Name: measuring solution strength
Uploaded: 2020-09-24T15:06:50.000Z
Duration: 2 min 48 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.6.1

Expressing Solution Concentration

If a small amount of solute is added to a large quantity of solvent, a dilute solution is formed. The concentrations of very dilute solutions, such as trace metal impurities in water, are often expressed in parts per billion or ppb, or in parts per million or ppm.
Ppm of a solute can be calculated by dividing the mass of solute by the mass of solution and multiplying times one million.
If a large amount of solute is added to a small quantity of solvent, a concentrated solution is formed.
Commonly used units include relative units expressed as percentages, such as: mass percent, which is the mass of solute divided by the mass of solution times one hundred; volume percent, which is the volume of solute divided by the volume of solution times one hundred; and mass per volume percent, which is the mass of solute divided by the volume of solution times one hundred.
In the laboratory, these units are used along with mole fraction, molarity, and molality.
A mole fraction of component i, which can be either solute or solvent, is the number of moles of the component divided by the total number of moles of all components in the solution. This is a ratio with no units, denoted by the letter &#967;

expressing solution concentration

A solute is a component of a solution that is typically present at a much lower concentration than the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
Concentrations may be quantitatively assessed using a wide variety of measurement units, each convenient for particular applications. Molarity (M) is a useful concentration unit for many applications in chemistry. Molarity is defined as the amount of solute in number of moles divided by the volume of the solution in liters:
 <img alt="Static equilibrium equation &#931;Fx=0 diagram, demonstrating forces in balance, educational physics concept." src="/files/ftp_upload/11366/11366_Equation%201.png" style="height: 90px;" data-altupdatedat="1761830439000" data-alt="Eq1" />
Because solution volumes vary with temperature, molar concentrations will likewise vary. When expressed as molarity, the concentration of a solution with identical numbers of solute and solvent species will be different at different temperatures due to the contraction/expansion of the solution. More appropriate for calculations involving many colligative properties are mole-based concentration units whose values are not dependent on temperature. Two such units are mole fraction (introduced in the previous chapter on gases) and molality.
The mole fraction, &#967;A, of a component is the ratio of its molar amount to the total number of moles of all solution components:
 <img alt="Static equilibrium diagram with force vectors &#931;Fx=0, illustrating balancing forces in physics." src="/files/ftp_upload/11366/11366_Equation%202.png" style="height: 90px;" data-altupdatedat="1761830439000" data-alt="Eq1" />
By this definition, the sum of mole fractions for all solution components (the solvent and all solutes) is equal to one.
Molality is a concentration unit defined as the ratio of the numbers of moles of solute to the mass of the solvent in kilograms:
 <img alt="Chromatography process diagram with mobile and stationary phases for substance separation analysis." src="/files/ftp_upload/11366/11366_Equation%203.png" style="height: 90px;" data-altupdatedat="1761830439000" data-alt="Eq1" />
Since these units are computed using only masses and molar amounts, they do not vary with temperature and, thus, are better suited for applications requiring temperature-independent concentrations.
This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/11-4-colligative-properties">Openstax, Chemistry 2e, Section 11.4: Colligative Properties.</a>

A solute is a component of a solution that is typically present at a much lower concentration than the solvent. Solute concentrations are often described ...

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Solutions and Colloids

KEY TERMS AND CONCEPTS

measuring solution strength

Solution strength can be described with terms like dilute and concentrated, and it can also be measured with several scientific units. A solute is the part of a solution present at a lower amount than the solvent. Different units are useful in different situations, especially in chemistry.

Molarity, written as M, is a common unit for concentration. It tells how many moles of solute are in one liter of solution. Because solution volume changes with temperature, molarity can change too when the amount of solute stays the same.

For some calculations, temperature-independent units are more useful. Mole fraction is one of these units. It is the ratio of the moles of one component to the total moles of all components in the solution, and the mole fractions of the solvent and all solutes add up to one.

Molality is another temperature-independent concentration unit. It is defined as the number of moles of solute divided by the mass of the solvent in kilograms. Because molality uses mass instead of volume, it does not change with temperature and is often better for colligative property calculations.

Measuring Solution Strength

solution formation

Why Some Substances Dissolve Better

Some substances dissolve easily in one solvent but not in another. A quick way to predict solubility is the idea that "like dissolves like." Polar substances, such as salt and sugar, dissolve well in polar solvents like water. Non-polar substances are more soluble in non-polar solvents such as carbon tetrachloride. This selective solubility depends on intermolecular forces, which are the attractions within and between molecules. Stronger forces between solute and solvent molecules lead to...

intermolecular forces in solutions

How Solutions Form Without Energy Change

A solution can form as a spontaneous process. That means it happens under the right conditions without energy from an outside source. When the attraction between solute and solvent particles is about the same as the attraction in the separate substances, the solution forms with no energy change. A solution like this is called an ideal solution. Mixtures of ideal gases are one example, and helium and argon behave close to that model. These gases do not have significant intermolecular...

enthalpy of solution

Dissolution and Heat Changes

Dissolution and heat changes help explain why some solutions form on their own. Two factors can favor the spontaneous formation of a solution. One is a decrease in internal energy, which happens in an exothermic change. The other is increased dispersal of matter, which means the solute spreads evenly through the solvent. When a substance dissolves, the internal energy often changes as heat is absorbed or released. This does not happen in every case, but it is common. A solution forms when...

aqueous solutions and heats of hydration

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Water dissolves ionic compounds because its polar molecules attract ions. This attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. It helps explain why many ionic solids can separate in water and form aqueous solutions. When an ionic compound dissolves, its ions separate and spread out evenly through the solution. Water molecules surround the ions and solvate them, which lowers the strong electrostatic forces between the ions. This separation is a...

solution equilibrium and saturation

Saturation Limits in Solutions

Saturation limits in solutions describe how much solute can dissolve in a solvent under given conditions. As sugar is added to water and stirred, it dissolves at first. More sugar can be added until the solution reaches its natural limit. That limit depends mainly on the relative strengths of three attractions: solute-solute, solute-solvent, and solvent-solvent forces. When no more sugar dissolves, even after long stirring, undissolved sugar stays behind. The concentration of sugar in the...

physical properties affecting solubility

Gas Solubility in Liquids

Gas solubility in liquids depends on the attractive forces between the gas and the liquid. When a gas dissolves, there is no strong solute-solute attraction to break apart first. Gas particles are already far apart, so their internal interactions are negligible. That makes solute-solvent interactions the main energetic factor that controls how much gas can dissolve. Examples show how these interactions matter. Oxygen is about three times more soluble in water than helium because oxygen has...

Solution strength can be described with terms like dilute and concentrated, and it can also be measured with several scientific units. A solute is the part of a solution present at a lower amount than the solvent. Different units are useful in different situations, especially in chemistry. Molarity, written as M, is a common unit for concentration. It tells how many moles of solute are in one liter of solution. Because solution volume changes with temperature, molarity can change too when the...

vapor pressure lowering

Raoult's Law and Lower Vapor Pressure

Raoult’s law explains why a solution with a nonvolatile solute has a lower vapor pressure than the pure liquid. Vapor pressure is the pressure from a liquid’s gas phase when vaporization and condensation happen at equal rates. When a nonvolatile substance dissolves in a volatile liquid, the liquid’s equilibrium vapor pressure drops. One reason for this drop is at the surface of the solution. Solvent molecules must be at the surface to vaporize, and added solute molecules reduce the surface...

ideal solutions

Raoult's Law in Real Solutions

Raoult's law describes how vapor pressure changes in a solution. For a solvent, the partial vapor pressure equals the vapor pressure of the pure solvent multiplied by its mole fraction in the solution. This relationship works best for ideal solutions. An ideal solution is one in which solvent-solute attractions are just as strong as solvent-solvent and solute-solute attractions. In that case, both components need about the same amount of energy to escape into the vapor phase as they do in...

freezing point depression and boiling point elevation

freezing-point-depression-and-boiling-point-elevation

Colligative Effects in Solutions

Colligative effects in solutions include boiling point elevation and freezing point depression. These properties depend on how many solute particles are present, not on the solute’s chemical identity. Because of that, a solution can behave differently from the pure solvent even when only a nonvolatile solute is added. Boiling point elevation happens because the vapor pressure of a solution is lower than the vapor pressure of the pure solvent. The boiling point is the temperature at which vapor...

osmosis and osmotic pressure of solutions

osmosis-and-osmotic-pressure-of-solutions

Semipermeable Membranes and Reverse Osmosis

Semipermeable membranes let some molecules pass while blocking others. They are found in biological cell membranes and in dialysis tubing used to remove metabolic wastes from blood. These examples show how selective permeation depends on factors such as size, shape, polarity, and charge. Osmosis is the net movement of solvent through a semipermeable membrane. In a U-shaped setup, pure solvent and a solution are separated by a membrane that allows only solvent molecules to pass. Solvent...

electrolytes: van't hoff factor

Electrolyte Ions and the van't Hoff Factor

Electrolyte ions affect colligative properties because these properties depend on the number of dissolved particles, not their identity. The concentration terms used for freezing point depression, boiling point elevation, and osmotic pressure include every solute species present in the solution. Nonelectrolytes dissolve without dissociation, so each molecule that enters solution counts as one particle. Electrolytes behave differently because they can form ions in water. If sodium chloride were...

colloids

Colloids and Everyday Mixtures

Colloids are mixtures with particles between the size of a solution and a suspension. They stay dispersed instead of settling out, even though their particles are larger than most simple molecules. This makes colloids different from cloudy suspensions like mud and water, flour and water, or tempera paint. It also makes them different from solutions, where dissolved molecules or ions are invisible and do not settle. Colloidal systems can be made in two main ways. In dispersion methods, larger...

key terms and concepts

Learn how solution concentration is measured with dilute and concentrated terms, molarity, mole fraction, and molality for chemistry and colligative properties.

Measuring Solution Strength | JoVE K12

chemistry

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Tennessee Academic Standards

High School

Matter and Its Interactions

CHEM1.PS1.1

CHEM1.PS1.15

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HIgh School

CH.5

CH.5.a

CH.5.b

CH.5.e

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CHEM.11

CHEM.11.E

Alabama Course of Study Science

Physical Science

9-12.PS.3.6.b

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New York State Science Learning Standards

HS. Structure and Properties of Matter

HS-PS1-10.

Georgia Standards of Excellence

SC6.

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Measuring Solution Strength

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