Genchemomsim.docx

Physical properties are properties that can be measured or observed without changing the chemical nature of the substance. Some examples of physical properties are:

The Classification of Matter

A chemical change (chemical reaction) is a change of materials into other, new materials with different properties, and one or more new substances are formed.

- Matter is classified into two broad categories, namely, pure substances and mixtures. Mixtures can be separated into pure substances by physical methods. Pure substances are further divided into categories as elements and compounds. Similarly, mixtures are also classified into types; homogeneous mixtures and heterogeneous mixtures:

Evidence of a chemical change - Change of odor. - Change of color (for example, silver to reddish-brown when iron rusts). - Change in temperature or energy, such as the production - (exothermic) or loss (endothermic) of heat. - Change of composition - paper turning to ash when burned. - Light and/or heat given off. - Formation of gases, often appearing as bubbles in liquids. - Formation of a precipitate (insoluble particles). - The decomposition of organic matter (for example, rotting food) - The change is difficult or impossible to reverse

Classification of Matter: -All matter is either a pure substance or a mixture. -A pure substance has a fixed composition and distinct properties -A mixture consists of two or more pure substances which retain their chemical identities. Pure Substances -Pure substances are either elements or compounds. -An element cannot be decomposed into simpler substances by physical or chemical means. -A compound is composed of two or more elements always in the same proportion Elements -There are about 100 elements. Their names and symbols are shown in the Periodic Table. Compounds - Compounds can be decomposed into their elements ONLY by a chemical means.

Example: the electrolysis of H2O - Compounds always give the same proportion of each element by mass. Compound Formulas - A chemical formula expresses the number of atoms of each type of element in the compound. The number of atoms is indicated with a subscript.

Mixtures  A mixture has a variable composition  If the properties of a mixture are not uniform throughout, the mixture is heterogeneous.  If the properties are uniform, the mixture is homogeneous, or a solution.  No ice in the Kool-Aid  The pure substances in a mixture can be separated through physical means.  Separation of salt from seawater.  Distillation of brandy, rum, etc.  Separation of fresh brewed coffee from coffee grounds (filtration) A Microscopic View  Pure substances are composed of atoms or molecules with fixed numbers of atoms bonded together.  Mixtures consist of variable numbers of atoms or molecules.

PROPERTY

BASE UNIT

SYMBOL

Length

Meter

m

Mass

Kilogram

Time

m

milli

10-3

kg

µ

micro

10-6

Second

S

n

nano

10-9

Electric current

Ampere

A

Temperature

Kelvin

K

Chemical Amount

Mole

mol

Luminous Intensity

Candela

cd

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Multiples or fractions of these units are used for really large or really small values and are indicated by the use of prefixes based on the powers of ten. For example in describing rather long distances unit kilometre is preferably used which is a multiple of a thousand, thus 1000 m = 1 x 103 km In cases such as this scientific notation is being used where N x 10 n where N is any continuous number between 1 and 10 and n is either positive or negative integer In the conversion to a scientific notation, n is determined by counting the number of places must be moved in order to make the value between 1 to 10.If the decimal point is moved to the left the n is negative and if its to the right the n is positive

PREFIX

Name

Meaning

G

giga

109

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M

mega

106

k

kilo

103

c

centi

10-2

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RULES FOR SIGNIFICANT FIGURES 1. All non-zero numbers are significant. The number 33.2 has THREE significant figures because all of the digits present are non-zero. 2. Zeros between two non-zero digits ARE significant. 2051 has FOUR significant figures. The zero is between a 2 and a 5. 3. Leading zeros are NOT significant. They're nothing more than "place holders." The number 0.54 has only TWO significant figures. 0.0032 also has TWO significant figures. All of the zeros are leading. 4. Trailing zeros to the right of the decimal are significant. There are FOUR significant figures in 92.00. 92.00 is different from 92: a scientist who measures 92.00 milliliters knows his value to the nearest 1/100th milliliter; meanwhile his colleague who measured 92 milliliters only knows his value to the nearest 1 milliliter. It's important to understand that "zero" does not mean "nothing." Zero denotes actual information,

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just like any other number. You cannot tag on zeros that aren't certain to belong there. 5. Trailing zeros in a whole number with the decimal shown ARE significant. Placing a decimal at the end of a number is usually not done. By convention, however, this decimal indicates a significant zero. For example, "540." indicates that the trailing zero IS significant; there are THREE significant figures in this value. 6. Trailing zeros in a whole number with no decimal shown are NOT significant. Writing just "540" indicates that the zero is NOT significant, and there are only TWO significant figures in this value. 7. Exact numbers have an INFINITE number of significant figures. This rule applies to numbers that are definitions. For example, 1 meter = 1.00 meters = 1.0000 meters = 1.0000000000000000000 meters, etc.

Determine how many significant figures occur in each of the following numbers: 1. 2. 3. 4. 5. 6.

926.9 707 123.06 0.0402 0.82610 338.00 • • • • • •

1. 926.9 has 4 Significant Figures (SF) 2. 707 has 3 SF 3. 123.06 has 5 SF 4. 0.0402 has 3 SF 5. 0.82610 has 5 SF 6. 338.00 has 5 SF

Significant figures in Calculation • Multiplying or dividing Answers should be rounded off to the same number of significant figures as that of the original value with the least number of significant figures.

Example 3.4

2 SF

x 8.32

3 SF 28.288 28 round off to 2 SF 0.5991 4 SF ÷ 0.77 2SF 0.07780519 0.078 round off to 2 SF Sample Problem • Edward measured three marbles using three different weighing instruments. If the three marbles each weigh 3.72g, 5.2g and 4.910g. What is the total weight of the tree marbles? Use the correct number of significant figures. Required: Total weight of the three marbles Given: Weight of Marble 1------ 3.72g Marble 2------ 5.2g Marble 3------ 4.910g Strategy Perform the calculation and express the final answer with the least number of decimal places. Solve the problem 3.72g 5.2g 4.910g 13.830 13.8 round off to one decimal place

Sedimentation - is the tendency for particles in suspension to settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration, or electromagnetism. © Wikipedia

- Filtration – it is the process of separating insoluble particles from a liquid. - Paper chromatography is a technique used to separate a mixture in its component molecules. The molecules migrate or moved up a paper because of its solubility, molecular mass and hydrogen bonding with the paper. - Distillation is a widely used method for separating mixtures based on differences in the conditions required to change the phase of components of the mixture. To separate a mixture of liquids, the liquid can be heated to force components, which have different boiling points, into the gas phase. The gas is then condensed back into liquid form and collected.

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Hand Picking – simplest method of separating substance. This method is only when unwanted material is in small quantity. Threshing – is a method that generally used by the farmers to separate grains from the stalks after harvesting. Winnowing – It is used to separate heavier and lighter components of a mixture by wind or blowing air. Sifting or Sieving – Is used to separate a dry mixture which contains substance of different sizes by passing through.

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Simple distillation may be used when the boiling points of two liquids are significantly different from each other or to separate liquids from solids or non volatile components. In simple distillation, a mixture is heated to change the most volatile component from a liquid into vapor. The vapor rises and passes into a condenser. Usually, the condenser is cooled (e.g., by running cold water around it) to promote condensation of the vapor, which is collected. Steam distillation is used to separate heat-sensitive components. Steam is added to the mixture, causing some of it to vaporize. This vapor is cooled and condensed into two liquid fractions. Sometimes the fractions are collected separately, or they may have different density values, so they separate on their own. An example is steam distillation of flowers to yield essential oil and a waterbased distillate. Separating organic compounds from plant parts. Example is lemon grass oil and eucalyptus oil Fractional distillation is used when the boiling points of the components of a mixture are close to each other, as determined using Raoult's law. A fractionating column is used to separate the components used a series of distillations called rectification. In fractional distillation, a mixture is heated so vapor rises and enters the fractionating column. As the vapor cools, it condenses on the packing material of the column. The heat of rising vapor causes this liquid to vaporize again, moving it along

the column and eventually yielding a higher purity sample of the more volatile component of the mixture. Example is fractionating crude oil Vacuum distillation is used to separate components that have high boiling points. Lowering the pressure of the apparatus also lowers boiling points. Otherwise, the process is similar to other forms of distillation. Vacuum distillation is particularly useful when the normal boiling point exceeds

the decomposition temperature of a compound. -

Centrifugation - A centrifuge is a device that uses centrifugal force to separate two or more substances of different density or mass from each other. Centrifugal force is the tendency of an object traveling around a central point to fly away from that point in a straight line. A centrifuge is able to separate different substances from each other because materials with heavier masses move faster and farther away from the central point than materials with lighter masses.