When magnesium chloride (MgCl₂) is dissolved in water, it dissociates into magnesium ions (Mg²⁺) and chloride ions (Cl⁻). The correct statements regarding this dissolution process are as follows:
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The sum of the mass of the Mg ions and the mass of the Cl ions must be equal to the mass of MgCl₂. - This statement is true, as the law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction.
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The sum of the number of moles of the Mg ions and the number of moles of the Cl ions must be equal to the number of moles of MgCl₂. - This statement is false. Upon dissolving, 1 mole of MgCl₂ produces 1 mole of Mg²⁺ and 2 moles of Cl⁻, totaling 3 moles of ions, which is not equal to the 1 mole of MgCl₂.
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The mass of the Mg ions and the mass of the Cl ions must each be equal to the mass of MgCl₂. - This statement is false. The mass of the Mg ions and the mass of the Cl ions are parts of the total mass of the dissolved MgCl₂, and individually, they are not equal to the mass of MgCl₂.
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The number of moles of the Mg ions and the number of moles of the Cl ions must each be equal to the number of moles of MgCl₂. - This statement is also false for the same reason as in statement 2. Specifically, the number of moles of Cl⁻ will be double compared to the moles of Mg²⁺ produced.
Therefore, the only true statement is:
The sum of the mass of the Mg ions and the mass of the Cl ions must be equal to the mass of MgCl₂.
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