Дано
m(H3PO4)=4.9 g
KOH
-------------------
n(H2O)-?
H3PO4+3KOH-->K3PO4+3H2O
M(H3PO4)=98 g/mol
n(H3PO4)=m/M=4.9/98=0.05 mol
n(H3PO4)=3n(H2O)
n(H2O)=3*0.05 =0.15 mol
ответ 0.15 моль
дано
m(Na)=4.6 g
n(S)=0.2 mol
----------------
m(Na2S)-?
4.6 X
2Na+S-->Na2S
2*23 78
M(Na)=23 g/mol
n(Na)=4.6/23=0.2 mol
n(Na)=n(S)
M(Na2S)=78 g/mol
m(Na2S)=4.6*78/46=7.8g
ответ 7.8 г
дано
m(NaOH)=0.4 mol
-----------------------
m(H2SO4)-?
0.4mol Xmol
2NaOH+H2SO4-->Na2SO4+2H2O
2mol 1mol
X=0.4*1/2=0.2 mol
M(H2SO4)=98 g/mol
m(H2SO4)=n*M=0.2*98=19.6 g
ответ 19.6 г