Chapter 4: Problem 93
Sodium sulfide and hydrochloric acid react to form a gas. Write the balanced molecular and net ionic equation for the reaction.
Short Answer
Expert verified
Balanced molecular equation: Na2S(aq) + 2HCl(aq) → H2S(g) + 2NaCl(aq). Net ionic equation: S^2-(aq) + 2H+(aq) → H2S(g).
Step by step solution
01
Write the Unbalanced Molecular Equation
Write down the reactants and products in their molecular form. The reactants are sodium sulfide (Na2S) and hydrochloric acid (HCl). The products of the reaction include hydrogen sulfide gas (H2S) and sodium chloride (NaCl), a salt. The unbalanced molecular equation is: Na2S(aq) + HCl(aq) → H2S(g) + NaCl(aq).
02
Balance the Molecular Equation
Balance the elements in the molecular equation. You need two HCl molecules for every Na2S molecule to balance the sodium (Na) and chloride (Cl) ions. The balanced molecular equation is: Na2S(aq) + 2HCl(aq) → H2S(g) + 2NaCl(aq).
03
Write and Balance the Net Ionic Equation
Break down all strong electrolytes (compounds that dissociate completely in solution) into their ions. HCl, NaCl, and Na2S are strong electrolytes, but H2S is not because it is a gas. Write the net ionic equation by removing the spectator ions (ions that do not participate in the reaction), which in this case are the sodium ions (Na+). The net ionic equation is: S^2-(aq) + 2H+(aq) → H2S(g).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molecular Equations
Understanding molecular equations is a vital part of learning chemistry, as they lay the groundwork for visualizing reactions. Molecular equations provide a way to represent chemical reactions using the formulae of the substances involved, presented as if they were molecules even in cases where they actually exist as ions in solution.
A molecular equation looks at the overall process without delving into the details of which ions are present. When writing a molecular equation, one of the most important factors to consider is balancing it correctly to adhere to the law of conservation of mass. This states that atoms are neither created nor destroyed in a chemical reaction.
To balance a molecular equation, count the atoms of each element in the reactants and products and use coefficients to equalize them. Keep in mind that coefficients in chemical equations represent the number of moles of a substance, a measure of chemical quantity. For instance, when sodium sulfide reacts with hydrochloric acid, the balanced molecular equation is: \( \text{Na}_2\text{S(aq)} + 2\text{HCl(aq)} \rightarrow \text{H}_2\text{S(g)} + 2\text{NaCl(aq)} \). The balancing reflects an accurate depiction of the quantities and substances involved in the reaction.
A molecular equation looks at the overall process without delving into the details of which ions are present. When writing a molecular equation, one of the most important factors to consider is balancing it correctly to adhere to the law of conservation of mass. This states that atoms are neither created nor destroyed in a chemical reaction.
To balance a molecular equation, count the atoms of each element in the reactants and products and use coefficients to equalize them. Keep in mind that coefficients in chemical equations represent the number of moles of a substance, a measure of chemical quantity. For instance, when sodium sulfide reacts with hydrochloric acid, the balanced molecular equation is: \( \text{Na}_2\text{S(aq)} + 2\text{HCl(aq)} \rightarrow \text{H}_2\text{S(g)} + 2\text{NaCl(aq)} \). The balancing reflects an accurate depiction of the quantities and substances involved in the reaction.
Net Ionic Equations
Net ionic equations strip a chemical reaction down to only the particles that participate in the change, removing the spectator ions that do not change during the course of the reaction. These equations are particularly useful in predicting the outcomes of precipitation, acid-base, and oxidation-reduction reactions.
To write a net ionic equation, you first need to understand which substances dissociate into ions in solution and which stay intact. For the reaction of sodium sulfide and hydrochloric acid, all reactants and products except hydrogen sulfide are strong electrolytes and hence, dissociate completely in aqueous solutions. The sodium ions, \( \text{Na}^+ \), do not participate in the formation of the hydrogen sulfide gas and are thus considered spectator ions.
The net ionic equation for this reaction shows only the sulfide ions reacting with the hydrogen ions to produce hydrogen sulfide gas: \( \text{S}^{2-}(\text{aq}) + 2\text{H}^+(\text{aq}) \rightarrow \text{H}_2\text{S(g)} \). This compact representation provides clear insight into the actual chemical change occurring in the reaction, which aids in predicting and understanding chemical behavior.
To write a net ionic equation, you first need to understand which substances dissociate into ions in solution and which stay intact. For the reaction of sodium sulfide and hydrochloric acid, all reactants and products except hydrogen sulfide are strong electrolytes and hence, dissociate completely in aqueous solutions. The sodium ions, \( \text{Na}^+ \), do not participate in the formation of the hydrogen sulfide gas and are thus considered spectator ions.
The net ionic equation for this reaction shows only the sulfide ions reacting with the hydrogen ions to produce hydrogen sulfide gas: \( \text{S}^{2-}(\text{aq}) + 2\text{H}^+(\text{aq}) \rightarrow \text{H}_2\text{S(g)} \). This compact representation provides clear insight into the actual chemical change occurring in the reaction, which aids in predicting and understanding chemical behavior.
Reaction Stoichiometry
Reaction stoichiometry refers to the quantitative relationship between reactants and products in a chemical reaction. It boils down to the simple question: How much of each substance is involved? Stoichiometry uses the mole concept (Avogadro’s number, 6.022×10^23 particles per mole) as the common measure to link the mass of substances to the number of particles in a chemical equation.
Stoichiometry is essential for determining the amounts of products that can be formed from given reactants, or conversely, the amounts of reactants needed to produce a certain amount of product—the very heart of chemical manufacturing and laboratory work. For example, in the reaction between sodium sulfide and hydrochloric acid, stoichiometry dictates that one mole of sodium sulfide reacts with two moles of hydrochloric acid to yield one mole of hydrogen sulfide and two moles of sodium chloride.
Understanding reaction stoichiometry allows scientists to make precise calculations and predictions regarding the outcomes of chemical reactions, ensuring that no reactants go to waste and that reactions proceed efficiently. Such calculations hinge upon a balanced chemical equation, as seen with \( \text{Na}_2\text{S(aq)} + 2\text{HCl(aq)} \rightarrow \text{H}_2\text{S(g)} + 2\text{NaCl(aq)} \), which permits the precise scaling of reactions to any desired size.
Stoichiometry is essential for determining the amounts of products that can be formed from given reactants, or conversely, the amounts of reactants needed to produce a certain amount of product—the very heart of chemical manufacturing and laboratory work. For example, in the reaction between sodium sulfide and hydrochloric acid, stoichiometry dictates that one mole of sodium sulfide reacts with two moles of hydrochloric acid to yield one mole of hydrogen sulfide and two moles of sodium chloride.
Understanding reaction stoichiometry allows scientists to make precise calculations and predictions regarding the outcomes of chemical reactions, ensuring that no reactants go to waste and that reactions proceed efficiently. Such calculations hinge upon a balanced chemical equation, as seen with \( \text{Na}_2\text{S(aq)} + 2\text{HCl(aq)} \rightarrow \text{H}_2\text{S(g)} + 2\text{NaCl(aq)} \), which permits the precise scaling of reactions to any desired size.
