Mg-O Ratios Lab

Using elemental analysis to determine the percent mass composition of each element in a compound is the first step in creating an empirical formula. There are many different types of elemental analysis, but in this experiment gravitational analysis and Beer’s Law are used. Elemental analysis is first used to find the moles of each element, then converted to mass, and then the percent mass of the element in the product is found (2).

There were five main purposes of the maalox lab that we wanted to accomplish. This included producing two precipitates, classifying reactions, providing visual evidence on a chemical change, using pH indicators to identify bases and acids, and describing what happens during neutralization. In the lab, there were two reactions that occurred. The reaction happened when there were reactants that combined to create end products. In the first reaction, the reactants used were alum and ammonia. The products that formed were aluminum hydroxide, potassium ammonium sulfate, and ammonium sulfate. In the second reaction, the reactants were magnesium sulfate and ammonia. The products that formed from the magnesium sulfate and ammonia were ammonium sulfate and magnesium hydroxide. Overall, we were able to accomplish the five main goals of the lab and were able to identify the reactants and products in each of the reactions.

This produces a 106% error causing a very large range of possible values causing our results to be very imprecise.

A few sources of potential error are as follows: loss of product on glassware throughout the experiment, inadequate measuring of chemicals, "impure" chemicals being worked with, and loss of final product during crystallization processes.

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"?

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

Hypothesis/Prediction: The percent composition by mass of magnesium in magnesium oxide will not change significantly with each group that conducted the experiment. The composition of each substance should stay the same and any differences must be due to some error.

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.

e) As stated in the law of definite proportion the percentage composition of Magnesium oxide was approximately same for our classmates. The following table shows the results of two other groups.

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

Background: According to George B. Kauffman of Britannica, a hydrate is “any compound containing water in the form of H2O molecules, usually, but not always, with a definite content of water by weight.” Within this, there are two aspects of the compound; the “water of hydration” and the anhydrous salt. When a hydrate is heated, the “water of hydration” leaves the compound as vapor due to the unsteady bonds between the water and salt molecules. The anhydrous salt ends up becoming the only piece that is leftover. From the two, the percent water in a hydrate and the mass of the salt can be determined from the loss of the “water of hydration.” As a result, the formula of the compound can be found because the masses of the salt and the water can be used to determine the mole ratio, which are both small, whole numbers.

7. When the crucible cooled down so that one was able to hold it, the

How empirical formula of Magnesium Oxide is obtained by heating Magnesium in the presence of air?

    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.

Why did the magnesium not begin reacting immediately after you placed it into the tube? What action was required in order to start the reaction?