Briefly explain why the stopcock/value on the buret must remain in the open posi

Question

Briefly explain why the stopcock/value on the buret must remain in the open position throughout the experiment. Why must the inside of large test tube be completely dry before the Alka-Seltzer sample and the small test inside tube with acid are placed inside it? Briefly explain why the water levels in the leveling bulb and in the buret must be equalized BEFORE and AFTER each reaction when a volume measurement is taken. The mass percentage of calcium carbonate in an eggshell was analyzed using the same technique described in this Gas Laws experiment. A 0.1625 g sample of eggshell reacts excess at volume was Hg and 22.8 degree C. The initial volume of water in the buret was 0.40 mL. After the reaction, the final 44.15 mL. Write the balanced chemical equation for the reaction between calcium carbonate and hydrochloric acid. Use the Properties of Water Website (shown on page 57) to obtain the vapor pressure of water (in atm) at the temperature indicated. Keep all digits _____ Convert the total pressure given to units of atm, then calculate the gas pressure of carbon dioxide by correcting for the vapor pressure of water indicated in part b.

Explanation / Answer

1. The stopcock valve must remain in open position on buret so that any gas released from tablet can escape through it.

2.The inside of the tube must be fully dry before purring tablet and HCl so that no contaminant effect the resulting reaction and give false reading.

3. Water level is balanced before the experiment to get zero pressure reading before experiment.

4.

a. Balanced equation,

CaCO3 + 2HCl --> CaCl2 + H2CO3

b. vapor pressure of water at 22.8 oC = 20.9 torr

c. total pressure = 758.4 - 20.9 = 737.5 mmHg = 0.97 atm

Gas pressure of CO2 = 0.97 atm

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