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| Physical Properties of Hydrogen Chloride Gas |
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| Color |
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| Hydrogen chloride gas is colorless. |
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| Odour |
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| It has a pungent and choking smell. If inhaled, it corrodes the delicate membrane of the respiratory passages. |
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| Taste |
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| It is sour to taste. |
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| Vapor density |
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| Its vapor density = 18.25 (Vapor density of air = 14.4), hence it is nearly 1.25 times denser than air. |
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| Solubility |
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| It is extremely soluble in water. One liter of water can dissolve nearly 535 liters of the gas at 0o C. |
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| Activity |
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| To show that hydrogen chloride gas is heavier than air (Vapor density = 18.25) |
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| Take two gas jars 'A' and 'B'. Fill jar 'A' with air and jar 'B' with dry hydrogen chloride gas. Invert 'B' over 'A' as shown in figure 5.4. |
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| Keep the jar 'A' inverted for a few minutes and then remove the gas jar 'B'. Introduce a rod dipped in ammonium hydroxide into the jar 'A'. White fumes (ammonium chloride) are seen. This shows the presence of hydrogen chloride gas in jar 'A'. Being heavier than air, hydrogen chloride gas displaces it from the lower jar 'A'. |
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| Hydrogen chloride gas also fumes in air as such. This is because of the high solubility of hydrogen chloride gas in water. It dissolves in the water vapor of air and forms a cloud of tiny droplets of hydrochloric acid that appear as mist. |
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| The high solubility aspect of the gas can be demonstrated by the "fountain experiment". |
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| Fountain experiment |
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| A round bottomed flask is first dried well. It is then filled with dry hydrogen chloride gas and fitted with a one holed rubber stopper as shown in the figure 5.5. |
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| A small quantity of blue litmus solution is added to the water in a trough. This gives a blue tinge to it. Over the flask is placed a layer of cotton or a piece of cloth soaked in a small quantity of alcohol or ether. As the vapors of alcohol or ether evaporate, they cause cooling and as a result the gas in the flask contracts. Hence a small quantity of water gets sucked into the flask. |
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| This small quantity of water dissolves all the gas in the flask. This causes partial vacuum inside the flask. The water from the trough rushes into the flask through the tube and sprays out like a fountain. Because of the acidic nature of the gas the blue color of the water changes to red. |
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