A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives \(3.38 \mathrm{~g}\) carbon dioxide, \(0.690 \mathrm{~g}\) of water and no other products. A volume of \(10.0\) litre (Measured at STP) of this welding gas is found to weigh \(11.6 \mathrm{~g}\). Calculate : (i) empirical formula, (ii) molar mass of the gas, and (iii) moleculat formula.

The empirical formula is the simplest representation of a compound that shows the ratio of elements present in it. It doesn't reflect the actual number of atoms but merely the ratio. For example, hydrogen peroxide's empirical formula is HO, indicating a 1:1 ratio of hydrogen to oxygen atoms.

When calculating an empirical formula from experimental data, you start by determining the mass of each element in a compound. This often involves a series of chemical reactions where you would convert the unknown compound to known compounds containing the desired elements. In the provided problem, we convert the welding gas to carbon dioxide and water, then use the mass of these products to backtrack to the original amounts of carbon and hydrogen in the welding gas.

Once you have the mass of the elements, the next step involves converting these masses to moles by dividing by the respective molar masses. Afterward, you find the mole ratio by dividing these amounts by the smallest number of moles present. This ratio provides you with the empirical formula.

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It's a bridge between the atomic, molecular world and the one we can measure in the lab because it relates a substance's mass to its amount in moles.

To determine the molar mass, you would sum the molar masses of all the atoms in the molecular formula of the substance. In the case of a compound like carbon dioxide (CO2), you would add the molar mass of one carbon atom to the molar masses of two oxygen atoms. In stoichiometric calculations, molar mass allows you to convert between the mass of a substance and the amount of substance in moles.

In our exercise, the molar mass is calculated by using the weight of a known volume of the gas at standard temperature and pressure (STP), allowing us to infer the molar mass without knowing the molecular formula first.

The molecular formula tells us the exact number of atoms of each element present in a molecule of a compound. Unlike the empirical formula, which gives the simplest ratio, the molecular formula equals the empirical formula multiplied by an integer. This integer is often determined by dividing the molar mass of the compound by the molar mass of the empirical formula.

Using the molar mass estimated from the gas's known mass and volume at STP, we compare it to the molar mass of the empirical formula. Our result will indicate how many times larger the actual molecule is compared to the empirical unit. This number, often close to an integer due to experimental error, is then used to scale up the empirical formula to the molecular formula.

The ideal gas law is a fundamental equation in chemistry and physics, connecting the temperature, pressure, volume, and amount of gas. Represented as PV=nRT, where P is pressure, V is volume, n is the amount of substance in moles, R is the ideal gas constant, and T is temperature in Kelvin.

At standard temperature and pressure (STP), which is 0°C (273.15K) and 1 atm, one mole of any ideal gas occupies 22.4 liters. This relationship allows us to determine the molar mass of a gas if we know the volume, mass, and conditions of temperature and pressure. For our exercise, the welding gas's mass measurement at given STP conditions made it possible to use the ideal gas law to calculate the molar mass of the gas.

Stoichiometry is the section of chemistry that relates quantitative relationships between the reactants and products in a chemical reaction. Stoichiometric calculations allow chemists to predict the amounts of products and reactants that are consumed or produced in a given reaction.

These calculations are based on the coefficients of a balanced chemical equation, which represent the molar ratio in which chemicals react. For the exercise, stoichiometry was used to determine the amount of carbon and hydrogen in the original gas sample from the masses of carbon dioxide and water produced. A deeper understanding of stoichiometry is crucial for anyone tackling exercises like the one ahead, as it impacts all quantitative aspects of chemistry, from the lab bench to industrial processes.