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Thursday 28 August 2014

10 Metal Alloy Facts

Gold is an alloy. - Schtone, Creative Commons LicenseYou use metal alloyseveryday. You encounter alloys in jewelry, cookware, tools, and most other items made of metal. Examples of alloys include white gold, Sterling silver, brass, bronze, and steel. Here are 10 interesting facts about metal alloys.
  1. An alloy is a blend of two or more metals. The blend can form a solid solution or it can be a simple mixture, depending on the size of the crystals that form and how homogeneous the alloy is.
  2. Although sterling silver is an alloy consisting mainly of silver, many alloys with the word "silver" in their name are only silver in color! German silver andTibetan silver are examples of alloys that don't actually contain any elemental silver.
  3. Many people believe steel is an alloy of iron and nickel, but actually steel is an alloy consisting primarily of iron, always with some carbon, with any of several metals.
  4. Stainless steel is an alloy of iron, low levels of carbon, and chromium. The chromium gives the steel resistance to "stain" or iron rust. A thin layer of chromium oxide forms on the surface of stainless steel, protecting it from oxygen, which is what causes rust. However, stainless steel can be stained if you expose it to a corrosive environment, such as seawater. The corrosive environment attacks and removes the protective chromium oxide coating more quickly than it can repair itself, exposing the iron to attack.
  5. Solder is an alloy that is used to bond metals to each other. Most solder is an alloy of lead and tin. Special solders exist for other applications. For example, silver solder is used in the manufacture of sterling silver jewelry. Fine silver or pure silver is not an alloy and will melt and join to itself.
  6. Brass is an alloy consisting primarily of copper and zinc. Bronze, on the other hand, is an alloy of copper with another metal, usually tin. Originally, brass and bronze were considered to be distinct alloys, but in modern usage, brass is any copper alloy. You may hear brass cited as a type of bronze or vice versa.
  7. Pewter is a tin alloy consisting of 85-99% tin with copper, antimony, bismuth, lead, and/or silver. Although lead is used much less commonly in modern pewter, even "lead-free" pewter typically contains a small amount of lead. This is because "lead-free" is defined as containing no more than .05% (500 ppm) lead. This amount remains appreciable if the pewter is used for cookware, dishes, or children's jewelry.
  8. Electrum is a naturally occurring alloy of gold and silver with small amounts of copper and other metals. The ancient Greeks considered it to be "white gold." It was used as far back as 3000 B.C. for coins, drinking vessels, and ornaments.
  9. Gold can exist in nature as a pure metal, but most of the gold you encounter is an alloy. The amount of gold in the alloy is expressed in terms of karats. 24 karat gold is pure gold. 14 karat gold is 14/24 parts gold, while 10 karat gold is 10/24 parts gold, or less than half gold. Any of several metals can be used for the remaining portion of the alloy.
  10. An amalgam is an alloy made by combining mercury with another metal. Almost all metals form amalgams, with the exception of iron. Amalgam is used in dentistry and in gold and silver mining because these metals readily combine with mercury.

Wednesday 28 May 2014

Understanding the Litmus Paper Test for Acids and Bases


The litmus test is a test used to identify and distinguish acidic and basic substances. It is one of the first tests taught to a chemistry student, and is the easiest to perform.

Here's some helpful tips on how to test acids and bases using the litmus paper test.



Litmus paper test for acids and bases


Understanding the Litmus Test

The litmus test is virtually always performed with a litmus paper (a litmus solution can also be used, as has been explained further on in this article, but a paper is much more practical). The dyes in a litmus paper react with acids and bases to produce specific colors; viz., red for acids and blue for bases. An ideal neutral litmus paper is violet.

► If a substance changes the color of a blue litmus paper to red, the substance is acidic. If a substance doesn't change the color of a red litmus paper, it may be acidic or neutral (salt), since neutral compounds have no effect on the litmus paper.

► Similarly, if a red litmus paper changes to blue, the substance is basic. Like with acids, a blue litmus paper remaining blue can mean that the substance is either basic or neutral.

acid
► Litmus paper reacts to the temporary presence of acidity- or alkalinity-determining ions in an aqueous solution of a compound. This means that the color change is temporary, and is reversed as soon as sufficient amounts of the opposite is presented. However, some substances cause color changes that are beyond the usual blue or red, and irreversible. Chlorine, for example, turns litmus paper very pale, by bleaching it.

► The test doesn't work with dry compounds. Common acids and bases are usually stored in the form of a solution, which facilitates the outcome of the test. If a litmus paper is wet, it can also test gases. For example, ammonia gas, whose aqueous solution is the basic ammonium hydroxide, turns a wet red litmus paper blue. Similarly, fumes from concentrated hydrochloric acid, consisting of the hydrogen chloride gas, turn a wet blue litmus paper red. If water isn't present in either litmus paper or the compound, the paper would remain unchanged regardless of the pH of the compound.

Litmus paper is formed by coating filter paper with litmus, a mixture of dyes obtained from various lichens, primarily of theRoccella genus. Commonly used lichens are R. montagneiDendrographa leucophoeaR. tinctoriaR. fuciformisLecanora tartareaOchrolechia parella, etc. These dyes are water-soluble, and can also be used to test a compound as a solution (without the intermediate step of having a filter paper absorb it), except that it won't be reusable in such a scenario. The color changes are the same as with paper; a blue litmus solution would turn red in the presence of acids, and vice versa.

         Litmus paper doesn't show the pH of a compound. It may even not change color if the pH of the compound in question is between 4.5 and 8.3. It only indicates whether the compound is acidic or basic, in a very rudimentary fashion. Various more sensitive indicators, commonly seen in the form of a pH paper, are used to obtain the pH value of an acid or a base.

base

Thursday 24 April 2014

Chemistry Questions Answers


  • 1. Who is regarded as father of modern chemistry ?

    1. Ruterford
    2. Einstein
    3. Lavoisier
    4. C.V. Raman

    Answer: Option C
  • 2. Which is not a type of elements ?

    1. Metals
    2. Non Metals
    3. Metalloids
    4. Gases
     
    Answer: Option D

  • 3. Which acid is present in lemon ?

    1. marlic acid
    2. citric acid
    3. lactic acid
    4. tartaric acid
     Answer And Explanation
    Answer: Option B
    Explanation:
    citric acid is present in lemon.
  • 4. Identify the wrong statement in the following

    1. Atomic radius of the elements increases as one moves down the first group of the periodic table
    2. Atomic radius of the elements decreases as one moves across from left to right in the 2nd period of the
    3. Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius
    4. Amongst isoelectronic species, greater the negative charge on the anion, larger is the ionic radius
     
    Answer: Option C
    Explanation:
  • 5. Rare gases are

    1. mono atomic
    2. di atomic
    3. tri atomic
    4. None of above

    Answer: Option B
    Explanation:
    Rare gases are di atomic.
  • 6. The term PVC used in the plastic industry stands for

    1. polyvinyl chloride
    2. polyvinyl carbobate
    3. phosphor vanadiu chloride
    4. phosphavinyl chloride
     Answer And Explanation
    Answer: Option A
  • 7. What among following is used to produce artificial rain ?

    1. copper oxide
    2. carbon monoxide
    3. silver iodide
    4. silver nitrate
     Answer And Explanation
    Answer: Option C
    • 8. Oil of vitriol is 


      1. nitric acid
      2. sulphuric acid
      3. hydrochloric acid
      4. phosphoric acid
       Answer And Explanation
      Answer: Option B
    • 9. Which is used in preparation of dynamite ?

      1. glycerol
      2. ethyl alcohol
      3. methyl alcohol
      4. glycol

      Answer: Option A

    • 10. What is Calcium sulphate ?

      1. epsom salt
      2. blue vitriol
      3. gypsum salt
      4. potash alum
       Answer
      Answer: Option C
      Explanation:
    • 11. Bleaching action of chlorine is by

      1. decomposition
      2. hydrolysis
      3. reduction
      4. oxidation
       Answer And Explanation
      Answer: Option A
    • 12. Which metal is heaviest ?

      1. osmium
      2. mercury
      3. iron
      4. nickle
       Answer: Option B