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Monday, August 15, 2011

CBSE CLASS 10 CHEMISTRY Metals and Non-Metals Solved Important questions

Metals and Non-Metals Solved Important questions
One mark questions with answers 
Q1. Which one of the following elements symbolized as A and B is a metal :
11A2316B32?
Ans1.  A is a metal as it contains one electron in its outer most shell.
Q2. Name the constituents of baking powder.
Ans2. Tartaric acid and sodium bicarbonate.
Q3. Name the main constituents of common brass.
Ans3. Zn and Cu are the main constituents of common brass.
Q4. What are washing soda and baking soda chemically?
Ans 4. Chemical formula of washing soda is Na2CO3.10H2O (sodium carbonate) and  baking soda is NaHCO3 (sodium bicarbonate).
Q5. Why are stainless steel cooking pans often given a copper outer bottom?
Ans5. Stainless steel cooking pans are often given a copper outer bottom because it is good conductor of heat.
Q6. Write the equation for the chemical reaction that takes place when steam is passed over red hot silicon.
Ans6. When steam is passed over red hot silicon, silicon dioxide is formed and hydrogen gas liberated.
Si (silicon) + 2H2O (steam) -------> SiO2 (silicon dioxide) + 2H2 (hydrogen)
Q7. Write the chemical equation to show the effect of heating on sodium carbonate crystals.
Ans7. When sodium carbonate crystals are heated water molecules are reduced.
Na2CO3.10H2O ------->Na2CO3 + 10H2O.
Q8. Name one metal element and one non-metal element which are obtained on a large scale generally from sea water.
Ans8. Sodium and Chlorine.
Q9. An iron knife kept dipped in a blue copper sulphate solution changes to light green. Why?
Ans9. Iron displaces copper from copper sulphate solution and forms ferrous sulphate solution which is light green.
Fe (iron) + CuSO4 (copper sulphate, green colour) --------> FeSO4 (ferrous sulphate, light green) + Cu (copper)
Q10. A given non-metal forms sulphuric acid on reacting with concentrated HNO3. Identify the non-metal.
Ans10. Sulphur is non-metal forms sulphuric acid on reacting with concentrated HNO3.
S + 6HNO3 (conc. nitric acid) ------> H2SO4 + 6NO2 + 2H2O

Two mark questions with answers
Q1. A trivalent metal X is manufactured by the process of electrolysis. It is the most abundant metal in the earth's crust. Identify the metal and state its two uses.
Ans1. The metal is Aluminium (Al).
Uses : 
(i) Aluminium is used for making cooking utensils because it is good conductor of heat. 
(ii) It is used for making silver paints.
Q2. A white powder having an odour of chlorine is used to remove yellowness of white clothes in laundries. Name this powder. How is it prepared? Write the chemical equation for the reaction involved in its preparation.
Ans2. White powder is bleaching powder (CaOCl2). It is prepared in the laboratory by passing the chlorine gas over dry slaked lime
Ca(OH)2 (Calcium hydroxide 'slaked lime') + Cl2 (Chlorine)  -------à CaOCl2 Calcium oxychloride 'bleaching powder') + H2O (Water)
Q3. Explain why zinc metal can displace copper from copper sulphate solution but copper cannot displace zinc from zinc sulphate solution.
Ans3. Zinc is more reactive element than copper so zinc displaces copper from copper sulphate solution.
Zn + CuSO4 (Copper sulphate) ------à  ZnSO4 + Cu
Copper is less reactive than zinc so it can't displace the zinc sulphate solution.
Q4. A non-metal belonging to group V in the periodic table has two major allotropic forms. Name its two forms. Identify the element. Write two distinctions between these two forms.
Ans4. Non-metal is phosphorus (P). The allotropes of phosphorus are white phosphorus (yellow phosphorus) and red phosphorus.
Distinctions :
(i) White phosphorus is soft and red phosphorus is brittle powder.
(ii) White phosphorus is poisonous while red phosphorus is non-poisonous.
Q5. What are the products formed? When silicon reacts with hydrochloric acid? Write the necessary equation.
Ans5. When silicon reacts with HCl it forms silicon tetrachloride and hydrogen gas is liberated.
Si + 4HCl (Hydrochloric acid) ---àSiCl4 (Silicon tetrachloride) + 2H2 (Hydrogen gas).
Q6. Describe the method of mining sulphur.
Ans6. The sulphur is mined from underground by Frasch Process. This process is based that sulphur has low melting point (159ºC). A hole is bored to the sulphur beds and three concentric pipes are pushed to sulphur beds, through the outer most pipe super heated water is forced down which melts sulphur beds. Through the inner most pipe, air at high pressure is forced which pushes the molten sulphur through the middle pipe which is collected in pots. 
Three mark questions with answers
Q1. You are given a sample of an ore containing sulphide of copper along with a high percentage of unwanted materials. With the help of a diagram describe the process by which you would remove the unwanted materials from the given ore.
Ans1. This ore is concentrated by Froth Flotation method, This method is used to concentrate the sulphide ores of copper and zinc. The crushed ore is put into a tank containing water and little pine oil. Compressed air is passed through the water. The froth that is produced because the pine oil rises to the surface and carries the ore particles with it. The gangue sinks to the bottom.


Q2. An element has two allotropic forms A and B and belongs to group V of the periodic table. A is much darker in colour than B. Ignition temperature of A is 260ºC and that of B is 30ºC. What may A and B be? Which one of them reacts with (i) chlorine on heating but not in the cold, (ii) hot concentrated solution of Na OH producing a gas? Write the chemical equations for the reactions involved.
Ans2. B is yellow phosphorus and A is red phosphorus.
(i) Red phosphorus reacts and form phosphorus penta chloride.
P4 (Red phosphorus) + 10Cl2 (Chlorine) --à 4PCl5 (Phosphorus penta chloride)
(ii) White phosphorus reacts with hot concentrated solution of NaOH producing phosphine gas and form sodium hypophosphite
P4 (White phosphorus) + 3NaOH (Sodium hydroxide) + 3H2O –--Heat--àPH3­ (Phosphine) + 3NaH2PO2 (Sodium hypophosphite).
Q3. What is chemical name and formula of limestone? What happens when limestone is strongly heated? Write the chemical equation involved. How can the presence of excess of CO2 be tested in a class room from the products formed.
Ans3. Lime stone is calcium carbonate (CaCO3) when limestone is strongly heated it decomposes and forms calcium oxide and carbondioxide.
The presence of excess of CO2 in the class room is tested by  passing the air through lime water (CaO). It will change to milky due to the formation of a white precipitate of calcium carbonate.
CaCO3 (Calcium carbonate or lime stone) CaO (Calcium oxide or lime water) + CO2 (Carbon dioxide)
Q4. What is meant by allotropy? Name the two allotropes of phosphorus. Mention any three differences in their properties
Ans4. Allotropy : "Existence of an element in two or more distinct forms which have different physical properties but same chemical properties is called allotropy and the forms are called allotropes."
Two allotropes of phosphorus are white phosphorus and red phosphorus.
Differences :
Red phosphorus
White phosphorus
(i) It is stored in open atmosphere.
(i) Its ignition temperature is very low 30ºC. So it is kept under water.
(ii) It is non-poisonous.
(ii) It is highly poisonous.
(iii) Red phosphorus does not react with sodium hydroxide.
(iii) White phosphorus reacts with sodium hydroxide.

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