Stoichiometry And Stoichiometric Calculations

We need to find the number of oxygen atoms in 0.36 g of water (H₂O). The condition "at STP" (Standard Temperature and Pressure) typically refers to gases and is irrelevant here for calculating the number of atoms in a given mass of liquid water. (A) Calculate the molar mass of water (H₂O):

Molar Mass = 2 (Atomic mass of H) + 1 (Atomic mass of O)
Molar Mass 2 (1.008 g/mol) + 1 (16.00 g/mol)
Molar Mass 18.016 g/mol (often approximated as 18 g/mol for calculations like this). Let's use 18 g/mol. (B) Calculate the number of moles of water:

Moles =
Moles = = 0.02 mol (C) Calculate the number of water molecules:

Number of molecules = Moles Avogadro's number (N_A)
Number of molecules = 0.02 mol (6.022 10²³ molecules/mol)
Number of molecules = molecules (D) Calculate the number of oxygen atoms:

Each molecule of water (H₂O) contains exactly one oxygen atom.
Number of oxygen atoms = Number of water molecules (1 oxygen atom / molecule)
Number of oxygen atoms = atoms Rounding this value to match the options gives oxygen atoms. This corresponds to option (B).

Given:
- Mass of gas in cylinder when full:
- Mass of gas remaining in the cylinder:
- Pressure of gas when full:
- Temperature during usage:
To find the volume of the used gas at normal usage conditions, we can use the ideal gas law: Steps for solving ideal gas law problem First, we calculate the number of moles of butane gas used: Molar mass of butane (C\textsubscript{4}H\textsubscript{10}) = 58 g/mol = 0.058 kg/mol.
Thus, the number of moles of butane used is: Now, use the ideal gas law to calculate the volume of the gas at standard conditions (1 atm, 27°C = 300 K): Where: - (the gas constant) - (temperature in Kelvin) - (pressure at normal usage) Substitute the values into the equation: Hence, the volume of the used gas is .