Small quantities of hydrogen can be prepared by the addition of hydrochloric acid to zinc. A sample of 195 mL of hydrogen was collected over water at 25°C and 753 torr. What mass of hydrogen was collected? (P_water = 24 torr at 25°C) A)0.00765 g B)0.0154 g C)0.0159 g D)0.0164 g E)0.159 g

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To find the mass of hydrogen collected, we first need to calculate the pressure of the hydrogen gas using Dalton's Law of Partial Pressures. The total pressure is given as 753 torr, and the vapor pressure of water at 25°C is 24 torr. Therefore, the pressure of the hydrogen gas is 753 torr - 24 torr = 729 torr.Next, we convert the pressure to atmospheres (since standard molar volume and R are often given in these units) and the volume to liters:$$729 \, \text{torr} \times \frac{1 \, \text{atm}}{760 \, \text{torr}} = 0.959 \, \text{atm}$$$$195 \, \text{mL} = 0.195 \, \text{L}$$We use the ideal gas law to find the number of moles of hydrogen gas:$$PV = nRT$$$$n = \frac{PV}{RT}$$$$n = \frac{(0.959 \, \text{atm})(0.195 \, \text{L})}{(0.0821 \, \text{L atm K}^{-1} \text{mol}^{-1})(298 \, \text{K})}$$$$n \approx 0.00765 \, \text{mol}$$Finally, we calculate the mass of hydrogen collected. The molar mass of hydrogen (H2) is approximately 2 g/mol:$$mass = n \times molar \, mass$$$$mass = 0.00765 \, \text{mol} \times 2 \, \text{g/mol} = 0.0153 \, \text{g}$$Rounding to the correct number of significant figures, the mass of hydrogen collected is approximately 0.0154 g.

Small Quantities of Hydrogen Can Be Prepared by the Addition