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Monday, January 6, 2014

Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Why decomposition reactions are called the opposite of combination reactions? Write equations for these reactions.
What are amphoteric oxides? Give two examples of amphoteric oxides.
Fe2O+ 2AL → AL2O3 + 2Fe
The above reaction is an example of a
(a) Combination reaction.
(b) Double displacement reaction.
(c) Decomposition reaction.
(d) Displacement reaction.
Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is 
(a) neutral?
(b) Strongly alkaline?
(c) Strongly acidic?
(d) Weakly acidic?
(e) Weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
How many structural isomers can you draw for pentane?
Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na (b) Mg (c) Al (d) Si
Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide (aq) + Barium iodide (aq)­ → Potassium iodide(aq)­ + 
Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide (s) + Carbon dioxide(g)
(c) Hydrogen(g)+ Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen ( (g)
How would you distinguish experimentally between an alcohol and a carboxylic acid?
Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) All of the above.
Give reasons
(a) Platinum, gold and silver are used to make jewellery. 
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminum is a highly reactive metal, yet it is used to make utensils for cooking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Why does an aqueous solution of an acid conduct electricity?
Why do ionic compounds have high melting points?
Write an equation to show the reaction between Plaster of Paris and water.
(a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
What change will you observe if you test soap with litmus paper (red and blue)?
Give two important uses of washing soda and baking soda.
In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
Compare and contrast the arrangement of elements in Mendeleev’s periodic Table and the Modern Periodic Table.
Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Name two metals which are found in nature in the free state.
What were the limitations of Dobereiner’s classification?
 What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Explain the mechanism of the cleaning action of soaps.
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.
(a) What will be the action of gas on 
(i) Dry litmus paper?
(ii) Moist litmus paper?
(b) Write a balanced chemical equation for the reaction taking place.
Translate the following statement into chemical equation and then balance them. 

Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2(g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidized.
(c) Carbon is getting oxidized.
(d) Lead oxide is getting reduced.

(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Translate the following statement into chemical equation and then balance them. 

Barium chloride reacts with aluminum sulphate to give aluminum chloride and a precipitate of barium sulphate.
In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?
Balance the following chemical equation.
NaCl + AgNO3 ------> AgCl + NaNO3
What are alloys?
Name the sodium compound which is used for softening hard water.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Which of the following hydrocarbons undergo addition reactions?
C2H6, C3H8, C3H6, C2H2 and CH4.
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Translate the following statement into chemical equation and then balance them. 

Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
What is a balanced chemical equation? Why should chemical equations be balanced?
You are given a hammer, a battery, a bulb, wires and a switch.
(a) How could you use them to distinguish between samples of metals and non-metals?
(b) Assess the usefulness of these tests in distinguishing between metals and non-metals.
How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Butanone is a four-carbon compound with the functional group
(a) Carboxylic acid.
(b) Aldehyde.
(c) Ketone.
(d) Alcohol.
Why are carbon and its compounds used as fuels for most applications?
Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, Si, Ba.
Plaster of Paris should be stored in a moisture-proof container. Explain why?
Would you be able to check if water is hard by using a detergent?
What chemical process is used for obtaining a metal from its oxide?
Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Give an example of a metal which
(i) Is a liquid at room temperature?
(ii) Can be easily cut with a knife.
(iii) Is the best conductor of heat?    
(iv) Is a poor conductor of heat?
Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
Which element has
(a) Two shells, both of which are completely filled with electrons?
(b) The electronic configuration 2, 8, 2?
(c) A total of three shells, with four electrons in its valence shell?
(d) A total of two shells, with three electrons in its valence shell?
(e) Twice as many electrons in its second shell as in its first shell?
Balance the following chemical equation.

NaOH + H2SO4 ------> Na2SO4 + H2O
An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)
N(7) F(9) P(15) Ar(18)
Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Which metals do not corrode easily?
Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b)  MgCl2 solution and aluminum metal
(c) FeSO4 solution and silver metal
(d) AgNOsolution and copper metal.
Why should curd and sour substances not be kept in brass and copper vessels?
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
What is a homologous series? Explain with an example.
Explain the formation of scum when hard water is treated with soap.
Explain the nature of the covalent bond using the bond formation inCH3Cl.
A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Why do you think the noble gases are placed in a separate group?
What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced. 
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Oil and fat containing food items are flushed with nitrogen. Why?
Translate the following statement into chemical equation and then balance them.
Hydrogen gas combines with nitrogen to form ammonia.

A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Food cans are coated with tin and not with zinc because 
(a) Zinc is costlier than tin.
(b) Zinc has a higher melting point than tin.
(c) Zinc is more reactive than tin.
(d) Zinc is less reactive than tin.
Write word equations and then balanced equations for the reaction taking Place when −
(a) Dilute sulphuric acid reacts with zinc granules.
(b) Dilute hydrochloric acid reacts with magnesium ribbon.
(c) Dilute sulphuric acid reacts with aluminum powder.
(d) Dilute hydrochloric acid reacts with iron filings.
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
What were the criteria used by Mendeleev in creating his Periodic Table?
Draw the electron dot structures for
(a) Ethanoic acid.
(b) H2S.
(c) Propanone.
(d) F2.
State two ways to prevent the rusting of iron.
Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
(a) The elements become less metallic in nature. 
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
A shiny brown-colored element ‘X’ on heating in air becomes black in color. Name the element ‘X’ and the black colored compound formed.
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
What will happen if a solution of sodium hydro carbonate is heated? Give the equation of the reaction involved.
Write equations for the reactions of 
(i) Iron with steam
(ii) Calcium with water
(iii) potassium with water
Ethane, with the molecular formula C2H6 has
(a) 6 covalent bonds.
(b) 7 covalent bonds.
(c) 8 covalent bonds.
(d) 9 covalent bonds.
What is a neutralization reaction? Give two examples.
Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water 
(b) Zinc + Silver nitrate → Zinc nitrate + Silver 
(c) Aluminum + Copper chloride → Aluminum chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate +Potassium chloride
What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint − the eight atoms of sulphur are joined together in the form of a ring.)
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Name the substance which on treatment with chlorine yields bleaching powder?
What effect does the concentration of H+ (aq) ions have on the nature of the solution?
Balance the following chemical equation.
HNO3 + Ca(OH)2 → Ca(NO3)2 + H2 O

In the Modern Periodic Table, which are the metals among the first ten elements?
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
What would be the electron dot structure of carbon dioxide which has the formula CO2?
Explain the meanings of malleable and ductile.
Give a test that can be used to differentiate chemically between butter and cooking oil.
(a) Three elements that have a single electron in their outermost shells.
(b) Two elements that have two electrons in their outermost shells.
(c) Three elements with filled outermost shells.
What type of oxides is formed when non-metals combine with oxygen?
Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Balance the following chemical equation.
BaCl+ H2SO4 --------> BaSO4 +HCl
What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
What does one mean by exothermic and endothermic reactions? Give examples.
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
Why respiration is considered an exothermic reaction? Explain.
(a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?
What are oxidizing agents?
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
(a) The food is not cooked completely.
(b) The fuel is not burning completely.
(c) The fuel is wet.
(d) The fuel is burning completely.
Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic 
(b) Analgesic
(c) Antacid
(d) Antiseptic
A solution turns red litmus blue; its pH is likely to be 
(a) 1 (b) 4 (c) 5 (d) 10
What will be the formula and electron dot structure of cyclopentane?
Why sodium is kept immersed in kerosene oil?
Why do we apply paint on iron articles?
10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralize it will be
(a) 4 mL (b) 8mL (c) 12 mL (d) 16 mL
By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?
A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Define the following terms.
(i) Mineral (ii) Ore (iii) Gangue
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
What do you mean by a precipitation reaction? Explain by giving examples.
Why does distilled water not conduct electricity, whereas rain water does?
Do basic solutions also have H+(aq) ions? If yes, then why are these basic?
Why do acids not show acidic behavior in the absence of water?

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