Q 1 – Identify the type of chemical reaction:
(i) Decomposition Reaction
(ii) Double Displacement Reaction
Q 2 – Which one is a chemical change- Rusting of iron or Melting of iron?
Rusting of Iron.
Q 3 – In refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved:
The reaction involved is:
Q 4 – Why does not silver evolve hydrogen on reacting with dil. H2SO4 ?
Silver do not evolve hydrogen on reacting with dil. H2SO4 as silver is less reactive metal than Hydrogen.
Q 5 – A student burnt a metal A found in the form of ribbon. The ribbon burnt with a dazzling flame & a white powder B is formed which is basic in nature. Identify A & B. Write the Balanced chemical equation.
Q 6 – Way do diamond and graphite, the two allotropic forms of carbon evolve different amounts of heat on combustion?
Diamond and graphite are the two allotropes of carbon but they do not evolve same amount of heat on combustion because they differ in the arrangement of carbon atoms and also their shapes are different.
Q 7 – Name and state the law which is kept in mind while we balance a chemical equation.
Law of conservation of mass as Mass can neither be created nor be destroyed during a chemical reaction.
Q 8 – What is the role of an oxidizing agent is a reaction?
The oxidizing agent supply the oxygen in a reaction or it removes the hydrogen.
Q 9 – Why a combustion reaction is an oxidation reaction?
Combustion reaction is an oxidation reaction because it is always carried out in the presence of air or oxygen for Ex .
Q 10 – What happens chemically when quick lime is added to water?
When quick lime is added to water, calcium hydroxide (slaked lime) is formed with a hissing sound and lot of heat is evolved during the reaction. The reaction involved is
CaO (s) (Quick Lime) + H2O = Ca(OH)2 (s) (Slaked Lime) + Heat
Q 11 – Why should a magnesium ribbon be cleaned before burning in air?
Magnesium ribbon is cleaned before burning to remove the protective layer of basic magnesium carbonate from the surface of magnesium ribbon.
Q 12 – Why are food particle preferably packed in aluminum foil?
Aluminium foil do not corrode in atmosphere even if kept for a long time because a protective coating of aluminium oxide (Al2O3) is formed on the surface of the foil and stops any further reaction of the metal with air and water thus food particles do not get spoiled.
Q 13 – State one basic difference between a physical change and a chemical change.
In a physical change, no new substance is formed. In a chemical change, a new substance is formed.
Q 14 – Write the balanced chemical equation with state symbols for the following reactions?
Balance chemical reaction with state symbols are as follows-
- BaCl2(aq) + Na2SO4 (aq) = BaSO4 (s) + 2NaCl (aq)
- NaOH (aq) + HCl (aq) = NaCl (aq) + H2O
Q 15 – What happens to lime water when CO2 gas is bubbled through it in excess?
When CO2 gas is bubbled through lime water in excess then initially it becomes milky but then its milkiness disappears due to the formation of a soluble salt Calcium Hydrogen Carbonate Ca(HCO3)2(aq)
Q 16 – Why is a Combustion reaction an oxidation reaction?
Combustion is an oxidation reaction as it is always carried out in the presence of oxygen. For eg.
Q 17 – What happens when quicklime is added to water?
Quicklime reacts with water vigorously to produce slaked lime and a large amount of heat.
Q 18 – Why cannot a chemical change be normally reversed?
Chemical change cannot be reversed back because products so formed in a chemical reaction are totally different from the reactants.
Q 19 – A substance X used for coating iron articles is added to a blue solution of a reddish brown metal Y,the color of the solution gets discharged Identify X and Y & also the type of reaction.
X= Fe, Y = Cu, Displacement reaction.
Q 20 – Identify the substance oxidized and reduced in the reaction.
Q 20 – Identify the substance oxidized and reduced in the reaction.
The substance oxidized is Zinc oxide and the copper oxide gets reduced to copper.
Q 21 – A student took 2-3 g of a substance X in a glass beaker & poured water over it slowly. He observed bubbles along with hissing noise. The beaker becomes quite hot. Identify X. What type of reaction is it?
X = Calcium oxide (Quick lime), Combination reaction.
Q 22 – A solution of a substance ‘X’ is used for white washing
i. Name the substance ‘X’ and writes its formula.
ii. Write the reaction of the substance ‘X’ named in (i) above with water
(i) The substance whose solution is water is used for white washing is calcium oxide. Its formula is CaO.
(ii) CaO (s) + H2O Ca(OH)2 (s)
Q 23 – What happens when ZnCO3 is heated in the absence of air? Give the relevant equation.
ZnO(s) and CO2(g) are formed. Chemical Equation:
Q 24 – Which of the following statement 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) Lead oxide is getting oxidized
(d) Lead is getting reduced
i. (a) and (b)
ii. (a) and (c)
iii. (a), (b) and (c)
iv. All
As statement (a) and (b) are correct, answer (i) is correct.
Q 25 – Is burning of a candle, a physical change or a chemical change ?
Both, chemical change and physical change.
Q 26 – Write the chemical equation for reactions in which lead nitrate and potassium iodide solutions are mixed.
Q 27 – What happens when magnesium ribbon burns in air?
When magnesium ribbon burns in air, it combines with the oxygen to form magnesium oxide.
Q 28 – “We need to balance a skeletal chemical equation.” Give reason to justify the statement.
Skeletal chemical equation are unbalanced. We need to balance chemical equation because of law of conservation of mass. It states that ‘matter can neither be created nor be destroyed’. Therefore chemical equation must be balanced in each and every chemical reaction.
Q 29 – Write a balanced chemical equation :
Ans – Balanced equation is
Q 30 – Which one is the chemical change – Fermentation of fruit juice or diluting fruit juice?
Fermentation of fruit juice.
Q 31 – On what chemical law, balancing of chemical equation is based?
Balancing of a chemical equation is based on the law of conservation of mass.
Q 32 – Give an example to list information which makes a chemical equation more useful (informative).
The Chemical equatons can be made more informative
(i) Physical state of reactants must be mentioned, e.g.
(ii) Condition in which reaction takes place are written on the arrow head, e.g.
Consider the following chemical reaction
(a) Identify ‘X’ and ‘Y’
(b) The type of reaction
(a) ‘X’ is Na2SO4 and Y is BaSO4 .
(b) The type of reaction
The reaction is a precipitation reaction. It is known as a double displacement reaction.
Q 33 – List four observations that help us to determine whether a chemical reaction has taken place.
(i) Evolution of gas
(ii) Change in temperature
(iii) Change in state
(iv) Change in color
Q 34 – Name the gas evolved when zinc reacts with dil. HCl.
The gas evolved is Hydrogen .
Q 35 – What is observed when carbon dioxide gas is passed through lime water.
(i) For a short duration
(ii) For long duration?
Also, write the chemical equations for the reaction involved.
(i) For short duration : Limewater turns milky due to the formation of CaCO3, Which is insoluble in water.
(ii) For Long duration :
A clear solution is obtained due to the formation of calcium bicarbonate. Ca(HCO3)2 which is soluble in water.
Q 36 – Name the raw materials that are required for the manufacture of washing soda by Solvay process. Describe the chemical reactions involved in the process.
The raw materials needed for the manufacture of washing soda are NaCl (sodium chloride), water, ammonia gas, and limestone to give CO2 gas. Chemical reactions involved:
Q 37 – Write the balanced chemical equation for the following reaction and write the name of the reaction
Barium Chloride + Aluminium Sulphate → Barium Sulphate + Aluminium Chloride
Q 38 – Why do we store silver chloride in dark-colored bottles? Explain in brief.
Silver chloride on exposure to sunlight may decompose as per the following reaction.
Therefore it is stored in dark colored bottles.
Q 39 – Name and state the law which is kept in mind while we balance a chemical equation.
Law of conservation of mass. Mass can neither be created nor be destroyed during a chemical reaction.
Q 40 – Define a combination reaction. Give one example of a combination reaction which is also exothermic.
A combination reaction is said to have occurred when two or more than two substances combine to form a single substance.
Q 41 – i) State the law which is followed in balancing a chemical equation.
(ii) Balance the following chemical equation :
(i) Mass can neither be created nor destroyed in a chemical reaction-Law of conservation of mass.
Q 42 – What happens when an iron nail is put inside the copper sulfate solution? Write a reaction with observation.
Iron nail turns brown, blue color of CuSO4 changes to colorless.
Q 43 – Balance the following chemical equations.
Q 44 – Name the raw materials that are required for the manufacture of washing soda by Solvay process. Describe the chemical reactions involved in the process.
The raw materials needed for the manufacture of washing soda are NaCl (sodium chloride), water, ammonia gas, and limestone to give CO2 gas. Chemical reactions involved:
Q 45 – A white solid when dropped in water produces a hissing sound. What the solid may be? Give the chemical reaction for the above. Name the product formed.
White solid is quicklime CaO
Chemical reaction involved with the name of products is
Q 46 – When Hydrogen gas is passed over heated copper (II) oxide, copper and steam are formed. Write the balanced chemical equation with physical states for this reaction. State what kind of chemical reaction is this?
This is a Redox reaction.
Q 47 – Why is photosynthesis considered an endothermic reaction?
The photosynthesis is considered an endothermic reaction because heat is absorbed in this process.
Q 48 – A solution of a substance ‘X’ is used for testing carbon dioxide. Write the equation of the reaction of X with carbon dioxide. (b) How is X obtained? Write chemical equation.
(a) Substance X is lime water which is aqueous solution of Calcium Hydroxide.
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O(l)
When limewater reacts with Carbon di oxide, it turns milky, that is Calcium Hydroxide.
(b) Calcium oxide reacts vigorously with water to produced slaked time (calcium hydroxide) releasing a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2 (aq) + Heat
(quick lime) (slaked lime)
Q 49 – What is percipitate?
Percipitate is insoluble metal compound formed after reaction.
Q 50 – Write the steps for balancing the chemical equation for the formation of ammonia by the combination of nitrogen and hydrogen.
First, we write the skeletal chemical equation for the process.
N2+H2→NH3
Examine the number of atoms of different elements present in the unbalanced equation.
In the above reaction both the sides Nitrogen and Oxygen both are unbalanced.
To balance hydrogen, H2 is multiplied by 3 LHS. It makes 6H-atoms on the left hand side.
Now, to balance hydrogen, in RHS, 2 is multiplied to NH3.
Nitrogen is balanced automatically.
N2 (g) + 3H2 (g) → 2NH3 (g)
Q 51 – State reason for the following:
(i) Potato chips manufactures fill the packet of chips with nitrogen gas.
(ii) Iron articles are shining when new, but get coated with a reddish brown powder, when left for some time.
(i) Potato chips manufactures fill the packet of chips with nitrogen gas to prevent rancidity.
(ii) Rusting and corrosion.
Q 52 – Using a suitable chemical equation, justify that some chemical reactions are determined by:
(i) change in colour,
(ii) change in temperature.
Q 53 – A student prepares aqueous solutions of the following salts: Copper sulphate : ferrous sulphate, Sodium sulphate, barium chloride. Write the colour of each solution thus formed.
Copper sulphate — Green
Ferrous sulphate — Pale green
Sodium sulphate — Milky white
Barium chloride — White
Q 54 – Barium chloride reacts with aluminium sulphate to give, aluminium chloride and barium sulphate.
(i) State the two types in which the above reaction can be classified.
(ii) Translate the above statement into a chemical equation.
(i) Double displacement reaction and Precipitation reaction.
(ii) 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4(↓)
Q 55 – Name the reducing agent in the following reaction:
3MnO2 + 4Al → 3Mn + 2Al2O3
State which is more reactive, Mn or Al, and why?
‘Al’ is reducing agent.
‘AT is more reactive than Mn v ‘Al’ displaces Mn from its oxide.
Q 56 – State the type of chemical reactions and chemical equations that take place in the following:
(i) Magnesium wire is burnt in air.
(ii) Electric current is passed through water.
(iii) Ammonia and hydrogen chloride gases are mixed.
Q 57 – Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity.
(i) Decomposition by heat of lead nitrate.
(ii) Decomposition by light of Silver Chloride
(iii) Decomposition by electricity of Water
Q 58 – State the kind of chemical reactions in the following examples in terms of loss and gain of energy:
(i) Digestion of food in stomach
(ii) Combustion of coal in air
(iii) Heating of limestone.
Digestion of food in Stomach
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
Energy is released in the process. It is exothermic reaction.
Combustion of Coal
Coal is Carbon. It is a combustion reaction.
C + O2 → CO2
Energy is released in the process hence it is known as exothermic reaction.
Heating of Limestone.
Limestone is calcium carbonate. Ca2CO3
Energy is absorbed in the process. So, the reaction is endothermic reaction.
Q 59 – (i) Write a balanced chemical equation for the process of photosynthesis.
(ii)When do desert plants take up carbon dioxide and perform photosynthesis?
(ii) In desert plants the stomata are open at night. They take CO2 at night and are stored in the form of acid and are used during day time for photosynthesis.
Q 60 – What is observed when a solution of potassium iodide solution is added to a solution of lead nitrate?
Name the type of reaction. Write a balanced chemical equation to represent the above chemical reaction.
A yellow precipitate of lead iodide is formed. It is a precipitation reaction.
It is also called double displacement reaction.
Q 61 – Write balanced chemical equations for the following reactions.
(i) Silver bromide on exposure to sunlight decomposes into silver and bromine,
(ii) Sodium metal reacts with water to form sodium hydroxide and hydrogen gas.
Q 62 – Identify the type of reaction(s) in the following equations.
(i) Combustion reaction and oxidation reaction.
(ii) Double displacement reaction and precipitation reaction.
(iii) Combination reaction.
(iv) Displacement reaction.
Q 63 – Write balanced equation for the reaction between magnesium and hydrochloric acid. Name the product obtained, identify the type of reaction.
The product formed is magnesium chloride and hydrogen gas. It is a displacement reaction.
Q 64 – (a) Define a balanced chemical equation. Why should an equation be balanced?
(b) Write the balanced chemical equation for the following reaction:
(i) Phosphorus burns in presence of chlorine to form phosphorus penta chloride.
(ii) Burning of natural gas.
(iii) The process of respiration.
(a) Balanced chemical equation has an equal number of atoms of different elements in the reactants and products. According to law of conservation of mass, matter can neither be created nor be destroyed in a chemical reaction.
(b)
Q 65 – (a) Explain the term “rancidity.” Name the type of chemical reaction responsible for causing rancidity and define it. (b) Write three methods for preventing rancidity of food.
We have seen food getting contaminated and having an unpleasant smell if it is left open in summer. In a hot weather, Oil present in food get oxidized and become Rancid. Such food is not recommended for consumption.
The food is getting oxidized so the reaction is oxidation reaction.
Methods for preventing food from getting oxidized are:-
(a) Food is kept in cool place like refrigerator.
(b) Packaging should be air tight.
(c) Antioxidants should be added to food.
Q 66 – (a) Explain two ways by which food industries prevent rancidity.
(b) Discuss the importance of decomposition reaction in metal industry with three points.
(a) (i) Rancidity can be prevented by adding antioxidants to food containing fat and oil, e.g. butylated hydroxy anisole is added to butter as antioxidant.
(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.
(b) (i) Molten NaCl is electrolytically decomposed to form sodium metal.
(ii) Aluminium metal is obtained by electric decomposition of bauxite ore mixed with cryolite.
(iii) Carbonate ores are thermally decomposed to give metal oxide which on reduction give metal.
Q 67 – (a) List any three observations that determine that a chemical reaction has taken place. Also list three information that cannot be obtained about a chemical reaction, merely by its chemical equation.
(b) Balance the following chemical equations.
(i) Fe + H2O → Fe3O4 + H2
(ii) CO2 + H2O → C6H12O6+O2
The three observations are
(i) Change of color
(ii) Change of temperature
(iii) Evolution of Gas
The three informations are
Atmospheric conditions
(i) Catalyst involved
(ii) Physical states of reactants and products
Balancing Equations
(i) 3Fe + 4H2O → Fe3O4 + 4H2
(ii) 6CO2 + 6H2O → C6H12O6 + 6O2
Q 68 – What is rancidity? Mention any two ways by which rancidity can be prevented.
The process in which taste and smell of food gets spoiled is called rancidity. It happens due to
oxidation.
Prevention from rancidity:
(i) Antioxidants are added to fatty acids to prevent oxidation, e.g. chips are packed in presence of nitrogen gas which prevents spoilage by oxidation.
(ii) Food should be kept in airtight container in refrigerator.
Q 69 – What is redox reaction? Identify the substance oxidised and the substance reduced in the following reactions.
Those reactions in which oxidation and reduction takes place simultaneously are called redox reactions.
(i) PbO is getting reduced and C is getting oxidised.
(ii) MnOs is getting reduced and HCl is getting oxidised.
Q 70 – Describe an activity to observe what happens when quick lime is added to water taken in a beaker. State two important observations and name the type of reaction taking place.
Aim: To observe what happens when quicklime is added to water taken in a beaker.
Materials Required:- Quicklime (calcium oxide), water, beaker.
Procedure:
1. Take 5 g of calcium oxide in a beaker.
2. Add water to it slowly.
3. Touch the beaker.
4. Note down the observations.
Observation: Calcium oxide reacts with water vigorously to form calcium hydroxide with the evolution of heat.
Chemical Reaction:
Conclusion: The reaction between CaO (Calcium oxide) and H2O is a combination reaction. It is an exothermic process because heat is evolved.
Q 71 – What is the colour of ferrous sulphate crystals? How does this colour change after heating?
The colour of ferrous sulphate is pale green. The colour changes to reddish brown on heating due to formation of iron (III) oxide.
Give an example each for thermal decomposition and photochemical decomposition reactions. Write relevant balanced chemical equations also.
Thermal decomposition reaction:
Q 72 – Write the balanced chemical equations for the following reactions and identify the type of reaction in each case. Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
Displacement Reaction in which the heat released in the reaction will melt the Iron (Fe)
It is a displacement reaction because Al is displacing Fe from Fe2O3 Iron (III) Oxide. The Molten iron is used for repairing broken railway tracks.
Q 73 – Describe an activity to demonstrate the change that takes place when white silver chloride is kept in sunlight. State the type of chemical reaction which takes place.
Aim: To demonstrate the change that takes place when white silver chloride is kept in sunlight.
Materials Required: AgNO3(aq), NaCl(aq), test tubes.
Procedure:
1. Take 5 ml of silver nitrate solution in a test tube.
2. Prepare sodium chloride solution in another test tube.
3. Add sodium chloride solution into test tube containing silver nitrate solution.
4. Observe the colour of silver chloride formed chloride to grey silver metal Dry it with the help of filter papers and place it on the watch glass.
5. Place the watch glass under sunlight for sometime.
6. Observe the colour of the silver chloride after sometime.
Observation: White silver chloride turns grey in sunlight because silver metal is formed.
- Decomosition Reaction
Explanation: Silver chloride is photosensitive. It decomposes in presence of sunlight to form silver metal and chlorine gas.
Conclusion: Decomposition of silver chloride in presence of sunlight is a photochemical decomposition reaction.