甲酸具有還原性，從理論上也是不難理解的。但關(guān)于它還原氫氧化銅的實(shí)驗(yàn)，在教學(xué)中做起實(shí)驗(yàn)來(lái)沒(méi)有把握，達(dá)不到預(yù)期的效果。為此從改進(jìn)實(shí)驗(yàn)條件人手進(jìn)行探索，以達(dá)到較好的效果。

Formic acid has reducibility, which is not difficult to understand theoretically. But in the experiment of reducing copper hydroxide with it, it is not sure to do the experiment in teaching, and it can not achieve the expected effect. Therefore, we should improve the experimental conditions to achieve better results.

1.試劑與配制

1. Reagent and preparation

5％CuSO4溶液：7.4g CuSO4·5H2O溶于93.6ml水中，

5% CuSO4 solution: 7.4g CuSO4 · 5H2O was dissolved in 93.6ml water,

10％NaOH溶液：11.1g NaOH配100ml溶液

10% NaOH solution: 11.1g NaOH mixed with 100ml solution

甲酸濃溶液：～80％(原裝)

Formic acid concentrated solution: ～ 80% (original)
                            

2.操作與現(xiàn)象

2. Operation and phenomenon

為了便于觀察和對(duì)比，令反應(yīng)在U形管中進(jìn)行(亦可甲試管)，采用水浴加熱(90－95℃)。 先在U形管內(nèi)倒入約20－30m110％NaOH溶液，使液面距管口約5cm，再?gòu)墓芸?I)小心滴入3－5滴5％CuSO4溶液，液面有Cu(OH)2沉淀析出，然后慢慢注入8－10滴甲酸濃溶液，沉淀溶解，液層呈藍(lán)色(切勿振蕩)。將U形管置水浴中加熱(90－95℃)，約2分鐘后，在藍(lán)色液層和無(wú)色液層界面處出現(xiàn)薄層土紅色沌液(含Cu2O)。隨著反應(yīng)的進(jìn)行，土紅色沌液層不斷擴(kuò)大，約5分鐘后全部藍(lán)色液層變?yōu)橥良t色濁液。

For the convenience of observation and comparison, the reaction was carried out in a U-tube (or a test tube) and heated in a water bath (90-95 ℃). First, pour about 20-30 ml 110% NaOH solution into the U-shaped tube to make the liquid level about 5 cm away from the tube orifice. Then, carefully drop 3-5 drops of 5% CuSO4 solution from the tube orifice (I). There is Cu (OH) 2 Precipitation on the liquid level. Then slowly inject 8-10 drops of concentrated formic acid solution. The precipitation dissolves and the liquid layer is blue (do not shake). After heating the U-shaped tube in a water bath (90-95 ℃) for about 2 minutes, a thin layer of earth red chaotic liquid (containing Cu2O) appeared at the interface between the blue liquid layer and the colorless liquid layer. As the reaction proceeds, the turquoise chaotic liquid layer expands, and after about 5 minutes, all the blue liquid layers turn into Turquoise turbid liquid.

再在管口(Ⅱ)滴入3－5滴5％CuSO4溶液，立即有黑色膠凝物(在熱堿中生成的Cu(OH)2立即分解為CuO沉淀，然后滴入2-3滴甲酸溶液。不久，液面出現(xiàn)土紅色濁液層，且部分黑色膠凝物浮于液面，漸變?yōu)橥良t色。

Then 3-5 drops of 5% CuSO4 solution were dropped into the nozzle (II), and immediately the Black Gel (Cu (OH) 2 formed in hot alkali) was decomposed into CuO precipitate, and then 2-3 drops of formic acid solution were dropped. Soon, a soil red turbid layer appeared on the liquid surface, and some black gels floated on the liquid surface and gradually turned into soil red.

含有Cu2O的濁液層所以呈土紅色，一是還原產(chǎn)物(Cu2O)的量較少，二是混有CuO2，但都不影響實(shí)驗(yàn)的良好效果。

The results show that the turbidity layer containing Cu2O is earthy red, one is that the amount of reduction product (Cu2O) is less, the other is that it is mixed with CuO2, but it does not affect the good effect of the experiment.