Question

An unknown amount of mercury (II) oxide was decomposed in the lab. Mercury metal was formed and 5.20 L of oxygen was released at a pressure of 0.970 atm and 390.0 K. What was the initial mass of mercury oxide in the sample?

Answer 1

Answer: C) 68.0 grams

Answer 2

• 68.3g

Step-by-step explanation:

1. Word equation:

• mercury(II) oxide → mercury + oxygen

2. Balanced molecular equation:

• 2HgO → 2Hg + O₂(g)

3. Mole ratio

Write the ratio of the coefficients of the substances that are object of the problem:

`2molHgO/1molO_2`

4. Calculate the number of moles of O₂(g)

Use the equation for ideal gases:

`pV=nRT\\\\\\n=(pV)/(RT)\\\\\\n=(0.970atm*5.20L)/(0.08206atm.L/K.mol* 390.0K)\\\\\\n=0.1576mol`

5. Calculate the number of moles of HgO

`(2molHgO)/(1molO_2)* 0.1576molO_2=0.315molHgO`

6. Convert to mass

• mass = # moles × molar mass

• molar mass of HgO: 216.591g/mol

• mass = 0.315mol × 216.591g/mol = 68.3g