Ex 3

‫بسم ال الرحمن الرحيم‬ Name: ayedzahran Group: Day:

Experiment 3 "The empirical formula of a chemical compound (Magnesium Oxide)" _________________________________________________________________ I. Observations and results: Mass of crucible and cover Mass of crucible and Magnesium sample Mass of crucible and residue after heating Mass of Magnesium sample Mass of Magnesium Oxide Mass of Oxygen in Magnesium Oxide Moles of magnesium Moles of Oxygen Moles ratio of Mg to O Empirical formula of Magnesium Oxide Percent by mass of O in Magnesium Oxide Percent by mass of Mg in Magnesium Oxide Percent by mass of O (based on formula Percent error

45.5 g 25.34 g (without cover) 26.02 g 1g 1.68 g (1) 0.042 mol (2) 0.0425 mol (3) 1:1 (4) MgO 40.5% (5) 59.5% (6) 40% (7) 0.0125 (8)

II. Calculation: (1) mMgO = 26.02-24.34=1.68 g (2) nMg =mMg/MMg=1/24=0.042 mol (3) nO=mO/MO=0.68/16=0.425 mol (4) nMg : nO == (0.042 : 0.0425)/0.042 == 1:1 (5) %O= (mO/msample)*100% =(0.68/1.68)*100%=40.5% (6) %Mg =(mMg/msample)*100%=(1/1.68)*100%=59.5%

(7) %Otheoretically= (mO/msample)*100%= (16/40)*100%=40%

(8) Error =(actual – theoretical)/theoretical=(40.5-40)/40=0.0125 III. Answer the following questions: 1. How mould your experimental results be affected if: a. The crucible was not dry and cleans before the initial weighing Maybe this impurities react with magnesium so that will increase the error of this experimental b. The produced magnesium nitride was not converted to oxide The mass of sample will be larger than the mass of magnesium oxide that’s will affect on moles of oxygen and the empirical formula of magnesium oxide c. Some of the solid residue was lost before the final weighing Any thing lost will affect on mass of oxygen in magnesium oxide because we will consider the mass of magnesium is 1 g, so the mole ratio will be not correct d. Magnesium was not completely convert to oxide The mass of oxygen will affect, so mole ratio will be not correct and empirical formula is wrong (oxygen decrease) 2. If we know that the empirical and the molecular formula of magnesium oxide are the same, basing on your results complete the equation (1) and (3) in the text and balance them. Write the balanced net equation of the process of the combustion of magnesium described in the experiment heat Mg + O2 + N2 2MgO + Mg3N2 Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3 3Mg(OH)2 3MgO + 3H2O 5Mg + O2 + N2 + 3H2O 5MgO + 2NH3

Not: For experiment number , For calculation number , For the solution of answers .