Question

2 g de calciu se arunca in 20 g apa. Se cere:
a) scrieti ecuatia transformarii ce a avut loc
b) calculati concentratia procentuala a solutiei

Answer 1

 64g         2 * 18 g       98g   
Ca (s) + 2 H2O (l) = Ca(OH)2 (aq) + H2 (g)
2g/y g      xg / 20g        zg

nCa= 64 g/mol
nH2O= 18 g/mol
nCa(OH)2 = 98 g/mol

x = 1,125 9 H2O < m H2O    I   => m H2O (exces) = 20 - 1,125 = 18,875 g
y =  35,55 g Ca > m Ca         I

z = 98 * 2/ 64 = 3 g Ca(OH)2
m solutie finala = m H2O (exces) + m Ca(OH)2 = 3 + 18,875 = 21,875 g solutie
c final = md*100/ms= 3*100/21,875 = 13.71 %