Chemistry, 14.12.2020 15:30 thu651777p0vibf

Calculate the molar mass of a gas with a mass of 3.15 g, a pressure of 785 mmHg, and a temperature of 20 Celsius. The gas has a volume of 750 ml.

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Answer from: huntbuck14

Molar mass = 105 g/mol

Explanation:

Given data:

Mass of gas = 3.15 g

Pressure = 785 mmHg

Temperature = 20°C

Volume of gas = 750 mL

Molar mass of gas = ?

Solution:

Pressure = 785 mmHg (785/760 = 1 atm)

Temperature = 20°C (20+273 = 293 K)

Volume of gas = 750 mL (750 mL× 1 L/1000 mL = 0.75 L)

PV = nRT

R = general gas constant (0.0821 atm.L/mol.K)

1 atm× 0.75 L = n×0.0821 atm.L/mol.K × 293 K)

0.75 atm.L = n× 24.06 atm.L/mol

n = 0.75 atm.L / 24.06 atm.L/mol

n = 0.03 mol

Molar mass of gas:

Molar mass = Mass / number of moles

Molar mass = 3.15 g/ 0.03 mol

Molar mass = 105 g/mol

Answer from: Quest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.