Question

How many grams of $Mg{{(OH)}_{2}}$ will be needed to neutralize 25 mL of stomach acid if stomach acid is 0.10 M $HCl$?

Answer 1

The answer is based on the basic concept of physical chemistry which includes calculation of molality and thus the formula is given by ratio of number of moles of solute to that of volume of the solution in litres that is $M=\dfrac{n}{V(litres)}$

Complete step by step answer:
- We have studied in our chapters of chemistry in the lower classes that deals with the basic concepts and the terminologies such as molarity, molality and also normality of the solutions and some other basic calculations related to it.
Now, let us see in detail about this which helps us to approach the required answer.
- Molarity is defined as the number of moles of a solute present in one litre of the solution and thus the formula is given by:
$M=\dfrac{{{n}_{solute}}}{{{V}_{solution(litres)}}}$
- Magnesium hydroxide is basic in nature and they react with acid to form salt and water that is they undergo neutralization reaction. The reaction taking place is as shown below,
$Mg{{(OH)}_{2}}+2HCl\to Mg{{I}_{2}}+2{{H}_{2}}O$
- Mass of magnesium hydroxide is 58.33 g and from the above reaction we can say that 2 moles of $HCl$ requires 58.33 g of $Mg{{(OH)}_{2}}$
Now, to know the mass of $Mg{{(OH)}_{2}}$ in 25 ml of 0.1M, we have to calculate moles of$HCl$ in it and thus this can be found by the molarity equation given above.
the data given is, M = 1m and V = 25ml, by substituting in the above equation, we get
$1=\dfrac{m\times 1000}{25}$
$\Rightarrow m = \dfrac{25}{1000}=0.025$ moles of $HCl$
therefore, 1 mole of hydrochloric acid will be neutralized by $=\dfrac{58.33}{2}$
and 0.025 mole of hydrochloric acid will be neutralized by $=\dfrac{0.025\times 58.33}{2} = 0.0729 g$
Thus, 0.0729 g of magnesium hydroxide is required to neutralize 25 ml of stomach acid.

Note: Note that molarity of the solution depends on the volume of the solvent which is nothing but the solution in litres whereas molality depends on the mass of the solvent which is measured in terms of kg of the solvent.