molarity was introduced in the previous section to help evaluate the concentration of solutions.
There are other measures of concentration.
Some other units of concentration will be introduced in this section, either for convenience or by convention.
The percent composition is a measure of the relative amount of elements in a compound.
Percentages are used to express the composition of a mixture.
It is possible to calculate the mass percentage of solvent, even though we are most interested in the mass percentages of solutes.
The percent sign is the most common symbol for mass percentage.
The more detailed symbols can be used to prevent confusion of mass percentages with other types of percentages.
Mass percentages are used for consumer products.
The concentration of the active ingredient in liquid bleach is listed on the bottle's label.
7.4 g of NaOCl is contained in a 100.0-g sample of bleach.
Liquid bleach is a solution of NaOCl.
The brand has a concentration of 7.4% NaOCl.
A sample of spinal fluid contains a lot of sugar.
The mass fraction of the sample should be a bit less than one part in 1000, since the sample contains roughly 4% of the total amount of fluid.
The mass percentage agrees with our estimate.
The same unit must be used for both the solute and the solution in order for the mass units to cancel.
The units of solute in the numerator were converted to match the units in the denominator.
We could have converted the denominator from g to g.
If identical mass units are used for both solute and solution, the computed mass percentage will be correct.
A bottle of tile cleanser contains a lot of water.
"Concentrated" hydrochloric acid can be used as a laboratory reagent.
The solution has a density of 1.19 g/mL.
A 100 g portion of this solution contains about 40 g of HCl.
Since the solution density isn't very different from water, a reasonable estimate of the HCl mass in 500 g is about five times greater than that in a 100 g portion.
We can convert the solution's volume to mass with the help of the given mass percentage.
The mass of HCl is in line with our estimate of 200 g.
Common and relatively inexpensive laboratory equipment can be used to measure liquid volumes.
A 70%vol aqueous solution is whatubbing alcohol is sold as.
The isopropanol volume is 70% of the total solution volume.
Wine is 12% alcohol by volume.
The density is 0.789 g/mL and the mass is 46.06 g/mol.
"Mixed" percentage units are derived from the mass of solute and the volume of solution.
Depending on the solution, the specific units used for solute mass and solution volume may be different.
The composition of the solution is 0.9 g of solute per 100 mL, indicating that it has a concentration of 0.9% mass/volume.
The mass-volume ratio is used to measure the concentration of blood sugar.
Its concentration is usually given in the amount ofglucose per deciliter of blood.
Mixed mass-volume units are common in medical settings.
The normal range for the concentration of blood sugar is around 70-100.
In terms of mass, volumes, or mixed mass-volume units, ppb and ppm can be defined.
The ppb units are defined by the number of atoms.
The concentrations of pollutants and other trace contaminants can be reported in both ppb and ppm.
Concentrations of these contaminants are typically very low in treated and natural waters, and their levels cannot exceed relatively low concentrations without causing adverse effects on health and wildlife.
The maximum safe level of fluoride in tap water is 4 parts per million, according to the EPA.
Inline water filters are designed to reduce the amount of fluoride in the water.
When the concentration of lead in tap water reaches 15 ppb, certain actions must be taken.
The ppb units can be used to convert the concentration from ppb to ppm.
The two unit definitions show that ppm is 1000 times greater than ppb.
If the mass of the solution is provided, the definition of the ppb unit may be used to calculate the requested mass.
The density is used to derive the mass of the Chapter 3 Composition of Substances and Solutions.
Since the concentrations of dissolved substances should not be very large, we can assume that the density of tap water is roughly the same as that of pure water.
A sample of industrial wastewater was found to have mercury.
The mercury concentration of the wastewater should be expressed in ppb units.
The formula mass of a substance is the sum of the average atomic mass of each atom in the formula and is expressed in atomic mass units.
The molecule mass is also called the formula mass.
The mole is a convenient amount unit for expressing large numbers of atoms.
Avogadro's number is 6.022 x 1023, which is the number of entities that compose 1 mole of substance.
The mass in grams of 1 mole is called the molar mass.
The formula mass and molar mass for any substance are numerically equivalent due to the use of the same reference substance in defining the atomic mass unit and mole.
The chemical identity of a substance is determined by the types and relative numbers of atoms that make up its fundamental entities.
The mass percentage of each element in a compound is provided by a compound's percent composition.
The empirical formula mass of a compound can be compared to the compound's mass to derive a formula.
Heterogeneous solutions are what they are.
Many solutions have a single component, called the solvent, in which other components are dissolved.
A solvent is water in an aqueous solution.
The relative amount of solute in a given amount of solution is the concentration of a solution.
One very useful unit for measuring concentration is the number of moles of solute per liter of solution.
Adding solvent may decrease the solute concentration of a solution.
Concentrations and volumes of a solution are related to the dilution equation.
A number of solution concentration units are used in various applications.
Percentage concentrations based on the solution components' mass, volumes, or both are useful for expressing relatively high concentrations, whereas lower concentrations are conveniently expressed using ppb units.
These units are popular in environmental, medical, and other fields where mole-based units are not used as often.
If we know the formula for determining the number of moles of a compound in a known mass, we should write a sentence about it.
A woman with a weight of 55 lbs has 7.5 mol of hemoglobin in her blood.
Determine the number of atoms and the mass of zirconium, ZrSiO4, a semiprecious stone.
Determine which of the following contains the most hydrogen: 1 mol of CH4, 0.6 mol of C6H6, or 0.4 mol of C3H8.
Determine which of the following contains the greatest mass of aluminum: 122 g of AlPO4, 266 g of Al2C16, or 225 g of Al2S3.
Diamond is a type of carbon.
There is an engagement ring with a diamond weighing 1.25 carats.
The largest natural diamond was found in 1905.
It weighed over 3000 carats.
The serving size of the nut crunch cereals is 60.0 grams.
Determine the percent ammonia, NH3 in Co(NH3)6Cl3 to three significant figures.
A compound of carbon and hydrogen has a mass of 78.1 g/mol.
Dichloroethane is often used for dry cleaning.
The mass is 99 g/mol.
The sample contains 24.3% carbon and 4.1% hydrogen.
Determine the formula for chrysotile asbestos.
The percent composition is as follows: 28.03% Mg, 21.60% Si, 1.16% H, and 49.21% O.
The mass of chrysotile is 520.8 g/mol.
A new yellow dye was developed by a major textile dye manufacturer.
A percent composition of 75.95% C, 17.72% N, and 6.33% H is found in the dye.
Determine the formula of the dye.
The OpenStax book can be found for free at http://cnx.org/content/col11760/1.9.
1.0 L of milk contains 1.0 g of calcium.
A bottle of concentrated HCl was purchased for the general chemistry laboratory.
The solution had 868.8 g of HCl.
Limits on the quantities of toxic substances that can be discharged into the sewer system are placed by the EPA.
There are limits for a number of substances, including hexavalent chromium, which is limited to 0.50 grams per liter.
The solution has a density of 1.109 g/mL.
The amount of CaCO3 in a liter of water is equivalent to parts per million of CaCO3.
The minimum safe level for mercury is 1 part per billion by weight.
The concentration was found to be 0.68 parts per billion.
Determine the molarity of mercury in the stream by assuming a density of 1.0 g/mL.
In Canada and the United Kingdom, there are devices that measure blood sugar levels.
A throat spray has mass phenol, C6H5OH, in it.
The molarity of the solution should be calculated if it has a density of 0.9956 g/mL.
Adding CuI to table salt can be used as a source of iodine.
A cough syrup has 5.0% ethyl alcohol.
The molarity of the alcohol in the cough syrup is determined by the density of the solution.
D5W is used as an IV fluid.
The mass solution of dextrose is in the water.
If the density of D5W is 1.029 g/mL, you can calculate the molarity of the solution.
The density is 1.3057 g/mL for the 40.0% by mass solution of sulfuric acid, H2SO4.