Molar mass points

Name Structure Molar Mass Point Solubility... 

Third, picking the point on the cui ve of retention versus molar mass where 90 percent falls is inexacl . The retention cui ve usually bends in a way that makes picking the 90 percent point somewhat arbitraiy. 

NaOH for complete neutralization. What is the molarity of the H2X solution (c) Beaker C contains 0.124 g of H2X and 25.00 mL of water. To reach the equivalence point, 22.04 mL of NaOH are required. What is the molar mass of H2X ... 

In an effusion experiment, argon gas is allowed to expand through a tiny opening into an evacuated flask of volume 120 mL for 32.0 s, at which point the pressure in the flask is found to be 12.5 mm Hg. This experiment is repeated with a gas X of unknown molar mass at the same T and P. It is found that the pressure in the flask builds up to 12.5 mm Hg after 48.0 s. Calculate the molar mass of X. 

Effect of Molar Mass on Boiling Points of Molecular Substances... 

When iodine chloride is heated to 27°C, the weak intermolecular forces are unable to keep the molecules rigidly aligned, and the solid melts. Dipole forces are still important in the liquid state, because the polar molecules remain close to one another. Only in the gas, where the molecules are far apart, do the effects of dipole forces become negligible. Hence boiling points as well as melting points of polar compounds such as Id are somewhat higher than those of nonpolar substances of comparable molar mass. This effect is shown in Table 9.3. 

Colligative properties, particularly freezing point depression, can be used to determine molar masses of a wide variety of nonelectrolytes. The approach used is illustrated in Example 10.9. 

In carrying out a molar mass determination by freezing point depression, we must choose a solvent in which the solute is readily soluble. Usually, several such solvents are available. Of these, we tend to pick one that has the largest kf. This makes ATf large and thus reduces the percent error in the freezing point measurement From this point of view, cyclohexane or other organic solvents are better choices than water, because their kf values are larger. 

The Rast method uses camphor (Ci0Hi O) as a solvent for determining the molar mass of a compound. When 2.50 g of cortisone acetate is dissolved in 50.00 g of camphor (kf = 40.0°C/m), the freezing point of the mixture is determined to be 173.44°C that of pure camphor is 178.40°C. What is the molar mass of cortisone acetate ... 

The water-soluble nonelectrolyte X has a molar mass of 410 g/mol A 0.100-g mixture containing this substance and sugar (MM = 342 g/mol) is added to 1.00 g of water to give a solution whose freezing point is —0.500°C. Estimate the mass percent of X in the mixture. 

Table 22.3 compares two physical properties, boiling point and water solubility, of alcohols, ethers, and alkanes of similar molar masses. Notice that—... 

Molal boiling point constant, 269,270t Molal freezing point constant, 269,270t Molality (m) A concentration unit defined as the number of moles of solute per kilogram of solvent, 259,261-262 Molar mass The mass of one mole of a substance, 55,68-68q alcohol, 591 alkane, 591... 

L.18 A tablet of vitamin C was analyzed to determine whether it did in fact contain, as the manufacturer claimed, 1.0 g of the vitamin. One tablet was dissolved in water to form 100.00 mL of solution, and 10.0-mL of that solution was titrated with iodine (as potassium triiodide). It required 10.1 mL of 0.0521 M I3-(aq) to reach the stoichiometric point in the titration. Given that 1 mol L,- reacts with 1 mol vitamin C in the reaction, is the manufacturer s claim correct The molar mass of vitamin C is 176 g-mol-1. 

FIGURE 5.8 The boiling points of most of the molecular hydrides of the p-block elements show a smooth increase with molar mass in each group. However, three compounds—ammonia, water, and hydrogen fluoride are strikingly out of line. 

The presence of a solute lowers the freezing point of a solvent if the solute is nonvolatile, the boiling point is also raised. The freezing-point depression can be used to calculate the molar mass of the solute. If the solute is an electrolyte, the extent of its dissociation, protonation, or deprotonation must also be taken into account. 

The lowering of freezing point and the generation of osmotic pressure both depend on the total concentration of solute particles. Therefore, by using the colligative property to determine the amount of solute present, and knowing its mass, we can infer its molar mass. 

The addition of 0.24 g of sulfur to 100. g of the solvent carbon tetrachloride lowers the solvent s freezing point by 0.28°C. What is the molar mass and molecular formula of sulfur ... 

Sf.lf-Tfst 8.14A When 250. mg of eugenol, the compound responsible for the odor of oil of cloves, was added to 100. g of camphor, it lowered the freezing point of camphor by 0.62°C. Calculate the molar mass of eugenol. 

When 1.32 g of a nonpolar solute was dissolved in 50.0 g of phenol, the latter s freezing point was lowered by 1.454°C. Calculate the molar mass of the solute. 

Suppose that 10.0 g of an organic compound used as a component of mothballs is dissolved in 80.0 g of benzene. The freezing point of the solution is 1.20°C. (a) What is an approximate molar mass of the organic compound (b) An elemental analysis of that substance indicated that the empirical formula is C3H2C1. What is its molecular formula (c) Using the atomic molar masses from the periodic table, calculate a more accurate molar mass of the compound. 

An elemental analysis of epinephrine resulted in the following composition 59.0% carbon, 26.2% oxygen, 7.15% hydrogen, and 7.65% nitrogen by mass. When 0.64 g of epinephrine was dissolved in 36.0 g of benzene, the freezing point decreased by 0.50°C. (a) Determine the empirical formula of epinephrine, (b) What is the molar mass of epinephrine ... 

Organic chemists once used freezing-point and boiling-point measurements to determine the molar masses of compounds that they had synthesized. When 0.30 g of a nonvolatile solute is dissolved in 30.0 g of CC14, the boiling point of the solution is 77.19°C. What is the molar mass of the compound ... 

Colligative properties can be sources of insight into not only the properties of solutions, but also the properties of the solute. For example, acetic acid, CH.COOH, behaves differently in two different solvents, (a) The freezing point of a 5.00% by mass aqueous acetic acid solution is — l.72°C. What is the molar mass of the solute Explain any discrepancy between the experimental and the expected molar mass, (b) The freezing-point depression associated with a 5.00% by mass solution of acetic acid in benzene is 2.32°C. Whar is the experimental molar mass of the solute in benzene What can you conclude about the nature of acetic acid in benzene ... 

Suppose that 4.25 g of an unknown monoprotic weak acid, HA, is dissolved in water. Titration of the solution with 0.350 M NaOH(aq) required 52.0 mL to reach the stoichiometric point. After the addition of 26.0 mL, the pH of the solution was found to be 3.82. (a) What is the molar mass of the acid (b) What is the value of pK, for the acid ... 

Z Name Symbol Molar mass (g-mol ) Melting point (°C) Boiling point (°C) Density (g em )... 

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