Question

An antacid tablet weighing $1g$ containing aluminium hydroxide as the only basic substance and the rest of its components being neutral, was dissolved in $200mL$ of $0.1M$ HCl. The excess HCl was back titrated and required $90mL$ of $0.1N$ base for exact neutralization. Mill equivalents of aluminium hydroxide in a sample of an antacid tablet is
A. 9
B. 11
C. 12
D. 20

Answer 1

Antacid helps to neutralize the stomach acidity. It is mainly used for heartburn, stomach upset, and indigestion. Antacid contains a salt of magnesium, aluminium, calcium, and sodium. The excess intake of antacid leads to loss of calcium level and thus, it weakens bones (Osteoporosis).

Complete answer:
The mass of the antacid tablet is given as $1g$. When aluminium hydroxide reacts with hydrochloric acid, a neutralization reaction occurs. The reaction can be written as follows,
$Al{(OH)_3} + 3HCl \to AlC{l_3} + 3{H_2}O$
Thus, aluminium hydroxide can be neutralized by dissolving it in $200mL$ of $0.1M$.
The moles present in $0.1M$ of HCl can be calculated by the Molarity formula.
$M = \dfrac{{Moles}}{{litre}}$
$0.1 = \dfrac{{Moles}}{{0.2L}}$
Since $1L = 1000ml$ and thus, $200ml = 0.2L$
$\Rightarrow Mole = 0.02$
Thus, $0.02$ moles are present in $0.1M$ HCl
The acid and base concentration must be the same in order to neutralize. Thus, the base contains $0.1M$ as similar to $0.1M$ of HCl for neutralization.
Thus, moles present in $0.1M$ of base present in $90mL$ can also be calculated by the Molarity formula.
$0.1 = \dfrac{{Moles}}{{0.09L}}$
Since $1L = 1000ml$ and thus, $90ml = 0.09L$
$\Rightarrow Mole = 0.009$
Thus, 0.009 moles are present in $0.1M$ base present in $90mL$ and it is used to neutralize the excess HCl present in the antacid tablet.
The number of moles of HCl neutralized by antacid must be equal to the number of moles of aluminium hydroxide present in the tablet.
Thus, the number of moles of HCl neutralized by antacid can be calculated by subtracting the number of moles of a base which is used for the neutralization of excess HCl to the number of moles of HCl present.
$\Rightarrow Mole = 0.02 - 0.009$
$\Rightarrow Mole = 0.011$
Thus, $0.011$ mole of HCl is neutralized by antacid. Therefore, the number of moles of aluminium hydroxide present in the tablet is also equal to $0.011$

So, the correct answer is Option B.

Note: Molarity of the solution is defined as the moles of solute per litre of the solution. One milliequivalent is equal to one- thousand of the equivalent. Neutralization is the process of neutralizing the acid with a base and it leads to the formation of salt. In an acid-base titration, a neutralization process is involved.