Question

1) A piece of magnesium weighing 2.00 gr. is dropped into 100 mL of 2.00 M H2SO4 when the reaction has ceased which of the reactants remains in excess and by how much? (Write the chemical reaction that takes place.) 

.

5- How many mL of 2.0 M H2SO4 would be required to react with 25.0 gr. of zinc? 

(Write the chemical reaction that takes place.)
.  

6- What is the molarity of a solution which contains 25.0% H2SO4 by weight and which has a density of 1.13 gr/mL? 


Answer 1

1)

Reaction between H₂SO₄ and Mg is

Mg + H₂SO₄ MgSO₄ + H₂ (g)

Hence, complete neutralization

moles of Mg = moles of Sulfuric acid .

Given , moles of Mg = ( mass of Mg / molar mass)

= (2.00/24)

= 0.0833.

Moles of Sulfuric acid

= Molarity × volume(L)

= 2.00× ( 100 ×10^-3)

= 0.2 .

Therefore , Sulfuric acid is excess.

Excess moles of sulfuric acid = 0.2 - 0.083 = 0.117

Now, excess volume of sulfuric acid =(moles/molarity)

= ( 0.117/2) = 0.0585 L = 58.5 mL

5.

Balanced reaction is

Zn + H₂SO₄ ZnSO₄ + H₂

Mole ratio of Zn and sulfuric acid = 1:1.

Now, moles of Zn = ( mass/molar mass)

= (25.0/65.38)

= 0.38

Now,

Moles of Sulfuric acid needed = 0.38.

So, molarity × volume = moles

Or, 2.0× Volume = 0.38

Or, Volume = (0.38/2.0) = 0.19 L = 190 mL.

6.

Mass percentage = ( mass of solute× 100/mass of solution) .

So, in 25% Sulfuric acid solution.

Mass of sulfuric acid = 25 g.

So, Moles of sulfuric acid = ( 25/98) = 0.255

Mass of solution = 100 g.

Volume of solution = ( mass/density)

= [ (100 g/1.13 (g/ml) ] = 88.49 mL.

Hence,

Molarity =

= (0.255×1000/88.49)

= 2.88 M.