Molality and mole fraction

We saw in Section 3-6 that concentrations of solutions are often expressed as percent by mass of solute or as molarity. Discussion of many physical properties of solutions is often made easier by expressing concentrations either in molality units or as mole fractions (Sections 14-9 to 14-14). 

The molality, m, of a solute in solution is the number of moles of solute per kilogrmn of solvent. 

What is the molality of a solution that contains 54.6 g of CH3OH in 108 g of water  

We convert the amount of solute (CH3OH) to moles, express the amount of solvent (water) in kilograms, and apply the definition of molality. 

It is very easy to confuse molality (m) with molarity Mj. Pay close attention to what is being asked. 

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A bottle of phosphoric acid is labeled 85.0% H3PO4 by mass density = 1.689 g/cm3. Calculate the molarity, molality, and mole fraction of the phosphoric acid in solution. 

Convert between molality and mole fraction or molarity (Toolbox 8.1 and Examples 8.6 and 8.7). 

Concentrated aqueous ammonia (also known as ammonium hydroxide) is 14.8 M and has a density of 0.898 g/mL. Determine the molality and mole fraction of ammonia in this solution. 

In this chapter, you learned about solutions. A solution is a homogeneous mixture composed of a solvent and one or more solutes. Solutions may be unsaturated, saturated, or supersaturated. Solution concentration units include percentage, molarity, molality, and mole fraction. The solubility of solids in liquids normally increases with increasing temperature, but the reverse is true of gases dissolving in liquids. The solubility of gases in liquids increases with increasing pressure. 

The (able below contains solubility and density data lor the salts Na SQ4 and MgS()4. Express their solubilities in terms of molar concentrations, molalities and mole fractions. Calculate the contractions in volume that occur when the solutions are made from the solid salts and the solvent. Comment on the results in terms of the ell ect of ionic charges. The concentrations have been cho-.cn to be comparable. 

It is important to be able to convert among the different concentration units. Conversions between molality and mole fraction are performed by considering a solution containing 1 kg of solvent ... 

A solution is prepared by dissolving 50.0 g cesium chloride (CsCl) in 50.0 g water. The volume of the solution is 63.3 mL. Calculate the mass percent, molarity, molality, and mole fraction of the cesium chloride. 

Calculate the molarity, molality, and mole fraction of each of the above reagents. 

A 1.37 M aqueous solution of citric acid (H3QH5O7) has a density of 1.10 g/cm3. What are the mass percent, molality, and mole fraction of the citric acid ... 

What are the molality and mole fraction of solnte in a 35.5 percent by mass aqueons solution of formic acid (HCOOH) ... 

Express the concentration of a solute in solution in units of mass percentage, molarity, molality, and mole fraction (Section ff.f. Problems 3-8). 

Because the concentration of a solution is so variable, we need two ways to indicate how much solute is in a particular solution. There are several ways to measure the concentration of a solution, including molarity, molality, and mole fraction. The type of measurements you use will often depend upon the situation or on the calculations that you want to be able to carry out. 

Express concentrations of solutions in terms of molality and mole fractions... 

Both molality and mole fraction are intensive properties, which is useful for an easy method to convert from one to the other. In such a problem, we can assume that we have any quantity of solution that will make our solving process easiest. 

FOLLOW-UP PROBLEM 13.5 A sample of commercial concentrated hydrochloric acid is 11.8 Af HCl and has a density of 1.190 g/mL. Calculate the mass %, molality, and mole fraction of HCl. 

You want to convert among molarity, molality, and mole fraction of a solution. You know the masses of solute and solvent and the volume of solution. Is this enough information to carry out all the conversions Explain. 

In earlier editions of the Handbook of Chemistry and Physics (CRC Press), percent composition and specific gravity data for solutions of many common reagent solutions are given. Let us take, for example, pairs of values for aqueous hydrochloric acid (%HC1, sp gr at 25°C) from the Handbook and copy the data into Quattro, and then calculate the molarity, molality and mole fraction of HCl for each of these solutions. 

For electrolyte solutions the molality is often used as a concentration scale instead of the mole fraction. Molality is defined as the number of moles of a solute in 1 kg solvent (solv). The relationship between molality and mole fraction is... 

An aqueous ammonium chloride solution contains 5.75 mass % NH4CI. The density of the solution is 1.0195 g/mL. Express the concentration of this solution in molarity, molality, and mole fraction of solute. 

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