Chemistry, 09.02.2021 05:50 bandnerd1

What is the molecular mass for a non-electrolyte if 35.0 g of it is dissolved in 45.0 grams of water and the solutions boiling point is 101.25oC? (The KB for H2O is .51°C/m)

Answers: 3

Show answers

Answers

The boiling point of water increases as the amount of impurities dissolved in it increases. For our purposes, we will consider the non-electrolyte to be the dissolved impurity. The change in the boiling point can be calculated using the equation:

$\Delta T_b = i \times K_b \times m$

where $\Delta T_b$ is the change in boiling point, is the van ‘t Hoff factor (whose value denotes the number of particles each formula unit of the dissolved substance dissociates into in water), K_b is the boiling point elevation constant, and is the molality (moles of solute/kilogram of solvent) of the solution.

Right off the bat, since we're dealing with a non-electrolyte, the dissolved substance can be assumed not to dissociate in water. So, our van ‘t Hoff factor, , would be 1 (by contrast, the for an ionic compound like NaCl would be 2 since, in water, NaCl would dissociate into two particles: one Na⁺ ion and one Cl⁻ ion). We're also given our K_b , which is 0.51 °C/m.

Assuming the normal boiling point of pure water to be 100 °C (a defined value for sig fig purposes), the change in boiling point from having dissolved 35.0 g of the non-electrolyte can be obtained by subtracting 100 °C from the final—elevated—boiling point of 101.25 °C:

$\Delta T_b = 101.25\text{ }^o\text{C} - 100\text{ }^o\text{C} = 1.25\text{ }^o\text{C}$

Now, recall what we're asked to determine: the molecular mass of the dissolved substance. There is one unknown left in the equation: the molality of the solution. Let's first solve for that:

$m = \frac{\Delta T_b}{K_b} = \frac{1.25^\text{ o}\text{C}}{0.51^\text{ o}\text{C}/m} \\ m = 2.45 \text{ mol solute/kg water}.$

Notice that we didn't include the i since its value is 1.

Now, what would happen if we multiplied our molality by the mass of water we've been given? We would be left with the moles of solute. And what are we asked to find? The molecular mass, or the mass per mole. We can accomplish this in two steps. Remember to convert your mass of water to kilograms:

$2.45 \text{ mol solute/kg water} \times 0.045 \text{ kg water} = 0.110 \text{ mol solute.}$

And, finally, we divide the mass of our solute by the number of moles of solute:

$\frac{35.0 \text{ g solute}}{0.110 \text{ mol solute}} = 317.5 \text{ g/mol}$

Our answer to two significant figures (which is the number of sig figs to which our K_b is given) would be 320 g/mol.

Answer from: Quest

c. is the answer

by love gaming

Answer from: Quest

i dont know the answe

Another question on Chemistry

Chemistry, 21.06.2019 20:30

Which sentence best describes the formation of igneous rock? a- lava on the surface dries up and makes arock b_melted rocks cools and forms crystals c_rocks under tremendous heat and pressure d_magma is melted rock underground

Answers: 1

Answer

Chemistry, 22.06.2019 00:30

Idon’t know how to solve this question

Answers: 1

Answer

Chemistry, 22.06.2019 05:00

Agas can holds 2.0 gal of gasoline. what is this quantity in cubic centimeters?

Answers: 2

Answer

Chemistry, 22.06.2019 06:00

There are 6.022, 104 atoms of hg in 1 mole of hg the number of atoms in 45 moles of hg can be found by multiplying 4.5 by 6.022, 102 which is the number of atoms in 4.5 moles of hg, correctly written in scientific notation with the correct number of significant figures? 0 21,109 0 21,100 271, 1024 27.099, 100 mark this and retum save and exit submit

Answers: 1

Answer

You know the right answer?

What is the molecular mass for a non-electrolyte if 35.0 g of it is dissolved in 45.0 grams of water...

Questions