Error analysis of experimental metal phase diagram Experiment 1: Determination of combustion heat
1. What systems are there in this experiment? What are the environments? Is there heat between the system and the environment? How does this heat affect the experimental results? How to correct it?
It is pointed out that the material and space in the barrel are a system, except for the calorimeter in the barrel, the rest are the environment, and there is heat between the system and the environment. The existence of heat will affect the accurate value of combustion heat measurement, and its influence can be reduced by Reynolds correction curve correction.
2. Why do solid samples need to be pressed into thin sheets? How to determine the dosage of naphthalene and benzene?
Tip: pressing into sheets is beneficial to the full combustion of samples; When the dosage is too small, the determination error of naphthalene and benzene is large, and when the dosage is too large, it can not be completely burned. The maximum dosage of the sample can be determined according to the volume of the bomb and the internal oxygen pressure.
3. Try to analyze the reasons why the sample can't burn and can't burn.
Tip: If the pill is too tight and the burning wire gets stuck in the pill, it won't ignite. Too loose pills and insufficient oxygen can cause burns.
4. What are the main factors that affect the experimental results? What is the key to the success of this experiment?
It is pointed out that whether the sample can be fully burned and the heat between the system and the environment are the main factors affecting the experimental results. The key to the success of this experiment is: the right amount of drugs, the tightness of tablets and the correction of Reynolds temperature.
5. What should I pay attention to when using oxygen cylinders and oxygen decompressors?
Tip: Read the textbook Physical Chemistry Experiment-
Experiment 2 Determination of Relative Molecular Weight by Freezing Point Reduction Method
1. What may cause overcooling? If it is too cold, is the freezing point of the tested solution low or high? Is the relative molecular weight of naphthalene obtained by this method low or high? Explain why.
A: Too low refrigerant temperature will cause too low cooling. If the supercooling is too high, the freezing point of the measured solution is low. According to formula and, it can be seen that the relative molecular weight of naphthalene is low because the freezing point of the solution is low and Tf is too large.
2. What's wrong with the cold agent being too high or too low?
A: On the one hand, if the coolant temperature is too high, there will be no supercooling and a large number of fine crystals will not precipitate, which will lead to the failure of the experiment. On the other hand, the time of the whole experiment is not conducive to the smooth completion of the experiment. However, if the refrigerant temperature is too low, it will cause too much supercooling, which will affect the determination of naphthalene relative molecular weight. See the answer to question 1 for details.
3. How to determine the dissolution quality in the solvent? What's the effect of adding too much or too little?
Answer: The amount of solute added depends on its solubility in the solvent. Because the freezing point reduction is the dependence of dilute solution, it is necessary to ensure that the amount of solute can not only make the freezing point reduction of solution not too small and easy to determine, but also ensure that it is a dilute solution. If the addition amount is too much, on the one hand, it will lead to too much drop in freezing point, which is not conducive to the determination of freezing point of solution, on the other hand, it may exceed the range of dilute solution, which is not exponential. Too little will make the freezing point drop inconspicuous and difficult to determine, which will increase the experimental error.
4. Estimate the error of the experimental results and explain the main factors that affect the results?
Answer: The main factors that affect the determination results are the control of supercooling, stirring speed and coolant temperature. In this experiment, the freezing point needs to be supercooled. Too much supercooling will lead to low freezing point measurement results, so it is necessary to control the degree of supercooling. Only when the solid-liquid contact is large can the solid-liquid balance be achieved. During the experiment, the degree of supercooling was controlled by suddenly stirring and changing the stirring speed. Too high or too low temperature of refrigerant is not conducive to the completion of the experiment.
5. What is the significance of the determination result when the solute dissociates, associates, solvates and forms a complex in the solution?
Answer: When the solute dissociates, associates, solvates and forms a complex in solution, the relative molecular mass determined by freezing point reduction method is the relative molecular mass of the solute dissociates, associates, solvates or forms a complex, so the result determined by freezing point reduction method reflects the actual existing form of the substance in the solvent.
6. What heat exists in the liquid in the freezing point measuring tube during cooling? How do they affect the determination of freezing point?
Answer: There is heat in the liquid and air sleeve in the freezing point measuring tube, the tube wall of the measuring tube, the stirring rod and the sensor of the temperature difference measuring instrument. Therefore, if the stirring rod rubs against the temperature sensor, the measured freezing point will be very high. There is water sticking on the outer wall of the measuring tube, which leads to low freezing point measurement.
Experiment 3 Determination of Saturated Vapor Pressure of Pure Liquid
1. What happens if the power plug is unplugged first when pumping stops?
Answer: The vacuum pump oil will flow backwards.
Can you check whether the equipment will leak when heated? How does air leakage affect the result?
A: No, during the heating process, the temperature can't be constant, the gas and liquid phases can't reach equilibrium, and the pressure is not constant.
Air leakage will lead to the instability of internal pressure in the system and the imbalance between gas and liquid during the whole experiment, which will lead to inaccurate measurement results.
3. Why do manometer readings often jump when there is no air leakage?
A: Because the system has not reached the gas-liquid balance.
4. Under what conditions does Creutzfeldt-Creutzfeldt equation apply?
A: The applicable conditions of the creaking equation are: first, the molar volume V of liquid can be ignored compared with the molar volume Vg of gas; The second is to ignore the influence of temperature on molar steaming △vapHm, which can be regarded as a constant in the experimental temperature range. Third, gas is considered as an ideal gas.
5. Is the molar heat of vaporization data measured in this experiment related to temperature?
A: Yes.
6. What is the main source of error in this experiment?
Answer: Whether the air tightness of the equipment is good and whether the water itself contains impurities.
Experiment 4 Drawing of Gas-liquid Equilibrium Phase Diagram of Two-liquid System
1. Why doesn't the boiling point meter need to be cleaned and dried after adding the system in this experiment?
Tip: The experiment only needs to measure the boiling points under different compositions and the composition of gas phase and liquid phase at equilibrium. It is not necessary to accurately describe the specific and general composition of the system.
2. When the system is in equilibrium, should the two phases have the same temperature? What about reality? How to insert the mercury ball of thermometer into the solution to accurately measure the boiling point?
Tip: The temperatures of the two phases should be the same, but they are actually different. Generally, it is better to reduce the mercury ball solution of thermometer to 1/3.
3. Does the volume of the small tank for collecting gas condensate affect the experimental results? Why?
Tip: Yes, the size of condensate tank will affect the composition of gas phase and liquid phase.
4. What should I pay attention to when using Abbe refractometer?
Tip: Strong acid, strong alkali and other substances with strong corrosiveness to the instrument cannot be determined.
5. Discuss the main error sources of this experiment.
Tip: Temperature measurement is affected by the depth of thermometer and boiling degree. The factors affecting the composition determination are: when the boiling point meter is moved, the gas phase condensate flows back to the liquid phase, and the determination speed is slow.
Experiment 5 Drawing of Binary Metal Phase Diagram
1. What is the difference in the horizontal section of the step cooling curve of different component mixtures?
A: The step cooling curve of pure substance has a horizontal segment at its melting point and a horizontal segment at its melting temperature. And the length is different.
2. What other methods are there to make a phase diagram?
A: There are other methods to make phase diagrams, such as solubility method and boiling point method.
3. It is generally believed that the thermal effect of the system is very small when the phase transition occurs, and it is difficult to measure the accurate phase diagram by thermal analysis. Why? What is the first turning point of the step cooling curve of two samples containing% and 80%? Why?
Answer: Because thermal analysis draws the phase diagram through the step cooling curve, it mainly judges the appearance of new phase through the inflection point and horizontal segment (slope change) on the step cooling curve. If the thermal effect of system phase change is small, thermal analysis will produce inflection points and horizontal segments. The first turning point in the step cooling curve of 30% sample is obvious, and the Sn with large heat of fusion is precipitated first, so it can provide more temperature compensation when the phase transition occurs, which makes the slope of the curve change greatly.
4. Sometimes there is a small concave bend at the turning point of the cooling record curve with solid phase. What caused it? How to read the transition temperature of the phase diagram at this time?
A: This is caused by supercooling. In this case, the transition temperature of the phase diagram can be determined by drawing a line.
Finding the error score of college physics experiment: the determination of metal linear expansion coefficient? 5. Why does the cooling curve break when the metal melting system is cooled? What is the turning point of pure metal, low melting point metal and alloy? Why are the shapes of curves different?
Answer: When the metal melting system cools, the heat dissipation of the system is compensated by the heat release of metal solidification, which leads to the change of the slope of the cooling curve and the occurrence of breakpoints. Pure metal and low melting point metal each have a horizontal segment, and the alloy has an inflection point and a horizontal segment. Because the shape of the curve is related to the melting point temperature and environmental temperature of the sample, the phase change heat of the sample, the insulation performance of the insulation heating furnace and the number of samples, the step cooling curve of the sample is different. For pure metals and metals with low melting point, there is only one melting point, so it appears. For alloys, one metal precipitates first, and then two metals precipitate at the same time, so there will be an inflection point and an inflection point.
6. One sample of Sn-Bi alloy has lost its label. What method is used to determine its composition?
A: Its composition can be determined by thermal analysis. Firstly, the binary phase diagram of Sn-Bi is drawn by thermal analysis, and then the step cooling curve of the alloy sample is drawn, and the composition of the alloy can be obtained by comparing it with the binary phase diagram of Sn-Bi.
Experiment 6 measurement of electromotive force of primary battery
1. What is the basic principle of measuring electromotive force by cancellation method? Why can't the voltmeter accurately measure the electromotive force of the battery?
Answer: The offset method is to offset the battery voltage with an applied voltage opposite to the original battery, so that the current in the loop approaches zero. Only in this way can the measured voltage be electromotive force. Electromotive force refers to the voltage across the battery when the current in the loop is zero, so we must find a way to make the current in the loop zero. When the electromotive force of the battery is measured by voltmeter, the current in the loop is not zero, and the voltage across the battery is less than the actual electromotive force, so the electromotive force of the battery cannot be accurately measured by voltmeter.
Error analysis of measuring specific heat capacity of metal by cooling method in physical experiment. What function does it have? What is the function of salt bridge? What kind of electrolyte should salt bridge choose?
Answer: The reference electrode is generally an electrode with a known constant potential value, which can be used as a standard electrode in measurement. In the experiment, the potential of the unknown electrode can be directly known by measuring the potential difference between the unknown electrode and the reference electrode.
The function of salt bridge is to reduce the liquid connection potential and connect the two solutions to form a closed loop. Electrolyte, as a salt bridge, should not react with two electrolyte solutions, and the ion migration number is equal and the concentration is high.
3. The measurement method of electromotive force belongs to balance measurement, and it should be carried out under reversible conditions as far as possible in the measurement process. What should I pay attention to for this?
A: It should be noted that before connecting the battery circuit, the battery should be stabilized for a period of time so that the ions can reach a relatively balanced state; It is also necessary to estimate the electromotive force of the battery before connecting the loop, and then set the knob of the potentiometer to estimate the electromotive force of the battery to avoid large current in the loop during measurement.
4. Compare the theoretical value with the experimental value, and analyze the reasons for the error.
Answer: There are many sources of error in the measurement of electromotive force of primary battery: the working time of standard battery is too long, the current passes for a long time, and the standard electromotive force is biased; Salt bridge is polluted; The potential of saturated electrode is unstable; Failing to set the potentiometer knob at a position where the electromotive force of the battery under test is large, so that current flows in the battery under test, and so on.
5. In the accurate experiment, it is necessary to inject nitrogen into the original battery. What is its function?
Answer: In order to remove oxygen from the solution and prevent oxygen from participating in the electrode reaction and corroding the electrode.
Experiment 7 First-order reaction-sucrose conversion
1. When preparing sucrose solution, the weighing is not accurate enough. Does it affect the measurement result k? What about the traffic?
Answer: The concentration of sucrose does not affect the slope of lnc=-kt+B, so the inaccurate concentration of sucrose has no effect on the determination of K. H+ acts as a chemical reagent in this reaction system, and its concentration will affect the size of K.
2. When the sucrose solution and the solution are mixed, we add the solution to the sucrose solution. Can we add sucrose solution to the solution? Why?
No. In this reaction, hydrogen ions are used as chemical reagents. If sucrose solution is added to the solution, the concentration of hydrogen ions in the instantaneous system is high, which leads to too fast reaction speed, which is not conducive to the determination.
3. When determining the final optical rotation, in order to speed up the hydrolysis process of sucrose, the constant temperature of about 60℃ is adopted to make the reaction go through to the end. Why can't we keep the temperature constant at a higher temperature?
A: If the temperature is too high, there will be side effects and the color will turn yellow.
4. In optical rotation measurement, why should we correct the zero point? If this experiment is not corrected, will it affect the result?
Answer: Because there may be other optically active substances besides the tested substances in the solution, it is generally necessary to use reagent blank to correct the zero point. No correction is needed in this experiment, because the difference between the two optical rotations is used in data processing.
5. If the reaction start time is recorded later, will it affect the determination of K value? Why?
A: It doesn't affect. The position of the straight line made at different times is different, but K (slope of the straight line made) is the same.
Experiment 8 Side Reaction-Saponification
1.Why should NaOH and NaOH be freshly prepared for experiments?
Answer: the solution is easy to absorb carbon dioxide in the air and deteriorate; Volatile, hydrolysis reaction changes the concentration.
2. Why should this experiment be carried out at a constant temperature, and it should be kept at a constant temperature in advance before mixing with NaOH solution? When stirring, can you pour the solution into NaOH solution to start timing?
Answer: (1) Because temperature has an effect on conductance. (2) No, the timer should be started immediately after stirring.
3. Which ions contribute to the conductivity of the tested solution? Why does the conductivity of the solution decrease during the reaction?
A: The ions involved in conduction are, and. When the concentration is constant before and after the reaction, the mobility is much larger. With the increase of time, it first decreases and then increases, so the conductivity of the system decreases.
4. Why should the concentrations of the two reactants be equal?
A: In order to simplify the mathematical formula of the second-order reaction.
Experiment 9 mixed reaction-iodination
1. What physical quantities are measured by spectrophotometer in the experiment? What does it have to do with iodine concentration?
Answer: measure the absorbance a of the solution; According to Lambert-Beer law, the measured absorbance is proportional to the concentration of I2 solution at a specific wavelength.
2. In this experiment, the reaction begins when the solution is added into an iodine bottle containing I2 and HCl solution, but the reaction time begins when the solution is mixed evenly and injected into a cuvette. Does this operation affect the experimental results? Why?
A: No effect. The position of the straight line made at different times is different, but K (the slope of the straight line made) is the same.
3. The rate constant k is related to t, but there is no thermostat in this experiment. How does this affect K? Is the measured k room temperature or camera temperature?
A: The whole process of this experiment was carried out at room temperature. Because the room temperature changes very little in a short time, it has little influence on K. The measured K is K at the camera temperature.
Experiment/determination of surface of 10/0 solution (maximum bubble pressure method)
1. When measuring the surface with the maximum bubble pressure method, why should I read the maximum pressure difference?
Tip: If a certain pressure difference is read in the middle, there is no guarantee that the pressure difference will correspond to bubbles of the same size every time.
2. Why should we control the bubble escape rate?
It is pointed out that the bubble escape rate will affect the bubble size, and the bubble size will affect the pressure difference, so the bubble escape rate should be kept constant during the determination.
3. Does this experiment need to be carried out at constant temperature? Why?
Tip: Due to the influence of large surface temperature, constant temperature is needed.
4. Why is it necessary to adjust the capillary tip properly before liquid cutting? Otherwise, what effect will it have on the experiment?
It is suggested that the capillary tip will not be cut to a certain depth with the liquid, and the measured value of the surface will be small.
5. What factors will affect the results of surface measurement? How to reduce or eliminate the influence of these factors on the experiment?
It is pointed out that temperature, bubble escape velocity, whether the capillary is clean and whether the capillary tip is cut off from the liquid will affect the determination results. The measures to reduce or eliminate the errors caused by these factors are: constant temperature, constant bubble escape rate, cleaning capillary and capillary-liquid cutting.
Experiment 1 1 colloid and electrophoresis
1. What is the function of auxiliary liquid in electrophoresis and what is the basis for selecting auxiliary liquid?
It is pointed out that the auxiliary liquid is mainly used as the medium and dielectric of colloid swimming, and forms a clear interface with colloid for easy observation. The selected auxiliary liquid cannot react chemically with colloid, and the conductivity is the same as colloid.
2. If the electrophoresis apparatus is not cleaned in advance, and there is a small amount of electrolyte on it, what effect will it have on the electrophoresis measurement results?
It is suggested that zeta potential may change and even cause colloid aggregation.
3. There should be no bubbles in the electrophoresis apparatus. Why?
Tip: Bubbles will block the medium.
4. What factors are related to the speed of electrophoresis?
It is suggested that Soviet electrophoresis is related to colloidal particle size, charge, voltage and the distance between two electrodes.
Determination of relative molecular weight of polymer by experiment 12 viscosity method
How does the capillary thickness of 1. viscometer affect the experimental results?
Answer: if the capillary of viscometer is too thick, the liquid time will be too short, so it can't be approximated by Poisuille formula, and the viscosity can't be replaced by the ratio of time; If the capillary is too thin, it will easily cause blockage and lead to the failure of the experiment.
2. What is the function of C tube in Ubbelohde viscometer? Can the C tube be detached and used as a viscometer?
Answer: The function of the C tube is to form an air bearing suspension column. You can't remove the C tube and replace it with a viscometer, because without the C tube, it becomes a device. After continuous dilution, the amount of liquid in the viscometer will be different, so you can't measure the liquid time under the same conditions, so there is no comparability. Only when the air-floating suspension column is formed and the liquid is in the atmospheric environment can the measured data be comparable.
3. If the solution is inhaled into latex tube, what effect will it have on the experimental results?
Answer: It will reduce the concentration of the solution and shorten the determination time, thus reducing the measured value of relative viscosity and affecting the experimental results.
4. What are the factors that affect the accurate determination?
Answer: The factors that affect the accurate determination are temperature, solution concentration, stirring speed and verticality of viscometer.
5. What are the limitations of viscosity method in determining the molar mass of polymers? What is the molar mass range of polymer for this method?
A: Viscosity method uses some empirical equation between viscosity and molecular weight of macromolecular solution to calculate molecular weight, which is suitable for various molecular weight ranges. The limitation is that different molecular weight ranges have different empirical equations.
The above is related to the third edition of physical chemistry answers, and it is about how to write the error analysis of measuring the specific heat capacity of metals by cooling method in physical experiments. Read the error analysis of the experimental metal phase diagram, I hope this will help everyone!