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# Chemistry Partial Pressure HELP PLEASE?

Helium is collected over water at 25°C and 1.00 atm total pressure. What total volume of gas must be collected to obtain 0.627 g of helium? (At 25°C the vapor pressure of water is 23.8 torr.)

### 1 Answer

- DragonLv 61 decade agoFavorite Answer
Answer: Total volume og gas equals 4.085 Liters (per following details)

Pressures: P (H2O) = 23.8 Torr = 23.8 mm

P (He) = 1.00 Atm - 23.8 mm = 760 mm - 23.8 mm = 736.2 mm

Volumes: V (He) = nRT / P

= moles x R x T / 736.2 mm

= (0.627 g / 4 g/mol) x ( 62.36 mmL/molK) x (273 +25 K) / 736.2

= 3.9567 Liters

Total Volume: Volume ratio = Pressure ratio (also equals Mole Ratio)

V (He) / V (Total) = P (He) / P (Total)

(3.9567) / V (Total) = 736.2 / 760 (rearrange to get)

V (Total) = (3.9567) / (736.2 / 760) = 4.085 Liters

Source(s): Dalton's law, Boyles, Law per Physical Chemistry Handbook, Wikipedia, and Spatknotes.com