Question

A 5.0-gram sample of zinc and a 50.-milliliter sample of hydrochloric acid are used in a chemical reaction. Which combination of these samples has the fastest reaction rate?
(1) a zinc strip and 1.0 M HCl(aq)
(2) a zinc strip and 3.0 M HCl(aq)
(3) zinc powder and 1.0 M HCl(aq)
(4) zinc powder and 3.0 M HCl(aq)

Answer 1

The answer is Zine powder and 3.0 M HCl (aq)

Answer 2

Answer:

(4) zinc powder and 3.0 M HCl(aq)

Explanation:

First consider the equation of reaction:

$Zn + 2HCl --> ZnCl_2 + H_2$

1 mole of Zinc requires 2 moles of HCl for reaction.

mole of zinc = mass/molar mass = 5.0/65.38 = 0.0765 mole

0.0765 mole of zinc will require: 0.0765 x 2 = 0.1530 mole HCl

Mole of 1.0 M HCl = Molarity x volume = 1 x 0.05 = 0.05 mole

Mole of 3.0 M HCl = 3 x 0.05 = 0.15

Hence, the 3.0 M HCl is what will give the required number of mole.

Zinc in powder form will react faster compared to in strip because the former has higher surface area for reaction.

Therefore, zinc powder and 3.0 M HCl will give the fastest reaction rate.

The correct option is option 4.