Mass percentages of solute

STRATEGY The molality is the number of moles of solute per kilogram of solvent. Therefore, consider a solution made with exactly 1 kg of solvent and work out the mass of solute present from the number of moles and the molar mass. Then calculate the mass percentage of solute by dividing the mass of solute by the total mass of the solution and multiply by 100%. 

Calculate the mole fraction and molality of a solute, given the masses or mass percentages of solute and solvent, Examples G.6 and G.7. 

In this example, we expressed the concentration quantitatively by giving the mass percentage of solute—that is, the mass of solute in 100 g of solution. However, we need a unit of concentration that is convenient for dispensing reactants in solution, such as one that specifies moles of solute per solution volume. 

Solution concentration is sometimes expressed in terms of the mass percentage of solute—that is, the percentage by mass of solute contained in a solution. 

SOLUTION To calculate the mass percentage of hydrogen in water, we simply find the mass of H atoms in 1 mol F120 molecules, noting that there are 2 mol H in 1 mol H20, divide that mass by the mass of 1 mol H2O, and multiply by 100% ... 

The stoichiometric point is reached when all the Fe2+ has reacted and is detected when the purple color of the permanganate ion persists. A sample of ore of mass 0.202 g was dissolved in hydrochloric acid, and the resulting solution needed 16.7 mL of 0.0108 M KMn04(aq) to reach the stoichiometric point, (a) What mass of iron(ll) ions is present (b) What is the mass percentage of iron in the ore sample ... 

C17-0121. Vinegar is a dilute aqueous solution of acetic acid. A sample of vinegar has a pH of 2.39 and a density of 1.07 g/mL. What is the mass percentage of acetic acid in the vinegar ... 

The mass percentage of a solution is the mass of the solute divided by the mass of the solution and then multiplied by 100% to yield percentage. 

What is the mass percentage of acetic acid in this solution ... 

A 0.3249 g sample of stainless steel was analyzed for iron by dissolving the sample in sulfuric acid and titrating the Fe2+ in the resulting solution with 0.018 54 M K2Cr2C>7. If 38.89 mL of the l C CV solution was required to reach the equivalence point, what is the mass percentage of iron in the steel ... 

By the percentage composition, or the number of mass units of solute per 100 mass units of solution. 

Percent concentration is the simplest concentration unit. The amount of solute is compared to the amount of solution in order to measure concentration. This concentration unit is generally used for concentrated solutions of acids and bases. The percentage of solute can be expressed by mass or volume. 

A 25 g sample of CuS04 5H20 is dissolved in 55 g of water. What is the mass percentage of the resulting solution ... 

How many grams of CoCl2 6H20 and water are required to obtain 180 g of cobalt(II) chloride solution with a mass percentage of 5% ... 

What is the mass percentage of a saccharose solution if 228 grams of it produces 72 grams of glucose after hydrolysis in acidic medium ... 

Sometimes mass percent is symbolized as % (w/w), indicating that the percentage is a ratio of weights (more accurately, masses). You may have seen mass percent values on jars of solid chemicals to indicate the amounts of impurities present. Two very similar terms are parts per million (ppm) by mass and parts per billion (ppb) by mass grams of solute per million or per billion grams of solution. For these quantities, in Equation 13.6 you multiply by 10 or by 10, respectively, instead of by 100. 

A 0.40()-g sample of toothpaste was boiled with a 50-mL solution containing a citrate buffer and NaCl to extract the fluoride ion. After cooling, the solution was diluted to exactly 100 niL. The potential of an ion-selective electrode with a Ag-AgCl(sat d) reference electrode in a 25.0-mL aliquot of the sample was found to be -0.1823 V. Addition of 5.0 mL of a solution containing 0.(X)107 mg F /mL caused the potential to change to - 0.2446 V. Calculate the mass percentage of I in the sample. 

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