Homework Help for Chemistry

Calculate the molecular weight of phosphorus if 2.3437 grams are dissolved in 50.000 grams of para-dibromobenzene and the solution freezes at 81.35 degrees Celsius. What is the molecular formula for phosphorus?

Suppose you are instructed to measure the density of a different metal using a 50ml pycnometer. The mass of the pycnometer is 23.721g. After filling the pycnometer with water at 24.0 C, you find the mass of the pycnometer and water is 72.457g. The water is emptied out and the metal is placed in the pycnometer. The metal, by itself, is found to weigh 51.118g. The pycnometer with the metal in it is filled with water again and the pycnometer, water, and metal are found to weigh 115.442g. What is the density of the metal?

An ion has the following Lewis structure where X is an unknown element.

Which of the following elements could be X?

Cl   Xe   Ne   F   Kr   Br  

(There may be more than one possible answer.)

Enter your answer by typing the symbol of the element(s) in the box below. If more than one element is possible, separate the symbols of the elements with a comma.

If a container can hold 2.0 gallons and 5.0 liters of water are added how many more liters of water can be added to completely fill the 2.0 gallon container 

I am a prospective international students aspiring to study in the US. I have not received an admission yet can I still apply for the scholarship?

A gas can holds 6.0 of gasoline. What is the quantity in cm

From the reaction

C10H8(s) + 12O2(g) → 10CO2(g) + 4H2O(l)   ΔrH°= -5153.0 kJ mol−1

and the enthalpies of formation of CO2 (-393.5 kJ/mol) and H2O (-285.8 kJ/mol), calculate the enthalpy of formation of naphthalene (C10H8).

Balance the following chemical equation: 

Fe + O2 -> Fe2O3

Calculate the molar mass of water (H2O) by adding up the atomic masses of hydrogen (H) and oxygen (O) atoms. Remember to consider the number of atoms in the molecule when calculating the molar mass.

PROBLEMS FOR PRACTICE

1. When gaseous HI is irradiated with radiation of 2350 A wavelength, it is observed that 1.85 • 10*2 mole decomposes per 1000 cal of radiant energy absorbed. Calculate the quantum efficiency of the reaction
[Ans. 1.9]

2. A certain system absorbs 3.0 • 1016 quanta of light per second. On irradiation for 20 minutes,
0.002 mole of the reactant was found to have reacted. Calculate the quantum efficiency of the process.
[Ans. 0.669]

PROBLEMS FOR PRACTICE

1. What is the energy in kcal of one mole of photons of 2573 A wavelength?

2. Calculate the energy of one photon of light of 2450 A wavelength. Will it be able to dissociate a bond in a diatomic molecules which absorbs this photon and has a bond energy equal to 95 kcal per mole?
Planck’s constant (ft) = 6.626 • 10*27 erg s molecule*1 Velocity of light (c) = 3 • 1010 cm sql

Avogadro’s number (N) = 6.02 • 1023
flint: Calculate the energy of the photon. If this energy is greater than that required to break the bond (bond energy), dissociation of the bond will happen.

3. Calculate the value of an einstein of energy in electronvolts for a radiation of 3 • 101S sql
frequency.

4. Calculate the value of the einstein corresponding to radiation of 6000 A wavelength.

5. Find the value of an einstein of energy for radiation of 4240 A wavelength.

4. If a 2 mm thick plate of material transmits 70% of the incident light, what percentage will be transmitted by a 0.5 mm thick plate?

1. 3. The percentage transmittance of an aqueous solution of disodium fumarate at 250 mm and 298 K is 19.2% for a 5 • 10“ molar solution in a 1 cm cell. Calculate the absorbance A and the molar absorption coefficient e. What will be the percentage transmittance of a 1.75 • 10’S molar
   solution in a 10 cm cell?
   [An s. A -  0.717, -  1.43 •  io 3 L mol*1 cmm l , T -  56.1%]

1. Please send me questions about ECAT test
2.  

Questions 1-5 solve please