CHEMICAL REACTIONS AND EQUATIONS- CHAPTER-1 -NCERT CLASS 10- CHEMISTRY- ACTIVITIES
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| chemical reactions and equations activities class 10 |
In this chapter, you are going to study chemical reactions.
The various sub-topics included are characteristics of chemical reactions, balancing chemical equations, the implication of balanced chemical equation, four types of chemical reactions like the combination, decomposition, displacement, double displacement, precipitation reactions, neutralisation, oxidation and reduction.
Many activities involving chemical reactions are given in your NCERT textbook and these are very important in the examination point of view. In previous years board exams, you can find many questions from these activities including diagrams.
So we shall start with some activities. More emphasis is given for the colour change during the activities. This will help you to crack questions from these sections.
ACTIVITY-1.1 explains the reaction of Magnesium with Oxygen. On burning magnesium ribbon in air, it makes a dazzling light with oxygen to form a white powder. It is magnesium oxide.
Mg + O2 → MgO
ACTIVITY- 1.2 explains the reaction of lead nitrate and potassium iodide. It will undergo a double displacement reaction to form lead iodide which is a yellow precipitate and potassium nitrate which is colourless. (*an example for double displacement and precipitation reaction).
Pb(NO3)2 + 2KI → PbI2 + 2KNO3
ACTIVITY- 1.3 explains the reaction of zinc granules with dilute HCl or dilute H2SO4.The resultant products are hydrogen gas and zinc salts like ZnCl2 or ZnSO4.
We can observe the bubbles of hydrogen gas around the zinc granules and can test the presence of hydrogen with the pop sound of a burning match stick. This reaction is exothermic and that is why the test tube is becoming hot during this reaction(* example for displacement reaction or exothermic reaction).
Zn + 2HCl → ZnCl2 + H2
CHANGES ACCOMPANYING A CHEMICAL REACTION are:
- change in state
- change in colour
- change in temperature
- evolution of gas
CHEMICAL EQUATIONS
Reactants → Products
Word equation- Shows change of reactants to products with an arrow between them.
Magnesium + Oxygen → Magnesium oxide
Unbalanced equation / skeletal equation- the number of atoms or the mass is not the same on the reactant side and product side.
Mg + O2 → MgO
Balanced equation - the reaction in which the number of atoms is the same on the reactant side and product side. The total mass of the reactants will be equal to the total mass of the products.
Mg + O2 → 2 MgO
* Balancing of a chemical reaction is based on the law of conservation of mass. It states that mass can neither be created nor destroyed in a chemical reaction.
ACTIVITY 1.4- explains the reaction of calcium oxide (quick lime) with water. This is an example of the combination reaction where CaO reacts with water to form calcium hydroxide Ca(OH)2. During this reaction, a large amount of heat is produced(exothermic reaction).
CaO + H2O → Ca(OH)2
ACTIVITY- 1.5 explains about the decomposition reaction of ferrous sulphate crystals. On heating light green coloured ferrous sulphate in a dry test tube, FeSO4.7H2O loses its water of hydration and will become white coloured anhydrous ferrous sulphate (FeSO4).
On further heating, it decomposes to form a dark brown coloured solid. the products formed are ferric oxide, sulphur dioxide and sulphur trioxide.
FeSO4.7H2O → FeSO4
2FeSO4 → Fe2O3(s) + SO2(g) + SO3(g)
ACTIVITY-1.6 explains about the thermal decomposition of lead nitrate. Lead nitrate is a white coloured powder. On heating, it will decompose to form a lead oxide, nitrogen dioxide and oxygen. The observation is the formation of brown fumes of nitrogen dioxide.
2Pb(NO3)2 → 2PbO + 4NO2 + O2
ACTIVITY - 1.7 explains about the electrolytic decomposition of water into hydrogen and oxygen.
On electrolysis, the bubbles are formed and it can be tested using a burning candle. Hydrogen burns with a pop sound. We can notice that the volume of the gas formed is not the same.
When two volumes of hydrogen are formed, only one volume of oxygen is formed. It is clear from the balanced equation given below:
2 H2O → 2 H2 + O2
ACTIVITY -1.8 explains about the photolytic decomposition of silver chloride (AgCl). When white coloured silver chloride is exposed to sunlight, it will decompose to form grey coloured silver and chlorine gas.
2AgCl(s) → 2Ag(s) + Cl2(g)
Similar is the case with silver bromide.
2AgBr(s) → 2 Ag(s) + Br2(g)
ACTIVITY- 1.9 explains the displacement reaction of the iron nail with copper sulphate. This topic was already studied in lower grades. The more reactive metal can displace a less reactive metal from its salt. So in this activity iron being more reactive displaces copper from copper sulphate.
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| iron nail |
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| blue coloured copper sulphate and green coloured iron sulphate |
The blue colour of copper sulphate fades and changes into a light green colour due to the formation of iron sulphate. Brown deposits of copper can be observed on iron nails.
Fe + CuSO4 → FeSO4 + Cu
ACTIVITY -1.10 explains about the double displacement reaction of barium chloride and sodium sulphate. On adding these, it undergoes double decomposition to form a white precipitate of barium sulphate and sodium chloride. This is an example of precipitation reaction as well.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
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| a white precipitate of barium sulphate |
* Another example for precipitation reaction was a reaction with lead nitrate and potassium iodide(yellow precipitate of lead iodide).
ACTIVITY-1.11 explains about the oxidation reaction of copper powder. Brown coloured copper powder on heating reacts with oxygen in the air to form black coloured copper oxide.
2Cu + O2 → 2 CuO
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| brown coloured copper vessels |
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| copper oxide coating on a copper vessel |
Do you want to study acids, bases and salts and metals and nonmetals? You can refer my blog for these topics.
YOU CAN ALSO READ: ACIDS, BASES AND SALTS
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