Unit A: Chemistry

Home , Ionic compound, Litmus, Solubility chart

2.2: EXPLAINING PROPERTIES OF SUBSTANCES IN THIS SECTION YOU WILL LEARN ABOUT...

• General Outcome #2 – Explain, using the periodic table, how elements combine to form compounds, follow IUPAC guidelines for naming ionic compounds and simple molecular compounds • Classify ionic and molecular compounds, on the basis of their properties • Predict whether an ionic compound is relatively soluble in water, using a solubility chart • Relate the molecular structure of simple substances to their properties: conductivity, pH, solubility and state

WHY IS THIS IMPORTANT??

• Both ionic and molecular compounds form crystals. Possibly the most important molecular crystal studied in the last century was DNA. DNA is the molecule responsible for passing genetic information from one generation to the next in all living things. An X-ray photograph of DNA taken by Rosalind Franklin in 1951 led to the understanding that DNA is composed of two long chains twisted into a helix. IDENTIFYING IONIC COMPOUNDS

• Recall that ionic compounds always contain positive and negative ions (the first is always a cation and the second is always an anion) • You can recognize an ionic compound by inspecting it’s formula, remember that it always begins with a metal (while molecular contain two non-metallic atoms) PROPERTIES OF IONIC COMPOUNDS

• High Melting Point • all have high melting point therefore solids at room temperature (above 300 oC) • because attractions between cations and anions in solids are so strong, they have a tight, highly organized crystal lattice • large amount of energy must be added in the form of heat before ions can move into the liquid state PROPERTIES OF IONIC COMPOUNDS

• Retention of Crystal Shape • each crystal is made of perfectly flat surfaces • before being hit, all ions alternate precisely (recall that opposites attract); however after being hit, the positive ions momentarily move close to the positive ions and negative ions momentarily move close to the negative ions, causing the crystal to split. • ionic compounds still retain crystal shape after being hit

PROPERTIES OF IONIC COMPOUNDS

• Solubility in Water • all ionic compounds dissolve in water to some extent because both cations and anions are strongly attracted to water molecules • this occurs because each water molecule is polar (one end has a slightly positive electric charge and one has a slightly negative charge) PROPERTIES OF IONIC COMPOUNDS

• Conductivity in Solution • solutions containing ionic compounds are good conductors of electricity, unlike pure water which has almost no conductivity • the greater the concentration of ions, the greater the conductivity (eg. 2g of NaCl in 1L of water is twice as conductive as 1g in 1L) • solutions of ionic compounds are considered to be excellent electrolytes (any solution that can conduct electricity)

• some molecular compounds, such as HCl(g) become ionic in solution, which is a general characteristic of acids SOLUBILITY OF IONIC COMPOUNDS

• The properties of solubility and conductivity are of great importance to chemists. Chemists often check the solubility or conductivity of a compound when analyzing it. Scientists test compounds for solubility many times and then put the results into a table of solubility. A table of solubility shows how soluble common ionic compounds are in water. • The solubility is rated as very soluble (dissolves well; recall when a chemical formula has the subscript (aq) it dissolves well) or slightly soluble (its chemical formula is followed by (s)). SOLUBILITY OF IONIC COMPOUNDS

• Group 1 contains mostly alkali metals, how soluble is this group? • very soluble • How soluble are chloride ions? Are there any exceptions? • most are very soluble; the exceptions are silver chloride, lead (II) chloride, mercury (I) chloride, copper (I) chloride and thallium (I) chloride

SOLUBILITY OF IONIC COMPOUNDS

• sometimes when ionic compounds are mixed, they form a precipitate (a solid with low solubility that forms from a solution) • precipitates may also form from mixing two solutions; the process of forming a precipitate is called precipitation SOLUBILITY OF IONIC COMPOUNDS

• Answer 1acehj and 2adg on p.58 SOLUBILITY OF IONIC COMPOUNDS

• 1a)(NH4)2S (aq)

• 1c) AgCl (s)

• 1e) Fe(OH)3 (s)

• 1h) Na3PO 4 (aq)

• 1j) AgCH3COO(s) • 2a) very soluble • 2d) very soluble • 2g) very soluble PROPERTIES OF MOLECULAR COMPOUNDS

• Recall: molecules are non-metallic atoms held together by covalent bonds (sharing of electrons) • Molecular compounds exhibit special properties due to the type of bonding that exists between individual atoms and between molecules of the compound. In molecular compounds, often the bonds between the individual atoms are very strong; but the bonds between molecules are weak. A property, such as a low melting point (less that 300 oC), is a direct result of this weak bond between molecules. PROPERTIES OF MOLECULAR COMPOUNDS

• Only a small amount of energy is required for the molecules to begin sliding past one another; this does not mean that the molecule breaks up during melting therefore melting is not considered a chemical change PROPERTIES OF MOLECULAR COMPOUNDS

• In general, the properties of molecular compounds are • most are colorless or white • most are liquid or gas however some are solid • low melting point and boiling point • generally insoluble in water, some may be slightly soluble • covalent bonds are neutral atoms therefore they are non- electrolytes and do not conduct electricity • not malleable (beaten or rolled into sheets) SPECIAL PROPERTIES OF WATER

• one of water’s most important properties is that it is polar (each water molecule has a positive and negative end) • water molecules are more attracted to each other, making it easier for water to form a liquid • What if water was not polar?? • oceans would boil away in cold winters • life on earth would either be non-existent or would be different than we know it today!

• Practice Investigation 2-B pg. 58 SPECIAL PROPERTIES OF WATER

• Why does ice float? • In most cases as a substance changes from gas to liquid to solid, the substance becomes denser. If the solid state is the densest, it should sink; yet, ice floats.  As liquid water turns to ice, the molecules spread out and form a three dimensional array that contains six-sided rings therefore the ordered structure of molecules in ice takes more space. So, there are fewer molecules in ice than in water for a given volume. Fewer molecules per unit volume results in a lower density hence Ice floats because it is less dense than liquid water!

UNIT A: CHEMISTRY

2.3: ACIDS AND BASES IN THIS SECTION YOU WILL LEARN ABOUT...

THIS IS WHY WE DON’T PLAY WITH ACIDS OR BASES... RECALL FROM SCIENCE 9...

• Acid – a compound that dissolves in water to form a solution with a pH lower than 7 • Base – a compound that dissolves in water to form a solution with a pH higher than 7 ACIDS AND BASES IN YOUR BODY

• Acids and bases are present in the foods you eat, the products you use, and the fluids in your body systems. Your stomach, for example, contains strong hydrochloric acid; other organs in your body produce bases to neutralize stomach acid at certain points in the digestive process.

PROPERTIES OF ACIDS AND BASES

• Acids • Bases • tastes sour (lemons) • tastes bitter (soap) • do not feel slippery • feels slippery (bleach) • react with metals • do not react with metals • pH lower than 7 • pH higher than 7 • conducts electricity • conducts electricity

INDICATORS

• Acids – turns blue litmus paper red • Bases – turns red litmus paper blue • In a neutral solution litmus paper does not change • Universal Indicator – a mixture of several indicators that change color as the acidity changes THE PH SCALE

• Every increase of 1 indicates an increase of 10 in how basic a substance is; similarly, a decrease of 1 indicated 10 times increase in acidity • Here are some common acidic and basic solutions NAMING ACIDS

• Acids have a hydrogen symbol (H) on the left side of the compound’s formula. Organic acids, like

CH3COOH, are the only exception. For these acids, the hydrogen symbol (H) is on the right. • Acids that contain hydrogen and one other non- metallic element can be written with the prefix “hydro-” and suffix “-ic” (eg. HCl – hydrochloric acid) NAMING ACIDS

• Acids that contain oxygen, such as H2SO4 (aq) follow a different set of rules • If the anion ends in the suffix “-ate” then use the first element of the anion (in this case sulfur) and the

suffix with “-ic”; therefore H2SO4 (aq) is sulfuric acid RECOGNIZING BASES BY THEIR FORMULAS

• The presence of the hydroxide ion (OH-) indicates a basic solution • This isn’t always the case though, for example - ammonia (NH3 (aq)) doesn’t contain (OH ) however for now you only need to use the basic solutions that end in (OH-) NEUTRALIZATION

• When acids and bases react together, both acidic and basic properties disappear, this is called neutralization • This reaction will produce water and a salt

Practice 20-23 pg. 70 UNIT A: CHEMISTRY

A2.5: OUR CHEMICAL SOCIETY IN THIS SECTION YOU WILL LEARN ABOUT...

TOPICS

• Issues Related to Chemicals • Introduction • Environmental Effects • Health Concerns • Introduction • Alcohol • Nicotine and Other Tobacco-Related Chemicals

TOPICS

• Benzene – A Regulated Substance • Introduction • Safe Transportation and Handling of Benzene • Chemistry Related Careers • Food Technologist • Cosmetics Formulator • Working With Chemistry • Introduction

YOUR MISSION...

• There are 10 topics, you may work with two or three other people to summarize each topic and give a 2 minute presentation about each. Every person in your group must say something in front of the class.