: Cho 200 ml dung dịch H2SO4 1M tác dụng với 300 ml dung dịch NaOH 2M, sau phản ứng thu được dung dịch X. (a) Viết các PTHH xảy ra. (b) Nếu cho mẩu quỳ tím vào dung dịch X thì có hiện tượng gì? Giải thích. (c) Cô cạn dung dịch X thu được bao nhiêu gam chất rắn khan?

1 câu trả lời

$n_{H2SO4}$ = 1.(200:1000) = 0,2 (mol)

$n_{NaOH}$ = 2.(300:1000) = 0,6 (mol)

a)

PT: H2SO4 + 2NaOH ---> Na2SO4 + 2H2O

PƯ:   0,2            0,4                 0,2                     (mol)

Lập tỉ lệ: $\frac{n_{H2SO4}}{1}$ (=$\frac{0,2}{1}$) < $\frac{n_{NaOH}}{2}$ (=$\frac{0,6}{2}$)

-> H2SO4 hết, NaOH dư.

b) Nếu cho mẩu quỳ tím vào dung dịch X thì quỳ tím chuyển sang màu xanh. Vì trong dung dịch X có NaOH dư, mà NaOH là bazơ nên làm quỳ tím hóa xanh.

c) $m_{Na2SO4}$ = 0,2 . 142 = 28,4 (g)

$m_{NaOH dư}$ = (0,6 - 0,4). 40 = 8 (g)

=> $m_{chất rắn khan}$ = $m_{Na2SO4}$ + $m_{NaOH dư}$ = 28,4 + 8 = 36,4 (g)

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