introduction to solutions

properties of solutions

When a solute dissolves in a solvent, it changes the physical properties of the solvent. Two properties that change when a solute is added are the freezing and boiling points. Generally, solutes lower the freezing point and raise the boiling point of solvents. You can see some examples of this in Figure below. To see why solutes change the freezing and boiling points of solvents, watch this video: (14:00). MEDIA Click image to the left or use the URL below. URL: In each of these examples, a solute changes the freezing and/or boiling points of a solvent.

how a solute dissolves

When a solute dissolves, it separates into individual particles that spread evenly throughout the solvent. Exactly how this happens depends on the type of bonds the solute contains. Solutes with ionic bonds, such as table salt (NaCl), separate into individual ions (Na+ and Cl ). Solutes with covalent bonds, such as glucose (H6 C12 O6 ), separate into individual molecules. In either case, the individual ions or molecules spread apart and are surrounded by molecules of the solvent. This is illustrated in Figure 10.1 and in the videos at the URLs below. MEDIA Click image to the left or use the URL below. URL: MEDIA Click image to the left or use the URL below. URL:

solutes and solvents

A solution forms when one substance dissolves in another. The substance that dissolves is called the solute. The substance it dissolves in is called the solvent. For example, ocean water is a solution in which the solute is salt and the solvent is water. In this example, a solid (salt) is dissolved in a liquid (water). However, matter in any state can be the solute or solvent in a solution. Solutions may be gases, liquids, or solids. In Table 10.1 and the video at the URL below, you can learn about solutions involving other states of matter. Solution Gas dissolved in gas Example: Earths atmosphere Gas dissolved in liquid Example: carbonated water Liquid dissolved in gas Example: moist air Solute oxygen (and other gases) Solvent nitrogen carbon dioxide water water air Solution Liquid dissolved in liquid Example: vinegar Solid dissolved in liquid Example: sweet tea Solid dissolved in solid Example: bronze Solute acetic acid Solvent water sugar tea copper tin When a solute dissolves in a solvent, it changes to the same state as the solvent. For example, when solid salt dissolves in liquid water, it becomes part of the liquid solution, salt water. If the solute and solvent are already in the same state, the substance present in greater quantity is considered to be the solvent. For example, nitrogen is the solvent in Earths atmosphere because it makes up 78 percent of air.

rate of dissolving

When you add sugar to a cold drink, you may stir it to help the sugar dissolve. If you dont stir, the sugar may eventually dissolve, but it will take much longer. Stirring is one of several factors that affect how fast a solute dissolves in a solvent. Temperature is another factor. A solid solute dissolves faster at a higher temperature. For example, sugar dissolves faster in hot tea than in ice tea. A third factor that affects the rate of dissolving is the surface area of the solute. For example, if you put granulated sugar in a glass of ice tea, it will dissolve more quickly than the same amount of sugar in a cube. Thats because granulated sugar has much more surface area than a cube of sugar. You can see videos of all three factors at these URLs: MEDIA Click image to the left or use the URL below. URL: MEDIA Click image to the left or use the URL below. URL:

textbook_image

the almostuniversal solvent

Water is a polar compound. This means it has positively and negatively charged ends. This is why it is so good at dissolving ionic compounds such as salt and polar covalent compounds such as sugar. Solutes that can dissolve in a given solvent, such as water, are said to be soluble in that solvent. So many solutes are soluble in water that water is called the universal solvent. However, there are substances that dont dissolve in water. Did you ever try to clean a paintbrush after painting with an oil-based paint? It doesnt work. Oil-based paint is nonpolar, so it doesnt dissolve in water. In other words, it is insoluble in water. Instead, a nonpolar solvent such as paint thinner must be used to dissolve nonpolar paint. You can see a video about soluble and insoluble solutes at this URL: (1:51). MEDIA Click image to the left or use the URL below. URL:

instructional diagrams

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questions

Particles of solute eventually settle to the bottom of a solution.

a. true

-->  b. false

Which statement about solvents is true?

a. They change to the same state as their solutes.

-->  b. They may be in any state of matter.

c. They are always in the liquid state.

d. They cannot be in the solid state.

Particles of solute dissolved in a solution are too small to see.

-->  a. true

b. false

What happens when an ionic solute dissolves?

a. It becomes negatively charged.

b. It breaks down into individual atoms.

c. It forms chemical bonds with the solvent.

-->  d. It separates into positive and negative ions.

The solvent in a solution is always in the liquid state.

a. true

-->  b. false

Sugar dissolves easily in water because, like water, its molecules have

-->  a. oppositely charged ends.

b. a lot of surface area.

c. ionic bonds.

d. all of the above

Road crews sprinkle salt on an icy road because the salt

a. prevents snow from falling on the road.

b. provides better traction than the ice.

-->  c. lowers the melting point of the ice.

d. dissolves the ice.

When sugar dissolves in water, it separates into individual ions.

a. true

-->  b. false

Smaller particles of solute dissolve more quickly than larger particles.

-->  a. true

b. false

Which statement about solutes is false?

a. They may be in any state of matter.

-->  b. They make up most of any solution.

c. They are too small to settle out of a solution.

d. They are mixed evenly throughout a solution.

Paint thinner is an example of a nonpolar solvent.

-->  a. true

b. false

A solute changes the chemical properties of a solvent.

a. true

-->  b. false

Pure water has a higher boiling point than salty water.

a. true

-->  b. false

Ionic compounds dissolve in nonpolar solvents.

a. true

-->  b. false

Water is a solute in moist air.

-->  a. true

b. false

Paint thinner dissolves well in water.

a. true

-->  b. false

Bronze is a solution of copper dissolved in brass.

a. true

-->  b. false

The solute in carbonated water is a gas.

-->  a. true

b. false

Stirring a solution interferes with dissolving.

a. true

-->  b. false

All solutes dissolve more quickly in warmer solvents.

a. true

-->  b. false

substance that dissolves another substance to form a solution

a. solution

b. solute

-->  c. solvent

d. water

e. soluble

f. insoluble

g. polar

having oppositely charged ends

a. solution

b. solute

c. solvent

d. water

e. soluble

f. insoluble

-->  g. polar

substance called the universal solvent

a. solution

b. solute

c. solvent

-->  d. water

e. soluble

f. insoluble

g. polar

unable to dissolve in a given solvent

a. solution

b. solute

c. solvent

d. water

e. soluble

-->  f. insoluble

g. polar

substance that dissolves in another substance to form a solution

a. solution

-->  b. solute

c. solvent

d. water

e. soluble

f. insoluble

g. polar

homogeneous mixture with dissolved particles

-->  a. solution

b. solute

c. solvent

d. water

e. soluble

f. insoluble

g. polar

able to dissolve in a given solvent

a. solution

b. solute

c. solvent

d. water

-->  e. soluble

f. insoluble

g. polar

Which statement about solutions is true?

a. They are mixtures.

b. They are compounds.

c. They are homogenous.

-->  d. two of the above

When a solid solute dissolves in a liquid solvent, the solute changes to

a. a different chemical than it was.

-->  b. the same state as the solvent.

c. a new type of compound.

d. the gaseous state.

When sodium chloride dissolves in water, the oxygen ends of water molecules attract the

-->  a. sodium ions in the salt crystals.

b. chloride atoms in the salt molecules.

c. negative ends of the other water molecules.

d. negative ions in the salt crystals.

Dissolving occurs more quickly if the

a. solvent has a lower temperature.

b. solute has less surface area.

-->  c. solution is stirred or shaken.

d. all of the above

Which substance does not dissolve in water?

a. salt

b. sugar

c. carbon dioxide

-->  d. oil-based paint

Adding antifreeze to water gives the water a

a. higher freezing point.

-->  b. higher boiling point.

c. lower boiling point.

d. two of the above

Any compound will dissolve in the universal solvent if the compound is

a. hot.

-->  b. ionic.

c. nonpolar.

d. covalent.

diagram questions

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