Question

The molecular weight of a gas that has a density of 5.75 g/l at stp is __________ g/mol.

Answer 1

Answer : The molecular weight of a gas is, 128.9 g/mole

Explanation : Given,

Density of a gas = 5.75 g/L

First we have to calculate the moles of gas.

At STP,

As, 22.4 liter volume of gas present in 1 mole of gas

So, 1 liter volume of gas present in $\frac{1}{22.4}=0.0446$ mole of gas

Now we have to calculate the molecular weight of a gas.

Formula used :

$\text{Moles of gas}=\frac{\text{Mass of a gas}}{\text{Molecular weight of a gas}}$

Now put all the given values in this formula, we get the molecular weight of a gas.

$0.0446mole=\frac{5.75g}{\text{Molecular weight of a gas}}$

$\text{Molecular weight of a gas}=128.9g/mole$

Therefore, the molecular weight of a gas is, 128.9 g/mole

Answer 2

128.8 g/mole.

Further explanation

Given:

Density of a gas = 5.75 g/l at STP

Question:

The molecular weight of this gas (in g/mol)

The Process:

This is a stoichiometric calculation.We will find out the molecular weight (or molar mass) of the gas measured at STP with known density.

Remember at STP 1 mole of gas = 22.4 L or referred to as a molar volume.

From the value of the gas density, we know that 1 L of gas has a mass of 5.75 g.

• Volume of gas = 1 L
• Mass of gas = 5.75 g
• Molar volume = 22.4 L/mole

The relationship between the mole (n), mass (m), molecular weight (M), volume (V), and molar volume (Vm) is as follows:

$\boxed{ \ n = \frac{V}{V_m} \ } \ and \ \boxed{ \ n = \frac{mass}{molecular \ weight} \ } \rightarrow \boxed{\boxed{ \ \frac{mass}{molecular \ weight} = \frac{V}{V_m} \ }}$

Let us calculate the molecular weight.

$\boxed{ \ \frac{m}{M} = \frac{V}{V_m} \ }$

$\boxed{ \ M = \frac{m \times V_m}{V} \ }$

$\boxed{ \ M = \frac{5.75 \times 22.4}{1} \ }$

$\boxed{\boxed{ \ M = 128.8 \ }}$

Thus the molecular weight of a gas that has a density of 5.75 g/L at STP equal to 128.8 g/mole.

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Notes:

• STP (in chemistry) is the abbreviation for Standard Temperature and Pressure, i.e., 273 K (0° Celsius or 32° Fahrenheit) and 1 atm.
• Remember the mole number of a substance can be found via mass, volume, or number of particles.

Learn more

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2. Conservation of mass brainly.com/question/9473007  
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