A piece of an unknown metal weighing 0.215 g is dissolved in concentrated hydroc

Question

A piece of an unknown metal weighing 0.215 g is dissolved in concentrated hydrochloric acid, producing 81.5 mL of hydrogen gas, which was collected in a container over water. The temperature of the water was 22°C, and the external barometric pressure was 30.05 inHg. (The vapor pressure of water at 22°C is 19.8 Torr.)

a) How many moles of hydrogen are produced?

b) Assuming that 1 mole of metal produces 1 mole of hydrogen gas, what is the molar mass of the metal?

c) What is the most likely identity of the metal?

Explanation / Answer

(a)

Volume = 81.5 mL = 0.0815 L

Barometric Pressure = 30.05 inHg = 30.05 * 25.4 mmHg = 763.3 mmHg

Pressure of H2 gas = 763.3 - 19.8 = 743.5 mmHg = 743.5 / 760 = 0.978 atm

R = 0.0821 L.atm.K-1.mol-1

T = 22 + 273 = 295 K

Ideal gas equation,

P V = n R T
n = 0.978 * 0.0815 / ( 0.0821 * 295 )

n = 0.00329 mol

(b)

Moles of metal = moles of H2 = 0.00329 mol

Molar mass = mass / moles = 0.215 / 0.00329 = 65.3 g/mol

(c)

The metal may be Zinc (Zn)

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.