EXPERIMENT 7: MoLAR VOLUME OF A GAS Contributed by: Dr. Weslene Tallmadge PURPOS

Question

EXPERIMENT 7: MoLAR VOLUME OF A GAS Contributed by: Dr. Weslene Tallmadge PURPOSE Determine the molar volume of a gas by experiment and compare the result to the accepted value. PRE-LAB QUESTIONS Ammonia gas and carbon dioxide gas react to form aqueous urea (NHCONHJ and water, what volume of ammonia at 25 and 1.5 atm pressure is needed to produce 500 g of urea? 1. BACKGROUND The volume that is occupied by one mole of a gas at standard temperature and pressure (STP) is known as the molar volume. According to Avogadro's hypothesis, equal volumes of gases under equal conditions of temperature and pressure contain equal numbers of molecules. It follows from this hypothesis that all gas samples containing one mole of molecules will occupy the same volume at STP. The basis of this experiment is the following reaction in which a known mass of magnesium is reacted with an excess of hydrochloric acid to produce the products shown: Mg (s) + 2HCI (aq) MgCl2 (aq) + H2 (g) Inspection of this equation reveals that one mole of magnesium (24.3 g) yields one mole of hydrogen gas (2.02 8). Hydrogen gas is the product of interest in this experiment. By determining the number of moles of magnesium that reacts, you will indirectly determine the number of moles of hydrogen gas produced. The combined gas law can be used to find the volume that the gas would occupy at STP. The number of moles and volume at STP will be used to calculate the molar volume of hydrogen gas

Explanation / Answer

The pre lab question:

Use the formula : PV = nRT ---> V = nRT/P
n = m/MM = 500 g / 60 g/mol = 8.33 moles
V = 8.33 * 0.0821 * 298 / 1.5 = 135.92 L
Vm = V/n = 135.92 / 8.33 = 16.3169 L/mol

For the post lab questions 1 and 3 (The ones I'm most sure):

1. You determine that to avoid any systematical error of the flask. As well to work with the real conditions and real conditions of gas, cause in this reaction we are involving gases. Si even as we know the volume of flask, the experimental calculation will give us info for the systematical error.

3. The postulates are:

1      The molecules in a gas are small and very far apart. Most of the volume which a gas occupies is empty space.

2      Gas molecules are in constant random motion. Just as many molecules are moving in one direction as in any other.

3      Molecules can collide with each other and with the walls of the container. Collisions with the walls account for thepressure of the gas.

4      When collisions occur, the molecules lose no kinetic energy; that is, the collisions are said to be perfectly elastic. The total kinetic energy of all the molecules remains constant unless there is some outside interference with the

5      The molecules exert no attractive or repulsive forces on one another except during the process of collision. Between collisions, they move in straight lines.

Hope this helps

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