The pH value of chromium hydroxide precipitation is between 2.0 and 7.5. In this range, when the pH value increases, the precipitation rate will also increase. Generally controlled at 4, the precipitation is considered complete. The stable range of aluminum hydroxide is 4 to 1 1, and both strong acid and alkali will dissolve. The ph value of the precipitate produced by chromium hydroxide is about 5.
PH value of metal hydroxide precipitation
1, rare earth fluoride English red and white powder.
2, hydrochloric acid, nitric acid, sulfuric acid, soluble in perchloric acid.
3. It can be used for thin film arc carbon rods, searchlight carbon rods, luminescent materials, steel additives, etc.
4. The aqueous solution of rare earth hydroxide or non-chlorinated rare earth reacts with non-hydrofluoric acid, but does not precipitate.
5. The preparation method of rare earth fluoride comprises the following steps.
6. The molar ratio of rare earth oxide to non-acetic acid is1:6-8, or the rare earth oxide is dissolved in 20%-40% dilute acetic acid to form a rare earth acetic acid aqueous solution.
Dissolve ammonium fluoride, a rare earth oxide with a molar amount of 10 times, in deionized water to form an ammonium fluoride aqueous solution.
8. It is planned to mix and react the aqueous solution of rare earth acetate in array A with the aqueous solution of ammonium fluoride in non-array B to precipitate rare earth fluoride.
Determination method of pH value
PH test paper and pH meter are usually used to determine the pH value of solution. The specific operation of measuring the pH value of solution with pH test paper is as follows: When measuring, put the pH test paper on the surface mirror, dip the solution to be measured with a clean glass rod and drop it on the pH test paper. After half a minute, compare the color displayed on the test paper with the standard colorimetric card, and read out the pH value of the solution, abbreviated as "one put, two dips, three drops and four ratios".
Matters needing attention in the determination of pH value
The pH test paper cannot be directly immersed in the solution to be tested, so as to avoid bringing in impurities, and at the same time, some indicators on the pH test paper may be dissolved, resulting in a large colorimetric error. Do not wet the pH test paper with water before determination. Because the solution to be measured drops on the pH test paper wetted with water, its solute mass fraction will become smaller. The pH value of the solution measured by pH test paper is generally an integer.
Method of changing pH value of solution
The pH value of the solution is essentially the external expression of the concentration of H or OH in the solution. Changing the concentration of H or OH in the solution will change the pH value of the solution. Method 1: adding water: only the pH value of the solution can be changed, but not the pH value of the solution, that is, the pH value of the solution can only be infinitely close to 7.