Calculer le volume V₁ qu'il faut prélever d'une solution (S1) de chlorure de sodium de concentration C₁ égale à 0,60 mol.L⁻¹ pour préparer un volume V₂ =100 ml d'une solution aqueuse (S₂) de concentration C₂ égale à 0,15 mol.L⁻¹.

We are given the initial concentration $C_1 = 0.60 \text{ mol.L}^{-1}$, the final volume $V_2 = 100 \text{ ml}$, and the final concentration $C_2 = 0.15 \text{ mol.L}^{-1}$. We need to find the initial volume $V_1$.

The principle of dilution states that the amount of solute remains constant, so $C_1 V_1 = C_2 V_2$.

Ensure units are consistent. Since $V_2$ is in ml, $V_1$ will also be in ml.

The volume $V_1$ to be taken from solution $S_1$ is $\boxed{\text{25 ml}}$.

2. Mode de préparation de la solution ($S_2$):

To prepare solution $S_2$ (100 ml of 0.15 mol.L$^{-1}$ NaCl solution) from solution $S_1$ (0.60 mol.L$^{-1}$ NaCl solution), follow these steps:

• Using a pipette graduée or pipette jaugée (volumetric pipette), accurately measure 25 ml of the stock solution ($S_1$).
• Transfer this volume into a fiole jaugée (volumetric flask) of 100 ml.
• Add distilled water up to about two-thirds of the flask, then stopper and mix.
• Carefully add distilled water until the bottom of the meniscus aligns with the jauge (calibration mark) on the neck of the flask.
• Stopper the flask and invert it several times to ensure thorough mixing of the solution.