Ask question

Ask question

All categories

2 years ago

10

in order to find the molar mass of an unknown compound, a research scientist prepared a solution of 0.930 g of an unknown in 125

g of a solvent. The pure solvent had a freezing point of 74.2 degrees celcius, and the solution had a freezing point of 73.4 degrees celcius. Given the solvents freezing point depreesion contant, Kf=5.50 degrees celcius/m, find the molar mass of the unknown

1 answer:

PtichkaEL [24]2 years ago

3 0

Answer:

Molar mass→ 0.930 g / 6.45×10⁻³ mol = 144.15 g/mol

Explanation:

Let's apply the formula for freezing point depression:

ΔT = Kf . m

ΔT = 74.2°C - 73.4°C → 0.8°C

Difference between the freezing T° of pure solvent and freezing T° of solution

Kf = Cryoscopic constant → 5.5°C/m

So, if we replace in the formula

ΔT = Kf . m → ΔT / Kf = m

0.8°C / 5.5 m/°C = m → 0.0516 mol/kg

These are the moles in 1 kg of solvent so let's find out the moles in our mass of solvent which is 0.125 kg

0.0516 mol/kg . 0.125 kg = 6.45×10⁻³ moles. Now we can determine the molar mass:

Molar mass (mol/kg) → 0.930 g / 6.45×10⁻³ mol = 144.15 g/mol

You might be interested in

A family of four lives in a three-bedroom house and uses an average of 900 kWh of electricity per month. The family cools their

agasfer [191]

<h2>Answer:</h2><h2>The percentage of the family’s total annual electricity that is used to run the two air conditioners for the three summer months = 19.4 %</h2>

Explanation:

Average electricity consumed per month = 900 kWh

The family cools their house for three months during the summer with two window-unit air conditioners

The power consumed by one window-unit air conditioners = 350 kWh

The power consumed by two window-unit air conditioners = 350(2) = 700 kWh

Power consumed for two air conditioners for the three summer months = 700 (3) = 2100 kWh

Total power consumed for 1 year = 900 (12) = 10800kWh

The percentage of the family’s total annual electricity that is used to run the two air conditioners for the three summer months = $\frac{2100}{10800}100$ = 19.4 %

5 0

1 year ago

What is the percentage of water in the following compound? Answer using three significant figures. Sodium carbonate decahydrate,

Karo-lina-s [1.5K]

The trick for this problem is to understand atomic mass: the fact that different atoms have different masses. What we need to do is add up all the atomic masses of the compound and work out the ratio of mass of water to the mass of sodium carbonate. Atomic masses are often given for each atom in the periodic table, but you can look them up on google too.

You can do this by adding up individual atoms for each molecule, or you can shortcut and lookup the molar mass of the compound (i.e.the task already done for you).

The molar mass of water is 18.01g/mole so for 10 moles of water we have a mass of 180.1g.

The molar mass of sodium carbonate is 106g/mole (google).

So the total mass of the sodium carbonate decahydrate compound is 180.1+106 = 286.1g, of which water would make up 180.1g, so the percentage of water is is 180.1/286.1 = 0.629, so we can round this to 63%

:)

3 0

1 year ago

Read 2 more answers

A solution of SO2 in water contains 0.00023 g of SO2 per liter of solution. What is the concentration of SO2 in ppm? in ppb?

Mnenie [13.5K]

Answer:

= 230 ppb

Explanation:

Considering that;

1ppm = 1mg/L

Then;

0.00023g = 0.23mg

Therefore;

0.00023 g/L = 0.23 mg/L

0.23 mg/L = 0.23 ppm

1 ppm = 100 ppb

Therefore;

0.23 ppm = 0.23 ×1000

= 230 ppb

5 0

2 years ago

Read 2 more answers

A well-insulated, closed device claims to be able to compress 100 mol of propylene, acting as a SoaveRedlich-Kwong gas and with

Setler79 [48]

Explanation:

The given data is as follows.

Moles of propylene = 100 moles, $T_{i}$ = 300 K

$T_{f}$ = 800 K, $V_{i} = 2 m^{3}$

$V_{f} = 0.02 m^{3}$ , $C_{p}$ of propylene = 100 J/mol

Now, we assume the following assumptions:

Since, it is a compression process therefore, work will be done on the system. And, work done will be equal to the heat energy liberating without any friction.

W = $mC_{p} \Delta T$

$100 moles \times 100 J/mol K (800 - 300) K$

= $5 \times 10^{6} J$

= 5 MJ

Thus, we can conclude that a minimum of 5 MJ work is required without any friction.

3 0

2 years ago

NO2 can react with the NO in smog, forming a bond between the N atoms. Draw the structure of the resulting compound, including f

ELEN [110]

First, let's write down the balanced chemical reaction between the given reactants:

NO₂ + NO → N₂O + O₂

The Lewis structure of the main product is shown in the attached picture. To determine the formal charge of each element, the formula is as follows:

Formal Charge = Valence electrons - Non-bonding valence electrons - (Bonding electrons/2)

For the leftmost N:
Formal charge = 5 - 2 - 6/2 = 0
For the middle N:
Formal charge = 5 - 0 - 8/2 = 1
For O:
Formal charge = 6 - 6 - 2/2 = -1

6 0

1 year ago