Question

Thionyl chloride, \(\mathrm{SOCl}_{2}\), is used as a very powerful drying agent in many synthetic chemistry experiments in which the presence of even small amounts of water would be detrimental. The unbalanced chemical equation is $$\mathrm{SOCl}_{2}(l)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{SO}_{2}(g)+\mathrm{HCl}(g)$$ Calculate the mass of water consumed by complete reaction of \(35.0 \mathrm{g}\) of \(\mathrm{SOCl}_{2}\).

Short answer

The mass of water consumed by the complete reaction of 35.0 g of SOCl2 is 2.65 g.

Step-by-step solution

Balance the chemical equation

To balance the chemical equation, we need to make sure that there are equal numbers of each type of atom on both sides of the equation. The balanced equation is: \(2 \mathrm{SOCl}_{2}(l)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2\mathrm{SO}_{2}(g)+2\mathrm{HCl}(g)\)

Determine the mole-to-mole ratio between SOCl2 and H2O

From the balanced chemical equation, the mole-to-mole ratio between SOCl2 and H2O is 2:1. This means that for every 2 moles of SOCl2 reacting, 1 mole of H2O is consumed.

Use stoichiometry to find the moles of H2O that would be consumed in the complete reaction

First, we need to find the moles of SOCl2 in the given mass. We know that the molar mass of SOCl2 is approximately: \(M_{\mathrm{SOCl_{2}}} = 32.1 \, \text{(S)} + 16.0 \, \text{(O)} + 2 \times 35.5 \, \text{(Cl)} = 119.0\,\mathrm{g/mol}\) Now we can find the moles of SOCl2 in 35.0 grams: \(\text{moles of } \mathrm{SOCl_{2}} = \frac{\text{mass of } \mathrm{SOCl_{2}}}{\text{molar mass of }\mathrm{SOCl_{2}}} = \frac{35.0\,\mathrm{g}}{119.0\,\mathrm{g/mol}} = 0.294\,\mathrm{mol}\) Using the mole-to-mole ratio, we can find the moles of H2O that would be consumed in the complete reaction: \(\text{moles of }\mathrm{H_{2}O} = \frac{1}{2} \times \text{moles of }\mathrm{SOCl_{2}} = \frac{1}{2} \times 0.294\,\mathrm{mol} = 0.147\,\mathrm{mol}\)

Convert the moles of H2O to grams

We know that the molar mass of H2O is approximately: \(M_{\mathrm{H_{2}O}} = 2 \times 1.0 \, \text{(H)} + 16.0 \, \text{(O)} =18.0\,\mathrm{g/mol}\) Finally, we can find the mass of H2O consumed in the reaction: \(\text{mass of }\mathrm{H_{2}O} = \text{moles of }\mathrm{H_{2}O} \times \text{molar mass of }\mathrm{H_{2}O} = 0.147\,\mathrm{mol} \times 18.0\,\mathrm{g/mol} = 2.65\,\mathrm{g}\) So, the mass of water consumed by the complete reaction of 35.0 g of SOCl2 is 2.65 g.

Key concepts

Chemical Equation Balancing

One of the fundamental skills in stoichiometry is balancing chemical equations. It demands that we have the same number of each type of atom on both sides of the reaction. Here's how to tackle this: list out all the elements involved in the reaction, count the number of atoms for each element on both sides, and then add coefficients (the numbers in front of molecules) to balance the atoms. For example, our thionyl chloride equation starts unbalanced but becomes balanced by placing the coefficient '2' in front of both SOCl₂ and the products SO₂ and HCl, signifying that two molecules of thionyl chloride react with one molecule of water to produce two molecules each of sulfur dioxide and hydrogen chloride gas.

This process ensures that the law of conservation of mass is obeyed, indicating that no atoms are lost or gained during a chemical reaction. Without this step, stoichiometric calculations would not be possible as the ratio of reactants to products would be unclear.

Mole-to-Mole Ratio

When we've balanced our chemical equation, we can deduce the mole-to-mole ratio, which is pivotal in predicting the amount of reactants or products involved in a reaction. It is derived directly from the coefficients in the balanced equation. For instance, in our balanced equation for the reaction of SOCl₂ with H₂O, a 2:1 ratio exists between SOCl₂ and H₂O. This means for every 2 moles of thionyl chloride, you'll need 1 mole of water for the reaction to happen with no leftovers.

Understanding this ratio is essential for converting between moles of different substances in a chemical reaction. It allows us to predict how much of each reactant is needed and how much of each product will be formed under ideal conditions.

Molar Mass Calculation

Molar mass acts as a bridge between the microscopic world of atoms and molecules and the macroscopic world we can measure and observe. To calculate the molar mass, sum up the atomic masses of all atoms in a molecule. For instance, the molar mass of SOCl₂ is calculated by adding the atomic masses of sulfur, oxygen, and two chlorines. Similarly, the molar mass of water, H₂O, is the sum of the atomic masses of two hydrogens and one oxygen.

In our exercise, knowing the molar mass of both SOCl₂ and H₂O is crucial to convert their masses in grams to an amount in moles, laying the groundwork for further stoichiometric calculations. Without accurate molar mass, these conversions would lead to incorrect results.

Stoichiometric Calculations

Once we've balanced our equation and understood the mole-to-mole ratios, we can perform stoichiometric calculations. These calculations enable us to quantify the reactants and products involved in chemical reactions. By converting the mass of a reactant to moles using its molar mass, applying the mole-to-mole ratio from the balanced equation, and then converting back to mass if necessary, we can solve a myriad of stoichiometry problems.

In our specific case, we're tasked with calculating the mass of water consumed by reacting 35.0 g of SOCl₂. We start by finding the number of moles of SOCl₂ using its molar mass. Then the mole-to-mole ratio guides us to the moles of H₂O involved. Finally, by multiplying the moles of H₂O by its molar mass, we obtain the mass of water used. Stoichiometric calculations are the heart of quantitative analysis in chemistry, allowing us to make precise predictions about chemical reactions.