A solution contains 3.95 g of carbon disulfide (CS₂) and 2.43 g of acetone (CH₃COCH₃). At 35 °C the vapor pressures of pure carbon disulfide and pure acetone are 515 torr and 332 torr, respectively. Assuming ideal behavior, calculate the vapor pressures of each component and the total vapor pressure above the solution. The experimentally measured total vapor pressure of the solution at 35 °C is 645 torr. Is the solution ideal? If not, what can you say about the relative strength of carbon disulfide–acetone interactions compared to the acetone–acetone and carbon disulfide–carbon disulfide interactions?

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SORT You are given the masses and vapor pressures of carbon disulfide and acetone and are asked to find the vapor pressures of each component in the mixture and the total pressure assuming ideal behavior. STRATEGIZE This problem requires that you use Raoult's law to calculate the partial pressures of each component. In order to use Raoult's law, first calculate the mole fractions of the two components. Convert the masses of each component to moles and then use the definition of mole fraction to calculate the mole fraction of carbon disul- fide. You can then find the mole fraction of acetone because the mole fractions of the two components add up to 1. GIVEN: 3.95 g CS₂ 2.43 g CH3COCH3 Pcs₂ = 515 torr (at 35 °C) PCH,COCH, = 332 torr (at 35 °C) Ptot (exp) 645 torr (at 35 °C) FIND: PCS, PCH,COCH3, Ptot (ideal) CONCEPTUAL PLAN 3.95 g CS₂ 1 mol CS₂ 76.15 g CS2 2.43 g CH3COCH3 mol CS₂ 1 mol CH3COCH3 58.08 g CH3COCH3 mol CS2, mol CH3COCH3 mol CH3COCH3 XCS₂ = XCS2, XCH3COCH3 NCS₂ ncs₂ +nCH, CO CH3