How would you prepare the following substances by a precipitation reaction? (b) Mg3(PO4)2

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Step 1: Identify two soluble compounds that contain the ions you need. In this case, we need Mg2+ and PO4^3-. A possible choice could be MgCl2 and Na3PO4, both of which are soluble in water.

Step 2: Write down the balanced chemical equation for the reaction. The equation is: 3MgCl2(aq) + 2Na3PO4(aq) -> Mg3(PO4)2(s) + 6NaCl(aq).

Step 3: Mix the solutions of the two compounds. The Mg2+ ions from the MgCl2 will react with the PO4^3- ions from the Na3PO4 to form Mg3(PO4)2, which is insoluble and will precipitate out of the solution.

Step 4: Separate the precipitate from the solution. This can be done by filtration. The solid Mg3(PO4)2 will remain on the filter, while the soluble NaCl will pass through.

Step 5: Dry the precipitate to obtain the pure Mg3(PO4)2.

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Key Concepts

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

Precipitation Reaction

A precipitation reaction occurs when two soluble salts react in solution to form an insoluble product, known as a precipitate. This process typically involves the exchange of ions between the reactants, leading to the formation of a solid that separates from the liquid phase. Understanding the solubility rules is crucial for predicting whether a precipitate will form.

Solubility Rules

Solubility rules are guidelines that help predict the solubility of various ionic compounds in water. For example, most phosphates are insoluble except for those of alkali metals and ammonium. Knowing these rules allows chemists to determine which reactants will yield a precipitate when mixed, which is essential for preparing compounds like Mg3(PO4)2.

Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between positively charged cations and negatively charged anions. In the case of Mg3(PO4)2, magnesium ions (Mg²⁺) and phosphate ions (PO4³⁻) combine in a specific ratio to create a neutral compound. Understanding the composition and stoichiometry of ionic compounds is vital for successfully conducting precipitation reactions.

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