Investigating the effect of varying concentration on the reaction between magnesium ribbon and hydrochloric acid

2. Obtained a 2-3 cm strip of magnesium metal ribbon and coiled it loosely into a small ball. Added the magnesium metal to the acid in the test tube.

During the immersion of the magnesium metal in the hydrochloric acid solution, white bubbles could be seen escaping the surface of the metal as gas was produced during the reaction. Depending on the temperature of the hydrochloric acid and the overall molar concentration, the rate of reaction differed but the same signs were shown. During the reaction between the magnesium metal and higher concentrations of hydrochloric acid, it was observed that the test tube grew quite warm to the touch. As the immersed magnesium strip sank down, it appeared coated in a layer of white bubbles that fizzed like a carbonated drink. In the lower concentrations of hydrochloric acid, the strip spent some time floating at the surface of the solution in the test tube, later sinking down to the bottom as the

Purpose: To determine the percent magnesium by mass in magnesium oxide and to observe if the percentage composition is constant by comparing class results.

    In this lab, a calorimeter was used to find the enthalpy of reaction for two reactions, the first was between magnesium and 1 molar hydrochloric acid, and the second was between magnesium oxide and 1 molar hydrochloric acid. After the enthalpy for both of these were found, Hess’ law was used to find the molar enthalpy of combustion of magnesium, using the enthalpies for the two previous reactions and the enthalpy of formation for water. The enthalpy of reaction for the magnesium + hydrochloric acid reaction was found to be -812.76 kJ. The enthalpy of reaction for the magnesium oxide + hydrochloric acid reaction was found to be -111.06 kJ. These two enthalpies and the enthalpy of formation for water were manipulated and added together using Hess’s law to get the molar enthalpy of combustion of magnesium. It was found that the molar enthalpy of combustion of magnesium was -987.5 kJ/mol. The accepted enthalpy was -601.6 kJ/mol, which means that there is a percent difference of 64%. This percent difference is very high which indicates that this type of experiment is very inefficient for finding the molar enthalpy of combustion of magnesium. Most likely, a there are many errors in this simple calorimeter experiment that make it inefficient for finding the molar enthalpy of combustion of magnesium.

In this experiment, the goal is to prepare a Grignard reagent from an unknown aryl halide and identify the identity of the aryl halide by converting it to a carboxylic acid to determine its melting point and molar mass (determined by titration). The experiment began by dissolving 0.25g of magnesium powder in a 25mL round-bottom with 5mL of anhydrous ether and stirring with a stir bar. Then the round-bottom flask was set up for reflux using a Claisen adapter where the vertical part is covered with a septum to prevent air from mixed with the solution. The septum is very important because the Grignard product can react with oxygen to produces a carboxylic acid, which is not wanted. Also, the choice of anhydrous solvent is important because the Grignard product can react with water to produce an alkane. With the reflux set up, the next step was to add the halide. 1.2mL of the unknown bromoarene mixed with 2.5mL ether was slowly added dropwise through the septum using the needle and syringe. The bromoarene had to be added slowly because there Grignard product would undergo another unwanted side reaction by reacting with the unknown bromoarene. The product with be a new carbon-carbon bond between the unknown bromoarene and the Grignard product. If the bromoarene is added slowly, the chances of the Grignard product reacting with the bromoarene over the magnesium is low because magnesium exists in larger concentration in the solution. Once all the unknown bromoarene

I could use a gas syringe to collect the gas that will evolve from my

About 80 mL of HCl was obtained and mixed with phenolphthalein. Using a LabQuest unit and Gas Pressure Sensor kit, the HCl mixture was added to the flask with the magnesium ribbon and allowed to react. When reaction was complete, the change of temperature and gas was recorded. This procedure was repeated for different masses of magnesium ribbon (masses found on page 89 of the lab manual). After the completed procedure, moles of H₂ produced in each trial were calculated. (The actual procedure can be found on pages 87-89 of the lab manual)

Experiment 2 focused on finding the enthalpy of solution of magnesium chloride. Testing the enthalpy of solution started with measuring out 10 mL of deionized water in a graduated cylinder for three separate trials, each trial having a different mass of magnesium chloride. The water was then poured into a well of a Styrofoam calorimeter then the initial temperature of water was taken using a temperature probe and the LoggerPro programming. A measured amount of magnesium chloride was placed in the same well as the water in the calorimeter,

Because it is dangerous to burn magnesium, it is not possible to directly record heat change. Our lab team suggests an indirect way of determining the heat of combustion for magnesium. To accomplish this, we need to perform two separate trials. One uses a solid (powder) version of MgO, while the other uses Mg ribbon. With the results from these, we can use Hess’ Law to determine q=∆H. This provides both a safe and successful way of indirectly determining the heat of combustion for magnesium.

Magnesium will react with hydrochloric acid, because it is higher in the reactivity series than hydrogen. The magnesium displaces the hydrogen in the acid, so it forms magnesium chloride and hydrogen gas.

It is expected that the concentration of hydrochloric acid will increase the rate of the reaction between magnesium ribbon and hydrochloric acid. By increasing the concentration of

As the acid was being added, the mixture was being stirred over a stir plate. Once completed, the reaction mixture was poured from the round bottom flask into a 500 mL separatory funnel and its top (organic) layer was extracted into another beaker. The bottom (aqueous) layer was placed back into the funnel and extracted twice with 50.0 mL of ethyl ether each. The newly extracted layers were combined and dried over magnesium sulfate (MgSO4). The dried solution was the decanted into a beaker to remove the MgSO4 salts and the product solution was collected via Buchner vacuum filtration. The resulting product was transferred into an Erlenmeyer flask with an inverted beaker on top and stored in a drawer.

5.3 mL of bromobenzne and 15 mL of anhydrous ether was then placed into the separatory funnel and was shaken and vented in order to mix the solution. Half of the bromobenzene solution was added first into the round bottom flask and as soon as a color change was observed, the remaining half of the bromobenzene was added drop wise into the round bottom flask. The mixture was then refluxed on a heating mantle for 10 minutes until most of the magnesium has been consumed.

Equation of magnesium and hydrochloric acid: 2 HCl+ + Mg [IMAGE]Mg2+ + H2 Measuring rates of reaction In this investigation there are two experiments that can be used to test rates of reaction. Using a gas syringe As more gas is produced the plunger inside the syringe moves out of the syringe so the gas can be measured by marks on the syringes length.

This is because when 10mL of 0.01 M Na2EDTA was added into, Mg2+ would rather form complexes with EDTA than with Eriochrome Black T because EDTA-metal complex is more stable than the metal- EBT complex. Part IV: Wine red colour of solution was observed in the conical flask when magnesium metal ions reacted with Eriochrome Black T and formed metal-EBT complex. Mg2+ + Hln2- ↔ Mgln- + H+ (Blue) (Wine