ひとりでできる半反応式④

[qwiz]

[q labels=”bottom”]

つぎの文章の半反応式を書いてみましょう。

「硫酸の存在下で、二クロム酸カリウムK₂Cr₂O₇水溶液が，酸化剤としてはたらいた」

半反応式を書くには，最初に酸化剤としてはたらいて変化するイオンや物質を探し出します。K₂Cr₂O₇やNaClOのように，KやNaが含まれる化合物は，水溶液中ではイオンになり，K⁺，Na⁺になります。K⁺やNa⁺は水溶液中では酸化剤にはならないので，変化するイオンは，K⁺やNa⁺のもう一方のイオンとなります。この場合は　　　　　が酸化剤としてはたらき，変化します。
　　

[l]K⁺

[f*] Good!

[fx] No.

[l] Cr³⁺

[f*] Excellent!

[fx] No, that’s not correct.

[l] Cr₂¹²⁺

[f*] Good!

[fx] No.

[l] Cr₂O₇^–

[f*] Excellent!

[fx] No, that’s not correct.

[l] Cr₂O₇^2-

[f*] Great!

[fx] No, that’s not correct.

[q labels=”bottom”]変化するイオンはCr₂O₇^2-であることはわかりました。つぎは，このイオンが酸化剤としてはたらいた後，何になるかを考えます。次の空欄に適するものを記入しなさい。
Cr₂O₇^2-　→　　　　　

[l]Cr

[f*] Great!

[fx] No, that’s not correct.

[l] Cr₂

[f*] Excellent!

[fx] No.

[l] O₂

[f*] Correct!

[fx] No.

[l] Cr^＋

[f*] Excellent!

[fx] Sorry, that’s not correct.

[l] Cr³⁺

[f*] Great!

[fx] Sorry, that’s not correct.

[l] Cr⁶⁺

[f*] Correct!

[fx] No.

[q labels=”bottom”]Cr₂O₇^2-→Cr³⁺

の変化がおこることがわかりました。左辺と右辺の原子数が合っていないので，原子数を合わせます。

下の空欄に適するものを記入しなさい。

　 Cr₂O₇^2-→ 　Cr³⁺

[l]1

[f*] Good!

[fx] No, that’s not correct.

[l] 2

[f*] Great!

[fx] Sorry, that’s not correct.

[l] 3

[f*] Good!

[fx] No.

[l] 4

[f*] Correct!

[fx] No, that’s not correct.

[l] 5

[f*] Good!

[fx] No.

[l] 6

[f*] Good!

[fx] Sorry, that’s not correct.

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O原子の数をそろえるために，次の空欄のどちらかに，H₂Oを記入しなさい。

　Cr₂O₇^2- → 2Cr³⁺ 　　

[l]+ H₂O

[f*] Good!

[fx] No, that’s not correct.

[l] +2H₂O

[f*] Good!

[fx] Sorry, that’s not correct.

[l] + 3H₂O

[f*] Excellent!

[fx] No, that’s not correct.

[l] + 4H₂O

[f*] Excellent!

[fx] No.

[l] + 5H₂O

[f*] Great!

[fx] No.

[l] + 6H₂O

[f*] Great!

[fx] No.

[l] + 7H₂O

[f*] Great!

[fx] No.

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H原子の数をそろえるために，次の空欄のどちらかに，H^＋を記入しなさい。

　Cr₂O₇^2- → 2Cr³⁺ + 7H₂O

[l]＋ H^＋

[f*] Correct!

[fx] No.

[l]＋ 2H^＋

[f*] Correct!

[fx] No, that’s not correct.

[l]＋ 5H^＋

[f*] Correct!

[fx] No, that’s not correct.

[l]＋ 7H^＋

[f*] Good!

[fx] No, that’s not correct.

[l]＋ 10H^＋

[f*] Excellent!

[fx] No.

[l]＋ 12H^＋

[f*] Good!

[fx] Sorry, that’s not correct.

[l]＋ 14H^＋

[f*] Good!

[fx] Sorry, that’s not correct.

[l]＋ 16H^＋

[f*] Great!

[fx] Sorry, that’s not correct.

[q labels=”bottom”]

左辺と右辺の電荷を調べます。

	Cr₂O₇^2-	＋	14H⁺	→	2Cr³⁺	＋	7H₂O
電荷
合計

[l]+

[f*] Correct!

[fx] Sorry, that’s not correct.

[l]-

[fx] No. Please try again.

[f*] Excellent!

[l] 0

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l] 1

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l] 2

[fx] No. Please try again.

[f*] Great!

[l] 3

[fx] No. Please try again.

[f*] Excellent!

[l] 4

[fx] No, that’s not correct. Please try again.

[f*] Good!

[q labels=”bottom”]

左辺の合計は+12，右辺の合計は＋6です。これを調整するために，次のアンダーラインのどちらかにe-を書き足します。

　　 Cr2O72-　＋14H+　　　　→　2Cr3+ ＋　7H2O　　　　　これで完成です。

Enter text
(double-click to format)

[l] Label

[f*] Good!

[fx] No, that’s not correct.

[/qwiz]