Funded by the National Natural Science Foundation of China (Grant No.: 20673080); Scientific Research Start-up Fund of Xi'an Polytechnic University (Grant No.: BS07047) 1. The concepts of quantity of matter, molar mass, molar volume of gas, quantity concentration of matter and the relationship between them.
2. Calculation of the amount of relevant substances, number of particles, molar mass, gas molar volume, and quantity concentration of substances.
3. Preparation of solutions with a certain amount and concentration of a certain substance.
We only consider two-component solutions at room temperature and pressure.
If the solution contains nA moles of component A and nB moles of component B, then any extensive property (Y) of the solution can be expressed as (1) Then, (2) (3) Define the apparent molar volume φV as (
4) In the formula, V is the volume of a solution containing nA moles of A and nB moles of B, and is the volume of moles of pure A when T and P are given.
Equation (4) is rearranged to get (5). Equation (5) is differentiated for nB and we get (6) Substitute , , V for , , , Y in equation (3), and find (7) joint equation (5), (
6) and (7) give (8) If φV can be expressed by nA, nB terms, and the molecular weight (MA, MB) and the density of the experimental solution (ρ) are known, equations (6) and (8) provide
How to calculate the sum when the solution concentrations are nA and nB.
Considering that it is more convenient to substitute this value into equation (4) using molar concentration (m), where nB=m, nA=1000/MA, equation (9) becomes (10)MA/VAO= = at T and P
The density of pure A at constant, so (11) In the calculation program, use equations (11), (8) and (6) to calculate the required quantities.
Thermostat (equipped with a water bath clamp and adjusted to a temperature deemed appropriate by the instructor); two 25 ml glass (or plastic) stoppered volumetric flasks (used as pycnometers and transferred into the calculation program as data); two 100 ml
beaker, two capillary pipettes with medical droppers, lens tissue.
In addition to the thermostatic bath, each student must have a set of instruments, including an analytical balance or a bench scale that can read close to milligrams; high-purity sodium chloride and distilled water.
Experimental steps: Students should wash and dry each volumetric flask and stopper and mark them to show the difference (it is recommended to mark the bottles and stoppers with non-fading ink in advance before the experiment and dry them in the oven).
Weigh each dry, air-filled volumetric flask.
Then, fill each volumetric flask with distilled water to approximately 1 cm below the mark on the flask, and place one of them in a constant temperature bath.
After placing it in the tank for 3-5 minutes, use a capillary pipette to fill the water exactly to the scale, and use lens paper to absorb the droplets adhered above the scale.
Remove the bottle, dry the outside thoroughly, and weigh it on a scale.
When the bottle is taken out of the thermostatic bath, place it into a second volumetric flask (if there is enough thermostatic bath, two or more volumetric flasks can be placed at the same time).
Then follow the steps for the first volumetric flask to process the second volumetric flask.
We now have the weight of each volumetric flask (pycnometer) filled with air and filled with water.
To correct for the mass of air and get the empty bottle weight, we assume the bottle has a volume of 25 ml.
At room temperature and atmospheric pressure, multiply the air density found in the manual by 25 ml, which is the mass of air in each bottle.
Subtract the mass of the air from the weight of the bottle filled with air to get the weight of the empty bottle.
Subtract the weight of the empty bottle from the weight of the bottle filled with water, and divide the difference by the density of water at the temperature of the thermostatic bath to get the exact volume of the bottle at that temperature.
Then, take another volumetric flask and fill it with one of the sodium chloride solutions in turn and weigh it (this bottle is in a constant temperature bath, as is the pretreatment and filling).
The density of a given sodium chloride solution is found by dividing the difference between the weight of the bottle when filled with solution and the weight of the empty bottle by the exact volume of the bottle.
Data Processing The weight percent composition of each solution was used to calculate the molarity of each solution.
Using equation (11) and various parameter values, calculate the φV value for each solution (if the solvent is not water, it must be the density of the pure solvent at the bath temperature).
Plot φV versus m1/2.
Draw the best straight line and determine the slope and intercept of the line.
The slope in this graph divided by m1/2 gives the partial derivative in equations (6) and (8).
The slope of the straight line on the graph is But based on your best straight line, interpolate the value of φV for each mole of weight.
Substituting this optimal φV into equation (6), calculate the value (solute) for each solution.
Then, use equation (8) to calculate the value (solvent) for each solution.
(In this calculation, remember nB = m and nA = ) If you need a discussion of the graphical differential method for determining partial molar volume, see Klotz, Chemical Thermodynamics, Pretice-Hall (1964) or other advanced thermodynamics textbooks.