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Saturday, December 5, 2015


Importance of the Periodic Table

Why Is the Periodic Table Important?


The modern periodic table has changed since Mendeleev's original table, yet both the first tables and the modern table are important for the same reason: The periodic table organizes elements according to similar properties so you can tell the characteristics of an element just by looking at its position on the table.
Before all the naturally occurring elements were discovered, the periodic table was used to predict the chemical and physical propertiesof elements in the gaps on the table.
Today, the table can be used to predict properties of elements yet to be discovered, although these new elements are all highly radioactive and break down into more familiar elements almost instantly.
The table is useful for modern students and scientists because it helps predict the types of chemical reactions that are likely for an element. Rather than memorize facts and figures for each element, a quick glance at the table reveals a lot about the reactivity of an element, whether it is likely to conduct electricity, whether it is hard or soft, and many other characteristics.

Thursday, May 7, 2015

How To Turn Water into Wine or Blood

This popular chemistry demonstration is often called turning water into wine or water into blood. It's really asimple example of a pH indicator. Phenolphthalein is added to water, which is then poured into a second glass containing a base. If the pH of the resulting solution is right, you can make the water turn from clear to red to clear again, as long as you like.
Here's How:
  1. Sprinkle sodium carbonate to coat the bottom of a drinking glass.
  2. Fill a second glass halfway full of water. Add ~10 drops phenolphthalein indicator solution to the water. The glasses can be prepared in advance.
  3. To change water into wine or blood, pour the water with indicator into the glass that contains the sodium carbonate. Stir the contents to mix the sodium carbonate, and the water will change from clear to red.
  4. If you like, you can use a straw to blow air into the red liquid to change it back to clear.
  5. The principle is the same as for thedisappearing ink formula. Phenolphthalein is an acid-base indicator.
  6. Tips:
    1. Phenolphthalein and sodium carbonate can be ordered freely from any scientific supplier. Most grade school and high school science labs have these chemicals, though you can order them yourself.
    2. Don't drink the water/wine/blood. It isn't particularly toxic, but it isn't good for you either. The liquid can be poured down the drain when the demonstration is complete.
    3. For a normal drinking glass, the ratio used to get the reversible color change reaction is 5 parts sodium carbonate per 10 drops of a phenolphthalein stock solution.

Bromine Facts


Bromine
Atomic Number: 35
Symbol: Br
Atomic Weight: 79.904
Electron Configuration:[Ar]4s23d104p5
Word Origin: Greek bromos: stench
Element Classification:Halogen
Discovery: Antoine J. Balard(1826, France)
Density (g/cc): 3.12
Melting Point (°K): 265.9
Boiling Point (°K): 331.9
Appearance: reddish-brown liquid, metallic luster in solid form
Isotopes: There are 29 known isotopes of bromine ranging from Br-69 to Br-97.
Magnetic Ordering: nonmagnetic
Electrical Resistivity (20 °C): 7.8×1010  Ω·m
Thermal Conductivity (300 K): 0.122  W·m−1·K−1
CAS Registry Number: 7726-95-6

Periodic Table of the Elements

Zinc
Atomic Number: 30
Symbol: Zn
Atomic Weight: 65.39
Discovery: known since prehistoric time
Electron Configuration: [Ar] 4s2 3d10
Word Origin: German zinke: of obscure origin, probably German for tine. Zinc metal crystals are sharp and pointed. It could also be attributed to the German word 'zin' meaning tin.
Isotopes: There are 30 known isotopes of zinc ranging from Zn-54 to Zn-83 .
Zinc has five stable isotopes: Zn-64 (48.63%), Zn-66 (27.90%), Zn-67 (4.10%), Zn-68 (18.75%) and Zn-70 (0.6%).
Properties: Zinc has a melting point of 419.58°C, boiling point of 907°C, specific gravity of 7.133 (25°C), with a valence of 2. Zinc is a lustous blue-white metal. It is brittle at low temperatures, but becomes malleable at 100-150°C. It is a fair electrical conductor. Zinc burns in air at high red heat, evolving white clouds of zinc oxide.
Uses: Zinc is used to form numerous alloys,including brass, bronze, nickel silver, soft solder, Geman silver, spring brass, and aluminum solder. Zinc is used to make die castings for use in the electrical, automotive, and hardware industries. The alloy Prestal, consisting of 78% zinc and 22% aluminum, is nearly as strong as steel yet exhibits superplasticity. Zinc is used to galvanize other metals to prevent corrosion. Zinc oxide is used in paints, rubbers, cosmetics, plastics, inks, soap, batteries, pharmaceuticals, and many other products.

Sources:
 The primary ores of zinc are sphalerite or blende (zinc sulfide), smithsonite (zinc carbonate), calamine (zinc silicate), and franklinite (zinc, iron, and manganese oxides). An old method of producing zinc was by reducing calamine with charcoal. More recently, it has been obtained by roasting the ores to form zinc oxide and then reducing the oxide with carbon or coal, followed by distillation of the metal.Other zinc compounds are also widely used, such as zinc sulfide (luminous dials andfluorescent lights) and ZrZn2 (ferromagnetic materials). Zinc is an essential element for humans and other animal nutrition. Zinc-deficient animals require 50% more food to gain the same weight as animals with sufficient zinc. Zinc metal is not considered toxic, but if fresh zinc oxide is inhaled it can cause a disorder referred to as zinc chills or oxide shakes.
Element Classification: Transition Metal
Density (g/cc): 7.133
Melting Point (K): 692.73
Boiling Point (K): 1180
Appearance: Bluish-silver, ductile metal
Atomic Radius (pm): 138
Atomic Volume (cc/mol): 9.2
Covalent Radius (pm): 125
Ionic Radius: 74 (+2e)
Specific Heat (@20°C J/g mol): 0.388
Fusion Heat (kJ/mol): 7.28
Evaporation Heat (kJ/mol): 114.8
Debye Temperature (K): 234.00
Pauling Negativity Number: 1.65
First Ionizing Energy (kJ/mol): 905.8
Oxidation States: +1 and +2. +2 is the most common.
Lattice Structure: Hexagonal
Lattice Constant (Å): 2.660
CAS Registry Number:7440-66-6
Zinc Trivia:
  • Zinc is the 24th most abundant element in the Earth's crust.
  • Zinc is the fourth most common metal used today (after iron, aluminum and copper).
  • Zinc exposed to air will form a layer of zinc carbonate by reacting with carbon dioxide. This layer protects the metal from further reactions with air or water.
  • Zinc burns white-green in a flame test.
  • Zinc is the last period four transition metal.
  • Zinc oxide (ZnO) was once called "philosopher's wool" by alchemists because it looked like wool when collected on a condenser after burning zinc metal.
  • Half of the zinc produced today is used to galvanize steel to prevent corrosion.
  • The U.S. penny is 97.6% zinc. The other 2.4% is copper.

Wednesday, March 18, 2015

Definition of carbon -carbon dabul bond

Definition: A carbon-carbon double bond is a double bond between two carbon atoms in a molecule.
.Examples: Ethylene (C2H4) is a hydrocarbon with a carbon-carbon double bond.

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