Question 1.
Why is magnesium ribbon cleaned before burning in air?
Answer
Before burning in air, the magnesium ribbon is cleaned by rubbing it with sandpaper to remove the layer of magnesium oxide and magnesium carbonate that formed on the ribbon as a result of the reaction with atmospheric oxygen and CO. Doing so causes the magnesium ribbon to burn easily.
Question 2.
Write balanced equations for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium Chloride + Aluminum Sulphate → Barium Sulphate + Aluminum Chloride
(iii) sodium + water → sodium hydroxide + hydrogen.
Answer
Question 3.
Write balanced chemical equations for the following reactions with their state signs:
(i) Solutions of barium chloride and sodium sulphate react in water to form a solution of sodium chloride and a precipitate of insoluble barium sulphate.
(ii) A solution of sodium hydroxide (in water) reacts with a solution of hydrochloric acid (in water) to form a solution of sodium chloride and water.
Answer
Question 1.
A solution of a substance ‘X’ is used for whitening.
(i) Name the substance X’ and write its formula.
(ii) Write the reaction of substance ‘X’ mentioned in (i) above with water.
Answer
(i) Substance ‘x’ is named as slaked lime, whose
(ii) The reaction of substance ‘X’ i.e. CaO with water is as follows-
CaO(s) + H2O(l) → Ca(OH)2(aq)
(slaked lime) slaked lime (calcium hydroxide)
Question 2.
Why is the amount of gas collected in one test tube twice that of the other in Activity 1.7? Name that gas.
Answer
We know that water is made up of 2 parts hydrogen and 1 part oxygen switch i.e. H2O. hydrogen atom and
Oxygen atoms are formed by combining 2 : 1. Therefore, by electrolysis of water, hydrogen and oxygen gases are obtained. Hence the gas collected at the cathode is hydrogen and the gas collected at the anode is oxygen.
double the quantity. (see Fig. 1.4)
Question 1.
Why does the color of the solution change when an iron nail is dipped in a solution of copper sulphate?
Answer
When an iron nail is dipped in a blue colored copper sulphate (CuSO) solution, the blue color of the solution becomes paler. This is because Fe is more reactive than Cu which displaces copper and forms iron sulphate and copper metal. the reaction goes like this
Identify the oxidised and reduced substances in the following reactions:
(i) 4Na(s) + O2(g) → 2Na2O(5)
(ii) Cuo(s) + H2(g) + Cu(s) + H2O(l)
Answer
(i) In this reaction sodium (Na) is oxidised to Na2O because Na is being combined with O2 and O2 is the substance to be reduced. So the substances to be oxidised and reduced are Na and O2 respectively.
Question 1.
Which statement is false regarding the reaction given below?
2PbO(s) + C(s) → 2PD(S) + CO2(g)
(a) Lead is being 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)
Question 2.
Fe2O3+ 2Al → Al2O3 + 2Fe
What type of reaction is given above?
(a) combination reaction
(b) double displacement reaction
(C) decomposition reaction
(d) displacement reaction
Answer
(2) Displacement reaction.
Question 3.
What happens when dilute hydrochloric acid is poured on iron powder? Mark the correct answer.
(a) Hydrogen gas and iron chloride are formed.
(b) Chlorine gas and iron hydroxide are formed.
(c) No reaction takes place.
(d) Iron salts and water are formed.
Answer
(a) Hydrogen gas and iron chloride are formed.
Question 4.
What is a balanced chemical equation? Why is it necessary to balance a chemical equation?
Answer
When the number of atoms of different elements in a chemical equation is equal on the left (L.H.S) and the right side (R.H.S), it is called a balanced chemical equation, that is, the total number of atoms of the elements in the reactants = the total number of elements in the products. number of atoms. It is necessary to balance the chemical equation because mass is neither created nor destroyed in any chemical reaction. That is, the total mass of the product elements = the total mass of the reactant elements, so the law of conservation of mass is followed in the chemical equation.
Question 5.
Convert the following statements into chemical equations and balance them.
(a) Nitrogen combines with hydrogen gas to form ammonia.
(b) Hydrogen sulfide gas is burnt in air to form water and sulfur dioxide.
(C) Barium chloride reacts with aluminum sulphate to give a precipitate of aluminum chloride and barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer
Question 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
balanced chemical equation
Question 7.
Write 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
Answer
balanced chemical equation
Question 8.
Write balanced chemical equations for the following reactions and state the type of each reaction.
(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(s) → Hydrogen chloride(g)
(d) Magnesium(5) + Hydrochloric acid(s) – Magnesium chloride(aq) + Hydrogen(g)
Question 9.
What is meant by exothermic and endothermic reaction? Give an example.
Answer
Exothermic Reaction: The reactions in which heat is produced along with the formation of a product are called exothermic chemical reactions. The heat emission is represented by the sign (A) written on the side of the product. For example-
Endothermic Reaction: The reactions in which heat is absorbed are called endothermic reactions. For example, the decomposition of CaCO is an endothermic reaction because energy is absorbed in the form of heat. The reaction is as follows-
Question 10.
Why is respiration called an exothermic reaction? Describe.
Answer
Respiration is called exothermic reaction because of two reasons
(i) Because glucose combines with oxygen present in our cells to form CO and water.
(ii) Heat energy is released in this reaction. the reaction goes like this
Question 11.
Why is a decomposition reaction called the opposite of a combination reaction? Write the equations for these reactions.
Answer
In a decomposition reaction, a reactant breaks down into two or more products.
Question 12.
Write one equation each for the decomposition reactions in which energy is given in the form of heat, light and electricity.
Answer
(a) dissociation by heat-
Question 13.
What is the difference between displacement and double displacement reactions? Write the equations for these reactions.
Answer
Displacement Reaction: A displacement reaction occurs when a more reactive element displaces a less reactive element from its compound.
Here, Zn is more reactive than Cu, which displaces Cu from CuCl2.
Double Displacement Reaction – In a double displacement reaction, there is an exchange of ions between the reactants. e.g. AB + CD → AC + BD
NaOH + HCl → NaCl + H2O
Question 14.
In the refining of silver, copper is displaced from a solution of silver nitrate to obtain silver. Write the reaction for this process.
Answer
Cu(s) + 2AgNO3(3) → Cu(NO3)2(aq) + 2Ag(s)
Question 14.
In the refining of silver, copper is displaced from a solution of silver nitrate to obtain silver. Write the reaction for this process.
Answer
Cu(s) + 2AgNO3(3) → Cu(NO3)2(aq) + 2Ag(s)
Question 18.
Why do we paint iron objects?
Answer
Iron articles get corrosive on exposure to air and humidity. Therefore, when painted, the surface of the iron is not exposed to air or moisture (humidity), due to which corrosion (rusting) does not occur. In this way the iron does not get damaged when painted.
Question 19.
Why are oily and fatty foods affected by nitrogen?
Answer
Foods containing oils and fats are affected by nitrogen because the smell and taste of these substances change due to anabolism. Nitrogen is an antioxidant, which prevents these substances from being oxidised. Therefore, the foul smell of oily and fatty foods does not happen. Fatty substances like this; As the chips don’t go bad.
Question 20.
Describe the following terms and give one example each.
(a) Corrosion
(b) rancidity
Answer
(a) Corrosion – When a metal comes in contact with the moisture and acid present in the atmosphere, a layer forms on its surfaces. This process is called corrosion. When iron rusts, it is called rusting.
Example- Silver metal (silver) is coated with a black layer of silver sulphide, copper is coated with a green colored copper carbonate layer and iron is coated with a reddish brown Fe,0:2H2O (hydrated ferric oxide). .
(b) Bad odor – Oily and fatty foods exposed to air (oxygen) become oxidised and become foul-smelling, due to which its taste and smell change. This process is called discoloration.
Measures to prevent odor-
adding nitrogen as an oxidising agent
keeping food in airtight containers
For example, the bag of chips becomes anabolized after a long time and smells bad, and when butter is kept at room temperature for a long time, its taste becomes sour and it smells bad, because it becomes anabolized.
