A green layer is gradually formed on a copper plate left exposed to air for a week in a bathroom. What could this green substance be ? (Delhi 2005)
Why is tungsten metal selected for making filaments of incandescent lamp bulbs? (Delhi 2005)
Write balanced chemical equation for the reaction taking place when steam is passed over red hot iron. (Delhi 2004C)
Which one of the metal in the following group are (a) most reactive (b) least reactive Au, Na, Cu, Ca ? (Delhi 2003)
Which chemical element is alloyed with copper to make bronze? (AI 2001)
An element X on reacting with oxygen forms an oxide X2O. This oxide dissolves in water and turns blue litmus red. State whether element X is metal or a non – metal.
Name the iron compound in haematite. Write its chemical formula.
Elements magnesium and oxygen respectively belong to Group 2 and Group 16 of the Modern periodic table. If the atomic numbers of magnesium and oxygen are 12 and 8 respectively, draw their electronic configurations and show the process of formation of their compound by transfer of electrons. (Foreign 2010)
A student has been collecting silver coins and copper coins. One day she observed a black coating on silver coins and green coating on copper coins. Give the chemical name of black and green coating. How are they formed? (CBSE Sample paper 2009)
Give reason of the following; (a) Gold and silver are used to make jewellery. (b) Carbonate and sulphide ores are usually converted into oxide prior to reduction during the process of extraction. (Delhi 2008C)
Choose a metal out of the following which reacts with hot water but not with cold water; Sodium, Magnesium, Iron Mention the products formed during the reaction. (Delhi 2006C)
Choose the metal (from the list given below( which can displace zinc from zinc sulphate solution- lead, copper, Magnesium, silver . Write the equation of the chemical reaction involved. (AI 2006C)
Write chemical equations for reactions taking place when (i) Cinnabar is heated in air. (ii) Calcium metal reacts with water (AI 2004)
Describe briefly the forth floatation process for the concentration of sulphide ores.
Why is sodium kept immersed in kerosene oil?
Why do ionic compounds have high melting points?
Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Give reasons; (i) Platinum, gold and silver are used to make jewellery. (ii) Sodium, potassium and lithium are stored under oil. (iii) Aluminium is a highly reactive metal, still it is used to make utensils for cooking. (iv) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Give the reason why copper is used to make hot water tanks but steel (an alloy) is not.
What is meant by rusting ? With labelled diagrams describe an activity to find out he conditions under which iron rusts. (Delhi 2009)
What is meant by refining of metals? Describe the electrolytic refining of copper with a neat labelled diagram. (Delhi 2009)
Give reasons for the following observation; (i) Ionic compounds in general have high melting and boiling points. (ii) Highly reactive metals cannot be obtained from their oxides by heating them with carbon. (iii) Copper vessels get a green coat when left exposed to air in rainy season. (Foreign 2009)
State reasons for the following observations; (i) The shining surface of some metals becomes dull when exposed to air for a long time. (ii) Zinc fails to evolve hydrogen gas on reacting with dilute nitric acid. (iii) Metal sulphides occur mainly in rocks but metal halides occur mostly in sea and lake waters. (Foreign 2009)
(a) Show on a diagram the transfer of electrons between the atoms in the formation of mgo. (b) Name the solvent in which ionic compounds are generally soluble. (c) Why are aqueous solutions of ionic compounds able to conduct electricity? (Delhi 2008)
A metal X loses two electrons and a non-metal Y, gains one electron. Show the electron dot structure of compound formed between them. Is it ionic or covalent? Does it have high melting point or low? Will it conduct electricity in solid state or in aqueous solution and why? Will it be soluble in water? (HOTS)