Chemistry2014-2015

CHEMISTRY PACKET 1: SECTIONS I AND II (PG.

3-51)

Safety Contract due Th 8/28Safety Quiz Th 8/28 (you MUST pass

this quiz and turn in your completed Safety Contract before you can participate in labs)

Section I/II Quiz F 9/12Section I/II Test W 9/17Element Research Project due M 9/29Labs on F 8/29, W 9/3, M 9/8

IMPORTANT DATES

SECTION I DEFINING MATTER

Chemists have specific tools and equipment that they use to study the world around them. They also have a set of guidelines for using tools and chemicals safely.

LAB EQUIPMENT AND SAFETY

Commonly-used equipment can be found on a page in this packet. You will need to be able to identify these pieces of equipment for your quiz/test, as well as on a daily basis. The most accurate glassware to use for

measuring liquid is a volumetric pipette (or just a pipette—these are not the flimsy plastic ones, but glass ones with clear markings on the side). Other accurate glassware pieces include the graduated cylinder and the burette. Erlenmeyer flasks and beakers are not considered accurate.

THE TOOLS CHEMISTS USE

Some containers are safe for heating substances. These include test tubes, beakers, flasks, crucibles, and evaporating dishes.

One common piece of equipment that is not shown in your packet is the hot plate.

Know the location of safety equipment and how to use it.Safety Shower: near calculatorsEye Wash: near calculators, attached to safety shower (must wash eyes for 15-20 minutes)

First Aid Kit: front of class, below clockFire Blanket: next to safety shower (used to smother fires)

Fume Hood: back corner of classroom (used to contain fumes or smoke)

Fire Extinguisher: below fire blanket

LABORATORY SAFETY

Laboratory Safety:Dress appropriately (roll up sleeves, tie hair back, wear closed-toe shoes); read instructions carefully; double-check that you are using the correct chemicals; do not put chemicals back into their original bottles; wear goggles; clean up your station and return equipment to its proper place before you leave the lab; if you have any questions in the lab, or if an accident occurs, ask/tell your teacher.

Personal safety equipment: goggles, gloves, apron

Classroom safety equipment: fire blanket, fire extinguisher, safety shower, eye wash station, fume hood

The Roots of ChemistryMore than a thousand years ago, people known as alchemists tried to transform substances into other substances (ex. turning ordinary metals into gold). They never succeeded, but as alchemists conducted experiments and looked over their successes and failures, they gradually created the early study of Chemistry. (Today we know that it actually is possible to convert one element to another, but it’s a very different process and sadly, it does not allow one to turn base metals into gold.)

INTRODUCTION TO CHEMISTRY

When the alchemists succeeded in making new substances, they faced the challenge of determining whether each substance was gold. In other words, the alchemists needed to figure out if the new substance had the properties of gold.

A property is a characteristic or quality of a substance. You are going to try a similar experiment tomorrow by turning a penny from copper to silver to gold. You will need to write a hypothesis to explain what happens.

A hypothesis is a proposed explanation for an observation or scientific problem, which can be tested by further investigation (it is not an educated guess).

Changes are constantly happening around us. These can be exciting (exploding fireworks) or mundane (baking cookies, which is still pretty nice). Chemistry is the study of what substances are made of, how they behave, and how they can be transformed. It is the study of matter and how matter changes.

THE STUDY OF MATTER AND CHANGE

Matter is the word chemists use to refer to all the materials and objects in the world. Although many examples of matter are obvious (your desk, your phone, you), your senses alone are not always enough to tell you whether something is matter (you can’t see viruses, but you can still get sick from them, for example).

DEFINING MATTER

The amount of substance, or material, in an object is called its mass. Mass is a property of matter that can be measured. (It is also the same no matter where you are; weight, however, is not.) The amount of space something takes up is called its volume and is also a property of matter that can be measured. So, matter is anything that has mass and volume.

Solids, liquids, and gases are all composed of matter.

Some things may seem like matter, but are not. Matter must have mass and it must take up space. Examples of non-matter include heat and sound. Ideas also are not matter.

IS IT MATTER?

Chemists measure mass in grams (g) and kilograms (kg). There are 1000 g in 1 kg.

Electronic balances and triple-beam balances can be used to measure mass. With both of these balances, mass must be measured and recorded as exactly as possible; it may seem to make sense to round, but rounding can affect your lab work (and your lab grade—don’t do it). If you use an electronic balance, record all digits shown. For triple beam balances, estimate one more decimal place than you can read.

MEASURING MATTER

Chemists measure the volume of liquids and gases in milliliters (mL) and liters (L). There are 1000 ml in 1 L. You can measure the volume of a sample of a liquid by pouring it into a graduated cylinder and reading the number of mL on the side. Make sure to read the liquid level at the bottom of the meniscus (the curvature of the top of the liquid).

Fun fact—mercury’s meniscus bends the opposite way.

You can measure the volume of a regularly shaped solid object by measuring its dimensions in centimeters (length, width, height) and using a mathematical formula. This will give you volume in cubic centimeters (cm3). 1 cm3 = 1 mL.

In certain cases, you can use water displacement (shown on the right with the dinosaur) to determine the volume of a (small, insoluble) solid.

Read the initial water volume; add the object; read the new volume; and subtract.

What was the volume of the dinosaur? ________ mL = ________ cm3

5.60 mL- 4.80 mL =0.80 mL

= 0.80 cm3

It is possible for two substances to have the same volume but different masses, or the same mass but different volumes. For example, 1.0 cm3 of gold has a mass of 19.3 g, but 1.0 cm3 of copper has a mass of 9.0 g. This means that if you had the same mass of each, the copper would take up more space (have more volume) than the gold. This is due to a difference in density.

MASS AND VOLUME

Which is heavier, copper or gold? If you have equal volumes of each, the gold will always be heavier. This is due to density, which is the mass of a substance per unit of volume.

The formula for calculating density is shown on the right. Density is calculated by dividing mass by volume, so its units are g/mL or g/ cm3.

DENSITY

A piece of metal has a volume of 30.0 cm3 and a mass of 252 g. What is its density?

PACKET 1 EXAMPLE 1: DENSITY

= 252 g / 30.0 cm3

= 8.40 g/cm3

Density = mass / volume

The density of a substance does not change with its size or shape. In other words, density is an intensive property (a property that does not change if the quantity of the substance changes). Intensive properties can be used to identify substances. (On the other hand, extensive properties

DO change depending on the amount of matter—examples include mass and volume.)

IDENTIFYING MATTER USING DENSITY

Because density is an intensive property, it can be used to help identify the type of matter that an object or sample is made of. First, calculate the density of an object, then compare it with known density values in a reference table like the one on the right.

Metal Density

Copper 9.0 g/ cm3

Zinc 7.1 g/ cm3

Gold 19.3 g/ cm3

Lead 11.4 g/ cm3

Aluminum 2.7 g/ cm3

Brass 8.4 g/ cm3

If someone tried to trick you by coating a block of lead with a thin layer of gold, how could you prove the bar is fake?

PACKET 1 EXAMPLE 2: THE FAKE BAR OF GOLD

Metal Density

Copper 9.0 g/ cm3

Zinc 7.1 g/ cm3

Gold 19.3 g/ cm3

Lead 11.4 g/ cm3

Aluminum 2.7 g/ cm3

Brass 8.4 g/ cm3

Use its mass and volume to determine its density. If the bar is actually lead coated with gold, its density will be higher than 8.4 g/cm3 (the density of lead is 11.4 g/cm3).

Look back at Example 1. What type of metal is this, and how do you know?

PACKET 1 EXAMPLE 3: USING DENSITY TO IDENTIFY A METAL

Metal Density

Copper 9.0 g/ cm3

Zinc 7.1 g/ cm3

Gold 19.3 g/ cm3

Lead 11.4 g/ cm3

Aluminum 2.7 g/ cm3

Brass 8.4 g/ cm3

The metal is brass; its density is 8.4 g/cm3.

 SECTION II BASIC

BUILDING MATERIALS

Some chemical names are used in daily language (ex. aluminum, iron, ammonia). Other names are used mainly by chemists, such as sodium chloride for salt and sodium bicarbonate for baking soda.

Elements are the building materials of all matter. There are about 118 known elements; each one has a name and a symbol. The chemical symbol may be an abbreviation for the element’s name, but it is sometimes taken from a word in another language instead.

CHEMICAL NAMES AND SYMBOLS

Name Mercury

Copper

Carbon

Phosphorous

Gold

Iron

Symbol

Hg Cu C P Au Fe

Elements combine in specific ratios to form compounds. A compound is represented by a chemical formula. For example, sodium chloride is NaCl and consists of a 1:1 ratio of sodium and chlorine. The chemical formula for carbon dioxide is CO2, which means it consists of a 1:2 ratio of carbon to oxygen (there are two oxygen atoms for every carbon atom).

Compounds can be very different in behavior and appearance from the elements they are composed of. For example, sodium is a shiny, soft, reactive metal and chlorine is a deadly gas, but sodium chloride is a white crystal that is relatively nontoxic.

Elements can exist as solids, liquids, or gases; these are represented with the symbols (s), (l), and (g) after the chemical formula. These are called the phases of matter. For example, water vapor is written H2O(g), liquid water is written H2O(l), and ice is written H2O(s).

There is another symbol for physical form, the symbol (aq) for aqueous. A substance is aqueous if it is dissolved in water (therefore, it has to be soluble).

PHYSICAL FORM

Most substances are mixtures of compounds. In a mixture, the different substances do not have to be present in a specific ratio. For example, you can make chocolate chip cookies with ½ cup of chocolate chips per batch, or 2 cups of chocolate chips per batch. They’re still chocolate chip cookies.

THE COPPER CYCLE

Copper is an element with the symbol Cu. As a solid powder, it has a distinctive orange-brown appearance. You are going to transform copper powder through a series of chemical reactions. If all works well, copper should reappear by the end of the experiment.

Evidence of a Chemical Change A chemical change or chemical reaction is a

transformation that alters the composition of one or more substances such that one or more new substances with new properties are produced. You can usually tell when a chemical reaction occurs because there is evidence of new substances forming.

Evidence of a chemical change includes a color change, evolution (production) of a gas, production of light, and a change in smell.

CONSERVATION OF MATTER

The copper cycle experiment brought you back full circle. No matter what was done to the copper, the copper was always present in some form. In other words, it was not created or destroyed during the chemical transformations, but its form was changed during each step.

Over many centuries, scientists have gathered evidence that matter can never be destroyed or created through a chemical change—enough evidence that this is considered a scientific law. The law of conservation of mass states that mass cannot be gained or lost in a chemical reaction—that matter cannot be created or destroyed.

As alchemists and chemists explored the world around them, they discovered a large number of elements. It became clear that these elements needed to be organized. In the late 1960’s, a Russian chemist and teacher named Dmitri Mendeleyev created his own organizational scheme by putting elements in groups based on similarities in their properties. Some of these properties are listed below. Reactivity Ratios in compounds Atomic mass

PROPERTIES OF THE ELEMENTS

Reactivity is a property that describes how easily an element will combine with other substances to form new compounds. An element that is highly reactive combines rapidly with other substances. For example, when metallic sodium comes into contact with water, it reacts vigorously.

Mendeleyev also paid attention to which elements combine with which, and he noted the ratios in which their atoms combine. For example, magnesium combines with chlorine in a 1:2 ratio, while sodium combines with chlorine in a 1:1 ratio. This means that magnesium and sodium must have similar reactivity (since both can combine with chlorine), but not exactly the same.

Mendeleyev used another property--atomic mass--to sort the elements. Atomic mass is the mass of an atom, and it is measured in atomic mass units, or amu. The elements can be placed in order of their atomic masses. However, this alone does not tell you which elements are similar by properties.

Mendeleyev put the elements with similar reactivity and chemical formulas of compounds into columns. He also sorted them by atomic mass, from smallest to largest. This way, the elements in each column have similar physical properties and reactivity, and they tend to form compounds with other elements in the same ratios. This table became the foundation of the modern periodic table of elements.

Scientists have detected around 114 elements on the planet (there are about 118 total). Each element is unique, but groups of elements have similar properties.

THE PERIODIC TABLE

Each element has a square on the periodic table. Within each square is information about that element including its name and symbol. The whole number (usually at the top of each square) is called the atomic number. The decimal number in each square on the periodic table is the average atomic mass in amu.

Most modern periodic tables have 18 vertical columns and 7 horizontal rows. The vertical columns are also called groups or families. The horizontal rows of the table are called periods because patterns repeat periodically (over and over again) in each row.

Chemists also have names for the sections of the periodic table. The main group elements include groups 1A (alkali

metals), 2A (alkaline earth metals), and 3A-8A (group 7A are the halogens, and group 8A are the noble gases).

The transition metals are in the middle of the periodic table.

The inner transition metals are below the periodic table. This section consists of the lanthanides and actinides.

Solids, liquids, and gases: most of the elements are solid at room temperature. Several are gaseous at room temperature; only three (gallium, bromine, and mercury) are liquid at room temperature.

Metals, metalloids, and nonmetalsThe majority of the elements are metals. On most periodic tables there is a stair-step line that divides the table. Metals are found to the left and nonmetals are found to the right. The elements found along the stair-step are called metalloids (similar properties to both metals and nonmetals).

Reactivity: elements in the lower left and upper right of the periodic table (excluding noble gases) are the most reactive. On the other hand, elements in the middle of the periodic table, such as copper, silver, and gold, are not very reactive.

FUN FACT

It is illegal to purchase francium in the United States due to its violently explosive reaction with water.

Gold is very nonreactive, but it can dissolve in aqua regia, a concentrated 1:3 mixture of nitric acid and hydrochloric acid. This reaction was used to keep two Nobel Prize medals out of Nazi hands in the 1940’s (the metals were dissolved; the dissolved gold was stored in common glassware; and after the war, the Nobel Foundation recast the medals using the dissolved gold).

FUN FACT