A 26.2-g sample of oxalic acid hydrate \(\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right.\). \(2 \mathrm{H}_{2} \mathrm{O}\) ) is heated in an oven until all the water is driven off. How much of the anhydrous acid is left?

To understand how to calculate the molar mass of a compound, you should begin by grasping what molar mass means. It represents the mass of one mole of a substance, expressed in grams per mole (g/mol). For instance, in the exercise, we must determine the molar mass of the hydrated form of oxalic acid, specifically \(H_{2}C_{2}O_{4}.2H_{2}O\). This involves adding the atomic masses of each individual element multiplied by their respective numbers in the formula.

For the hydrated compound, you add together the atomic masses of hydrogen (H), carbon (C), oxygen (O), and water molecules (2 \times\ H_{2}O). Using the periodic table, you obtain the atomic masses and perform the calculation:\[2 \times\ (1.01) + 2 \times\ (12.01) + 4 \times\ (16.00) + 2 \times\ (2 \times\ 1.01 + 16.00) = 126.07 \text{ g/mol}\].

When you're faced with a hydrate, like the oxalic acid hydrate in our exercise, you might want to know the proportion of the anhydrous compound to the entire hydrated form. To find this, you would divide the molar mass of the anhydrous acid by the molar mass of the hydrated acid.

In the described solution, we calculate the proportion by dividing 90.03 g/mol by 126.07 g/mol, giving us a result representing the fraction of the mass that is accounted for by the anhydrous compound:\[\frac{90.03 \text{ g/mol}}{126.07 \text{ g/mol}} = 0.714\].
This indicates that approximately 71.4% of the hydrated compound's mass is the anhydrous component. Understanding this proportion is vital when you're dealing with stoichiometric calculations in chemistry.

Stoichiometry is a core concept in chemistry that involves the quantitative relationship between reactants and products in a chemical reaction. It's based on the conservation of mass and the balanced chemical equation for the reaction. In our case, stoichiometry comes into play when determining the relationship between the hydrated and anhydrous forms of a compound during dehydration.

The stoichiometric calculation involves using the molar masses and proportions, as described in previous steps, to calculate the mass of anhydrous oxalic acid obtainable from a known mass of the hydrated form. By multiplying the proportion of the anhydrous compound by the total mass of the hydrated compound, stoichiometry allows us to predict the mass of anhydrous acid left after dehydration.

In chemistry, a dehydration reaction is a chemical reaction that involves the removal of water molecules from a substance. It's crucial in converting hydrated compounds to their anhydrous counterparts. In the context of our exercise, heating oxalic acid hydrate causes the water molecules to evaporate, leaving behind anhydrous oxalic acid.

The amount of anhydrous compound obtainable after such a reaction can be calculated by applying stoichiometric principles. By taking the initial mass of the hydrated substance and multiplying it by the previously calculated proportion of the anhydrous component within it, one can determine the final mass of the anhydrous compound. It's a straightforward yet fundamental application of stoichiometry in understanding dehydration reactions.