Câu 7 :
\(n_{Na_2CO_3}=n_{Na_2CO_3\cdot10H_2O}=\dfrac{85.5}{286}=0.3\left(mol\right)\)
\(C_{M_{Na_2CO_3}}=\dfrac{0.3}{0.146}=2.1\left(M\right)\)
Câu 8 :
\(a.\)
\(V_A:V_B=3:1\)
\(\Rightarrow V_A=3\left(l\right),V=1\left(l\right)\)
\(n_{HNO_3\left(0.5M\right)}=0.5\cdot3=1.5\left(mol\right)\)
\(n_{HNO_3\left(0.5M\right)}=1\cdot1=1\left(mol\right)\)
\(b.\)
\(Đặt:\)
\(V_{dd_{HNO_3\left(0.5M\right)}}=a\left(l\right)\)
\(V_{dd_{HNO_3\left(1M\right)}}=b\left(l\right)\)
\(n_{HNO_3}=0.5a+b\left(mol\right)\)
\(C_{M_{HNO_3}}=\dfrac{0.5a+b}{a+b}=0.8\left(M\right)\)
\(\Leftrightarrow0.5a+b=0.8a+0.8b\)
\(\Leftrightarrow0.3a=0.2b\)
\(\Leftrightarrow\dfrac{a}{b}=\dfrac{2}{3}\)
\(n_{HNO_3}=1.5+1=2.5\left(mol\right)\)
\(V_{dd}=3+1=4\left(l\right)\)
\(C_{M_{HNO_3}}=\dfrac{2.5}{4}=0.625\left(M\right)\)
