Very short answer type questions
Q1. Give the the formula for lime
Ans.CaO
Q2. Give the formula for iron(ii)oxide and iron (iii) oxide.
Ans.FeO is iron(ii) oxide
Fe2O3 is iron (iii) oxide
Q3. Give the formula for rust.
Ans: Fe2O3xH2O.
Q4. Name the conditions necessary for rusting .
Ans. Oxygen and moisture
Q5. Name the reaction seen during rancidity of food.
Ans.:Oxdation
Q6. Name the different forms of energy required for breaking down the reactants in decomposition reaction
Ans.Heat, light and electricity
Q7. What is the insoluble substance formed in a chemical reaction called?
Ans. precipitate
Q8. What the does(ii) in lead (ii) nitrate indicate?
Ans.It Indicates that valency (oxidation state ) of lead in this case is 2 and it from+2 ions.
Q9. What are noble metals?
Ans.metals which do not react at any temperature e.g.., gold.
Q10. Name two metals which do not corrode?
Ans.Gold and platinum
Q11. Name the product obtained when silver bromide is exposed to sunlight.
Ans. Silver and bromine
Q12. Name the gas which Burns with pop sound.
Ans. Hydrogen gas.
Q13. Name the compound used to test the elevation of carbon dioxide gas.
Ans. Calcium hydroxide solution (freshly prepared) also called lime water is used to test CO2 gas.
Q14. Name the the gas evolved when lead nitrate is heated.
Ans. Nitrogen dioxide and oxygen.
Q15. Write the formula for two oxides of sulphur.
Ans.SO2 and SO3
Q16. Give the the example of exothermic reaction.
Ans.Respiration and water added to lime
Q17. Give one example of decomposition reaction that occurs in nature.
Ans. Rotting of fruits and vegetables
Q18. Name the type of reaction in which two or more than two reactants form a single compound.
Ans combination reaction
Q19 what is breaking and making of bonds in chemicals called ?
Ans.chemical reaction
Q20. Name the chemical used in black and white photography.
Ans. Silver bromide
Q21. Name the ions present in barium sulphate.
Ans. Ba2+ and so
Q22. Name the reaction which forms insoluble salts.
Ans. Precipitation reaction
Q23. State the reaction in which hydrogen acts as a reducing agent.
Ans. CuO + H2 → Cu + H2O
Q24. Give one use of quick lime.
Ans. It is used in manufacture of cement.
Q25. Give one example of decomposition reaction in which solid and gas are two products
obtained
Ans. CaCO3 → CaO + CO2
CaO is a solid and carbon dioxide is a gas.
Q26. AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
FeS + H2SO4
→ FeSO4 + H 51
Consider the above mentioned two chemical equations with two different kinds of
arrows (T and b) along with product. What do these two different arrows indicate?
Ans. T shows the gas is evolved whereas shows insoluble substance (precipitate) is
formed.
III. SHORT ANSWER TYPE QUESTIONS (2 or 3 Marks)
Q1. What happens when carbon dioxide and water react in the same ratio?
Ans. When 6 molecules of carbon dioxide and 6 molecules of water react together glucose
is formed with the evolution of oxygen gas.
6CO2 + 6H2O → C6H12O6 + 602
Q2. How can you chemically remove the black coating of copper
oxide?
Ans. The black coating of copper oxide can be removed chemically by passing hydrogen
gas over heated copper oxide. The black coating turns brown as oxygen is removed
by hydrogen.
Q3. Products formed when A and B react together are zinc chloride and hydrogen gas.
Find reactants A and B.
Ans. The reactant A is zinc metal and the reactant B is hydrochloric acid.
Zn + 2HCl → ZnCl2 + H2
04. Name the products obtained and type of reaction given below:
Na2SO4 + BaCl2
Ans. The products obtained in the above reaction are as follows:
NaSO4 + BaCl2 - BaSO4 + 2NaCl
The reaction is double displacement.
Q5. When quick lime is added to water a hissing sound is produced. Write the chemical
reaction and name the type of reaction taking place.
Ans. CaO + H2O - Ca(OH)2 + A
It is exothermic and combination reaction.
Q6.Three test tubes are taken and labelled as A B & C in test tube A iron nail is dipped in water. In test tube B iron nail is Dipped in mixture of Water and oil And in a test tube C Iron nail is added with Dry calcium Chloride.Name the test tube In which the iron nail Will rust and why?
Ans.the iron nail is rust in a test tube A Because it provides the condition Required for rusting, both moisture as well as air is present in it.
Q7. Metal X becomes green when left in air, turns black when heated in a name the metal and the compounds formed in both the cases.
Ans.X is copper
Q8. Give two examples of a reaction which is both endothermic and decomposition in nature.
Ans.CaCO3 --> CaO+CO2 ZnCO3-->ZnO+CO2
Q9. Explain why most of the metal articles become dull when kept exposed to air?
Ans. Metal articles react with the gases present in the area and their surface gets coated with the layer of compound it forms making them look dull and the luster is lost for example aluminium metal reacts with oxygen to form Aluminium oxide and its surface becomes dull.
Q10. What is rancidity? What is the general name of chemicals which are added to fat and oil containing food so as to prevent the rancidity?
Ans. The oil and fat containing food when left exposed to air reacts with oxygen and gets oxidized and become rancid this process is called rancidity in this process their smell and taste changes the general name of the chemicals that are added to prevent this oxidation are called as antioxidants for example nitrogen gas is an antioxidant.
Q11. Define displacement reaction give one example of it how is it different from double displacement reaction?
Ans. The reaction in which more reactive metal displaces (takes place of) the less reactive metal from its compound is called as displacement reaction. It is different from double displacement reaction because in double displacement reaction to different elements or items or ions or exchanged for each other.
Q12. Give difference between the exothermic and endothermic reactions.
Ans.Exothermic reaction-in this reaction heat is given out during the reaction. Endothermic reaction-Hindi song reaction heat is taken in to break the bonds and to form New compounds.
Q13. Explain and name the type of reaction scene when iron reacts with hydrochloric acid.
Ans. Iron reacts with HCl to form hydrogen gas and iron chloride. this reaction is called as displacement reaction
NCERT IN -TEXT QUESTIONS SOLVED
Q1. Why should a magnesium ribbon be cleaned before burning in air?
ANSWER:
Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with the atmospheric oxygen and forms Magnesium Oxide (MgO) layer which is a very stable compound. In order to prevent further reactions with Oxygen, it is therefore necessary to clean the ribbon by to remove the layer of MgO.
Q 2. Write a balanced equation for the following chemical reactions.
i) Hydrogen + Chloride —-> Hydrogen chloride
ii) Barium chloride + Aluminium sulphate —-> Barium sulphate + Aluminium chloride
iii) Sodium + Water —-> Sodium hydroxide + Hydrogen
ANSWER:
i) H2 + Cl2 → 2HCl
ii) 3BaCl2 + Al2(SO4)3 →3BaSO4 + 2AlCl3
iii) 2Na + 2H2O → 2NaOH + H2
Q 3. Write a balanced chemical equation with state symbols for the following reactions
i) Solutions of Barium chloride and Sodium sulphate in water react to give insoluble Barium sulphate and solution of Sodium chloride.
ii) Sodium hydroxide solution in water reacts with hydrochloric acid solution to produce Sodium chloride solution and water.
ANSWER:
i) BaCl2 + Na2SO4 → BaSO4 + 2NaCl
ii) NaOH + HCl → NaCl + H2O
Q 4. A solution of a substance ‘X’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
ANSWER:
i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide and its formula is CaO.
ii) CaO + H2O → Ca(OH)2
Q 5. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas
ANSWER:
In activity 1.7, gas collected in one of the test tubes is double of the amount collected in the other because water gets hydrolysed to release H2 and O2 gas. Here, after electrolysis two molecules of Hydrogen and one molecule of oxygen gas is released, hence the amount of Hydrogen collected would be double than that of oxygen.
Q 6. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
ANSWER:
When an iron nail dipped in the copper sulphate solution, iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes. The reaction is:
Fe + CuSO4 → FeSO4 + Cu
Q 7. Give an example of a double displacement reaction other than the one given in Activity 1.10.
ANSWER:
Reaction Between silver nitrate (AgNO3) and Sodium chloride (NaCl) is an example of double displacement reaction. During the reaction negative and positive ions trade positions as a result in the formation of white silver chloride precipitate. The chemical reaction is given below.
Ag+ + NO3– + Na+ + Cl– → AgCl + Na+ + NO3–
Q 8. Identify the substances that are oxidized and that are reduced in the following equation.
i) 4Na(s) + O2(g) → 2Na2O(s)
ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
ANSWER:
The Sodium (Na) in the first equation is getting oxidized with the addition of Oxygen (O2) and the Copper (Cu) in the second equation is reduced due to the addition of Hydrogen (H2)
NCERT TEXTUAL QUESTIONS SOLVED
1. 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 oxidised
(c) Carbon is getting oxidised
(d) Lead oxide is getting reduced
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
ANSWER:
(i) (a) and (b)
Explanation: (a) because Oxygen is being removed and (b) because the removed oxygen from Lead is added to the elemental Carbon.
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
Combination reaction.
Double displacement reaction.
Decomposition reaction.
Displacement reaction.
Solution:
Answer is 4. Displacement reaction.
Explanation: The Oxygen from the Ferrous oxide is getting displaced to the Aluminium metal to form Aluminium Oxide. In this reaction Aluminum is more reactive metal than Fe. Therefore Al will displace Fe from its oxide. This type of chemical reactions in which one of the elements displace another is called displacement reaction. Here less reactive metal is displaced by more reactive metal. Since one-time displacement is occurring, therefore, it is called a single displacement reaction.
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
Hydrogen gas and Iron chloride are produced.
Chlorine gas and Iron hydroxide are produced.
No reaction takes place.
Iron salt and water are produced.
ANSWER: Hydrogen gas and Iron chloride are produced.
Explanation: The Chlorine from Hydrogen chloride is displaced by the Iron fillings to undergo the following reaction.
2HCl + Fe → FeCl2 + H2
4. What is a balanced chemical equation? Why should a chemical equation be balanced?
ANSWER:
A balanced equation is the one in which number of different atoms on both the reactant and product sides are equal. Balancing chemical equation is necessary for the reaction should obey The Law of Conservation of energy. Balancing the chemical equation has no defined method and is purely a trial and error attempt.
5. Translate the following statements into chemical equations and balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give Aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and Hydrogen gas.
ANSWER:
(a) Unbalanced: H2 + N2 → NH3
Balanced: 3H2 + N2 → 2NH3
(b) Unbalanced: H2S + O2 → H2O + SO2
Balanced: 2H2S + 3O2 → 2H2O + 2SO2
(c) Unbalanced:
BaCl2 + Al2(SO4)3 → AlCl3 + BaSO4
Balanced: 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
(d) Unbalanced: K + H2O → KOH + H2
Balanced: 2K + 2H2O → 2KOH + H2
6. Balance the following chemical equations.
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
ANSWER:
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl
7. Write the balanced chemical equation for the following reactions.
Calcium hydroxide + Carbon dioxide —-> Calcium carbonate + Water
Zinc + Silver nitrate —-> Zinc nitrate + Silver
Aluminium + Copper chloride —-> Aluminium chloride + Copper
Barium chloride + Potassium sulphate —-> Barium sulphate + Potassium chloride
ANSWER:
2Ca(OH)2 + 2CO2 → 2CaCO3 + 2H2O
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
2Al + 3CuCl2 → 2AlCl3 + 3Cu
BaCl2 + K2SO4 → BaSO4 + 2KCl
8. Write a balanced chemical equation for the following and identify the type of reaction of each case
KBr + BaI2 → KI + BaBr2
ZnCO3 → ZnO + CO2
H2 + Cl → HCl
Mg + HCl → MgCl2 + H2
ANSWER:
2KBr + BaI2 → 2KI + BaBr2 (Double Displacement Reaction)
ZnCO3 → ZnO + CO2 (Decomposition Reaction)
H2 + Cl → 2HCl (Combination Reaction)
Mg + 2HCl → MgCl2 + H2 (Displacement Reaction)
9. What is meant by exothermic and endothermic reactions? Give examples.
ANSWER:
An endothermic reaction occurs when energy is absorbed from the surroundings in the form of heat.(Example: Photosynthesis, melting of ice, evaporation). Conversely, an exothermic reaction is one in which energy is released from the system into the surroundings. (Example: Explosions, concrete setting, nuclear fission and fusion).
10. Why is respiration considered to be an exothermic reaction?
ANSWER:
For the survival of life, we require energy. We obtain this energy from the food we eat. The food molecules, through the process of digestion, is broken down into a simpler molecule like glucose. These substances come in contact with the Oxygen present in our body cells to form Carbon dioxide and water along with a certain amount of energy (Respiration process). Since the energy is in the form of heat (that maintains our body temperature) the respiration is considered to be an exothermic reaction. The reaction taking place is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
11. Why are decomposition reactions called the opposite of Combination reactions? Write equations for decomposition reactions.
ANSWER:
Combination reaction is said to be the reaction between two or more molecules to form a larger molecule; whereas the decomposition reaction is defined as the splitting of larger molecules into two or more smaller molecules. This essentially explains that the decomposition reaction is the opposite of the combination reaction.
In most of the cases the decomposition reaction is endothermic since heat from the surrounding or induced heat is used to break the bonds of the larger molecule. Few examples of decomposition reactions are:
ZnCO3 → ZnO + CO2
CaCO3 + Energy → CaO + CO2
2HgO → 2Hg + O2
12. Write one equation each for decomposition reactions in which energy is supplied in the form of heat, light or electricity.
ANSWER:
(a) Thermal decomposition reaction (Thermolysis)
Decomposition of potassium chlorate: When heated strongly, potassium chlorate decomposes into potassium chloride and oxygen. This reaction is used for the preparation of oxygen.
2KClO3 + Heat → 2KCl + 3O2
(b) Electrolytic decomposition reaction (Electrolysis)
Decomposition of sodium chloride: On passing electricity through molten sodium chloride, it decomposes into sodium and chlorine.
(c) Photodecomposition reaction (Photolysis)
Decomposition of hydrogen peroxide: In the presence of light, hydrogen peroxide decomposes into water and oxygen.
13. What is the difference between displacement and double displacement reactions? Write relevant equations for the above.
ANSWER:
A displacement reaction is the one when a more reactive substance displaces a less reactive one from its salt solution whereas a double displacement reaction is the one where a mutual exchange of ions happens between two compounds.
In a displacement reaction, only a single displacement takes place whereas in the double displacement reaction, as the name suggests two displacement takes place between the molecules.
Example:
Displacement reaction
Mg + 2HCl → MgCl2 + H2
Double displacement reaction
2KBr + BaI2 → 2KI + BaBr2
14. In the refining of Silver, the recovery of silver from Silver nitrate solution involves displacement reaction by Copper metal. Write down the reaction involved.
ANSWER:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
15. What do you mean by a precipitation reaction? Explain by giving examples.
ANSWER:
When two solutions containing soluble salts are combined, a double displacement reaction takes place in which the ions are exchanged between the compounds. When one of such compounds formed is in solid form (that is insoluble in aqua) then it settles down at the bottom of the container. This solid is known as the precipitate and the respective reaction is termed as the precipitation reaction. Few examples of precipitation reactions are:
CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)
2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)
16. Explain the following in terms of gain of oxygen with two examples each.
(a) Oxidation
(b) Reduction
ANSWER:
(a) In a chemical reaction, when the oxygen is added to the element to form its respective oxide it is the element being oxidised. Example:
4Na(s) + O2(g) → 2Na2O(s)
H2S + O2 → H2O + SO2
(b) In a chemical reaction, when the oxygen is being removed from the compound then it is said to be reduced. Example:
CuO(s) + H2(g) → Cu(s) + H2O(l)
2HgO → 2Hg + O2
17. A shiny brown coloured element ‘X’ on heating in the air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
ANSWER:
The shiny brown coloured element is the Copper metal (Cu). When the metal is heated in air, it reacts with atmospheric oxygen to form copper oxide. Hence, the black coloured compound is the copper oxide.
2Cu(s) + O2(g) → 2CuO(s)
18) Why do we apply paint on iron articles?
ANSWER:
Iron articles are painted to prevent them from rusting. When left unpainted, the metal surface comes in contact with the atmospheric oxygen and in the presence of moisture it from Iron(III) oxide. But if painted the surface does not come in contact with moisture and air thus preventing Rusting.
19) Oil and Fat containing food items are flushed with Nitrogen. Why?
ANSWER:
The main purpose of flushing Nitrogen into food packets that contain oil and fat items is to prevent Rancidity which occurs when the oil or fat reacts with the oxygen letting out an unpleasant smell and taste. Therefore, by flushing Nitrogen, an unreactive surrounding is created thus preventing rancidity.
20) Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
ANSWER:
(a) Corrosion: It is a process in which metals reacts with substances like moister and gases present in the atmosphere to form surface compounds. Rusting of iron is a good example of corrosion where the iron is converted to Iron oxide. Millions of dollars are spent annually in preventing rusting from bridges and other monuments.
(b) Rancidity: It is the process in which food material gets spoiled when it comes in contact with oxygen ,giving bad smell and taste to the food items . Example: food items, containing fats and oils, give bad smell when they are exposed to air for a long time
Post a Comment