4.00g/(mol) You can obtain the molar mass of any chemical element by using the periodic table: The molar mass is usually listed underneath the chemical symbol. The units associated with molar mass is grams per mole (g/(mol)). Properties of Various Ideal Gases (at 300 K) Gas: Formula: Molar Mass: Gas constant: Specific Heat at Const. Specific Heat at Const.
Molar mass of He = 4.002602 g/mol
Convert grams Helium to moles or moles Helium to grams
Properties of Various Ideal Gases (at 300 K) Gas: Formula: Molar Mass: Gas constant: Specific Heat at Const. Specific Heat at Const. The molar mass of a particular gas is therefore equal to the mass of a single particle of that gas multiplied by Avogadro’s number (6.02 x 10 23). To find the molar mass of a mixture of gases, you need to take into account the molar mass of each gas in the mixture, as well as their relative proportion.
|Symbol||# of Atoms||Helium||He||4.002602||1||100.000%|
In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all of these products together.
If the formula used in calculating molar mass is the molecular formula, the formula weight computed is the molecular weight. The percentage by weight of any atom or group of atoms in a compound can be computed by dividing the total weight of the atom (or group of atoms) in the formula by the formula weight and multiplying by 100.
Formula weights are especially useful in determining the relative weights of reagents and products in a chemical reaction. These relative weights computed from the chemical equation are sometimes called equation weights.
Finding molar mass starts with units of grams per mole (g/mol). When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula.
The atomic weights used on this site come from NIST, the National Institute of Standards and Technology. We use the most common isotopes. This is how to calculate molar mass (average molecular weight), which is based on isotropically weighted averages. This is not the same as molecular mass, which is the mass of a single molecule of well-defined isotopes. For bulk stoichiometric calculations, we are usually determining molar mass, which may also be called standard atomic weight or average atomic mass.
A common request on this site is to convert grams to moles. To complete this calculation, you have to know what substance you are trying to convert. The reason is that the molar mass of the substance affects the conversion. This site explains how to find molar mass.
Using the chemical formula of the compound and the periodic table of elements, we can add up the atomic weights and calculate molecular weight of the substance.
Graham's Law of Effusion
Examples and Problems only
Example #1: 8.278 x 10¯4 mol of an unidentified gaseous substance effuses through a tiny hole in 86.9 s Under identical conditions, 1.740 x 10¯4 mol of argon gas takes 81.3 s to effuse.
a) What is the molar mass of the unidentified substance (in g/mol)?
b) What is the molecular formula of the substance?
c) Under identical conditions, how many moles of ethene (C2H4) gas would effuse in 91.0 s?
Example #2: It takes 354 seconds for 1.00 mL of Xe to effuse through a small hole. Under the same conditions, how long will it take for 1.00 mL of nitrogen to effuse?
Example #3: What is the rate of effusion for a gas that has a molar mass twice that of a gas that effuses at a rate of 4.2 mol/min?
Example #4: It takes 110. seconds for a sample of carbon dioxide to effuse through a porous plug and 275 seconds for the same volume of an unknown gas to effuse under the same conditions. What is the molar mass of the unknown gas (in g/mol)?
Example #5: What is the molar mass of a compound that takes 2.65 times as long to effuse through a porous plug as it did for the same amount of XeF2 at the same temperature and pressure?
Example #6: If a gas effuses 4.25 times faster than iodine gas (I2), what is its molar mass?
A. 59.7 g/mol
B. 163 g/mol
C. 123 g/mol
D. 158 g/mol
Example #7: Calculate the density of a gas at STP, if a given volume of the gas effuses through an apparatus in 6.60 min and the same volume of nitrogen, at the same temperature andpressure, effuses through this apparatus in 8.50 minutes.
Example #8: If 0.0949 moles of NH3 effuses in 881 seconds, how many seconds would it take for the same number of moles of B2H6 to effuse?
Example #9: The rate of diffusion of an unknown gas was determined to be 2.92 times greater than that of NH3. What is the approximate molar mass of the unknown gas?
Example #10: If a molecule of C2H6 diffuses a distance of 0.978 m from a point source, calculate the distance (m) that a molecule of CH4 would diffuse under the same conditions for the same period of time.
Example #11: A sample of oxygen gas (O2) effuses into a vacuum 1 times faster than an unknown gas. O2 has a molecular weight of about 32.00 g mol¯1. What is the molecular weight of this unknown gas (in g mol¯1)?
Example #12: Argon effuses from a container at a rate of 0.0260 L/s. How long will it take for 3.00 L of I2 to effuse from the same container under identical conditions?
Example #13: Calculate the density of a gas at STP, if a given volume of the gas effuses through an apparatus in 6.60 min and the same volume of oxygen at the same temperature and pressure, effuses through this apparatus in 8.50 minutes.
Bonus Example #1: The rate of effusion of an unknown gas at 480 K is 1.6 times the rate of effusion of SO2 gas at 300 K. Calculate the molecular weight of the unknown gas.
Bonus Example #2: Heavy water, D2O (molar mass = 20.0276 g mol¯1), can be separated from ordinary water, H2O (molar mass = 18.0152 g mol¯1), as a result of the difference in the relative rates of diffusion of the molecules in the gas phase. Calculate the relative rates of diffusion for H2O when compared to D2O.
Problem #1: If equal amounts of helium and argon are placed in a porous container and allowed to escape, which gas will escape faster and how much faster?
Problem #2: What is the molecular weight of a gas which diffuses 1/50 as fast as hydrogen?
Problem #3: Two porous containers are filled with hydrogen and neon respectively. Under identical conditions, 2/3 of the hydrogen escapes in 6 hours. How long will it take for half the neon to escape?
Problem #4: If the density of hydrogen is 0.090 g/L and its rate of effusion is 5.93 times that of chlorine, what is the density of chlorine?
Problem #5: How much faster does hydrogen escape through a porous container than sulfur dioxide?
Problem #6: Compare the rate of diffusion of carbon dioxide (CO2) & ozone (O3) at the same temperature.
Molar Mass Of Helium He
Problem #7: 2.278 x 10¯4 mol of an unidentified gaseous substance effuses through a tiny hole in 95.70 s. Under identical conditions, 1.738 x 10¯4 mol of argon gas takes 81.60 s to effuse. What is the molar mass of the unidentified substance?
Problem #8: A compound composed of carbon, hydrogen, and chlorine diffuses through a pinhole 0.411 times as fast as neon. Select the correct molecular formula for the compound:
Problem #9: Which pair of gases contains one which effuses at twice the rate of the other in the pair?
(a) He and Ne
(b) Ne and CO2
(c) He and CH4
(d) CO2 and HCl
(e) CH4 and HCl
Problem #10: If a molecule of CH4 diffuses a distance of 0.530 m from a point source, calculate the distance (in meters) that a molecule of N2 would diffuse under the same conditions for the same period of time.
Bonus Problem #1: Calculate the density of a gas at STP, if a given volume of the gas effuses through an apparatus in 6.60 min and the same volume of nitrogen at the same temperature and pressure, effuses through this apparatus in 8.50 minutes.
Bonus Problem #2: At 25.0 °C and 380.0 mmHg, the density of sulfur dioxide is 1.31 g/L. The rate of effusion of sulfur dioxide through an orifice is 4.48 mL/s. (a) What is the density of a sample of gas that effuses through an identical orifice at the rate of 6.78 mL/s under the same conditions? (b) What is the molar mass of the gas?
Problem #11: What is the rate of effusion for a gas that has a molar mass twice that of a gas that effuses at a rate of 3.62 mol/min?
Problem #12: Calculate the rate of effusion of NO2 compared to SO2 at the same temperature and pressure.
Problem #13: Assume you have a sample of hydrogen gas containing H2, HD, and D2 that you want to separate into pure components. What are the various ratios of relative rates of effusion?
Problem #14: A 3.00 L sample of helium was placed in container fitted with a porous membrane. Half of the helium effused through the membrane in 25 hours. A 3.00 L sample of oxygen was placed in an identical container. How many hours will it take for half of the oxygen to effuse though the membrane?
Problem #15: At a certain temperature, hydrogen molecules move at an average velocity of 1.84 x 103 m/s. Estimate the molar mass of a gas whose molecules have an average velocity of 311 m/s.
Problem #16: An unknown gas effuses 1.66 times more rapidly than CO2. What is the molar mass of the unknown gas.
Problem #17: A sample of hydrogen gas effuse through a porous container 8.91 times faster than an unknown gas. Estimate the molar mass of the unknown gas.
Problem #18: N2 is contaminated with a noble gas.The contaminant effuses at 1.87x N2. What is the noble gas?
Problem #19: In an effusion experiment, it was determined that nitrogen gas, N2, effused at a rate 1.812 times faster than an unknown gas. What is the molar mass of the unknown gas?
Problem #20: Why are the rates of diffusion of nitrogen gas and carbon monoxide almost identical at the same temperature?
Problem #21: In running a diffusion experiment, ammonia is found to diffuse 30.0 cm during the same amount of time hydrogen chloride moves 20.0 cm. Calculate the percentage deviation from Graham's Law.
Problem #22: A sample of Br2(g) take 10.0 min to effuse through a membrane. How long would it take the same number of moles of Ar(g) to effuse through the same membrane?
Problem #23: At a particular pressure and temperature, it takes just 8.256 min for a 4.893 L sample of Ne to effuse through a porous membrane. How long would it take for the same volume of I2 to effuse under the same conditions?
Problem #24a: How much faster does U235F6 effuse than U238F6?
Problem #24b: Calculate the ratio of effusion rates for U238F6 and U235F6. Express your answer using five significant figures and as the following ratio:
rate U238F6 / rate U235F6
Problem #25: O3 effuses 0.8165 times as fast as O2. What % of the molecules effusing first would be O2?
Molar Mass Of Helium In Kg/kmol
Bonus Problem #1: HCl and NH3 diffuse through a tube and a white disc of NH4Cl is formed. Where in the tube?
Bonus Problem #2: One way of separating oxygen isotopes is by gaseous diffusion of carbon monoxide. The gaseous diffusion process behaves like an effusion process. Calculate the relative rates of effusion of:
Molar Mass Of Elements Table