Question

3. When 0.275 moles of Strontium metal and hydrochloric acid that contains 0.750 mol of HCl are combined they react to completion according to the equation below. How many liters of hydrogen gas, are produced at standard temperature and pressure (STP)?

Sr(s) + 2HCl(aq) → SrCl2(aq) + H2(g)

A. 6.2 L

B. 11.2 L

C.

4.5 L

D. 2.4 L

Answer 1

Moles of Strontium metal = 0.275 mol

Moles of HCl = 0.750 mol

Solution:

From the given moles of metal and HCl we get limiting reactant. Once we get limiting reactant, we get moles of product here H2

By using STP we get volume from moles of H2.

Calculation of limiting reactant:

Limiting reactant is the one which limits the product formation. To find limiting reactant we calculate moles of H2 from both metal and acid

Moles of H2 from moles of metal

Moles of H2 = moles of metal * 1 mol H2/ 1 mol metal (Sr)       ( mol ratio Sr : H2 is 1 : 1)

= 0.275 mol Sr metal * 1mol H2/ 1 mol Sr

= 0.275 mol H2

Moles of H2 from moles of HCl

Moles of H2 = moles of HCl * 1 mol H2 / 2 mol HCl

= 0.750 mol HCl * 1mol H2/ 2 mol HCl

= 0.375 mol H2

Moles of H2 from metal are less than we get from acid so metal Sr is limiting reactant.

We use the moles of from metal.

Moles of H2 = 0.275 moles

At STP , T = 273.15 K , P = 1 atm

We use ideal gas law

pV = nRT

here p is pressure in atm, V is volume in L , n is number of moles , R is gas constant = 0.08206 L atm per K per mol

T is temperature in K

Lets plug all the values.

V = nRT / P

= [0.275 mol * 0.08206 L atm / ( K Mol) * 273.15 K ] / 1 atm

= 6.16 L

= 6.2 L

Answer is A ) 6.2 L