Stoichiometry

The correct answer is B, sodium carbonate (Na₂​CO₃​).

Let’s check each option based on the correct chemical formulas and naming conventions:

• A. Cobalt(II) chloride: The correct formula for cobalt(II) chloride is CoCl₂​. The Roman numeral (II) indicates that cobalt has a charge of +2 (Co²⁺). Since chloride ions have a -1 charge (Cl−), two chloride ions are needed to balance the charge.
• B. Sodium carbonate: The sodium ion has a +1 charge (Na+). The carbonate ion has a -2 charge (CO₃²⁻​). To balance the charges, you need two sodium ions for every one carbonate ion, making the correct formula Na₂​CO₃​.
• C. Xenon: Xenon is a noble gas and exists as individual atoms. Its formula is simply Xe, not Xe₂​. Noble gases are monatomic.
• D. Ammonium sulfate: The ammonium ion has a +1 charge (NH⁴⁺​). The sulfate ion has a -2 charge (SO₄²⁻​). To balance the charges, you need two ammonium ions for every one sulfate ion. The correct formula is (NH₄​)₂​SO₄​.

1. Calculate the number of moles of magnesium carbonate (MgCO₃​).

• The formula for calculating moles is: moles= Given Mass / Mr​
• Mass of MgCO₃​ = 21.0g.
• The relative formula mass (Mr​) of MgCO3​ = 84.
• moles of MgCO3​=21.0 g / 84 g/mol ​= 0.25 mol

1. Determine the mole ratio between the reactant and product.

• The balanced chemical equation is: MgCO3​→MgO+CO2​
• The ratio of MgCO3​ to MgO is 1:1.
• This means that for every 1 mole of MgCO3​ that decomposes, 1 mole of MgO is formed.
• Therefore, 0.25 moles of MgCO3​ will produce 0.25 moles of MgO.

1. Calculate the mass of magnesium oxide (MgO) formed.

• First, find the relative formula mass (Mr​) of MgO.
• Mr​ of MgO=24+16=40
• Now, use the moles and Mr​ to find the mass: mass=moles×Mr​
• mass of MgO = 0.25 mol × 40 g/mol = 10.0 g