Cilculate the \(\mathrm{pH}\) of the resultant mixtures : (ii) \(10 \mathrm{ml}\). of \(0.2 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}+25 \mathrm{~mL}\) of \(0.1 \mathrm{MHCl}\), (b) \(10 \mathrm{ml}\). of \(0.01 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}+10 \mathrm{~mL}\) of \(0.01 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}\), (c) \(10 \mathrm{ml}\) of \(0.1 \mathrm{MH}_{2} \mathrm{SO}_{4}+10 \mathrm{~mL}\) of \(0.1 \mathrm{M} \mathrm{KOH}\).

Acid-base neutralization is a chemical reaction where an acid and a base react to form water and a salt. This type of reaction is important in many chemical processes, including the calculation of pH in mixtures. The general form of this reaction is:
\[ \text{Acid} + \text{Base} \rightarrow \text{Water} + \text{Salt} \]
Understanding this reaction allows us to predict the outcome when an acidic solution is mixed with a basic solution. For example, if hydrochloric acid \( \text{HCl} \) is mixed with calcium hydroxide \( \text{Ca(OH)}_2 \), they neutralize each other to produce water \( \text{H}_2\text{O} \) and calcium chloride \( \text{CaCl}_2 \). If one reactant is present in excess, the resulting solution’s pH will depend on the amount of the excess reactant. For instance, if we have more \( \text{HCl} \) than \( \text{Ca(OH)}_2 \), the excess hydrochloric acid will dictate the pH of the solution.

Molar concentration, denoted as 'M' for molarity, measures the amount of a solute contained in a unit volume of solution. It is expressed in moles per liter \( (mol/L) \). To calculate it, we use the formula:
\[ \text{Molarity} (M) = \frac{\text{moles of solute}}{\text{volume of solution in liters}} \]
In the context of our acid-base reactions, knowing the molarity of the reactants helps us determine how many moles of each substance we have in a given volume of solution. This is crucial for stoichiometry calculations, as it allows us to use the molar ratios derived from balanced chemical equations to predict the products of the reaction and their amounts.

Stoichiometry involves using balanced chemical equations to calculate the quantities of reactants and products involved in a chemical reaction. It's based on the principle of conservation of mass, where the total mass of the reactants equals the total mass of the products.
When dealing with acid-base reactions, stoichiometry is essential in figuring out how much of each reactant is needed to neutralize the other and what the concentration of any excess reactant will be after the reaction has taken place. This is shown through the stoichiometric coefficients in the balanced equation, which indicate the precise molar relationship between reactants and products.
By applying the concepts of stoichiometry, we can solve problems such as those presented in the exercise above. For instance, by calculating the moles of \( \text{HCl} \) and \( \text{Ca(OH)}_2 \), we can use their molar ratio to determine if there is an excess of any reactant, and thereby, predict the pH of the resultant mixture. This approach is not only useful in academic exercises but also in real-world applications where accurate measurements are vital, such as in medication dosages or industrial chemical manufacturing.