SURVEY OF CHEMISTRY LABORATORY I CHEM 1151L DETERMINATION OF ATMOSPHERIC PRESSURE

# SURVEY OF CHEMISTRY LABORATORY I CHEM 1151L DETERMINATION OF ATMOSPHERIC PRESSURE

## SURVEY OF CHEMISTRY LABORATORY I CHEM 1151L DETERMINATION OF ATMOSPHERIC PRESSURE

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1. SURVEY OF CHEMISTRY LABORATORY I CHEM 1151L DETERMINATION OF ATMOSPHERIC PRESSURE

2. CAUTION!!! BE SURE TO WEAR SAFETY GLASSES AT ALL TIMES IN THE LABORATORY NO EXCEPTIONS TO THIS RULE!

3. DETERMINATION OF ATMOSPHERIC PRESSURE - To form and collect a sample of hydrogen (H2) gas through a chemical reaction - Students will measure the volume of hydrogen gas - Students will use the room temperature and the calculated moles of the H2 gas to determine the atmospheric pressure

4. DETERMINATION OF ATMOSPHERIC PRESSURE - The pressure of the gas is the total pressure of all gases present - Hydrogen gas is collected over water so contains some water vapor - Ideal gas relationship will give pressure due to the H2 gas only - Water vapor pressure can be determined using room temperature and Table 1 Atmospheric Pressure = calculated H2 pressure + water vapor pressure

5. THE IDEAL GAS LAW PV = nRT P = pressure of a gas (1 atmosphere = 760 mm Hg) V = volume of the gas expressed in liters (L) n = moles of the gaseous substance T = temperature of the gas in Kelvin (K = ˚C + 273) R = gas constant

6. MAGNESIUM METAL - Mass a piece of magnesium (Mg)metal - Make sure the mass is between 0.030 g and 0.050 g - Record the mass

7. MAGNESIUM METAL - Bend the Mg metal strip - Wrap some copper wool loosely around the Mg metal - Tie the bundle securely with about 2-3 ft of string

8. OBTAIN BEAKER AND STAND - Obtain a ring stand and a buret clamp - Also obtain a 1000 mL beaker - Fill the beaker with water (about half-filled) - Set them aside

9. FILL TUBE WITH HCl - Using the dispensing bottle - Dispense about 10 mL of 12 M hydrochloric acid (HCl) directly into a gas collection tube

10. FILL WITH WATER AND SUBMERGE SAMPLE - Carefully and quickly fill the rest of the tube with distilled water - Avoid mixing Click on picture to play video

11. FILL WITH WATER AND SUBMERGE SAMPLE - Submerge the metal sample in the tube to the 50 mL mark - Completely fill the tube

12. IMMERSE TUBE IN BEAKER - Cover the tube opening with your finger and invert the tube - Immediately insert the tube into the beaker of water - Take finger off when the tube is completely immersed in the water - Place the gas tube in the buret holder clamp and adjust the gas tube so it is just touching the bottom of the beaker

13. H2 GAS EVOLES Mg + 2HCl → MgCl2 + H2 - The HCl will move slowly down the tube - HCl will react with Mg upon contact - H2 gas will be evolved and trapped in the tube - Equal volume of water will be displaced by the H2 gas - Make sure no gas escapes from the tube Click on picture to play video

14. REACTION GOES TO COMPLETION - No more gas bubbles will be given off when reaction is complete - That is Mg is completely used up - Tap the tube to dislodge any clinging gas bubbles

15. MEASURE VOLUME OF H2 GAS - Unclamp the gas tube and lift slightly (open end still under water) - Cover the open end with your finger and remove from the beaker - Gas collection tube should remain in the inverted position

16. MEASURE VOLUME OF H2 GAS - Transfer tube to a large graduated cylinder filled with water - Remove your finger once the end of the tube is under water - Immerse the gas tube until the liquid level in the gas tube is even with the liquid level in the large container - Read and record the volume of the hydrogen gas (in mL) from the gas collection tube

17. MEASURE ROOM TEMPERATURE - Measure and record the room temperature (in oC) around the time volume measurement is taken - Do not hold thermometer by the bulb - Use the temperature to determine the water vapor pressure from Table 1 in the manual

18. COMPLETE CALCULATIONS AND CLEAN UP - Remove and dispose of the copper wadding - Complete all calculations