Why do some chemical experiments have to use newly made copper hydroxide?

Let's take a look at the test first:

Add a little copper hydroxide to a test tube.

crystal powder, and then add 40 formaldehyde aqueous solution.

1ml。Copper hydroxide is a light blue precipitate, put it in boiling water and heat it without reaction, and then add 10 NaOH solution dropwise to change its pH in turn. It was found that when pH 9, there was still no reaction.

When pH 11 12, a small fraction of Cu(Oh)2 dissolves into Cu(Oh)42-, and the solution turns light blue (there is still a light blue Cu(Oh)2 precipitate in the tube). When heated in a boiling water bath, Cu(OH)42- reacts with formaldehyde to form a Cu2O red precipitate (at the same time, Cu(OH)2 at the bottom of the test tube is heated to decompose into CuO black precipitate under strong alkaline conditions). At pH 14, the crimson blue color of the solution deepens, indicating that there is more Cu(OH)2 converted to Cu(OH)42-.

Heating rapidly produces Cu2O red precipitates.

The above experiments fully illustrate the importance of the presence of a strong base (NaOH) for this specific reaction. Based on this, let's analyze the description in the textbook again.

The experimental method is as follows: in a test tube, add 2ml of 10 NaOH solution, drop 2 CuSO4 solution 4 8 drops, and shake. Acetaldehyde is then added.

Aqueous solution, heat to boiling, and observe whether there is red precipitate in the solution.

It can be seen that the so-called "new copper hydroxide" in this experimental condition actually refers to copper hydroxide and sodium hydroxide.

of the mixture. Because, in a far excess of 10 NaOH solution, add 4 drops of 8 drops of 2 CuSO4 solution and mix the solution.

A considerable portion of pH 14,Cu2+ exists in the form Cu(OH)42-. This is also illustrated by the fact that the solution is crimson blue in color from the experimental phenomenon (Cu(OH)2 precipitation is barely visible). Therefore, we believe that sodium hydroxide directly participates in the reaction, so the chemical equations in the textbook will be used.

It would be more practical to change to the following formula.

ch3cho＋2cu(oh)2+naoh ch3coona+cu2o↓＋3h2o

The original textbook emphasizes the use of "freshly made copper hydroxide" because the copper hydroxide formed from the newly precipitated solution is relatively soluble in NaOH solution and produces Cu(OH)42- ions. The reaction of Cu(OH)42- ions and aldehyde solutions is a homogeneous reaction, and the reaction speed is relatively fast. Otherwise, the solid Cu(Oh)2 particles react with aldehydes, and even if Cu2O is generated, it is deposited and wrapped around the Cu(Oh)2 particles, separating the two reactants and making the reaction unable to proceed.

Because the previously prepared copper hydroxide is a precipitation, and the new copper hydroxide is a suspension, some reactions must be suspended, such as the new copper hydroxide is a suspension and formaldehyde reaction.

The laboratory uses copper sulfate solution mixed with sodium hydroxide solution to filter to produce copper hydroxide, and the reaction is as follows:

cuso4+2naoh=na2so4+cu(oh)2�1�0

If you look at it in the air, it will deteriorate.

Conservation with atoms reflects the conservation of anterior and posterior cus.

then n(cu) = n(cuo).

So m(cuo)=(3 64)*80=

CuO+H2==== Cu+H2O relative molecular weight 80 64

Mass x then 80 x=64 3 gives x=

Solution: Copper oxide x is required for copper extraction.

h2+cuo=cu+h2o

x80/64=x/

x=A: The mass of copper oxide that needs to be oxidized is.

Heating H2+CuO=Cu+H2O

x80/64=x/3

x=A: The mass of copper oxide that needs to be oxidized is.

Copper oxide is a blue flocculent precipitate that will decompose into black copper oxide when left or heated for a long time.

The most important thing is that:

Copper sulfate is added to sodium hydroxide, and the amount added at the beginning is small, and the resulting copper hydroxide immediately reacts with NaOH to form a complex (the alkali used in the reaction should be the concentrated alkali of ").

cu2+naoh

cu(oh)2

naohcu(oh)4]2-

This complex is used for water and is purple-blue in color.

Therefore, both the Halolin reagent and the biuret reagent are formulated with very low concentrations of CuSO4 and NaOH.

To prepare a new Cu(OH)2, Na(OH)2 (2mol L) should be dropped dropwise into the CuSO4 solution (at any concentration).

1.The vast majority of organic matter containing aldehyde groups.

Such as formaldehyde reducing sugar.

Glucose) should be noted here, fructose, chemically fructose has a ketone group, which is not reducible and cannot react with copper hydroxide.

But biologically, fructose can react with newly produced copper hydroxide.

2.Acidic organic compounds.

Such as formic acid acetic acid.

Hydrogen reacts with copper oxide, which is essentially hydrogen seizing the oxygen in copper oxide to form water, making copper oxide turn into red metallic copper.

Cuo + H2 = Cu + H2O (heating).

In this reaction, copper oxide loses oxygen and becomes copper, and copper oxide is reduced, i.e., copper oxide undergoes a reduction reaction. This reaction in which oxygen-containing compounds lose oxygen is called a reduction reaction. A substance that can seize the oxygen in the oxide and cause it to undergo a reduction reaction is called a reducing agent.

Reducing agents are reducible.

According to the combustion properties of hydrogen, it can be used as a fuel, which can be used in aerospace, welding, military and other aspects; According to its reducibility, it can also be used to smelt certain metal materials.

Junior Chemistry - Carbon Reduction Copper Oxide.

Here's an animation to make it clear how to do it.

1.Most of the organic matter containing aldehyde groups, such as formaldehyde, reducing sugar (glucose), here we should pay attention to fructose, fructose chemically has a ketone group, which is not reducible and cannot react with copper hydroxide.

But biologically, fructose can react with newly produced copper hydroxide.

2.Acidic organic compounds such as formic acid acetic acid.

aldehyde-containing organic matter, such as glucose;

Acidic organic matter, that is, it can ionize H+ ions;

The exception is fructose, which does not contain aldehydes but can react with the new copper hydroxide suspension.