分析化学实验(英文)

Experiment 1PH standard solution preparation and concentration comparison
A Purpose of the experiment
1.Learning to master the instrument commonly used in titration of washing and proper use.
2.Titration analysis of practice operations through an initial grasp of methyl orange, phenolphthalein indicator end point determination.
3.Grasp the pH standard solution preparation method.
Two Experimental principle
0.1 mol / L HCl solution (strong acid) and0.1 mol / L NaOH solution (alkaline) when each titration, pHsp 7.0, the pH titration jump range of 4.3- 9.7, select the color range in jump indicator ( such as methyl orange, phenolphthalein), can be measured to ensure sufficient accuracy.In the case of the same indicator, a certain concentration of HCl solution and NaOH solution each titration, the ratio of the volume consumed by V HCl / V NaOH should be certain, to, you can test titration technique and the ability to judge the end .
Three Main reagents and instruments
1. HCl solution of 6 mol / L.
2.Saturated NaOH solution (concentration of about15-19 mol /L).
3.Methyl orange solution1g / L.
4.Phenolphthalein solution of 2 g / L ethanol.
Four Experimental procedure
1.Solution preparation
(1) 0.1 mol / L HCl solution in a clean graduated cylinder to measure small-about8.3 mL 6 mol / L HCl solution was poured into480 mL of water containing about500 mL reagent bottle, add water, diluted to500 mL,covered with glass Cyprus, shaking.
(2) 0.1 mol / L NaOH solution in a clean graduated cylinder to measure small about3.3 mL saturated NaOH,poured into480 mL of water containing about500 mL reagent bottle, add water, diluted to500 mL,covered with rubber plug, shake uniform.
2.Titration between pH solution
(1) with0.1 mol / L NaOH alkaline solution rinse buret2-3times, each time with 5-10 mL solution rinse.And then directly into the alkaline titrant buret in the buret liquid level adjusted to0.00scale.
(2) with0.1 mol / L HCl solution, rinse Acid Burette2-3times, each time with5-10 mL solution rinse.And then directly into the acidic titrant in the buret, buret liquid level adjusted to0.00scale.
(3)from the buret in the release of alkaline NaOH solution20.00 mL in250 mL conical flask, add2drops of methyl orange indicator, with0.1 mol / L HCl titration to change from yellow to orange.Note reading, parallel to the determination of three.Data record in Table 1, calculate the volume ratio V HCl / V NaOH.
(4)from the buret in the release of acidic solution of20.00 mL HCl in250 mL conical flask, add2drops of phenolphthalein indicator, with0.1 mol / L NaOH solution titration to change from colorless to reddish, the red does not maintain the30s fade to end. Note reading, parallel to the determination of three.Data recorded in Table 2, calculate the volume ratio V HCl / V NaOH,and compare the Table1and Table 2, the volume ratio V HCl / V NaOH.
Five Data Processing
In this study, the data recording and processing are shown in Table1and Table 2..
Table 1 HCl NaOH solution titration(using methyl orange as indicator)
Table 2 NaOH titration of HCl solution (phenolphthalein as indicator)
Six Thinking problems
1. HCl and NaOH solution concentration can be accurately prepared me directly?Why?
2.Titration analysis in the experiment, buret, pipet titrator and why the need to take to move the solution washed several times Run?Titration flask used have to apply the titrant Run wash?Why?
3.Why NaOH titration with HCl using methyl orange as an indicator when, while titration of HCl with NaOH using phenolphthalein as an indicator of when (or other appropriate indicator)?
Experiment 2NaOH solution calibration and the determination of total acidity in vinegar
A Purpose of the experiment
1. To understand base material and potassium dihydrogen phthalate (KHP)the nature of its application.
2.Master NaOH standard solution of the preparation, standardization and save points.
3.Titration weak acid strong base titration to master the process of jump range and choice of indicator principle.
4.To understand the analysis of total acidity of vinegar.
Two Experimental principle
Acetic acid is an organic weak acid(Ka = 1.8 × 10- 5), and NaOH in the reaction is
HAc + NaOH = NaAc + H 2 O
Reaction product was weak alkali salt, alkaline titration jump in the context of such optional alkaline range of phenolphthalein indicator color.Consumption of acetic acid in vinegar is about30-50 g / L (3- 5%).
NaOH standard solution prepared with the calibration method, commonly used potassium dihydrogen phthalate (KHP)as the base material and calibration of its concentration. Calibration reaction is:
KHC 8 H 4 O 4 + NaOH = NaKC 8 H 4 O 4 + H 2 O
Three Main reagents and instruments
1.Saturated NaOH solution (concentration of about15-19 mol /L).
2.Phenolphthalein solution of 2 g / L ethanol.
3.Potassium dihydrogen phthalate (KHP) standard substance1h at100-125℃ after drying, placed in a desiccator spare.
Four Experimental procedure
1. 0.1 mol / L NaOH standard solution in the preparation and calibration
(1) 0.1 mol / L NaOH solution prepared in a clean small graduated cylinder to measure about 3.3 mL saturated NaOH, poured into480 mL of water containing about500 mL reagent bottle, add water, diluted to500 mL,covered with rubber plug , shake well.
(2) 0.1 mol / L NaOH solution to poor calibration of the weighing bottle, weighed KHP three subtraction, each0.4-0.6 g,were poured into250 mL conical flask, adding25-35 mL of water, heating to KHP to dissolve completely.Coolish after blowing flask with distilled water (why?).When completely cooled solution by adding2-3drops of phenolphthalein indicator, calibrated with NaOH solution to be titrated to maintain the30s reddish and shall end not fade.Note the reading, the data records shown in Table 1, calculate the concentration of NaOH solution.
2.Determination of total acidity in vinegar
Pipet25.00 mL of vinegar solution in250 mL conical flask, add2drops of phenolphthalein indicator, titrated with NaOH standard solution changed from colorless to reddish, the red does not fade as the end to keep 30s.Note reading, parallel to the determination of three.Data recorded in Table 2, calculate the total acidity of vinegar, the result in g/100 mL said.
Five Data Processing
In this study, the data recording and processing are shown in Table1and Table 2..
Table 1 NaOH standard solution calibration
Table2Determination of total acidity in vinegar
Six Thinking problems
1.Calibration standard solution of NaOH the base material used is what?Compared with other benchmark materials, it has any significant advantage?
2.Determination of vinegar content, why use phenolphthalein as the indicator? Whether the use of methyl orange or methyl red as indicator?
3.Phenolphthalein indicator from colorless to reddish, the solution pH,how many?Red solution in the air, then placed into a colorless why?
Experiment 3HCl solution, calibration and determination of total alkalinity of alkali dust
A Purpose of the experiment
1.Learn anhydrous sodium carbonate and borax base material and the nature of its application.
2.Master HCl standard solution of the preparation and calibration procedure.
3.To master the dual bases, titration acid titration process of jump range and choice of indicator principle.
4.To master the basic elements of quantitative transfer operation.
Two Experimental principle
Alkaline ash (that is, industrial soda ash) is mainly composed of sodium carbonate, soda brand name, which may also contain a small amount of NaCl, Na 2 SO 4,NaOH and NaHCO and other ingredients.Often HCl standard solution for the determination of total 3
alkalinity titrant to measure the quality of the product.Titration reaction
Na 2 CO 3 + 2HCl = 2NaCl + H 2 CO 3
H 2 CO 3 = H 2 O + CO 2↑
Reaction H 2 CO 3is easy to form the supersaturated solution and decomposes to CO
and escape.Stoichiometric point,pH value of 3.8- 3.9, can be used methyl orange 2
as indicator, titrated with HCl standard solution, the solution changed from yellow to orange to end.Sample of NaHCO 3were in the same time and.
As the sample is easy to absorb moisture and CO 2,the sample should be dried at270-300℃ 2 h, to remove adsorbed water and to all of NaHCO 3into Na 2 CO 3,alkali dust of the total alkalinity is usually Or Said that as the poor uniformity of samples, more
samples should be weighed to make it more representative.Determination of allowable error may be relaxed.
Calibration method using HCl standard solution preparation, often with methyl orange as indicator, with anhydrous Na 2 CO 3as the base material and calibration concentration. Calibration reaction is:
Na 2 CO 3 + 2HCl = 2NaCl + H 2 CO 3
Can also be used borax(Na 2 B 4 O 7 · 10H 2 O)as the base material, using methyl red as indicator, calibration standard solution of HCl concentration.Calibration reaction is:
Na 2 B 4 O 7 · 10H 2 O + 2HCl = 2NaCl + 4H 3 BO 3 + H 2 O
Three Main reagents and instruments
1. HCl solution of 6 mol / L.
2.Anhydrous Na 2 CO 3base material Drying at180℃ for2-3 h later, placed in
a desiccator spare.
3.Methyl orange solution1g / L.
Four Experimental procedure
1. 0.1 mol / L HCl standard solution for preparation and calibration
(1) 0.1 mol / L HCl solution prepared in a clean graduated cylinder to measure
small-about8.3 mL 6 mol / L HCl solution was poured into480 mL of water containing about500 mL reagent bottle, add water, diluted to500 mL,cover the glass stopper, shake.
(2) 0.1 mol / L HCl solution to poor calibration of the weighing bottle, subtraction, said anhydrous Na 2 CO 3three, each of0.15-0.20 g,respectively, into250 mL conical flask, adding25-35 mL water, heated to completely dissolve Na 2 CO 3.Coolish after blowing flask with distilled water (why?).When completely cooled solution, add2drops of methyl orange indicator to be calibrated with HCl titration solution from yellow to orange as the end point exactly.Note the reading, the data records shown in Table 1, calculate the concentration of HCl solution.
2.Alkaline ash Determination of total alkalinity
Accurately weighed sample 1.8-2 g and the beaker, add appropriate amount of water, heated to dissolve the sample completely.After cooling, quantitatively transfer the solution to250 mL volumetric flask with water set to the mark, shake it well.Pipet
25.00 mL test solution three in250 mL conical flask, adding20 mL water and2drops of methyl orange indicator, titrated with HCl standard solution from yellow to orange as the end point exactly.Note the reading.Data recorded in Table 2, calculate the total alkalinity of the sample, the results indicated by Na 2O%.
Five Data Processing
In this study, the data recording and processing are shown in Table1and Table 2..
Table 1 HCl standard solution for calibration
Table2Determination of total alkalinity of alkali dust (m alkali gray= g)
Six Thinking problems
1.Why are prepared0.1 mol / L HCl solution,500 mL requirements take 6 mol / L HCl solution of8.3 mL?Write a calculation formula.
2.Anhydrous Na 2 CO 3kept properly, absorb the1%water, with this reference material and calibration of the concentration of HCl solution, what the impact on its results?
3. When titrated with HCl solution, the use of methyl orange and phenolphthalein indicator to distinguish the two samples are from the Na 2 CO 3-NaOH or Na 2 CO 3-NaHCO 3 composition?
4.Demarcation of the two reference substances HCl,Na 2 CO 3and anhydrous borax(Na
B 4 O 7 · 10H 2 O)is what advantages and disadvantages of each?
2
Experiment 4EDTA solution calibration and determination of water hardness
A Purpose of the experiment
plexometric titration study the theory and application.
2.Grasp the complexometric titration of the direct titration.
3.Master EDTA solution preparation and calibration.
Two Experimental principle
Determination of water hardness and total hardness of water into calcium - magnesium hardness of the former is to measure the total calcium and magnesium, the latter were measured concentration of calcium and magnesium.
Countries in the world that the method of water hardness varies, generally use the degrees (°) said,1°= 10 mg CaO / L.Less than16° for the soft water, greater than16° for the hard water.The total hardness of tap water generally is less than 16°.In addition, China also uses mmol / L or mg / L (CaCO 3)as the unit of water hardness.
In this study EDTA complexometric titration of total water hardness.The ammonia in pH10buffer to chrome black T as indicator, with triethanolamine, and Na 2 S masking Fe 3 +, Al 3 +, Cu 2 +, Pb 2 +, Zn 2 +and other ions, with EDTA standard solution titration, can be directly measured total water hardness.Titration reaction
Ca 2 + + Mg 2 + +Y → CaY + MgY
EDTA standard solution prepared with the calibration.In this experiment, chrome black T (EBT)as indicator, as the base material with CaCO 3concentration of calibration.Chrome black T indicator to improve the color of sensitivity, can be added to an appropriate amount of MgY.Calibration reaction is:
CaCO 3 + 2HCl = 2CaCl + H 2 CO 3
Ca 2 + + MgY +Y → CaY + MgY
Three Main reagents and instruments
1. EDTA solution0.01 mol / L.
2. NH 3-NH 4 Cl buffer solution of pH = 10.
CaCO 3reference material dried at110℃, 2 h,coolish placed in the desiccator 3.
after cooling to room temperature and set aside.
4.Eriochrome Black T indicator 5 g / L (containing 25%triethanolamine and20% Na 2 S).
5. HCl solution6mol / L.
Four Experimental procedure
1. 0.01 mol / L EDTA standard solution for calibration
Subtraction Method in the weighing bottle to accurately weigh0.2-0.3 g CaCO 3,poured into250 mL beaker, add a little water before wetting, cover the surface of dish, from beaker to beaker mouth Department dropping about 5 mL 6 mol / L HCl solution, so that CaCO 3is completely dissolved.Water50 mL,micro boiling a few minutes to remove CO 2.After cooling, rinse the beaker and watch glass, quantitative transfer of CaCO
solution in250 mL volumetric flask with water set to the mark, shake well.Pipet 3
25.00 mL Ca 2 +solution in the250 mL conical flask, adding20-25 mL water and5-10 mL MgY(obtained from the experiment in step 2), and then adding10 mL NH 3-NH
Cl buffer solution ,3drops of Eriochrome Black T indicator, immediately EDTA
4
titration, when the solution stabilized by a wine red to blue purple and then just end shall be.Note reading, measured three times in parallel, the data record shown in Table 1, calculate the concentration of EDTA solution.
2.Determination of water hardness
Graduated cylinder to measure water with100 mL in250 mL conical flask, (adding1 -2drops of acid to sample solution, boil a few minutes to remove CO 2.Cooling), by adding10 mL NH 3-NH 4 Cl buffer solution,3drops of Eriochrome Black T indicator, immediately with EDTA titration, when the solution stabilized by a wine red to blue purple and then just shall end.Note reading, measured three times in parallel, the data record shown in Table 2,calculate the total water hardness, results in (°) said. Five Data Processing
In this study, the data recording and processing are shown in Table1and Table 2.
Table 1 EDTA standard solution for calibration
Table2Determination of water hardness
Six Thinking problems
1. EDTA used in this experiment with what indicator should be calibrated? The most appropriate benchmark for material that?
2.In the calibration process, adding MgY What is the role?MgY it should be accurate to join?
3.In this study, the total hardness in tap water (°) that should be reserved several significant figures? A brief explanation.
Five calibration experiments EDTA solution and Bi 3+, Pb2+ content of Determination
A Purpose of the experiment
1.Control the acidity increase by the control theory and application of selective EDTA.
2.To master continuous titration with EDTA method.
3.Master EDTA solution preparation and calibration.
Two Experimental principle
Mixed ions were commonly used control acidity titration method, masking method can be demonstrated according to the side reaction coefficient of the possibility of their titration, respectively.
Bi 3+,Pb2+and EDTA can form a stable1: 1complex,lgK 27.94and 18.04,respectively. Because of the difference lgK vary widely, it can make use of pH effect, control of different acidity, for each titration.At pH ≈ 1时titration Bi 3+, at pH ≈ 5-6时titration of Pb 2+.
EDTA standard solution prepared with the calibration.In this experiment, xylenol orange (XO)as indicator, calibrated with ZnO as the base material and its concentration. Calibration reaction is:
ZnO + 2HCl = ZnCl 2 + H 2 O
Zn 2 + +Y → ZnY
Three Main reagents and instruments
1. EDTA solution0.01 mol / L.
2.Hexamethylenetetramine solution of200 g / L.
3. ZnO base material and dried at300℃ for 2 h,coolish placed in the desiccator after cooling to room temperature and set aside.
4.Xylenol orange (XO) indicator 2 g / L.
5. HCl solution of 6 mol / L.
Four Experimental procedure
1. 0.01 mol / L EDTA standard solution for calibration
Subtraction Method in the weighing bottle to accurately weigh0.16-0.24 g ZnO,into 250 mL beaker, add a little water before wetting, cover the surface of dish, from beaker to beaker mouth Department dropping about5 mL 6 mol / L HCl solution to ZnO completely dissolved.Water20 mL,micro boiling a few minutes.After cooling, rinse the beaker and watch glass, quantitative transfer of Zn 2 +solution in250 mL volumetric flask with water set to the mark, shake well.Pipet25.00 mL solution of the Zn 2 +in250 mL conical flask, dropping hexamethylenetetramine solution to a stable red solution was then over3 mL,then add2drops of xylenol orange indicator immediately with EDTA titration, when the solution stabilized by the purple into a bright yellow orange and then just end shall be.Note reading, three parallel determination, calculated the concentration of EDTA solution.
2. Bi 3+, Pb2+ content of Determination
Accurately pipet Bi 3+,Pb2+test solution was10.0 mL in250 mL three conical flask, add2drops of xylenol orange indicator, titration with EDTA, (adding1-2drops to test solution acidification, boiling minutes to remove CO 2.cooling), by adding10 mL NH 3-NH 4 Cl buffer solution, when the solution from purple through orange and then just turned into a stable bright yellow shall be Bi 3+ in the end.Note reading, calculating mixture of Bi 3+ content results in g / L,said.
In the titration of Bi 3+ solution after the adding hexamethylenetetramine solution to a stable red solution was then over3 mL,then add2drops of xylenol orange indicator, and immediately titrated with EDTA,when solution stabilized by the purple into a bright yellow orange and then just shall Pb2+in the end.Note reading, calculating mixture of Pb2+ content, results in g / L,said.
Five Data Processing
In this study, data records and forms from the column.
Six Thinking problems
1. EDTA used in this experiment with what indicator should be calibrated? The most appropriate benchmark for material that?
2.Why not NaOH, NaAc or ammonia, but with hexamethylenetetramine adjust pH to5 - 6?
experiment six Back titration samples of aluminum content in aluminum
A Purpose of the experiment
1.Grasp the back titration.
2.Learn replacement titration.
3.Mental and physical, hands-on experimental design.
Two Experimental principle
Al 3 +is easy to form a series of polynuclear hydroxy complexes, the polynuclear hydroxyl complexes with EDTA complex and slow; the same time,Al 3 +closed indicator xylenol orange, it is usually determined by back titration of aluminum.Quantitative and adding excess EDTA standard solution, boil a few minutes at pH≈ 3.5,so that Al 3 +and EDTA complex completely, then at pH 5- 6, with xylenol orange as indicator, with Zn 2 +salt standard excess of EDTA solution and back titration of aluminum content.Reactive as follows:
Al 3 + + Y = AlY (pH≈ 3.5)
Zn 2 + + Y = ZnY (pH5- 6)
(Indicator has just changed from yellow to purple XO)
Three Main reagents and apparatus
Aluminum nitrate samples; ZnO; HCl (1 +1),(1+3); EDTA (0.01mol / L);xylenol orange(2 g / L);
Hexamethylenetetramine(200 g / L);ammonia(1 +1).
Four Experimental procedure
1 Zn
2 + salt standard solution preparation
Weigh accurately0.20-0.21 g ZnO in a small beaker, dropping(1 +1) HCl to ZnO completely dissolved, then supplement of1drop (1 +1) HCl, heating, cooling, into250 mL volumetric flask , set the volume, shake and set aside.ZnO calculated according to the quality of the material in the amount of standard solution concentration (in Zn 2 +dollars).
2 0.01mol / L EDTA standard solution for preparation and calibration
Measure out50 mL EDTA solution(0.1mol / L)in the reagent bottle, diluted to500 mL with distilled water around, shake and set aside.Dispense25 mL Zn 2 +standard solution (three) in the conical flask, add2drops of xylenol orange, was added dropwise to the solution of hexamethylenetetramine just become purple, then over 3 mL;with homemade The EDTA titration to the solution just becomes bright yellow for the end, record the volume consumed EDTA solution.According to the data of the exact concentration of EDTA solution.
3 Determination of aluminum in aluminum-containing samples
Weigh accurately0.53-0.55 g aluminum nitrate samples in small beaker, add3drops (1 +3) HCl, add the appropriate amount of water dissolved, transferred to a250 mL volumetric flask, volume, shaking.Dispense the Al test solution25 mL(three) in the conical flask, were added50 mL EDTA solution accuracy(about 0.01mol / L), 2drops of xylenol orange, then yellow test solution, add ammonia to the solution was purple, together with(1 +3) HCl solution, the solution yellow.Boiled 3 min,cooling.Add 20 mL of hexamethylenetetramine, then the solution should be yellow, red if the solution must also dropping (1 +3) HCl,to turn plement plus1drop of xylenol orange, Zn 2 +standard solution with flat to just drop into the purple to finish, recording the consumption of Zn 2 +standard solution volume.According to the experimental data of the content of aluminum in aluminum-containing samples (in percentage terms of quality).
Five Data recording and processing
Table1 EDTA standard solution for calibration(m ZnO = g, c ZnO = mol / L)
Table2Determination of aluminum in aluminum-containing samples (G sample= g)
The formula is:
Six Thinking problems
1.For complex alloy sample without replacement titration, while the use of back titration, the result is high or low?
2.Back titration with the replacement of EDTA used in titration What is the difference?
Experiment 7KMnO 4solution,H 2 O 2
calibration and determination
A Purpose of the experiment
1.Grasp the KMnO 4solution preparation and calibration process, understand the autocatalytic reaction.
2.Master KMnO 4 H 2 O 2determination of the principles and methods.
3.On the KMnO 4have experience of the characteristics of its own indicator.
Two Experimental principle
Hydrogen peroxide in the industry, biology, medicine, have a wide range of applications, therefore, often required to determine its practical content.Determination by KMnO H 2 O 2content, often using KMnO 4in sulfuric acid solution standard solution direct 4
titration.Titration reaction
5H 2 O 2 +2 MnO 4-+ 6 H + =2Mn2+ + 5O2↑ + 8H2 O
The beginning of the slow reaction rate, reaction products to be generated after Mn 2 +, Mn 2 +as a catalyst to accelerate the reaction rate, it can be successfully titrated to a stable reddish presented to the end, so called auto-catalytic reaction.Slightly excessive titrant(2 × 10-6 mol / L)itself purple to display the end.
KMnO 4standard solution prepared with the calibration method, often in dilute sulfuric acid solution, at75-85℃, using Na 2 C 2 O 4as the base material, calibration concentration.Calibration reaction is:
5C 2 O 4 2-+2 MnO 4-+ 16 H + =2Mn2+ + 10CO2↑ + 8H2 O
The calibration response is autocatalytic reaction, the chemical reaction process should pay attention to acidity, temperature and titration rate.
Three Main reagents and instruments
1. H 2 SO 4solution of 3 mol / L.
Na 2 C 2 O 4reference material Dried at105℃ for 2 h after the backup.
2.
3. KMnO 4solution of0.02 mol / L.
Four Experimental procedure
1. KMnO 4solution preparation
Weigh KMnO 4solid1.6 g,dissolved in500 mL water, cover the surface of pan, heated to boiling and maintain micro-boiling state 1 h,after cooling, with a porous glass funnel (No.3or 4) filter.Filtrate stored in a brown reagent bottle.The solution at room temperature,2-3days after the filtration reserve.
2. KMnO 4solution calibration
Subtraction Method in the weighing bottle to accurately weighed Na 2 C 2 O 4three, each of0.15-0.20 g,respectively, into250 mL conical flask, adding50-60 mL water and 15 mL H 2 SO 4, blowing a small amount of distilled water flask(Why?),heated to75-85℃, hot to be calibrated with a solution of KMnO 4titration.When the reaction began to slow titration, the solution had to be Mn 2 +,the titration speed may be faster, until the solution showed reddish and continued for half a minute does not fade shall end. Data record in Table 1, calculate the concentration of KMnO 4solution.
3. H 2 O 2content
Accurate, pipet25.00 mL test solution in250 mL conical flask, three, by adding50 mL water and20 mL H 2 SO 4,KMnO 4standard solution with a titration solution and continued for half a minute showed reddish discoloration shall not end.When the reaction began to slow titration, the solution had to be Mn 2 +,the titration speed may be accelerated.Data recorded in Table 2,calculation of test solution in H 2 O 2content, results in g / L,said.
Five Data Processing
In this study, the data recording and processing are shown in Table1and Table 2..
Table 1 KMnO 4standard solution for calibration
Table2 H 2 O 2content
Six Thinking problems
1. KMnO 4solution preparation process to use porous glass filter funnel, how can quantitative filter paper filter?Why?
2.Prepared KMnO 4solution should pay attention to?With Na 2 C 2 O 4calibration KMnO 4solution, why start drops of KMnO 4purple disappear slowly?Then they disappear faster and faster, until the endpoint of stability of the purple?
3.With KMnO 4 H 2 O 2determination, the ability to use HNO 3, HCl or HAc control of acidity?Why?
4.Preparation of KMnO 4solution, the filtration after the filter on the adhesion of the material for that?What material should be used to clean?
5. H 2 O 2What are the important properties, should pay attention to what use?
Experiment 8CuSO 4 · 5H 2 O in the Cu content
A Purpose of the experiment
1.Master Na 2 S 2 O 3solution preparation and calibration points.
2.To understand the role of starch indicator principle.
3.Indirect iodometric method for the determination to master the principle and operation of copper.
4.To understand the decomposition of copper alloy samples.
Two Experimental principle
Copper alloy sample and CuSO 4 · 5H 2 O in the determination of copper, generally use the iodometric method.
In weak acid solution,Cu 2 +and the role of excess KI to generate Cu I precipitation, while precipitation of I 2,titration reaction
Cu 2 + + 4 I-+ 6 H+= 2 Cu I↓+ I 2
2
Precipitation of I 2,with starch as indicator, with Na 2 S 2 O 3standard solution titration:
I 2 + 2 S 2 O 3 2-=2 I-+ S4O62-
Cu 2 +and I- the reaction is reversible by adding excess KI, the reduction of Cu 2 + can become completely, but,CuI precipitate strongly adsorbed I 2,then the results will lower.The usual approach is to be incorporated in the near end of thiocyanate, the CuI (Ksp = 1.1 × 10-12)into the solubility of smaller CuSCN (Ksp = 4.8 × 10-15) precipitation, the adsorption of iodine released CuI to respond more fully.That
CuI + SCN-= CuSCN + I-
KSCN near the finish line should be added, or SCN- would restore the abundance of I 2,led to lower measured results.Solution pH should generally be controlled at3.0 -4.0between.Acidity is too low,Cu 2 +easily hydrolyzed, the reaction is not complete, the result is low, and slow reaction rate, the end extension; acidity is too high, then I- oxidation by oxygen in the air as I 2,so that the results high.
Determination of copper in copper alloys, the samples of Fe 3 +oxidation of I-,affects the determination, but may be masked by adding NH 4 HF 2.NH 4 HF 2is a good buffer solution, can control the solution pH 3.0- 4.0between.
Na 2 S 2 O 3standard solution prepared with the calibration method, often using K 2 Cr
O 7as the base material, calibration concentration.Calibration reaction is:
2
Cr 2 O 7 2-+ 6 I-+ 14 H + = 2 Cr 3 + + 3I 2 + 7H 2 O
I 2 + 2 S 2 O 3 2-=2 I-+ S4O62-
Three Main reagents and instruments
1. KI solution of 4%.。