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A 7.337 gram sample of chromium is heated in the presence of excess oxygen. A metal oxide is formed with a mass of 9.595 g. Determine
the empirical formula of the metal oxide.

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Answer:

Empirical formula is CrO

Explanation:

We are given;

  • Mass of sample of Chromium as 7.337 gram
  • Mass of the metal oxide formed as 9.595 g

We are required to determine the empirical formula of the metal oxide.

Step 1 ; Determine the mass of oxygen used

Mass of oxygen = Mass of the metal oxide - mass of the metal

                          = 9.595 g - 7.337 g

                         = 2.258 g

Step 2: Determine the moles of chromium and oxygen

Moles of chromium metal

Molar mass of chromium = 51.996 g/mol

Moles of Chromium = 7.337 g ÷ 51.996 g/mol

                                 = 0.141 moles

Moles of oxygen

Molar mass of oxygen = 16.0 g/mol

Moles of Oxygen = 2.258 g ÷ 16.0 g/mol

                            = 0.141 moles

Step 3: Determine the simplest mole number ratio of Chromium to Oxygen

Mole ratio of Chromium to Oxygen

          Cr : O

0.141 mol : 0.141 mol

             1 : 1

Empirical formula is the simplest whole number ratio of elements in a compound.

Thus the empirical formula of the metal oxide is CrO

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