Quantity of $Na_2CO_3$ required to prepare 500 ml of 0.1N $Na_2CO_3$ is _______________.
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For a $1\text{N}\ Na_2CO_3$ solution, you need $53\text{ g/L}$. For a $0.1\text{N}$ solution, you need $5.3\text{ g/L}$. Therefore, for half a liter ($500\text{ ml}$), you need exactly half of that weight: $2.65\text{ g}$.