黄铜中铜锌含量的测定(Determination of copper and zinc content in brass)
黄铜中铜锌含量的测定(Determination of copper and zinc content
in brass)
Determination of copper and zinc content in brass.Txt
(1) purpose of the experiment:
1. grasp the principle of the determination of copper and zinc by complexometric titration.
2. master the solution of brass.
(two) the principle of experiment:
Two cresol orange is a purple crystalline, soluble in water, it has 6 levels of acid dissociation. H6In to H2In4- is yellow, and HIn5- to In6- is red. When pH=5 ~ 6, the two cresol orange is mainly in the form of H2In4-. The acid-base dissociation balance of H2In4- is as follows:
H2In4-H2In4-, pKa=6.3, H++HIn5-pKa=6.3, H++HIn5-, H2In4-, pKa=6.3, H++HIn5-
Huang Huanghonghong Huang Hong
Thus, when pH>6.3, it assumes the red; when pH<6.3 appears yellow; when pH=p Ka=6.3, presents the intermediate color. The two cresol orange is formed with a mixture of red and purple, so it is only available in the acidic solution of pH<6.
Two cresol orange can be used for the direct titration of many
metal ions, such as ZrO2+ (pH<1), Bi3+ (pH=1 to 2), Th4+ (pH=2.5 to 3.5), etc. the endpoint is changed from bright red to bright yellow, with sharp discoloration. Al3+, Fe3+, Ni2+, Ti4+ and pH was 5 ~ 6 Th4+ has closed on two xylenol orange, Al3+ Ti4+, available NH4F masking, ascorbic acid mask Fe3+, two adjacent Orthophenanthroline mask Ni2+, Th4+, Al3+ and acetylacetone masking, to eliminate the blocking phenomenon;
Two cresol orange is usually formulated with an aqueous solution of 2G L-1, which is stable for about 2~3 weeks.
The chromogenic reaction of PAN and Cu2+ are very sensitive, the Cu-PAN indicator is a mixture of CuY and PAN, following the replacement reaction of the liquid to be measured in solution when the metal ion M:
When pH=10~12 is added with proper amount of CuY in PAN, the following reaction can take place
CuY (blue) +PAN (yellow) +M = MY + Cu-PAN
(Huang Lvshai) (purple red)
Cu-PAN is an indirect indicator. After the addition of EDTA and Cu2+, the PAN will dissociate from the Cu-PAN in a slightly excessive amount of Cu2+.
Cu-PAN+Y=, CuY, +PAN indicated the titration reached the end point
(purple red) (Huang Lvshai)
(three) experimental procedures:
Configuration of 1.0.01mol L-1EDTA standard solution
With a clean 500mL beaker, weigh the EDTA two sodium salt solids required for the 300mL0.01mol L-1EDTA standard solution. Add water, warm and dissolve in the beaker and transfer to a reagent bottle after cooling. Shake well.
Preparation of 2.Ca2+ standard solution
Take exactly the CaCO3 (150mL 0.1001 + 0.0002g) required for 100mL0.01mol L-1 Ca2+ in the beaker. First use a small amount of water wetting, cover the surface of the dish, from the beaker mouth drip 5mL6mol ? L-1HCl solution to make CaCO3 all dissolved (Note: 5mLHCl do not add, dissolved completely, and then add 1~2 drops of HCl can be). Add water to make the solution about 50mL and boil for a few minutes to remove the CO2. After cooling, rinse the surface dish with a small amount of water and transfer it to the 100mL capacity bottle. Dilute it to the scale and shake it well.
3., the standard 0.01mol L-1EDTA standard solution was calibrated at pH 10 using CaCO3 as the reference material
Absorb 10.00mLCa2+ standard solution in a conical flask, add 1 drops of 0.05% methyl red, neutralize (with) NH3 (1+2) H2O solution to the solution, turn pale yellow from red. Add 20mL water and 3mLMg2+-EDTA, add 5mLpH 10 buffer solution and 4 drops of black T indicator. Titrate immediately with the 0.01mol
L-1EDTA standard solution until the wine is pure red and blue is the finish line. Parallel calibration three parts, calculate the accurate concentration of EDTA solution.
4. dissolution of brass
Accurate quantity of 0.20 ~ 0.25g brass style in 150ml beaker, add 10ml (1+1) HCl, covered dish on the surface, partial drop 2 mL of 30% H2O2, heating the solution to form dissolved, then add 0.5g (NH4) S2O8, carefully graded and 10mL (1+1) 15mL ammonia, adding concentrated ammonia the heating and cooling, 1min, solution and precipitation transfer to a 250mL volumetric flask, constant volume, shake, dry filter.
Five
Determination of Zn2+
We took three 10mL filtrate, placed in a conical flask with 6 mol - L-1HCl (in addition to precipitation and acid dissolution, i.e. solution, adding blue fade) 6ml 10%Na2S2O3, 10ml pH 5.5 strain, adding NaAc to HAc buffer solution, XO (two with xylenol orange as indicator), add 4 drops. EDTA, 0.02 mol, L-1 titration, titration end point, the color of the solution by the red, yellow wine. Make a note of the amount of EDTA consumed per titration V1, and find the average value V (-) 1.
Determination of 6. Cu2+
We took three 10mL filtrate, placed in a conical flask with 6mol / L HCl 10ml pH joined the acidification, 5.5 NaAc ~ HAc buffer
solution, heating to boiling, then add 10mL ethanol, using PAN as indicator, adding 4~8 drops, the end point of titration, the color of the solution from purple to green grass. Make a note of the amount of EDTA consumed per titration V2, and find the average value V (-) 2.
(four) calculation formula
Zn%=[(CEDTA * V (-) 1 * 65.39) / (m * 10250 * 1000) * 100
Cu%=[(V (-) 2 - V (-) 1) * 63.54) / (m * 10250 * 1000) * 100 CEDTA