Question

Calculate the mass of (NaOH) that you must dissolve in 200 ml of solution to make a solution with a molar concentration of 6,4 mol.dm³

Answer 1

To calculate the mass of sodium hydroxide (NaOH) needed to create a solution with a specific molar concentration, you can use the formula:

\[
\text{mass (g)} = \text{molarity (mol/L)} \times \text{volume (L)} \times \text{molar mass (g/mol)}
\]

First, you need to convert the volume from milliliters to liters:

\[
200 \, \text{ml} = 0.200 \, \text{L}
\]

Next, identify the molar mass of sodium hydroxide (NaOH). The molar mass can be calculated as follows:

- Sodium (Na): Approximately 23.0 g/mol
- Oxygen (O): Approximately 16.0 g/mol
- Hydrogen (H): Approximately 1.0 g/mol

\[
\text{Molar mass of NaOH} = 23.0 + 16.0 + 1.0 = 40.0 \, \text{g/mol}
\]

Now, substitute the values into the formula:

- Molarity (M) = 6.4 mol/dm³ = 6.4 mol/L
- Volume (L) = 0.200 L
- Molar mass (g/mol) = 40.0 g/mol

\[
\text{mass (g)} = 6.4 \, \text{mol/L} \times 0.200 \, \text{L} \times 40.0 \, \text{g/mol}
\]

Calculating this gives:

\[
\text{mass (g)} = 6.4 \times 0.200 \times 40.0 = 51.2 \, \text{g}
\]

Therefore, you need to dissolve **51.2 grams of NaOH** in 200 mL of solution to achieve a concentration of 6.4 mol/dm³.