Question

what volume of hydrogen gas is evolved from a reaction between 0.52 g of Na and water? This gas is collected at 20 C and 745mmHg

Answer 1

The  volume of  hydrogen  gas  that evolved  is   calculated  as  follows
by  use  of   ideal  gas  equation

that  is  PV = nRT
P=745  mm hg
V= ?
R(gas  constant)= 62.36 L.mm hg/mol.k
T= 20 + 273 = 293 k
n=number  of  moles which is calculated as  follows
find the  moles  of Na  used
= 0.52/23=0.023  moles

write the reacting equation
2Na +2H2O =2NaOH +H2
by  use  of reacting  ratio  between  Na : H2  which  is  2:1  therefore  the mole  of H2 = 0.023/2 =0.0115  moles

by  making  the  volume  the   subject  of  the formula
v=nRT/P
V= (0.0115 x 62.36  x 293) / 745  = 0.283 L