The purple double salt crystal $\mathbf{A}$ dissolves in water to form a yellow solution. Adding a colorless weakly acidic solution (solute is $\mathbf{B}$) to the solution of $\mathbf{A}$ causes the color to fade to colorless, producing $\mathbf{C}$. $\mathbf{B}$ and $\mathbf{A}$ contain the same cation, and the point group of the anion of $\mathbf{B}$ is $D_{\infty h}$. Adjusting the solution of $\mathbf{A}$ to alkaline, adding excess sodium hypochlorite for oxidation, and then reacting with $\mathrm{Ba}(\mathrm{OH})_{2}$ produces $\mathbf{D}$, which is also purple. Adding an alkaline solution of sodium tetraphenylborate to the solution of $\mathbf{B}$ produces a white precipitate $\mathbf{E}$. The molecular weight of $\mathbf{A}$ rounded down is 503. $\mathbf{A}$ ~ $\mathbf{E}$ refer to the complete chemical formulas of the species, and these species can exist with strong stability under normal temperature and pressure.

How many of the following descriptions are correct?

- The most common crystal form of $\mathbf{A}$ is cubic crystal system
- The molecular weight of $\mathbf{E}$ is greater than 400
- The cation of $\mathbf{B}$ is composed of multiple atoms
- $\mathbf{D}$ has poor water solubility
- The yellow color of $\mathbf{A}$ dissolving in water is due to the ionization of a Brønsted acid
- The molecular weight of $\mathbf{C}$ rounded down is a prime number
紫色的复盐晶体 $\mathbf{A}$ 溶于水变成黄色溶液。向 $\mathbf{A}$ 的溶液中加入无色弱酸性溶液 (溶质为 $\mathbf{B}$), 颜色褪为无色,
生成 $\mathbf{C}$。$\mathbf{B}$ 与 $\mathbf{A}$ 中存在相同的阳离子，$\mathbf{B}$ 的阴离子所属的分子点群为 $D_{\infty h}$。将 $\mathbf{A}$ 溶液调至碱性, 再加入过量次氯酸钠氧化后, 再与 $\mathrm{Ba}(\mathrm{OH})_{2}$ 反应生成 $\mathbf{D}$, $\mathbf{D}$也为紫色。将 $\mathbf{B}$ 溶液中滴入碱性四苯硼钠溶液, 有白色沉淀 $\mathbf{E}$ 生成。$\mathbf{A}$ 的分子量向下取整为503。$\mathbf{A}$ ~ $\mathbf{E}$ 代指物种的完整化学式，且这些物种都能在常温常压下以很强的稳定性存在。

下列描述中，正确的有几个？

- $\mathbf{A}$ 最常见的晶型为立方晶系
- $\mathbf{E}$ 的分子量大于400
- $\mathbf{B}$ 的阳离子由多个原子组成
- $\mathbf{D}$ 的水溶性较差
- $\mathbf{A}$ 溶于水变黄是由于Brønsted酸的电离
- $\mathbf{C}$ 的分子量向下取整后是质数
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Sodium tetraphenylborate is often used to identify $\mathrm{K^+}$ ions, but it is also effective for $\mathrm{NH_4^+}$. Therefore, the cation in $\mathbf{A}$ and $\mathbf{B}$ is most likely $\mathrm{K^+}$, but $\mathrm{NH_4^+}$ etc. cannot be excluded.

<Checkpoint>[Sodium tetraphenylborate is often used to identify $\mathrm{K^+}$, the cation in $\mathbf{B}$ is most likely $\mathrm{K^+}$, $\mathbf{E}$ might be $\mathrm{KB(C_6H_5)_4}$](1)</Checkpoint>

The purple solid $\mathbf{A}$ turns yellow after dissolving, and after being oxidized by the strong oxidant sodium hypochlorite under alkaline conditions, $\mathbf{D}$ is obtained, which is still purple. Possible elements include iodine, manganese, iron, etc.

Under alkaline conditions, iodine will be oxidized to periodate by sodium hypochlorite, both of which are colorless, so iodine can be excluded.

<Checkpoint>[Periodate is colorless, excluding iodine](0.5)</Checkpoint>

Manganese in stable valence states at normal temperature and pressure rarely has yellow solutions, so it can be excluded.

<Checkpoint>[Yellow and stable manganese-containing solutions are rare, excluding manganese](1)</Checkpoint>

$\mathrm{[Fe(H_2O)_6]^{3+}}$ is purple, and hydrolysis occurs after dissolution, turning yellow. $\mathrm{Fe^{3+}}$ is oxidized to ferrate $\mathrm{FeO_4^{2-}}$ under alkaline conditions, forming a precipitate with $\mathrm{Ba^{2+}}$. All are consistent with the question.

<Checkpoint>[$\mathrm{[Fe(H_2O)_6]^{3+}}$ is purple](1)</Checkpoint>
<Checkpoint>[$\mathrm{Fe^{3+}}$ is oxidized to purple $\mathrm{FeO_4^{2-}}$ under alkaline conditions](1)</Checkpoint>
<Checkpoint>[$\mathbf{D}$ is $\mathrm{BaFeO_4}$](1)</Checkpoint>

Common crystals containing $\mathrm{[Fe(H_2O)_6]^{3+}}$ include potassium (or ammonium) ferric sulfate dodecahydrate, ferric nitrate nonahydrate, etc. And the question requires that $\mathrm{A}$ is a double salt, calculate the molecular weight of $\mathrm{KFe(SO_4)_2\cdot12H_2O}$ as $39.10+55.85+2\times(32.07+4\times16.00)+12\times(2\times1.008+16)=503.282$.

<Checkpoint>[Calculate the molecular weight of $\mathrm{KFe(SO_4)_2\cdot12H_2O}$ as 503. $\mathbf{A}$ is $\mathrm{KFe(SO_4)_2\cdot12H_2O}$](1)</Checkpoint>

$\mathrm{F^-}$ can decolorize the $\mathrm{Fe^{3+}}$ solution to generate $\mathrm{FeF_6^{2-}}$, and the fluorine-containing weakly acidic $D_{\infty h}$ point group anion is $\mathrm{HF_2^-}$.

<Checkpoint>[$\mathbf{B}$ is $\mathrm{KHF_2}$. $\mathbf{C}$ is $\mathrm{K_3FeF_6}$](1)</Checkpoint>

|Option |Judgment |
|-----|-----|
|The most common crystal form of $\mathbf{A}$ is cubic crystal system|Correct|
|The molecular weight of $\mathbf{E}$ is greater than 400|Incorrect|
|The cation of $\mathbf{B}$ is composed of multiple atoms|Incorrect|
|The water solubility of $\mathbf{D}$ is poor|Correct|
|Dissolving $\mathbf{A}$ in water turns yellow accompanied by the ionization of Brønsted acid|Correct|
|The molecular weight of $\mathbf{C}$ rounded down is a prime number|Incorrect|

<Checkpoint>[3 items are correct, the answer is D](1)</Checkpoint>
四苯硼钠常用于鉴别$\mathrm{K^+}$离子, 但也对$\mathrm{NH_4^+}$有效. 因此 $\mathbf{A}$ 与 $\mathbf{B}$ 中的阳离子最可能是$\mathrm{K^+}$, 不能排除$\mathrm{NH_4^+}$等. 

<Checkpoint>[四苯硼钠常用于鉴别$\mathrm{K^+}$, $\mathbf{B}$ 中的阳离子最可能是$\mathrm{K^+}$, $\mathbf{E}$可能是$\mathrm{KB(C_6H_5)_4}$](1)</Checkpoint>

紫色固体 $\mathbf{A}$ 溶解后变黄, 在碱性条件下被强氧化剂次氯酸钠氧化后得到$\mathbf{D}$, 仍为紫色. 可能的元素有碘, 锰, 铁等. 

碱性条件下碘会被次氯酸钠氧化为高碘酸根, 均为无色, 可以排除. 

<Checkpoint>[高碘酸根均为无色, 排除碘 ](0.5)</Checkpoint>

常温常压下稳定价态的锰较少有黄色溶液, 可以排除. 

<Checkpoint>[黄色且稳定的含锰溶液较少见, 排除锰](1)</Checkpoint>

$\mathrm{[Fe(H_2O)_6]^{3+}}$为紫色, 溶解后发生水解, 变为黄色. $\mathrm{Fe^{3+}}$在碱性条件下被氧化为高铁酸根$\mathrm{FeO_4^{2-}}$, 与$\mathrm{Ba^{2+}}$形成沉淀. 均与题干相符. 

<Checkpoint>[$\mathrm{[Fe(H_2O)_6]^{3+}}$为紫色](1)</Checkpoint>
<Checkpoint>[$\mathrm{Fe^{3+}}$在碱性条件下被氧化为紫色$\mathrm{FeO_4^{2-}}$](1)</Checkpoint>
<Checkpoint>[$\mathbf{D}$是$\mathrm{BaFeO_4}$](1)</Checkpoint>

常见的含有$\mathrm{[Fe(H_2O)_6]^{3+}}$的晶体有十二水合硫酸铁钾(或铵), 九水合硝酸铁等. 且题目中要求 $\mathrm{A}$ 为复盐，计算$\mathrm{KFe(SO_4)_2\cdot12H_2O}$的分子量为$39.10+55.85+2\times(32.07+4\times16.00)+12\times(2\times1.008+16)=503.282$. 

<Checkpoint>[计算$\mathrm{KFe(SO_4)_2\cdot12H_2O}$的分子量为503. $\mathbf{A}$ 是$\mathrm{KFe(SO_4)_2\cdot12H_2O}$](1)</Checkpoint>

能使$\mathrm{Fe^{3+}}$溶液变无色的为$\mathrm{F^-}$, 生成$\mathrm{FeF_6^{2-}}$, 含氟弱酸性 $D_{\infty h}$ 点群的阴离子为$\mathrm{HF_2^-}$. 

<Checkpoint>[$\mathbf{B}$是$\mathrm{KHF_2}$. $\mathbf{C}$是$\mathrm{K_3FeF_6}$](1)</Checkpoint>

|选项 |判断 |
|-----|-----|
|$\mathbf{A}$ 最常见的晶型为立方晶系|正确|
|$\mathbf{E}$ 的分子量大于400|错误|
|$\mathbf{B}$ 的阳离子由多个原子组成|错误|
|$\mathbf{D}$ 的水溶性较差|正确|
|$\mathbf{A}$ 溶于水变黄伴随着Brønsted酸的电离|正确|
|$\mathbf{C}$ 的分子量向下取整后是质数|错误|

<Checkpoint>[共3项正确, 答案为D](1)</Checkpoint>