If `100 mL` of `0.100 M HCl` solution and `100 mL` of `0.100 M NaOH` are mixed, what is the molarity of the salt in the resulting sollution? Assuming that the volumes are additive.

Options

A. `0.0100 M`
B. `0.0500 M`
C. `0.0033 M`
D. `0.0025 M`

Answer

2

Explanation

First write the balance equation for the acid-base reaction and then construct the reaction summary that shows the amounts (moles) of `HCl` and `NaOH`, Determine the amount of salt formed the reaction summary.
Experiments have shown that volumes of dilute aqueous solutions are very nearly additive. No significant error is introduced by making this assumption. Thus, the final (total) volume is the sum of the volumes mixed. Finally we calculate the molarity of the salt.
We often express the volume of a solution in milliliters rather than in litres. Likewise, we express the amount of solute in millimoles (mmol) rather than in moles. Because one milliliter is `1//1000` of a liter and one millimole is `1//1000` of a mole, molarity also may be expressed as the number of millimoles of solute per milliliter of solution.
Molarity `=(no . mol)/L`
Since, `1 mol = 1000 mmol`
`1 L=1000 mL`
Molarity`=(no . mmol)/(mL)`
`=("Number of millimoles of solute")/("Number of milliliters of solution")`
For volumes and concentrations that are commonly used in laboratory experiments, solving problems in terms of millimoles and millilitress often involves more convenient numbers than using moles and litres. We should note also that the reaction ratio that we obtain from any balanced chemical equation is exactly the same whether we express all quantities in moles or in millimoles.

The above tabulation shows that equal numbers of the `HCl` and `NaOH` react, i.e., `HCl` and `NaOH` neutralize each other exactly. The resulting solution contains only `NaCl` (the salt formed by the reaction) and water.
Since the amount of water produced by the reaction is negligible, the resulting solution contains `10.0 mmol` of NaCl in `200 mL` of solution. its molarity is
`M=(10.0 mmol NaCl)/(200 mL)`
`=0.0500 M NaCl`
Note that the reaction ratio is the relative numbers of moles of reactants and products shown in balanced equation.