. The hydrogen (H2) generated in the reaction is a real gas; however, you treated it like an ideal gas a. Under what conditions do you expect hydrogen gas to deviate from ideal gas behavior? Explain your answer. b. Is it reasonable to treat hydrogen as an ideal gas under the conditions of this experiment? Explain your answer.
Ideal and Real Gases
Ideal gases obey conditions of the general gas laws under all states of pressure and temperature. Ideal gases are also named perfect gases. The attributes of ideal gases are as follows,
Gas Laws
Gas laws describe the ways in which volume, temperature, pressure, and other conditions correlate when matter is in a gaseous state. The very first observations about the physical properties of gases was made by Robert Boyle in 1662. Later discoveries were made by Charles, Gay-Lussac, Avogadro, and others. Eventually, these observations were combined to produce the ideal gas law.
Gaseous State
It is well known that matter exists in different forms in our surroundings. There are five known states of matter, such as solids, gases, liquids, plasma and Bose-Einstein condensate. The last two are known newly in the recent days. Thus, the detailed forms of matter studied are solids, gases and liquids. The best example of a substance that is present in different states is water. It is solid ice, gaseous vapor or steam and liquid water depending on the temperature and pressure conditions. This is due to the difference in the intermolecular forces and distances. The occurrence of three different phases is due to the difference in the two major forces, the force which tends to tightly hold molecules i.e., forces of attraction and the disruptive forces obtained from the thermal energy of molecules.
Objective:
- Determine the molar volume of hydrogen gas generated by the reaction of magnesium metal with hydrochloric acid.
- The reaction of magnesium metal with hydrochloric acid will be used to generate hydrogen gas:
- Mg (s) + 2 HCl (aq)→ Mg2+ (aq) + 2 Cl– (aq) + H2 (g)
Procedure:
1. Obtain a metal strip of magnesium approximately 3 cm in length, and sand the strip with sandpaper to remove the oxide film (we want to obtain a mass for Mg not MgO). Weigh the magnesium strip.
2. Obtain a 50 mL eudiometer. Pour a maximum of 9 mL of dilute (6 M) hydrochloric acid into it, and fill the rest of the eudiometer with DI water. Add the DI water slowly to avoid undue mixing of the acid.
3. Insert a piece of thin copper wire through a one-hole stopper, and wrap the copper wire carefully around the magnesium strip. Insert this assembly into the eudiometer so that the magnesium strip is about 3–4 cm into the eudiometer. (Note: The hole in the stopper should not be sealed off.) Firmly press the stopper into the eudiometer making certain that no air bubbles are trapped under the stopper.
4. Immediately place your finger over the hole of the stopper, invert the eudiometer slowly, and immerse it in a 250 mL beaker of water.
5. Remove your finger, and clamp the eudiometer so that the end is about 3–4 mm from the bottom of the beaker (see Figure 1). The reaction will commence almost immediately as the acid settles to the bottom and comes in contact with the magnesium strip. Note: If the magnesium strip is not inserted far enough into the eudiometer, small bubbles of gas may escape from the bottom of the eudiometer. If this occurs, the experiment must be repeated.
6. When all of the magnesium metal has reacted, allow the equipment to cool to room temperature (heat is generated in the reaction). Tap the side of the eudiometer to free any adhering bubbles of gas. Measure the difference between the water level in the eudiometer and the water level in the beaker (record your value in mm).
7. Read and record the volume of gas in the eudiometer. Place a thermometer in the beaker of water, and record this value as the gas temperature. Record the barometric pressure from the barometer in the laboratory.
Using the procedure above, please answer the below question:
1. The hydrogen (H2) generated in the reaction is a real gas; however, you treated it like an ideal gas
a. Under what conditions do you expect hydrogen gas to deviate from ideal gas behavior? Explain your answer.
b. Is it reasonable to treat hydrogen as an ideal gas under the conditions of this experiment? Explain your answer.
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Using the procedure above, please annswere the below question:
a. In step 1 of the experiment, you sanded the magnesium strip before weighing (and reacting) to remove any magnesium oxide. If you skipped step 1 and left a MgO film on the strip, would the calculated molar volume of hydrogen gas collected be higher or lower than if the weighed mass were all magnesium metal? Explain which experimental data would be incorrect for the measured mass.
b. The gas collected in the eudiometer was a mixture of hydrogen gas and water vapor. How is the calculated molar volume affected if the partial pressure of water vapor collected is not accounted for? Explain.
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