Remeasure the mass of the original container and the remaining material. Calculate the mass removed, and repeat the process until you have removed the mass desired. For preparation of all additional samples, be sure to use the same balance so that systematic errors in the balance will continue to be eliminated when you take the difference readings between masses. 1. In a previous laboratory period you will have obtained about 6 grams of primarystandard grade potassium acid phthalate (KHP) in a vial, dried it in an oven at 110 ° C for 2 hours, and stored it in a desiccator for use today. 2. In what follows, use a folded paper strip to handle the vial; this will keep oils from
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This note was uploaded on 05/04/2011 for the course CHEM 2B taught by Professor Clemens during the Spring '08 term at UC Davis.

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lab 4 procedure - Part I. Preparing your Solutions You will...

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