1) 1.12 dm3 of a gas at STP is found to weigh 3.55g.Find molecular weight and vapour density of gas

2)5.6 dm3 of a gas at STP weighs 11g Find out its relative molecular mass & vapour density

1.

n = mols of gas = 1.12/22.4 = ?
n = grams/molar mass. You have grams and n, solve for molar mass.

Then vapor density = molar mass/molar mass H2 = molar mass/2.016 = ?

2. See #1.

To find the molecular weight and vapor density of a gas, we need to use the ideal gas law equation. The ideal gas law equation is given as:

PV = nRT

Where:
P = pressure of the gas
V = volume of the gas
n = number of moles of gas
R = ideal gas constant
T = temperature of the gas

For both problems, we are provided with the volume, pressure, and temperature. The pressure and temperature are given as STP, which means the pressure is 1 atmosphere (atm) and the temperature is 273.15 Kelvin (K).

1) To find the molecular weight and vapor density of the gas for the first problem:
Given:
Volume (V) = 1.12 dm3
Weight (m) = 3.55 g
Pressure (P) = 1 atm
Temperature (T) = 273.15 K

Step 1: Convert the volume to liters:
1 dm3 = 1 liter
1.12 dm3 = 1.12 liters

Step 2: Convert the weight to moles:
To convert grams to moles, we need to use the molar mass of the gas. We can find the molar mass (M) using the formula:

M = m/n

Where:
m = mass of the gas (in grams)
n = number of moles of the gas

In this problem, m = 3.55 g.

Step 3: Calculate the number of moles (n):
n = m/M

Step 4: Use the ideal gas law equation to solve for the molecular weight (M):
PV = nRT
M = (mRT) / (P*V)

Substituting the values we have:
M = (3.55 g * 0.0821 L.atm/mol.K * 273.15 K) / (1 atm * 1.12 L)

Simplifying the equation will give you the molecular weight of the gas.

To find the vapor density, you need to divide the molecular weight by 2, as vapor density is defined as the mass of one mole of a gas divided by the mass of one mole of hydrogen gas.

2) Similarly, for the second problem:
Given:
Volume (V) = 5.6 dm3
Weight (m) = 11 g
Pressure (P) = 1 atm
Temperature (T) = 273.15 K

Follow the same steps as mentioned above to find the relative molecular mass and vapor density of the gas.

Remember, to get accurate results, it is essential to use the correct units and values in the calculations.