Dissolving Solids, Liquids and Gases

http://www.inquiryinaction.org/chemistryreview/dissolving/

Solubility POGIL

Molarity POGIL

Investigation 4: Dissolving Solids, Liquids and Gases

Key concepts for students● Dissolving applies to solids, liquids, and gases.● Dissolving involves the interaction between the solvent and the solute.● The extent to which a substance dissolves in a liquid is a characteristic property of that substance.● Heat increases the solubility of most solids.● Heat does not increase the solubility of all solids by the same amount.● Heat decreases the solubility of most gases.

Learning objectivesStudents will be able to:● Identify and control variables to design and conduct valid experiments.● Develop a definition of “dissolve” that applies to solids, liquids, and gases.● Use observations and results of experiments to develop explanations to answer a question.● Explain that the solubility of a substance depends on the characteristics of both the solute and the

solvent giving each substance a unique solubility.● Draw pictures and write captions showing the stages of a solid dissolving.● Explain that heat affects the solubility of solids and gases differently.

Investigation 4: Dissolving Solids, Liquids and Gases

Investigation questionsCan solids, liquids, and gases all dissolve?● How can you tell when a substance is dissolved?● Does colored sugar dissolve equally well in water, vegetable oil, and

alcohol?● Does cocoa mix dissolve better in hot water or cold water?● Do salt and sugar dissolve better in hot water than in cold water?● Do all liquids dissolve in water?● Can a gas dissolve in a liquid?● Does temperature have an effect on how quickly dissolved gas escapes

from a soda?● How can you make a lemon soda that keeps as much carbonation as

possible?

Dissolving - Summary• Solids, liquids, and gases can all dissolve.• Dissolving depends on the molecules of the substance doing the dissolving, called the solvent, and the molecules of the substance being dissolved, called the solute.• Dissolving is the process in which these molecules interact and attract each other to form a solution.• The extent to which a substance dissolves is a characteristic property of that substance called its solubility.• Water is a good dissolver because of its areas of positive and negative charge. The mutual attraction between water molecules and other substances with positive and negative charges causes these substances to dissolve.

Chemical Change

http://www.inquiryinaction.org/chemistryreview/chemical_change/

Acid/Base POGIL

Calculating pH POGIL

Acid:

A substance that releases H+ ions in an aqueous solution

“aqueous” means: water

Characteristics of Acids:

Acids have a sour taste Acids react with metals

Acids contain Hydrogen

Many are poisonous and corrosive to skin

H

Strong Acids(break down completely to give off many H+ ions)

Weak Acids(only partially breaks down, gives less H+)

Acids and BasesAcids:

Some common acids in our daily life:Ethanoic Acid, CH3COOH: found in vinegar, tomato juice

Citric Acid, C6H8O7: found in citrus fruits

Lactic Acid: found in sour milk, yogurt

Tannic Acid: Found in tea

Tartaric Acid: Found in grapes

What about those commonly found in our lab?Hydrochloric acid, HCl

Sulfuric Acid, H2SO4

Nitric Acid, HNO3Which of these is found in batteries? Sulfuric Acid

Base:

A substance that releases OH- ions in an aqueous solution

Characteristics of Bases:

Bases usually taste bitter Bases feel slippery Bases contain hydroxide ions STRONG bases are also poisonous and corrosive to skin

OH-

Strong Bases The Formulae

Lithium hydroxideSodium hydroxidePotassium hydroxideRubidium hydroxideCaesium hydroxideBarium hydroxideCalcium hydroxideStrontium hydroxide

LiOHNaOHKOHRbOHCsOHBa(OH)2

Ca(OH)2

Sr(OH)2

Common Bases:

(Hydroxides of Group 1 and Group 2 Metals are STRONG)

All others are WEAK

Some bases (VERY FEW) don’t have OH-

Most commonly: ammonia NH3

Reactions between acids and bases

When and acid and a base react with each other, the characteristic properties of both are destroyed. This is called neutralization.

Reactions between acids and bases

General formula for acid base reaction:

Acid + Base → H2O +Salt

“Salt” means any ionic compound formed from an acid/base reaction

NOT JUST NaCl !!

Neutralization Reaction Animation

Neutralization

HCl + NaOH → H2O + NaCl acid base water salt

NeutralizationAnother Example

HNO3 + KOH → H2O + KNO3

H OHKNO3

acid base water salt

IndicatorsAn indicator is a compound that will change color in the presence of an acid or base

Universal indicator (pH paper) Used for the full pH range

Red Litmus-Turns blue in baseBlue Litmus-Turns red in acid

Phenolphthalein-Turns pink in base

pHpH stands for “potential hydrogen” and is a measure of how many H+ ions there are in solution.

The MORE H+ there are, the LOWER the pH will be.

pH = - log [H+]

pH ScaleShows the range of H+

concentrations

High H+ concentration Low H+ concentration

Virtual demonstration - Detecting acid/base

Investigation 5: Chemical Change Key concepts for students● Substances react chemically in characteristic ways.● Evidence that a chemical reaction has occurred includes: production of a gas, change in temperature, color change, and formation of a precipitate.● A chemical reaction can be controlled by adjusting the amount of reactants.● A chemical reaction can result in an increase in temperature (exothermic) or a decrease in temperature (endothermic).● The color change of an acid–base indicator can help classify a solution as an acid or a base, identify when a solution has been neutralized, and compare the amount of acid or base in a solution.● In a chemical reaction, the bonds holding one atom to another are broken, atoms rearrange, and then combine in new ways to create one or more different substances.● In a chemical reaction, the atoms that make up the reactants are never destroyed or disappear. They rearrange and bond in new ways to form the products.

Learning objectivesStudents will be able to:● Design a testing procedure to compare the chemical reactions of different substances.● Use the characteristic chemical reactions to identify an unknown substance.● Recognize that production of a gas, change in temperature, color change, and formation of a precipitate are evidence of chemical change.● Use a thermometer and graduated cylinder accurately.● Control chemical reactions by adjusting the amount of the reactants.● Use the color changes of an acid-base indicator to classify and compare different substances.● Determine whether a new substance is created during a chemical reaction.

Investigation 5: Chemical Change Investigation questions● Do powders that look the same have the same chemical reactions?● How can you use the characteristic ways substances react to tell similar-looking

substances apart?● How can you identify an unknown powder?● What are the active ingredients in baking powder?● Aside from bubbling, what else happens during a reaction between baking soda and

vinegar?● How can you control the amount of gas produced in a baking soda-and-vinegar

reaction?● Can the temperature increase during a chemical reaction?● How can you tell if a substance is an acid, a base, or neutral?● How can you return the color of a red cabbage indicator solution back to blue?● How can neutralizing acids help you compare the amount of acid in different solutions?● What happens when soap is added to hard water?

Chemical Change - Summary• A chemical reaction happens when one or more substances change into entirely new substances with different properties.

• The clues of a chemical reaction are production of a gas, change in temperature, color change, production of a precipitate.

• In a chemical reaction, it takes energy to break the bonds in the reactants and energy is released when bonds are formed in the products.

• If more energy is required to break the bonds than is released when new bonds are formed, the reaction is endothermic.