I need help writing a purpose for a chemistry experiment. I feel I was always do
ID: 887499 • Letter: I
Question
I need help writing a purpose for a chemistry experiment. I feel I was always do a great job, but my professor always gives me 3 out of 6. Im out of ideas. She wants us to summarize the introduction, and the goal of this experiment being like a page 1/2 long. Please help me right a better purpose for the experiment below.
Introduction:
Some metals, when reacted with an acid, dissolve producing the metal cation and hydrogen gas. The stoichiometry of such a reaction will be studied in this experiment. A known quantity of magnesium will be reacted with a HCl solution of known strength. After titrating the excess HCl with a base solution of known strength, the number of moles of HCl which reacted will be determined. The H2 gas given off will be collected; after measuring its volume under known temperature and pressure conditions, the number of moles of H2 given off will be determined. From this information, the chemical equation for the reaction of magnesium with hydrochloric acid can be deduced.
Procedure:
Set up apparatus as shown in Figure 1. With the Florence flask filled with water to the neck, blow gently into the tubing from the end which attaches to the test tube to start a siphon action between the flask and the beaker. Reverse the siphon a few times by raising and lowering the beaker. This will fill the tube connecting the flask and the beaker with water and will also remove air bubbles from the system.
Add approximately 200 mL of water to the beaker, and adjust the siphon such that the flask is filled to the neck. Close the pinch clamp. Measure a length of magnesium ribbon sufficient to weigh between 0.20 and 0.24 grams. Record the mass of the magnesium ribbon to 3 s.f. Coil the magnesium ribbon around a pencil. Using a rotatable-arm clamp to hold the 8-inch test tube, place exactly 25.0 mL of standard HCl solution in the large test tube. Record the exact molarity of the HCl solution. Rotate the test tube such that the solution reaches slightly over halfway up the length of the test tube. Place the coiled magnesium ribbon over the long projection of glass tubing on the inside end of the rubber stopper. Holding the stopper assembly (with ribbon) at the same angle as the tube, the ribbon should remain on the glass tube. If it doesn’t, adjust the angle of the test tube until the ribbon will remain on the glass tube. Carefully attach the tubing to the test tube (don’t jar the magnesium ribbon loose). Open the pinch clamp and raise the level of the water in the beaker higher than the level of water in the flask. If a significant amount of water runs into the flask, you have and air leak in your system. If you have an air leak, it must be closed before you proceed. Equalize the pressure in the flask with atmospheric pressure by bringing the water level in the beaker to the same height as the water level in the flask. After closing the pinch clamp, empty and dry the beaker. Open the pinch clamp. A small amount of water will run into the beaker: this will not affect your results since later in the experiment, you will again equalize the pressure in the flask with atmospheric pressure. Rotate the test tube so that the magnesium ribbon drops into the HCl solution. In the resulting reaction, hydrogen gas will be released. The hydrogen gas will force water from the flask into the beaker. After all the magnesium has dissolved, remove the test tube from its clamp (don’t disturb the tubing connections!); and place it into another beaker of water to cool the acid mixture to room temperature. Allow 10 minutes for cooling. Equalize the pressure in the same manner as before; then open the system. Quickly measure the temperature of the gas in the flask; also measure the temperature of the water in the flask. With a graduated cylinder, measure the volume of water in the 600 mL beaker. The volume of water displace is equal to the volume of hydrogen gas given off by the reaction. Record the barometric pressure reading which has been taking by your professor. Pour the solution left in the test tube into a 250 mL Erlenmeyer flask. Rinse the test tube twice (15 mL each) with distilled water and pour the rinse water into the Erlenmeyer flask. Add 3 drops pf phenolphthalein solution. Fill a clean buret with standard 1.00 N NaOH solution. Slowly add the NaOH to the acid solution until the endpoint has been reached. The endpoint for this titration has been reached when the solution first remains pink with swirling. Record the volume of NaOH required to reach the endpoint. Return all equipment.
Explanation / Answer
Purpose of the experiment:
The chemical equation of the reaction of magnesium metal with hydrochloric acid can be deduced by determining amount of hydrochloric acid reacted with weighed amount of magnesium metal and by measuring amount of hydrogen evolved in this reaction.
The amount of hydrochloric acid reacted can be measured by reacting weighed quantity of magnesium metal with excess quantity of hydrochloric acid of known molarity. The unreacted hydrochloric acid is titrated against sodium hydroxide solution of known concentration using phenolphthalein indicator. The difference between amount of hydrochloric acid taken and amount of hydrochloric acid remained unreacted gives the actual quantity of hydrochloric acid reacted in the reaction with magnesium metal.
The amount of hydrogen gas evolved in the reaction can be determined by measuring volume of water displaced by the hydrogen gas. The temperature and pressure during the reaction can be used to calculate amount of hydrogen gas evolved.
The number of moles of magnesium metal, hydrochloric acid and hydrogen gas in the reaction can be calculated by knowing amount of these reagents involved in the reaction, which in turn can help in deducing chemical equation of the reaction.