The main test points of sodium hydroxide deterioration include: deterioration reason, test deterioration method, test deterioration degree, and get pure sodium hydroxide by removing impurities. (total metamorphism: Na2CO3, partial metamorphism: Na2CO3, NaOH)

1、氫氧化鈉變質的原因：敞口放置，與空氣中的二氧化碳反應，生成了碳酸鈉。

1. The reason for the deterioration of sodium hydroxide: it is placed open and reacts with carbon dioxide in the air to form sodium carbonate.

原理：2NaOH + CO2 = Na2CO3 + H2O

Principle: 2naoh + CO2 = Na2CO3 + H2O

2、檢驗氫氧化鈉是否變質的方法：(分別滴加酸、堿、鹽溶液，各為一種方法)

2. Method for testing whether sodium hydroxide is deteriorated: (add acid, alkali and salt solutions dropwise respectively, one method for each)

①取少量樣品于試管中，滴加足量稀鹽酸(或者稀硫酸)，如果產生氣泡，說明已變質。無明顯現象，說明未變質。

① Take a small amount of sample into the test tube and add enough dilute hydrochloric acid (or dilute sulfuric acid). If bubbles appear, it indicates that it has deteriorated. No obvious phenomenon, indicating no deterioration.

原理：Na2CO3 + 2HCl = 2NaCl + H2O + CO2↑

Principle: Na2CO3 + 2HCl = 2nacl + H2O + CO2 ↑

②取少量樣品于試管中，滴加氫氧化鈣溶液(或者氫氧化鋇溶液)，如果產生白色沉淀，說明已變質。

② Take a small amount of sample into the test tube and add calcium hydroxide solution (or barium hydroxide solution) dropwise. If white precipitation occurs, it indicates that it has deteriorated.

原理：Na2CO3 + Ca(OH)2 = CaCO3↓ + 2NaOH

Principle: Na2CO3 + Ca (OH) 2 = CaCO3 ↓ + 2naoh

③取少量樣品于試管中，滴加氯化鈣溶液(或者硝酸鈣等其它可溶性鈣鹽、鋇鹽溶液。)

③ Take a small amount of sample into the test tube and add calcium chloride solution (or calcium nitrate and other soluble calcium salt and barium salt solutions) dropwise

原理：Na2CO3 + Ca Cl2 = CaCO3↓ + 2NaCl

Principle: Na2CO3 + CaCl2 = CaCO3 ↓ + 2nacl

3、檢驗氫氧化鈉變質程度的方法：取少量樣品于試管中，滴加足量的CaCl2溶液，有白色沉淀生成；過濾，向濾液中滴加少量酚酞溶液，如果溶液變紅色，說明溶液部分變質；如果溶液呈無色，說明氫氧化鈉完全變質。

3. Method for testing the deterioration degree of sodium hydroxide: take a small amount of sample in the test tube, drop sufficient CaCl2 solution, and white precipitation will be formed; Filter and add a small amount of phenolphthalein solution to the filtrate. If the solution turns red, it indicates that part of the solution has deteriorated; If the solution is colorless, sodium hydroxide is completely deteriorated.

原理：（1）氫氧化鈉和變質后生成的碳酸鈉溶液都呈堿性，滴加足量的氯化鈣溶液是為了除盡生成的碳酸鈉，這時會產生白色沉淀，然后滴加酚酞溶液【還可以加入：MgCl2（白色沉淀）、CuCl2（藍色沉淀）、FeCl3（紅褐色沉淀）、FeCl2（白色沉淀）、NH4Cl（刺激性氣味）、紫色石蕊溶液】，如果溶液呈紅色，說明溶液呈堿性，有未變質的氫氧化鈉，部分變質。如果溶液不變紅，說明沒有氫氧化鈉了，完全變質了。

Principle: (1) sodium hydroxide and sodium carbonate solution generated after metamorphism are alkaline. Add sufficient calcium chloride solution to remove the generated sodium carbonate. At this time, white precipitation will be generated, and then drop phenolphthalein solution [you can also add MgCl2 (white precipitation), CuCl2 (blue precipitation), FeCl3 (reddish Brown precipitation), FeCl2 (white precipitation), NH4Cl (pungent smell), purple litmus solution], If the solution is alkaline, it indicates that there is no deterioration of sodium hydroxide solution. If the solution remains red, it indicates that there is no sodium hydroxide and it has completely deteriorated.

Na2CO3 + CaCl2 = CaCO3↓ + 2NaCl(注意：除去碳酸鈉時，不能用氫氧化鈣，因為氫氧化鈣與碳酸鈉反應會生成新的氫氧化鈉，會干擾對氫氧化鈉的檢驗。

Na2CO3 + CaCl2 = CaCO3 ↓ + 2nacl (Note: calcium hydroxide cannot be used when removing sodium carbonate, because the reaction between calcium hydroxide and sodium carbonate will produce new sodium hydroxide, which will interfere with the inspection of sodium hydroxide.

原理：Na2CO3 + Ca(OH)2 = CaCO3↓ + 2NaOH )

Principle: Na2CO3 + Ca (OH) 2 = CaCO3 ↓ + 2naoh)

4、如何除去部分變質的氫氧化鈉中的碳酸鈉。

4. How to remove sodium carbonate from partially deteriorated sodium hydroxide.

滴加適量氫氧化鈣溶液，然后過濾，就得到氫氧化鈉溶液，再蒸發，就得到氫氧化鈉固體。

Add an appropriate amount of calcium hydroxide solution dropwise, then filter to obtain sodium hydroxide solution, and then evaporate to obtain sodium hydroxide solid.

原理：Na2CO3 + Ca(OH)2 = CaCO3↓ + 2NaOH

Principle: Na2CO3 + Ca (OH) 2 = CaCO3 ↓ + 2naoh

(注意：①不能選用鹽酸或硫酸等酸液，因為酸與碳酸鈉反應的同時也會與氫氧化鈉反應，而且會生成NaCl或Na2SO4，引入了新的雜質。②不能用氯化鈣等鹽溶液，因為它們會碳酸鈉反應生成了NaCl，引入了新的雜質。)

(Note: ① acid solutions such as hydrochloric acid or sulfuric acid cannot be selected, because the acid will react with sodium hydroxide while reacting with sodium carbonate, and will generate NaCl or Na2SO4, which introduces new impurities. ② salt solutions such as calcium chloride cannot be used, because they will react with sodium carbonate to generate NaCl and introduce new impurities.)