Mass-Number Conversions Involving Solutions

Mole-Mass-Number Conversions Involving Solutions 

Calculating Mass of Solute in a Given Volume of Solution 

Problem A buffered solution maintains acidity as a reaction occurs. In living cells, phosphate ions play a key buffering role, so biochemists often study reactions in such solutions. How many grams of solute are in 1.75 L of 0.460 M sodium monohydrogen phosphate Plan We know the solution volume (1.75 L) and molarity (0.460 M), and we need the mass of solute. We use the known quantities to find the amount (mol) of solute and then convert moles to grams with the solute molar mass, as shown in the roadmap. 

Converting from moles of solute to grams Mass (g) Na HPOa = 0.805 

FOLLOW-UP PROBLEM 3.13 In biochemistry laboratories, solutions of sucrose (table sugar, C12H22O11) are used in high-speed centrifuges to separate the parts of a biological cell. How many liters of 3.30 M sucrose contain 135 g of solute  

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Mole-Mass-Number Conversions Involving Solutions... 

Amount-Mass-Number Conversions Involving Solutions 100 Diluting a Solution 100 Stoichiometry of Reactions in Solution 103... 

Recall that the coefficients in a balanced equation give the relative number of moles of reactants and products, aexs (Section 3.6) To use this information, we must convert the masses of substances involved in a reaction into moles. When dealing with pure substances, as we did in Chapter 3, we use molar mass to convert between grams and moles of the substances. This conversion is not valid when working with a solution because both solute and solvent contribute to its mass. However, if we know the solute concentration, we can use molarity and volume to determine the number of moles (moles solute = M X F). T Figure 4.17 summarizes this approach to using stoichiometry for the reaction between a pure substance and a solution. 

There are circumstances where weight is an important factor (Example 3), but the calculations involving gases may be in terms of volumes of gases involved. The conversion from volumes of gas to mass is done through the numbers of moles. The methods used in these problem solutions are as in Chapter 4 except that the numbers of moles converted to mass (g, lb, etc.) must be determined from the volume, temperature, and pressure of the gases. 

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