**Calculating the Mass of CO2 Gas at STP**

To calculate the mass of CO2 gas at STP (Standard Temperature and Pressure), we need to use the ideal gas law and the molar mass of CO2.

The ideal gas law is given by the equation PV = nRT, where:
- P is the pressure of the gas (in this case, it is STP, which is 1 atm)
- V is the volume of the gas (112 L in this case)
- n is the number of moles of gas
- R is the ideal gas constant (0.0821 L·atm/mol·K)
- T is the temperature of the gas (STP temperature is 273.15 K)

We can rearrange the ideal gas law to solve for n, the number of moles of gas:
n = PV / RT

Given that the molecular mass of CO2 is 44 g/mol, we can calculate the mass of CO2 gas using the formula:
mass = n × molar mass

**Calculating the Number of Molecules of CO2**

To calculate the number of molecules of CO2, we need to use Avogadro's number, which is 6.022 × 10^23 molecules/mol.

The number of molecules can be calculated using the formula:
number of molecules = number of moles × Avogadro's number

Now, let's perform the calculations step by step:

1. Calculate the number of moles of CO2 gas:
n = (1 atm) × (112 L) / [(0.0821 L·atm/mol·K) × (273.15 K)]
n = 5.02 moles

2. Calculate the mass of CO2 gas:
mass = 5.02 moles × (44 g/mol)
mass = 221.88 g

3. Calculate the number of molecules of CO2:
number of molecules = 5.02 moles × (6.022 × 10^23 molecules/mol)
number of molecules = 3.02 × 10^24 molecules

Therefore, the mass of 112 L of CO2 gas at STP is 221.88 g, and the number of molecules present in it is approximately 3.02 × 10^24 molecules.