100cm³ of 0.1 mol/ dm³ of sodium hydroxide how do l measure that

The formula for moles is: $\text{moles} = \text{concentration} \times \text{volume}$
Given:
Concentration = $0.1 \text{ mol/dm}^3$
Volume = $100 \text{ cm}^3 = 0.1 \text{ dm}^3$ (since $1 \text{ dm}^3 = 1000 \text{ cm}^3$)

$$\text{Moles of NaOH} = 0.1 \text{ mol/dm}^3 \times 0.1 \text{ dm}^3$$ $$\text{Moles of NaOH} = 0.01 \text{ mol}$$

First, find the molar mass ($M_r$) of NaOH:
Na = 23.0 g/mol
O = 16.0 g/mol
H = 1.0 g/mol
$M_r(\text{NaOH}) = 23.0 + 16.0 + 1.0 = 40.0 \text{ g/mol}$

Now, use the formula: $\text{mass} = \text{moles} \times M_r$

$$\text{Mass of NaOH} = 0.01 \text{ mol} \times 40.0 \text{ g/mol}$$ $$\text{Mass of NaOH} = \boxed{0.4 \text{ g}}$$

So, you need 0.4 g of solid sodium hydroxide.

• Weighing: Accurately weigh out 0.4 g of solid NaOH using a balance.
• Dissolving: Transfer the weighed NaOH into a beaker. Add a small amount of distilled water (e.g., 20-30 cm³) to the beaker and stir with a glass rod until the NaOH completely dissolves. (Note: NaOH dissolving is exothermic, so the beaker might get warm).
• Transferring: Carefully pour the NaOH solution from the beaker into a 100 cm³ volumetric flask.
• Rinsing: Rinse the beaker and the glass rod several times with small amounts of distilled water, pouring each rinsing into the volumetric flask. This ensures all the NaOH is transferred.
• Making up to volume: Add distilled water to the volumetric flask until the bottom of the meniscus reaches the 100 cm³ calibration mark. Use a dropping pipette for the final few drops to ensure accuracy.
• Mixing: Stopper the volumetric flask and invert it several times to ensure the solution is thoroughly mixed.

You will then have 100 cm³ of 0.1 mol/dm³ sodium hydroxide solution.