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The calibration of the standard solution is very important. When the indicator is calibrated with methyl orange for the sulfuric acid solution, the end point is not good, because the color change is not acute. This should be noted at the time of calibration: 1 Accurately weigh and dry 0.02g of anhydrous sodium carbonate, and fully dissolve in 55ml of distilled water. Be sure to add 2.5 drops of methyl orange indicator until the solution is bright yellow, because the indicator plus or less will not be bright yellow. 2 too little indicator, the end color is not obvious, easy to make excessive titration of sulfuric acid solution; excessive indicator, the endpoint color is a bit purple. 3 When titrating, try not to calibrate in poor light or in the evening, because one-side natural light is the light source, can achieve the best titration effect. 4 In order to make the color more easily discernible, a few pages of filter paper can be added under the conical flask to make the color of the solution more obvious and easier to determine the end point.
In the determination process of the nitrogen determination instrument, we need to pay attention to the details. There is a slight oversight that will lead to an error in the results. We must always operate in accordance with the provisions of the national standard, but also on the basis of the national standard, sum up experience, improve the actual operation of the experiment and accuracy.
The color mixer is a machine that uses mechanical force and gravity to evenly mix two or more materials. Color mixing machines are widely used in various industries and daily life.
The color mixer can mix a variety of materials into a uniform mixture, such as cement, sand, crushed stone and water into wet concrete; It can also increase the contact surface area of materials to promote chemical reaction; It can also accelerate physical changes, such as adding solvent to granular solute, and accelerating dissolution and mixing through the action of mixing machinery.
Commonly used color mixers are divided into four categories: gas and low-viscosity liquid mixers, medium-high viscosity liquid and paste mixing machines, thermoplastic material mixers, and powder and granular solid material mixing machines. The gas and low viscosity liquid color mixing machine is characterized by simple structure, no rotating parts, small maintenance and low energy consumption. This type of mixing machinery is divided into four types: air flow mixing, pipe mixing, jet mixing and forced circulation mixing.
The color mixing machine of medium and high viscosity liquid and paste generally has strong shearing effect; Thermoplastic material mixer is mainly used for mixing thermoplastic materials (such as rubber and plastic) with additives; The mixing machines for powdery and granular solid materials are mostly intermittently operated, and also include machines with mixing and grinding functions, such as wheel rolling machines. During mixing, all materials involved in mixing shall be evenly distributed. The degree of mixing can be divided into three states: ideal mixing, random mixing and complete non-mixing. The mixing degree of various materials in the mixing machine depends on the proportion, physical state and characteristics of the materials to be mixed, as well as the type of mixing machine used and the duration of mixing operation.
The mixing of liquid mainly depends on the mechanical stirrer, air flow and the jet of the liquid to be mixed, so that the materials to be mixed are stirred to achieve uniform mixing. Stirring causes part of the liquid to flow, and the flowing liquid pushes the liquid around it, resulting in the formation of a circulating liquid flow in the solvent. The resulting diffusion between liquids is called the main body convection diffusion. When the liquid flow velocity caused by agitation is very high, there will be shear action at the interface between the high-speed liquid flow and the surrounding low-speed liquid flow, thus generating a large number of local vortices. These vortices spread rapidly around and bring more liquid into the vortex. The turbulent convection diffusion formed in a small range is called eddy diffusion.
The mixing mechanism of a small amount of insoluble powdery solid and liquid is different from the density component, and the mixing mechanism of immiscible liquid is the same, but stirring cannot change the particle size of powdery solid. If the settling velocity of solid particles cannot be less than the flow velocity of liquid before mixing, no matter what mixing method is used, it will not form a uniform suspension.
The mixing of different pastes is mainly to divide the materials to be mixed repeatedly and make them subject to the strong shearing effect caused by the actions of pressing, rolling, squeezing, etc., and then merge and knead repeatedly to reach the required mixing degree. This kind of mixing is difficult to achieve ideal mixing and can only achieve random mixing. The powdery solid is mixed with a small amount of liquid to form a paste, and its mixing mechanism is the same as that of paste material.
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