a)

Gọi số mol Fe, Fe₂O₃ là a, b (mol)

=> 56a + 160b = 48,8 (1)

PTHH: 2Fe + 6H₂SO₄ --> Fe₂(SO₄)₃ + 3SO₂ + 6H₂O

               a-------------------->0,5a------>1,5a

            Fe₂O₃ + 3H₂SO₄ --> Fe₂(SO₄)₃ + 3H₂O

               b----------------------->b

=> \(0,5a+b=\dfrac{140}{400}=0,35\) (2)

(1)(2) => a = 0,3 (mol); b = 0,2 (mol)

=> \(\left\{{}\begin{matrix}\%m_{Fe}=\dfrac{0,3.56}{48,8}.100\%=34,426\%\\\%m_{Fe_2O_3}=\dfrac{0,2.160}{48,8}.100\%=65,574\%\end{matrix}\right.\)

b) n_SO2 = 1,5a = 0,45 (mol)

n_NaOH  = 1.0,45 (mol)

Xét tỉ lệ: \(\dfrac{n_{NaOH}}{n_{SO_2}}=\dfrac{0,45}{0,45}=1\) => Tạo muối NaHSO₃

PTHH: NaOH + SO₂ --> NaHSO₃

             0,45-------------->0,45

=> \(C_{M\left(dd.NaHSO_3\right)}=\dfrac{0,45}{0,45}=1M\)

\(a,=2\sqrt{2}\left(\sqrt{5}-1\right)\sqrt{4+\sqrt{\left(\sqrt{5}-1\right)^2}}\\ =2\sqrt{2}\left(\sqrt{5}-1\right)\sqrt{4+\sqrt{5}-1}\\ =2\left(\sqrt{5}-1\right)\sqrt{6-2\sqrt{5}}\\ =2\left(\sqrt{5}-1\right)\sqrt{\left(\sqrt{5}-1\right)^2}\\ =2\left(\sqrt{5}-1\right)^2=2\left(6-2\sqrt{5}\right)=12-4\sqrt{5}\\ b,=\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)\sqrt{8-2\sqrt{15}}\\ =\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)\sqrt{\left(\sqrt{5}-\sqrt{3}\right)^2}\\ =\left(4+\sqrt{15}\right)\left(\sqrt{5}-\sqrt{3}\right)^2\\ =\left(4+\sqrt{15}\right)\left(8-2\sqrt{15}\right)\\ =32-8\sqrt{15}+8\sqrt{15}-30=2\)

\(R_{tđ}=\dfrac{R_1\cdot R_2}{R_1+R_2}=\dfrac{24\cdot12}{24+12}=8\Omega\)

\(I=\dfrac{U}{R}=\dfrac{12}{8}=1,5A\)

\(P=\dfrac{U^2}{R}=\dfrac{12^2}{8}=18W\)

\(Q_{tỏa1}=A_1=U_1\cdot I_1\cdot t=12\cdot\dfrac{12}{24}\cdot1\cdot3600=21600J\)

\(Q_{tỏa2}=A_2=U_2\cdot I_2\cdot t=12\cdot\dfrac{12}{12}\cdot1\cdot3600=43200J\)

jimmmmmmmmmmmmmmmmmmmmmmmmmmm

he he he he he he

bài 1:

bn lấy giá trị của √(4^2-3,9^2) là dc

bài 2

AB+BC=2√(3^2+4^2)=??

nSO3=0,75(mol)

mH2SO4(bđ)= 600.15%=90(g) => nH2SO4(bđ)= 90/98=45/49(mol)

PTHH: SO3 + H2O -> H2SO4

0,75______0,75____0,75(mol)

=> mH2SO4(tổng)= 0,75.98+90= 163,5(g)

mddH2SO4= mSO3+mddH2SO4(bđ)= 0,75.80 + 600= 660(g)

=>C%ddH2SO4(sau)= (163,5/660).100=24,773%

VddH2SO4(sau)= 660/1,25= 528(ml)=0,528(l)

nH2SO4(tổng)= 45/49 + 0,75= 327/196(mol)

=> CMddH2SO4(sau)= 327/196 : 0,528=3,16(M)