When a 20.0 g sample of an unknown compound is dissolve in 500. G of benzene, the freezing point of the resulting solution is 3.77 o C. The freezing point 9f pure benzene is 5.48 o C and Kf for benzene is 5.12 o C/m. Calculate the molar mass of the unknown

The correct answer is 116.3 g/mol

Explanation:

When a solute is added to a solvent, the freezing point decreases. That is called freezeing point depression and is given by the following expression:

ΔTf= Kf x m

Where ΔTf is the decrease in freezing point (final temperature - initial temperature), Kf is the freezeing point constant, m is the molality of the solution.

We have the following data:

Kf= 5.12ºC/m

ΔTf= 5.48ºC - 3.77ºC = 1.71ºC

We can calculate the molality of the solution from the mathematical expression for freezeing point as follows:

m = ΔTf/Kf = 1.71ºC/(5.12º C/m)= 0.334 m

The molality is the number of moles of solute in 1 kg of solvent. The solute was added to 500 g of solvent (benzene), so we can multiply the molality by the grams of solvent (500 g = 0.5 kg) to obtain the number of moles:

0.334 mol/kg x 0.5 kg = 0.172 moles

We know that the molar mass is equal to the mass of compound per mole, so we divide the mass into the moles to obtain the molar mass as follows:

MM = mass/moles= 20.0 g/0.172 moles = 116.3 g/mol

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

answer: any goods being imported from another country may be subject to issued by the federal government are tariffs

explanation:  

tariffs are a tax on anything that are imported from abroad. government use them to protect and boost their local industries and the thought is that they encourage consumers to buy local instead of importing and they will hope will protect jobs and economy in the country that implements them