Quantitative Stoichiometric Reactions Lab

2. When the magnesium ignited, removed it from the flame and held it over an evaporating dish or a pyrex watch glass until the metal had burned completely. Let the product fall into the evaporating dish.

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

Stoichiometry is a very important part of chemistry. Stoichiometry refers to calculating the masses of molecules and their products . The reactants are usually given and stoichiometry is used to find the products of the equations as well balancing the equation. An example of this would be sodium chloride (NaCl). Stoichiometry will say that if there are ten thousand atoms of sodium and one atom of chlorine, only one molecule of sodium chloride can be made and that fact can never be changed.

2. The second source of error in the lab is when opening the lid of the crucible which allowed smoke of magnesium oxide to escape. During the lab, we removed the lid a couple of times to allow oxygen to enter the crucible so the magnesium reacts with the air to form magnesium oxide. However, the smoke could have easily escaped from the crucible because of the strong force of heat from the laboratory burner. This could have affected the lab results by decreasing the final mass when some of the product have escaped.

Materials:Magnesium stripCrucibleCrucible coverClay triangleIron ringRetort standTongsBalanceBunsen burnerProcedure:1.obtained a strip of magnesium between 30-40 cm long2.coiled magnesium strip into a tight roll3.measured the mass of the crucible and cover4.Added the magnesium strip to the crucible and measured the

The first experiment is about the combustion of magnesium after which the ash is formed.

The purpose of this lab was to test the law of definite proportions for the synthesis reaction of combusting magnesium. In this lab, the polished magnesium ribbon was placed in covered crucible and was heated in order for it to react with Oxygen presented in air and in water provided. The result showed that Magnesium oxide formed through chemical reaction was made up of 60.19% magnesium and 39.81% oxygen, which is approximate proportion of both particles in every Magnesium oxide compound. From this lab it can be concluded that the law of definite proportion stating that the elements in a pure compound combine in definite proportion to each other is factual.

    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.

A chemical reaction is when substances (reactants) change into other substances (products). The five general types of chemical reactions are synthesis (also known as direct combination), decomposition, single replacement (also known as single displacement), double replacement (also known as double displacement), and combustion. In this lab, the five general types of chemical reactions were conducted and observations were taken before, during, and after the reaction. Then the reactants and observations were used to determine the products to form a balanced chemical equation. The purpose of this lab was to learn and answer the question: How can observations be used to determine the identity of substances produced in a chemical reaction?

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)

In a combustion reaction, a compound or element reacts with oxygen, releasing a large amount of energy in the form of light and heat.

| After ignition of magnesium light and toxic fumes are made, and white powder (2MgO or Magnesium Oxide) is left over.

A1.Work under the hood! With a pair of tongs, hold a strip of magnesium in a bunsen burner flame. Do not look directly at the flame. Save the ash in a small beaker for the next procedure. If magnesium is substance "A" in the general equation, what is "B"?

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.

The purpose of this experiment is to verify the formula of magnesium oxide based on the masses of magnesium and the product (MgO). We verify the formula firstly by calculating the empirical formula of magnesium oxide and then calculating creating the magnesium oxide itself- a magnesium ribbon is combined with oxygen in the presence of air through combustion and this forms MgO. The empirical formula of a compound is the simplest method of expressing a chemical formula in whole-number ratios of the constituent atoms that are consistent with masses measured in the experiment; whereas the molecular formula expresses the chemical formula using the actual number of atoms. For example, the molecular formula of anthracene is C14H10 while the empirical formula is C7H5.