Solutions, Acids, Bases, and Solubility. Objective 4 TEK 9 The student knows how solution chemistry...

Solutions, Acids, Bases, and Solubility

Objective 4

TEK 9 The student knows how solution chemistry is a part of everyday life.(A)The student is expected to relate the structure of water to its function as the universal solvent.(B) Relate the concentration of ions in a solution to physical and chemical properties such as pH, electrolytic behavior, and reactivity.(D) Demonstrate how various factors influence solubility including temperature, pressure, and nature of the solute and solvent.

We all use Chemical Solutions

• Average Family spends: $ 1200.00 / year on chemical solutions?

• Make-up, laundry detergent, motor oil, gasoline, food preservatives, deodorant, lawn fertilizers & weed killers, shampoo, air fresheners, floor wax, furniture polish, toothpaste, mouthwash, oven cleaner, glass cleaner, etc…

Solutions• Most of chemistry is based on solution

chemistry, where water is the solvent (called aqueous solutions).

• Solutions—homogeneous mixture of two or more substances The dissolved substance is completely dispersed, i.e., its composition is the same throughout its volume.

• Usually a solid is dissolved in a liquid, but liquids can be dissolved in other liquids and gases can be dissolved in a liquid as well.

•Component present in greater proportion is called the solvent, the one in minor proportion is called the solute•Oceans are salt water solutions—water is the solvent, salt is the solute.•Sweet tea in another example — sugar is the solute and water is the solvent

Solute and solvent

The Solution ProcessThe Solution Process

Solution Process

Step 1. The solute molecules separate. This process requires energy.

Step 2: The solvent molecules must separate. This process requires energy

Step 3: The solute and solvent attract. This process releases energy.

What is solubility?The amount of a substance that dissolves in a given volume of solvent at a given temperature.

Common units: grams solute/ 100 grams of solvent

or

grams solute/ 100mL of water

Factors Affecting Solubility•Solute-solvent interaction Solute-solvent interaction - Like dissolves like•Temperature Factor -Temperature Factor -

i) Solids/Liquids- Solubility increases with Temperature. Increase K.E. increases motion and collision between solute / solvent.

ii) gas - Solubility decreases with TemperatureIncrease K.E. result in gas escaping to atmosphere.•Pressure Factor -Pressure Factor -

i) Solids/Liquids - Very little effect. Solids and Liquids are already lose together, extra pressure will not increase solubility.

ii) gas - Solubility increases with Pressure.Increase pressure squeezes gas solute into solvent.

Properties of Water

2-

+

+

Water is polar

Water forms hydrogen bonds

When water freezes it expands

•hydrogen bonding is the weak intermolecular bond between the H end of one molecule and the O, N, or F end of another molecule

•2-

+

+

2-

+

+

Solute-Solvent Interaction• Polar liquids tend to dissolve in polar solvents.

“Likes dissolve likes”• Miscible liquids: mix in any proportions.• Immiscible liquids: do not mix.• Intermolecular forces are important: water and

ethanol are miscible because the broken hydrogen bonds (a bond between the hydrogen end of one dipole and the O, N, or F end of another dipole) in both pure liquids are re-established in the mixture.

• The number of carbon atoms in a chain affect solubility: the more C atoms the less soluble in water.

Factors Affecting Factors Affecting SolubilitySolubility

Solute-Solvent Interaction• The number of -OH groups within a molecule

increases solubility in water.

Generalization: “like dissolves like”.• The more polar bonds in the molecule, the

better it dissolves in a polar solvent.• The less polar the molecule the less it dissolves

in a polar solvent and the better is dissolves in a non-polar solvent.

• The greater the contact between the solute and solvent, the faster the substance will dissolve. Therefore, stirring and crushing, which increases the surface area, increase the rate of solution


Ionic Solutes

Ionic solids (or salts) contain positive and negative ions, which are held together by the strong force of attraction between particles with opposite charges. When one of these solids dissolves in water, the ions that form the solid are released into solution, where they become associated with the polar solvent molecules.

NaCl(s) Na+(aq) + Cl-(aq)

We can generally assume that salts dissociate into their ions when they dissolve in water.

Polar water molecules interacting with positive and negative ions of a salt.

+

+

+

+

+

+

++

++

++ +++++

+

+++

+

+

+++

++

--

- ----

--

-- -

-

-

-

---

-

--

- -

--

-

-

--

-- - -

- -

+

-

-

+ -

The positive end of the water molecule attracts to the anion (negative ion) and the negative end of the water molecule attracts to the cation (positive ion). Solutions of ionic compounds are strong electrolytes.

Electrolytes

compounds which when dissolved in water produce solutions that conduct an electric current. The strength of an electrolyte is due to the number of ions in solution. Strong electrolytes conduct a much stronger current than weak electrolytes because they have more ions.

Nonelectrolytes compounds which when dissolved in water produce solutions that do not conduct an electric current. These solutions do not contain ions.

Electrolytes

Strong Weak NonElectrolyte Electrolyte Electrolyte

Polar Molecules

The sugar we use to sweeten coffee or tea is a molecular solid, in which the individual molecules are held together by relatively weak intermolecular forces. When sugar dissolves in water, the weak bonds between the individual sucrose molecules are broken, and these C12H22O11 molecules are released into solution. Sugar does not form ions in solution.

In order for a substance to dissolve in water, the water molecules must be more attracted to the new substance added.

Remember water molecules are weakly bonded to each other by hydrogen bonds.

Will this substance dissolve in water?

Yes, because water will be attracted to it.

OO

Covalent acids form ions in solution, with the help of the water molecules. For instance, hydrogen chloride molecules, which are polar, give up their hydrogens to water, forming chloride ions (Cl-) and hydronium ions (H3O+). Some covalent compounds IONIZE in solution

H

H

H

H

HClH Cl

+ -++

If the molecule ionizes completely it is a strong electrolyte, if it partially ionizes it is a weak electrolyte. HCl, hydrochloric acid, is a strong electrolyte and CH3COOH, vinegar or acetic acid, is a weak electrolyte.

Substances that don’t dissolve are called insolubleE.g. Petroleum (crude oil), which are non-polar

So if you want to dissolve grease which is non-polar, you need to use a non-polar solvent.

Petroleum in a non-polar organic molecule

Temperature will affect solubility. If the solution process absorbs energy then the solubility will be INCREASED as the temperature is increased. If the solution process releases energy then the solubility will DECREASE with increasing temperature.


Temperature Effects

• Experience tells us that sugar dissolves better in warm water than cold.

• As temperature increases, solubility of solids generally increases.

• Sometimes, solubility decreases as temperature increases (e.g. Ce2(SO4)3).


Temperature Effects

• Experience tells us that carbonated beverages go flat as they get warm.

• Therefore, gases get less soluble as temperature increases.

• Thermal pollution: if lakes get too warm, CO2 and O2 become less soluble and are not available for plants or animals.

• For solid solutes, as temp ↑, solubility ↑.

• For gas solutes, just the opposite.


Pressure Effects


Pressure Effects• The higher the pressure, the more molecules

of gas are close to the solvent and the greater the chance of a gas molecule striking the surface and entering the solution.– Therefore, the higher the pressure, the greater the

solubility.– The lower the pressure, the fewer molecules of

gas are close to the solvent and the lower the solubility.


Pressure Effects• Carbonated beverages are bottled with a

partial pressure of CO2 > 1 atm.

• As the bottle is opened, the partial pressure of CO2 decreases and the solubility of CO2 decreases.

• Therefore, bubbles of CO2 escape from solution.


Saturated Solutions

Saturated/unsaturated solutions• The solubility of a solute

in a solvent is also related to temperature (if T ↑, solubility ↑)

• Solutions whose solute concentration is at a maximum are called saturated.

• Solutions where the solute concentration is below its solubility are called unsaturated.

• Some solutions can be super-saturated, a concentration of solute > than solubility

To dissolve 120 g the temp must

be raised to 80oC

at 50o 88.0 g of KNO3 will dissolve

1. Which substance’s solubility increases the most with temperature?

2. Which substance’s solubility changes the least with temperature?

3. What is the solubility of KI at 8oC?

4. What temperature is needed to dissolve 160 g of potassium iodide, KI, in 100 g of water?

OH

HO

H

H

H+

++OH

HO

H -

Water molecules form ions. One water molecule strips a hydrogen (H+) from another water molecule. The ions formed are a hydronium ion and a hydroxide ion. In pure water, the concentration of these ions are not enough to conduct an electric current, therefore pure water in not an electrolyte.

Hydronium Hydroxide

ion (H3O+) ion (OH-)

• Acid - increases H+ (H3O+) concentration

• Bases - increases OH- concentration • Acids are substances that are able to ionize to form hydrogen ions and thereby increase

the concentration of H+(aq) ions in aqueous solutions.

• H2SO4 (aq) H+ (aq) + HSO4 - (aq)

• Bases are substances that accept (react with) H+ ions. Hydroxide ions, OH-, an ion which readily react with H+ ions to form water:

• H+ (aq) + OH - (aq) H2O (l)

Acids (Properties)• Taste Sour• Turn Blue litmus Red • Neutralizes bases• Reacts with metals• pH below 7Examples:• Juices: Tomato, Orange,

Grapefruit• Wine• Banana• Coffee• Vitamin C• Soda

Acids-Bases CharacteristicsBase (Properties)

•Taste Bitter•Turns Red litmus Blue•Neutralizes acids•Turns metal into hydroxides

• pH above 7• SlipperyExamples:

•Milk of Magnesia •Lime water•Lye, Draino•Ammonia•blood•Soap

Scientists use the "pH" scale to measure how acidic or basic a liquid is. pH is a measure of the concentration of hydrogen ions (protons) per liter The scale goes from "0" to "14". Distilled water (pure water) is 7 (right in the middle). Acids are found between "0" and "7". Bases are from "7" to "14".

pH (power of Hydrogen)

pH Values•pH Values for various samples:

• Acid: pH : 1 -- 6• Neutral: pH 7• Base: pH 8 -- 14

• Smaller the pH value the greater the acidity

• larger the pH value the lower the acidity

• Smaller the pH value the greater the acidity

• larger the pH value the lower the acidity

Other sources of Acidic Rain:Other sources of Acidic Rain:SO2(g) + O2(g) 2 SO3(g) & NN2 g)2 g) + O + O2 g)2 g) 2 NO 2 NO2(g2(g) from burning fossil from car combustionfuels and from volcanoes2 SO3(g) + H2O(l) H2SO4(aq)

sulfuric acid

2 NO2 NO2(g) 2(g) + H+ H22OO(l) (l) HNO HNO3(aq) 3(aq) + HNO+ HNO2 (aq)2 (aq) nitric acid nitrous acid

Rainwater pH (H20) < 7.0Rain water isn’t

neutralDissolving CO2 CO2(g) + H2O(g) H2CO3 (aq ) carbonic acid

H2CO3 (aq) ionization: H2CO3 (aq) H+ (aq) + HCO3 -

(aq)

Overall: CO2(g) + H2O(l) H+ (aq) + HCO3 -

(aq)

Neutralization

• Addition of either acid or base to a solution until acid and base are in perfect balance (equilibrium)

• Think of Tums, Rolaids, Mylanta, Gaviscon, Milk of Magnesia, Alka-Seltzer, Di-Gel, etc., etc., etc. to an acid stomach

• Acid + Base Salt + water

Solutions, Acids, Bases, and Solubility. Objective 4 TEK 9 The student knows how solution chemistry...

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