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Ch.4 - Chemical Quantities & Aqueous Reactions
Tro - Chemistry: A Molecular Approach 4th Edition
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All textbooksTro 4th EditionCh.4 - Chemical Quantities & Aqueous ReactionsProblem 91c
Chapter 4, Problem 91c

Complete and balance each gas-evolution equation. c. HBr(aq) + Na2S(aq) →

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Identify the reactants: Hydrobromic acid (HBr) and sodium sulfide (Na2S).
Determine the products: When an acid reacts with a sulfide, hydrogen sulfide gas (H2S) is typically evolved, along with a salt. In this case, the salt is sodium bromide (NaBr).
Write the unbalanced chemical equation: HBr(aq) + Na2S(aq) → H2S(g) + NaBr(aq).
Balance the equation: Start by balancing the number of sodium (Na) atoms, then balance the bromine (Br) atoms, and finally ensure the hydrogen (H) and sulfur (S) atoms are balanced.
Verify the balanced equation: Check that the number of each type of atom is the same on both sides of the equation and that the charges are balanced.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gas-Evolution Reactions

Gas-evolution reactions are chemical reactions that produce a gas as one of the products. These reactions often involve the combination of an acid with a sulfide, carbonate, or bicarbonate, leading to the release of gases such as H2S, CO2, or NH3. Understanding the nature of the reactants and the expected gaseous products is crucial for predicting the outcome of these reactions.

Balancing Chemical Equations

Balancing chemical equations is the process of ensuring that the number of atoms for each element is the same on both the reactant and product sides of the equation. This is achieved by adjusting the coefficients of the compounds involved. A balanced equation reflects the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
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Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between reactants. In the case of HBr and Na2S, HBr acts as an acid, donating a proton, while Na2S, containing the sulfide ion (S2-), can accept protons. Recognizing the roles of acids and bases in a reaction helps in predicting the products formed, including any gases that may evolve.
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