Properties of Solutions
Solutions are homogeneous mixtures of two or more substances. The substance with the highest concentration within the mixture is known as a solvent, and the other substance(s) are called the solute(s). Solutions have uniform composition where solvent and solute cannot be seen separately with the naked eye.
A solution can be in any of the three states of matter: gas, solid, or liquid. For example, when sugar (C12H22O11), a covalent solid, is dissolved in water, its molecules get uniformly dispersed in water molecules and form a homogeneous aqueous solution, as shown below. The subscript “aq” beside C12 H22 O11 shows that sugar molecules are solutes and are evenly distributed in the aqueous solution where water is the solvent.
C12 H22 O11(s) ⟶ C12 H22 O11(aq)
When ionic compounds are dissolved in water, they dissociate to yield ions in an aqueous solution. For example, when potassium dichromate (K2Cr2O7) dissolves in water, it dissociates to give potassium ions and dichromate ions that are uniformly dispersed in the mixture, as shown below:
K2Cr2O7(s) ⟶ 2K+(aq) + Cr2O72−(aq)
Solutions display the following defining characteristics:
Concentration and Molarity
Concentration as a Percent
Concentration can be expressed as a mass percent when the mass of the solute and solution are known. It can be calculated using the following formula:
In the given solution, there is 110.605 g of solvent and 6.0508 g of solute present. Find the mass percent.
Concentration as PPM
Parts per million (ppm) is defined as the ratio of solute-to-solution mass multiplied by 106, as shown below:
ppm = 1 g/m3 = 1 mg/ L= 1 μg/mL
A solution has a concentration of 1.35 g /L. What is its concentration in ppm?
Convert the mass in grams to a mass in milligrams:
1.35 g = 1.35 × 1000 mg = 1350 mg
Re-write the concentration in mg/L:
Concentration in mg/L= 1350 mg/ L = 1350 ppm
Molarity, or molar concentration of a solution, is the amount of solute (in moles) per litre of solution. It is calculated using the following formula:
A 455-mL soft drink sample contains 0.153 mol of sucrose (table sugar). What is the molar concentration of sucrose in the beverage?
Converting 455 ml to L gives 0.455 L