Problem 107 - Chemistry Matter and Change

Question

Write skeleton equations for the following reactions. a. ammonium phosphate(aq) \(+\) chromium(III) bromide(aq) \(\rightarrow\) ammonium bromide (aq) \(+\) chromium (III) phosphate(s) b. chromium(VI) hydroxide(s) \(\rightarrow\) chromium (VI) oxide(s) \(+\) water ( \((1)\) c. aluminum(s) \(+\) copper \((1)\) chloride (aq) \(\rightarrow\) aluminum chloride(aq) \(+\) copper \((s)\) d. potassium iodide(aq) \(+\) mercury (I) nitrate(aq) \(\rightarrow\) potassium nitrate(aq) \(+\) mercury (I) iodide(s)

Step-by-Step Solution

Answer

\[(NH_4)_3PO_4(aq) + CrBr_3(aq) \rightarrow NH_4Br(aq) + CrPO_4(s)\] \[Cr(OH)_6(s) \rightarrow CrO_3(s) + H_2O(l)\] \[Al(s) + CuCl(aq) \rightarrow AlCl_3(aq) + Cu(s)\] \[KI(aq) + Hg_2(NO_3)_2(aq) \rightarrow KNO_3(aq) + Hg_2I_2(s)\]

Step 1: Reaction A: ammonium phosphate + chromium(III) bromide → ammonium bromide + chromium(III) phosphate

Identify the compounds and their chemical formulas: - ammonium phosphate: (NH₄)₃PO₄ (aqueous) - chromium(III) bromide: CrBr₃ (aqueous) - ammonium bromide: NH₄Br (aqueous) - chromium(III) phosphate: CrPO₄ (solid) Now write the skeleton equation: \[(NH_4)_3PO_4(aq) + CrBr_3(aq) \rightarrow NH_4Br(aq) + CrPO_4(s)\]

Step 2: Reaction B: chromium(VI) hydroxide → chromium(VI) oxide + water

Identify the compounds and their chemical formulas: - chromium(VI) hydroxide: Cr(OH)₆ (solid) - chromium(VI) oxide: CrO₃ (solid) - water: H₂O (liquid) Now write the skeleton equation: \[Cr(OH)_6(s) \rightarrow CrO_3(s) + H_2O(l)\]

Step 3: Reaction C: aluminum + copper(I) chloride → aluminum chloride + copper

Identify the compounds and their chemical formulas: - aluminum: Al (solid) - copper(I) chloride: CuCl (aqueous) - aluminum chloride: AlCl₃ (aqueous) - copper: Cu (solid) Now write the skeleton equation: \[Al(s) + CuCl(aq) \rightarrow AlCl_3(aq) + Cu(s)\]

Step 4: Reaction D: potassium iodide + mercury(I) nitrate → potassium nitrate + mercury(I) iodide

Identify the compounds and their chemical formulas: - potassium iodide: KI (aqueous) - mercury(I) nitrate: Hg₂(NO₃)₂ (aqueous) - potassium nitrate: KNO₃ (aqueous) - mercury(I) iodide: Hg₂I₂ (solid) Now write the skeleton equation: \[KI(aq) + Hg_2(NO_3)_2(aq) \rightarrow KNO_3(aq) + Hg_2I_2(s)\]

Key Concepts

Chemical Reactions

Imagine a delightful dance where partners swap to create new couples - that's a bit like a chemical reaction. It's a process where substances, known as reactants, transform into new substances called products. This happens because the atoms in the reactants exchange partners due to chemical bonds breaking and forming. For example, when baking soda reacts with vinegar, they form carbon dioxide, water, and sodium acetate - totally different from what you started with!
Chemical reactions can be simple, like the fizz when an antacid tablet is dropped in water, or complex, like the countless reactions taking place inside your body every second. The key takeaway is that during these reactions, atoms aren't created or destroyed; they're merely rearranged, following the law of conservation of mass.
In the given exercises, we see different types of chemical reactions – combinations, decompositions, single replacements, and double replacements – each illustrating the dance of atoms in their unique way.

Chemical Formulas

If you ever need to decode the tiny letters and numbers scribbled beside chemicals, you're looking at chemical formulas. They are the shorthand notations that tell us the type and number of atoms in a compound. These formulas, like recipes, let us peek into the compositions of substances. Take water (H₂O), for example; its chemical formula tells us that each molecule consists of two hydrogen atoms and one oxygen atom.
Understanding the symbols (representing elements) and the subscripts (telling how many of each element) are crucial. In our exercise, compounds like chromium(VI) hydroxide (Cr(OH)₆) need you to pay attention not just to the Cr and O, but also the 'little' 6 that makes a big difference. That subscript means six hydroxide groups attached to one chromium atom!
Remember, getting the formulas right is the foundation for writing correct skeleton equations and finding solutions to our chemical equations puzzle.

Balanced Chemical Equations

Balancing a chemical equation is much like balancing a seesaw – both sides must be equal to achieve harmony. It's a step beyond writing skeleton equations, as it involves ensuring that the number of atoms for each element is the same on both sides of the arrow. This is to obey the law of conservation of mass, which tells us that matter cannot appear out of thin air or vanish into it.
A skeleton equation is like the outline of a story, and when we balance it, we fill in the details to tell the complete tale. For instance, the reaction between aluminum and copper(I) chloride is unbalanced in its skeletal form, but when we adjust the coefficients – the numbers placed before the chemical formulas – we make sure the atoms on both sides tally. The balanced equation confirms that no atoms were lost or gained, just shuffled around to create new substance alliances.
Balancing is an essential skill in chemistry because it represents the actual quantities we need for a reaction to occur as planned, and as science reminds us, precision is key!