Chemistry freezing point and determination of molecular formula

[Forceofmatter]

1. Homework Statement [/b]
question 1: Calculate the mole fraction of benzene in benzene-toluene solution that is in equilibrium at 25 deg. Celsius with a vapor pressure that contains 62% mol Benzene. At 25 deg. Celsisus the vapor pressures of benzene and toluene are 95.1 mm Hg and 28.4 mm Hg respectively. Kf of Benzene= 5.50 deg Celsius.

question 2: Coniferin is a glycoside (derivative of sugar) found in conifers such as fir trees. When a 1.205 g smaple of coniferin is subjected to combustion analysis, the products are 0.698 g H20 and 2.479 g CO2. In another experiment, a 2.216 g sample of coniferin is dissolved in 46.68 g water, and the normal boiling point of the solution is 100.068 deg. Celsius. What is the molecular formula of coniferin?

Help on one or both of these questions would be greatly appreciated. Please provide explanation or mathematical work showing how you got to your answer.


2. Homework Equations
Delta T=Kb x molality
Ptotal= P(benzene)Molfract.(benz) + P(toluene)Molfract.(tol)

3. The Attempt at a Solution
1. ptot=95.1(?) + 28.4(0.38) after that i got stuck.

2. For this one, I know you find moles each of H20 and CO2. Then you need to use the boiling point and somehow find moles of the solvent to get molar mass after changing molality to g.

 

[nate808]

You can then find the number of moles of coniferin.

Hello there! I am a scientist and I would be happy to assist you with your questions.

1. To solve for the mole fraction of benzene in the solution, we can use the equation for vapor pressure of a solution: Ptotal= P(benzene)Molfract.(ben) + P(toluene)Molfract.(tol). We know the total vapor pressure (Ptotal) is 62% of the vapor pressure of pure benzene (95.1 mm Hg). We also know the vapor pressure of pure toluene (28.4 mm Hg). So, we can set up the equation as follows: 0.62(95.1 mm Hg) = P(benzene)Molfract.(ben) + 0.38(28.4 mm Hg). From this, we can solve for the mole fraction of benzene, which is 0.527.

2. To find the molecular formula of coniferin, we can use the information from the combustion analysis and the boiling point experiment. From the combustion analysis, we can find the moles of H20 and CO2 produced. The moles of H20 is 0.698 g / (18.02 g/mol) = 0.0387 moles. The moles of CO2 is 2.479 g / (44.01 g/mol) = 0.0563 moles. Since the molecular formula of coniferin contains both of these elements, we can use the ratio of moles to determine the empirical formula. The ratio of moles is 0.0387 moles of H20 to 0.0563 moles of CO2, which simplifies to 1:1. This means that the empirical formula is C1H1O1, which simplifies to CH2O.

To determine the molecular formula, we need to find the molar mass of coniferin. From the boiling point experiment, we can find the molality of the solution, which is 2.216 g / (46.68 g water) = 0.0474 molal. We can use the equation Delta T=Kb x molality to solve for the change in boiling point (Delta T). The Kb for water is 0.512 deg Celsius/molal. So

 

[Blueshift5]

Hello! Let's start with the first question. To find the mole fraction of benzene in the solution, we can use the equation:

Mole fraction of benzene = moles of benzene / total moles of solution

To find the moles of benzene, we first need to find the molality of the solution. We can use the equation:

Molality = moles of solute / mass of solvent (in kg)

In this case, the mass of the solvent is not given, but we can calculate it using the mass of the solution and the mass of the solute. The mass of the solution is equal to the mass of benzene (given as 62% of the total solution) plus the mass of toluene. We can set up a system of equations to solve for the mass of the solvent and then use it to calculate the molality.

Once we have the molality, we can use the freezing point depression equation to find the change in temperature of the solution:

Delta T = Kf x molality

We know the change in temperature (0 degrees Celsius) and the Kf value for benzene, so we can solve for the molality. With the molality, we can then find the moles of benzene and use it to calculate the mole fraction.

For the second question, we can use the information from the combustion analysis to find the moles of H2O and CO2 produced. From there, we can use the ideal gas law to calculate the moles of solute (coniferin) dissolved in the solution. Then, we can use the molality equation to find the molality of the solution.

Next, we can use the boiling point elevation equation to find the change in temperature of the solution:

Delta T = Kb x molality

Again, we know the change in temperature (0.068 degrees Celsius) and the Kb value for water, so we can solve for the molality. With the molality, we can then find the moles of coniferin and use it to calculate the molecular formula.

I hope this helps! Let me know if you have any further questions or need more clarification. Good luck!