Question

In testing the effectiveness of an antacid compound, 20.0g of Hydrochloric Acid is mixed with 28.0g of Magnesium Hydroxide. will the base neutralize (Completely use up) all of the acid? How much of which substance is in excess?
2HCL + (OH)2 -> MgCl2 + 2H20

Answer 1

Answer:

Yes ,The base neutralize all of the acid because it(base) is present in excess quantity .

Mg(OH)2 is in excess by 0.205 mole

Explanation:

The balanced equation is :

$Mg(OH)_{2} + 2 HCl \rightarrow MgCl_{2} + 2H_{2}O$

Calculate the moles of Hydrochloric Acid and Magnesium hydroxide

For HCl

$Moles = \frac{given\ mass}{molar\ mass}$

Given mass = 20.0 g

Molar mass of HCl = 36.5 g/mol

$Moles = \frac{20}{36.5}$

mole of HCl = 0.55

For Mg(OH)2

Given mass = 28.0 g

Molar mass of Mg(OH)2 = 58.3 g/mol

$Moles = \frac{28}{58.3}$

mole of Mg(OH)2 = 0.48

According to the balanced equation ,

$Mg(OH)_{2} + 2 HCl \rightarrow MgCl_{2} + 2H_{2}O$

1 mole of Mg(OH)2 would require = 2 mole of HCl for neutralisation

So,

0.48 mole of Mg(OH)2 would require = 2(0.48) =  0.96 mol

HCl needed for complete neutralisation = 0.96 mole

Available HCl = 0.55 mole

HCl is less by  = 0.96 -0.55 = 0.41 mole

So,

Mg(OH)2 is in  excess by =  0.41/2 mole [because 1 HCl = 2 Mg(OH)2]

= 0.205

Here HCl is less than need and Mg(OH)2 is in excess.