When \( 300 \, \text{J} \) of heat given to an ideal gas with \( C_{p} = \dfrac{7}{2} R \) its temperature raises from \( 20^\circ \text{C} \) to \( 50^\circ \text{C} \) keeping its volume constant. The mass of the gas is (approximately) __________ \( \text{g} \). \( ( R = 8.314/\text{mol.K} ) \).
