Why should I be careful not to touch the bottom of the beaker at the bottom of the test tube in the

The bottom of the test tube is close to the beaker, which is easy to cause uneven heating of the test tube and burst the test tube, so the bottom of the test tube should not touch the bottom of the beaker.

Methods for the identification of soluble reducing sugars:

1) Using Filin reagent: Filin reagent is prepared by NaOH solution with mass concentration and CuS04 solution at mass concentration, and after the two are mixed, a light blue Cu(OH)2 precipitate is generated immediately. Cu(OH)2 reacts with the aldehyde group under heating conditions and is reduced to a brick-red Cu2O precipitate, and the aldehyde group is oxidized to a carboxyl group.

It can be seen that only reducing sugars can be identified with Filin reagent, but not soluble non-reducing sugars. When the soluble reducing sugar is identified with Filin reagent, the color change process of the solution is: light blue, brown, brick red (precipitate).

2) Using Ban's reagent: Ban's reagent is prepared from liquid A (copper sulfate solution) and liquid B (sodium citrate and carbonic acid solution). Pour solution A into human solution B, stir while adding, and filter if there is precipitation.

The experimental principle is similar to that of Filin reagent, except that Ban's reagent can be used for a long time.

3) Use silver ammonia solution: silver ammonia solution is a drop of dilute ammonia water in the agno3 solution of 2 until the initial precipitate is just dissolved, and the solution obtained at this time is the silver ammonia solution. The silver ammonia solution contains Ag(NH3)2OH (silver diamine hydroxide), which is a weak oxidizing agent that oxidizes the aldehyde group to a carboxyl group and reduces Ag+ to metallic silver.

The silver produced by reduction adheres to the wall of the test tube, forming a silver mirror. It can be seen that the silver mirror reaction can also be used to identify soluble reducing sugars. The result of the identification was the appearance of a silver mirror.

This is a chemical problem, the temperature of the test tube directly touching the bottom of the cup will be too high, and the heating in the water is to be uniform.

If the bottom of the tube touches the bottom of the beaker, the tube will be heated unevenly.

Answer D The bottom of the test tube is close to the beaker, which is easy to cause uneven heating of the test tube and make the test tube burst.

Answer D In the experiment of identifying soluble sugar, when heating the solution in the test tube, the upper part of the test tube should be clamped with a test tube clamp, and put it in a large beaker filled with boiling water to heat the front rise, pay attention to the bottom of the test tube do not touch the bottom of the beaker, and at the same time, the mouth of the test tube should not be facing the experimenter, so as to avoid flushing out of the test tube when the old silver potato solution in the test tube is boiling and dusty, causing burns. If the solution in the tube is too boiling, you can use your hand to lift the tube clamp that holds the tube.

1.Feilin's reagent is prepared from a sodium hydroxide solution with a mass concentration of 0 1 g ml and a copper sulfate solution with a mass concentration of 0 05 g ml. Cu(OH)2 and the added glucose can produce a brick-red rock-tolerant Cu2O precipitate under heated conditions, and the glucose itself is oxidized to gluconic acid.

When the soluble reducing sugar is carefully identified with Filin reagent, the color change process of the solution is: light blue - brown - brick red (precipitate). 2.

When identifying the presence of proteins in biological tissues, the biuret method is commonly used, and the biuret reagent is used. The components of the biuret reagent are a solution of sodium hydroxide at a mass concentration of 0 1 g ml and a solution of copper sulfate at a mass concentration of 0 01 g ml. In alkaline solution (NaOH), diurea biscination (H2NOC-NH-ConH2) can react with copper ions to form purple or purplish-red complexes.

3.Iodized water is used for starch, but iodized salt does not seem to be possible. Blue.

(1) Identification of reducing sugar using Filin reagent, because Filin reagent is a mixture of sodium hydroxide and copper sulfate, reaction to generate copper hydroxide, so the configured reagent is blue After mixing the reagent with the apple tissue sample solution evenly, it must also be heated in a water bath, and when carrying out this operation, it is necessary to pay attention to the bottom of the test tube not to touch the bottom of the beaker The reagent interacts with the reducing sugar in the cell, and finally forms a brick-red precipitate

2) In the experiment of identifying the fat in the cotyledons of peanut, the Sudan dye solution will dye the fat orange, and the Sudan dye solution can dye the fat red, and when dyeing with it, it is necessary to rinse the floating color with 50% alcohol

3) When identifying proteins, when adding diuret reagent dropwise, reagent A solution (or solution) should be added first to create an alkaline environment, and then reagent B solution (or solution) should be added The amount of the latter is only 4 drops, and not excessive, because excessive diuret reagent B will react with reagent A, making the solution blue and covering up the purple color generated

So the answer is: 1) Filin reagent blue water bath heating beaker bottom brick red.

2) Sudan 50% alcohol.

3) Liquid A (or G ml NaOH solution) and Solution B (or G mLcuSO4 solution).

Excess biuret B reacts with Reagent A, giving the solution a blue color, masking the purple color that is generated.