1) Answer the following question related to gravimetric analysis. This question continues on the next page. In the first of two experiments, a student is assigned the task of determining the number of moles of water in one mole of a hydrate of magnesium chloride. The student collects the data shown in the following table. 22.347 g Mass of empty container Mass of sample and container Mass of sample and container after first heating Mass of sample and container after second heating Mass of sample and container after third heating 25.825 g 23.982 g 23.976 g 23.977 g (a) Explain why the student can correctly conclude that the hydrate was heated a sufficient number of times in the experiment. (b) Use the data above to perform the following: (i) Calculate the total number of moles of water lost when the sample was heated. (ii) Determine the formula of the hydrated compound. (c) A different student heats the hydrate in an uncovered crucible, and some of the solid spatters out of the crucible. What effect will this spattering have on the calculated mass of the water lost by the hydrate? Justify your answer. Question 1 (continued) In the second experiment, a student is given 2.94 g of a mixture containing anhydrous MgCl2 and KNO3. To determine the percentage by mass of MgCl2 in the mixture, the student uses excess AgNO3 (ag) to precipitate the chloride ion as AgCl (9). (d) Starting with the 2.94 g sample of the mixture dissolved in water, briefly describe the steps necessary to quantitatively determine the mass of the AgCl precipitate. (e) The student determines the mass of the AgCl precipitate to be 5.48 g. On the basis of this information, calculate each of the following. (i) The number of moles of MgCl2 in the original mixture (ii) The percent by mass of MgCl2 in the original mixture 2) In part (i) write a BALANCED equation and in part (ii) answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. Еxample: (i) A strip of magnesium is added to a solution of silver (I) nitrate. (5 points) → 1 Mg²+ + 2 Ag 1 Mg +2 Ag*- (ii) Which substance is oxidized? Magnesium (Mg) metal Aqueous hydrobromic acid is added to a beaker containing solid calcium carbonate. How could the aqueous product here be distinguished from the aqueous product formed if strontium carbonate were substituted for calcium carbonate? i) Balanced equation: ii) Answer:
1) Answer the following question related to gravimetric analysis. This question continues on the next page. In the first of two experiments, a student is assigned the task of determining the number of moles of water in one mole of a hydrate of magnesium chloride. The student collects the data shown in the following table. 22.347 g Mass of empty container Mass of sample and container Mass of sample and container after first heating Mass of sample and container after second heating Mass of sample and container after third heating 25.825 g 23.982 g 23.976 g 23.977 g (a) Explain why the student can correctly conclude that the hydrate was heated a sufficient number of times in the experiment. (b) Use the data above to perform the following: (i) Calculate the total number of moles of water lost when the sample was heated. (ii) Determine the formula of the hydrated compound. (c) A different student heats the hydrate in an uncovered crucible, and some of the solid spatters out of the crucible. What effect will this spattering have on the calculated mass of the water lost by the hydrate? Justify your answer. Question 1 (continued) In the second experiment, a student is given 2.94 g of a mixture containing anhydrous MgCl2 and KNO3. To determine the percentage by mass of MgCl2 in the mixture, the student uses excess AgNO3 (ag) to precipitate the chloride ion as AgCl (9). (d) Starting with the 2.94 g sample of the mixture dissolved in water, briefly describe the steps necessary to quantitatively determine the mass of the AgCl precipitate. (e) The student determines the mass of the AgCl precipitate to be 5.48 g. On the basis of this information, calculate each of the following. (i) The number of moles of MgCl2 in the original mixture (ii) The percent by mass of MgCl2 in the original mixture 2) In part (i) write a BALANCED equation and in part (ii) answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. Еxample: (i) A strip of magnesium is added to a solution of silver (I) nitrate. (5 points) → 1 Mg²+ + 2 Ag 1 Mg +2 Ag*- (ii) Which substance is oxidized? Magnesium (Mg) metal Aqueous hydrobromic acid is added to a beaker containing solid calcium carbonate. How could the aqueous product here be distinguished from the aqueous product formed if strontium carbonate were substituted for calcium carbonate? i) Balanced equation: ii) Answer:
Principles of Modern Chemistry
8th Edition
ISBN:9781305079113
Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler
Chapter11: Solutions
Section: Chapter Questions
Problem 50P
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