Half-Life Worksheet

1) Fluorine-21 has a half life of approximately 5 seconds. What fraction of the original nuclei would remain after 1 minute?


2) Iodine-131 has a half life of 8 days. What fraction of the original sample would remain at the end of 32 days?



3) The half-life of chromium-51 is 28 days. If the sample contained 510 grams, how much chromium would

remain after 56 days?


4) How much would remain after 1 year? (refer to question #3)


5) The half life of Uranium-238 is 4.5 billion years and the age of earth is 4.5 X 10^9 years. What fraction of Uranium-238 that was present when Earth was formed still remains?


6) Chromium-48 decays. After 6 half-lives, what fraction of the original nuclei would remain?


7) The half life of iodine-125 is 60 days. What fraction of iodine-125 nuclides would be left after 360 days?


8) Titanium-51 decays with a half life of 6 minutes. What fraction of titanium would remain after one hour?


9) A medical institution requests 1 g of bismuth-214, which has a half life of 20 min. How many grams of bismuth-214 must be prepared if the shipping time is 2 h?
 
10) The half life of radium 226 is 1602 years. What fraction of a sample radium-226 would remain after 9612 years?
 
Answers: (coming soon)

Raioactivity: Supplementary Material



http://www.google.com/imgres



science.howstuffworks.com/nuclear-bomb.htm

www.cddc.vt.edu/host/atomic/hiroshim/hiro_med.html

epa.gov/rpdweb00/understand/radiation.html

 

RADIOACTIVITY: TERMINOLOGY AND HISTORICAL BACKGROUND

1. What is the name of the scientist who discovered x-rays in 1895?


2.What part of the body was pictured using x-rays?


3. Study the picture carefully and make a hypothesis as to what the person was wearing on one of their fingers?


4. Name the scientist who initially thought that the sun’s energy was being absorbed by a uranium sample which then emitted x-rays.


5.Briefly describe the circumstances that lead the scientist in Question # 4 to change his hypothesis about the sun’s energy and the uranium sample.


6.What had been discovered (refer to Question #5)?


7.How was the natural radiation different from x-rays?


8.Who coined the word “radioactivity”?


9.What two elements did the scientist in Question # 8 discover?


10.Identify the scientist who named and described the alpha particle, the beta particle and the proton. He is known as the “Father of Nuclear Physics”.


11.Elements such as uranium, thorium and plutonium undergo a change in the nucleus by emitting radiation which changes the original (parent) element into another element known as __(a)__ element. This radioactive –(b)__ process continues until the element produced is no longer radioactive.


12.The three types of nuclear radiation are __(a)__ particles, __(b)__ particles and __(c)__ rays.


13.What do you call the type of radiation that is described as having a positive charge with an atomic mass of 4; making it a Helium atom without any electrons?


14.What do you call the type of radiation that is described as having a negative charge with an atomic mass of 0; making it an electron?


15. What do you call the type of radiation that is emitted by nearly all radioactive materials and is described as high energy rays having no mass or charge?


16.What is meant by the term “half-life”?


17.What is the term applied to the process of changing one element into another element through nuclear decay?


18.What can stop alpha particles? Beta particles? Gamma rays?


19.What is the process of splitting an atom’s nucleus into two nuclei with smaller masses called?


20.What is the “atomic bullet” that causes the U-235 nucleus to undergo fission?


21.How many neutrons are released when U-235 nucleus splits?


22.Name two daughter products that form as a result of the splitting of the U-235 nucleus?


23What is the term given to the series of on-going fission reactions (billions occurring each second) which result in the release of tremendous amounts of energy?


24Name the scientist who, on December 2, 1942, achieved the first man-made self-sustaining nuclear chain reaction?


25.What are the great scientific implications of his discovery?


ATOMIC BOMB: CONSTRUCTION, USE AND ITS EFFECTS

1.What was the name given to the program during World War II to develop the first nuclear weapons in the United States?


2.What are the “fuels” used in the Nagasaki bomb and in the Hiroshima bomb?


3. What are the four ways that inanimate object were damage or destroyed in both Nagasaki and Hiroshima blasts?


4.What were he four causes of human casualties in Hiroshima and Nagasaki?


5. What is “flash burn”?


6. How much damage did gamma rays cause in the structures of Hiroshima and Nagasaki?


7.Describe what is like directly beneath the blast zone (ground zero).


8.Describe what happened in the outlying areas of Hiroshima.


9.What was the radius of total destruction for both Hiroshima and Nagasaki?


10. How much harmful radiation existed in Hiroshima and Nagasaki after the explosion?


11.When were people exposed to radiation?


12. The explosion in Hiroshima was equivalent to how much TNT?

4th Quarter 2012-2013: Colloids Handout

COLLOIDS

Mixtures are either homogeneous or heterogeneous, but sometimes the distinction is not easily made.  These are the systems that appear homogeneous to the naked eye but are actually heterogeneous.  These are the colloids.

Colloidal particles are larger than those of the solution but smaller than those of the suspension.  ( 1nm to 100 nm)

glue-like”, Greek word for glue is Kolla, for like it is eidos.
Thomas Graham is the Father of Colloidal Chemistry.

All colloidal systems have two components; the dispersed phase, the substance that is suspended, and the dispersion medium, the substance in which another substance is suspended.

For the formation of colloids, the dispersed phase and the dispersion medium must be mutually insoluble.

There are two classification of colloids based on the degree of attraction between the dispersed phase and the dispersion medium.  Colloids in which the attraction between the dispersed phase and the dispersion medium.  Colloids in which the attraction is strong are called lyophilic (solvent-loving), and those in which there is very little attraction or no attraction at all are called lyophobic (solvent-hating)

Classifications of Colloidal Systems

Phase of Colloid	Dispersion Medium	Dispersed Phase	Colloid	Examples
Gas	Gas	Gas	-	-
Gas	Gas	Liquid	Liquid aerosol	Fog
Gas	Gas	Solid	Solid aerosol	Smoke
Liquid	Liquid	Gas	Foam	Whipped cream
Liquid	Liquid	Liquid	Emulsion	Milk
Liquid	Liquid	Solid	Sol	Paint
Solid	Solid	Gas	Solid foam	Marshmallow
Solid	Solid	Liquid	Solid emulsion	Butter
Solid	Solid	Solid	Solid sol	Ruby glass

1. Solid emulsion
• lyophilic colloids

Examples: 

                         Jellies, gel, slimy precipitate of aluminum hydroxide, protoplasm

                                    Application:  

Syneresis - skin gets wrinkled as one gets older, Separation of serum from blood clot and sweating of butter.

2. Emulsion

lyophobic colloids

An emulsion is a colloid that contains tiny droplets of a liquid dispersed in another liquid.  It is formed only in the presence of a substance called emulsifying agent that helps disperse tiny particles of one liquid to another.

Oil and water in mayonnaise will not mix normally.  But in the presence of egg yolk intimately mixed with them, oil and water will not separate.

prepared by shaking two immiscible liquids

            Emulsifying agent/ stabilizing agent/ protective colloids

a substance used to make or form an emulsion

                                    Example: 

Milk- casein

                                                Mayonnaise- egg yolk

                                                Oil and water- soap

                                    Application: 

Removing dirt using soap

Preparation of Colloidal System

The dispersion method of preparing colloids involves is the breaking down of large particles into colloidal size.

Grinding - a colloid mill is used (preparation of paint pigments or face powders)

beating, stirring, whipping -  examples:  mayonnaise, creams

Peptization - chemicals are used to break down big particles (NaOH, sodium hydroxide is used to break up clay, glue, starch).  Gelatin peptized in water

homogenizing

using an emulsifying agent

     2.  The condensation method involves the clustering of small particles into colloidal size.  This is accomplished by chemical reactions in which the starting materials are in true solutions.

Carbon black is prepared by burning methane in limited air and collecting the soot or carbon atoms on cool surfaces.  Carbon black is used as filler for rubber tires and in dispersions such as printers ink and Indian ink

favorable weather conditions can lead to formation of clouds, fogs and mists

Properties of colloidal systems

A colloidal system is a two-phased mixture with particles that are not large enough to be seen by an ordinary microscope but big enough to diffuse light, giving a Tyndall Effect.

Colloidal systems manifest five properties that distinguish them from the true solutions and suspensions.  These properties are:

a.) Tyndall Effect – ability of colloidal particles to scatter a beam of light that passes through them.  (John Tyndall)

                        Applications:

blue color of the sky and sea

brilliant colors of  sunset

of different shades or even blue and violet colors are obtained with different sizes of dispersed gold particles

different colors of your eyes and those of other people are not due to pigments, but rather to the scattering of light by colloidal substance in the iris

            b.)  Adsorption - a surface property

the ability of a substance to physically hold another substance on its surface

                                                            Absorption vs. Adsorption (laboratory results)        

the greater the surface area, adsorption increases

colloids make good adsorbers

                        Applications:

Toxic hydrocarbons accumulate on the surface of asbestos particles.  For this reason, asbestos is more hazardous when inhaled than when ingested.  The same reason may apply to smoking marijuana.  The smoke particles carry along with it more toxic compounds.

Activated carbon is widely used to remove objectionable odors and colors in foods or chemical products and to eliminate contaminating gases such as oil vapor and sulfur dioxide from industrial gases like Hydrogen, acetylene, CO₂ and CO.  The sugar industry uses large quantities of activated carbon in refining.  Similarly the activated carbon is used in refining corn syrup and corn sugar. Low boiling petroleum components are recovered by fractional adsorption with gas adsorbing carbon.  The military utilizes activated carbon in gas masks.

Filtration plants also treat the domestic water supply with activated carbon to remove unpleasant odor, color and taste.

Piece of charcoal can put inside the refrigerator to remove unpleasant odors.

Cigarette filters contain activated charcoal to remove carcinogenic compounds from tobacco smoke.

c.) Electrical Charge Effect – the positive or negative charge acquired by colloidal particles due to the ions adsorbed on their surface.

What causes the colloidal particles to carry a charge?  Colloid particles, because of their high adsorptive capacity, adsorb on their surface ions from water or from solutions of electrolytes.  A given kind of colloid adsorb on its surface only one kind of ions, hence the particles become either all negative or all positive.

Electrophoresis - the movement of charged colloidal particles toward the electrodes.

Example: clay and water

Clay becomes negative in water because it adsorbs the hydroxyl ion (OH^–1).  Since all the particles in a colloid have the same charge, they repel each other.  This is the principal reason why colloidal particles do not aggregate or precipitate.

  

Applications:

Electrodeposition of rubber latex into anodes of various shapes e.g. tires, gloves, etc.

in industry, electrostatic precipitates are used to remove colloidal particle pollutants from smoke (Cottrell precipitator)

d.) Brownian Movement - rapid zigzag movement of colloidal particles.  (Robert Brown)

The zigzag movement of colloidal particles is caused by unequal number of collisions of colloidal particles on different sides of the molecules.  This property of colloidal system explains why colloidal particles do not settle.

Applications:

Formation of fogs, mist and smog.  Traveling becomes dangerous.  Too much colloid in the air also endangers a person’s health.  Colloidal particles in the air contributes to the air pollution problems

e.)  Rate of Settling - dependent on the size of particles, the gravitational force acting on the colloidal particles and the viscosity of the medium.

Applications: 

The above factors are useful in identifying viruses, proteins, plastics and other macromolecules.

Importance of Colloids to Daily Life

Colloid chemistry is important in the manufacture of paint, ceramics, plastics, textile, glue, adhesive, ink, cement, rubber, leather, photographic paper and film, salad dressing, spray, detergent, and many more. 

It is also involved in processes like bleaching, deodorizing, tanning, dyeing, and purification and flotation of minerals.

The protoplasm of living cells and tissue, most of the body fluids, glandular secretions, blood, and many foods are colloidal substances.  Thus, the essential vital processes – nutrition, digestion, and secretion – are concerned with colloidal systems.

Dialysis – is the process of separating ions from colloids by diffusion through a semi permeable membrane.

4th Quarter: Dilution

Dilutions Worksheet - Solutions

1)        If I add 25 mL of water to 125 mL of a 0.15 M NaOH solution, what will the molarity of the diluted solution be?

M₁V₁ = M₂V₂

(0.15 M)(125 mL) = x (150 mL)

x = 0.125 M

2)        If I add water to 100 mL of a 0.15 M NaOH solution until the final volume is 150 mL, what will the molarity of the diluted solution be?

M₁V₁ = M₂V₂

(0.15 M)(100 mL) = x (150 mL)

x = 0.100 M

3)        How much 0.05 M HCl solution can be made by diluting 250 mL of 10 M HCl?

M₁V₁ = M₂V₂

(10 M)(250 mL) = (0.05 M) x

x = 50,000 mL

4)        I have 345 mL of a 1.5 M NaCl solution.  If I boil the water until the volume of the solution is 250 mL, what will the molarity of the solution be?

M₁V₁ = M₂V₂

(1.5 M)(345 mL) = x (250 mL)

x = 2.07 M

5)        How much water would I need to add to 500 mL of a 2.4 M KCl solution to make a 1.0 M solution?

M₁V₁ = M₂V₂

(2.4 M)(500 mL) = (1.0 M) x

x = 1200 mL

            1200 mL will be the final volume of the solution.  However, since there’s already 500 mL of solution present, you only need to add 700 mL of water to get 1200 mL as your final volume.  The answer:  700 mL.