CHEMISTRY ADDA: 10th Chemical and chemical Equations

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Tuesday, August 7, 2012

CBSE ADDA: X Chemical reactions and Chemical Equation:FA-Eva...

Very short answer questions (V.S.A)

1. Arrange the following metals in the decreasing under of reactivity or electro positive character.

K Zn Na Fe Pb Cu

2. Which of them will be a reducing agent a metal or non metal?

3. Balance the chemical equation

Na(s) + H₂O --------------à NaOH + H₂

4. Select the combination reaction from following

(i)KClO3 -----------à KCl + 3 O₂

(ii) S + O₂--------------à SO₂

5. Select the decomposition reaction from following

(i) 2H₂O + O₂ ----------------à 2H₂ O

(ii) CaCO₃ ------Heat---------à CaO + CO₂

6. Select the double displacement reaction

(i) BaCl₂ + H₂SO₄-----à Ba SO₄+H₂

(ii) 2KBv + Cl₂ ------à K Cl₂+ Bv₂

7. Fill in the following about reactivity series of metal

(a) the …………………. Metal replaces the ………………. Metal from its salt solution.

8. Which of the following is not the necessary condition for rusting

(i) Presence of oxygen (ii) Presence of catalyst (iii) Presence of moisture

9. Which of the following is required for prevention of corrosion?

(i) coating of less electropositive metal

(ii) coating of move electropositive metal

10. Choose the correct about rancidity

(i) Rancidity is a reduction process (ii) Rancidity is an oxidation process

Answers

1. K > Na > Zn > Fe > Pb > Cu

2. Non metal

3. 2 Na(s) +2 H₂O --------------à 2NaOH + 2H₂

4. S + O₂--------------à SO₂

5. CaCO₃ ------Heat---------à CaO + CO₂

6. BaCl₂ + H₂SO₄-----à Ba SO₄+H₂

7. Strong, Weak

8. Presence of catalyst

9. Coating with move electropositive metal

10. Rancidity is an oxidation process

See some questions: Short Answer type Question (2 marks)

1. (i) What happens when aqueous solution of barium chloride is added to aqueous sodium sulphate solution?

(ii) When silver coloured metal (A) is added to dilute sulphuric acid, solution (B) is formed which is colourless solution and a gas (c) is evolved which is colourless name ‘A’, ‘B’ and ‘C’ and write the equation?

(iii) An ‘A’ blue coloured crystalline salt on heating decomposes to ‘B’ white substance. W hen in

blue salt solution, a metal (Zinc) is added, its gives rise to colourless solution ‘C’ wth leaving behind ‘D’ reddish brown metal.

2. Name the compounds ‘A’, ‘B’, ‘C’ and ‘D’

(iv) A reaction mixture of chromium Oxide is heated with aluminum powder on strong heating

3. a. Write the reaction?

b. Give one application of this reaction?

(v) Define Rusting?

4. Give two methods of protection of metal trans rusting.

5. (i) Rusting is a slow electrochemical process in which hydrated oxide of metal in formed from metal when it comes in with air moisture (ii) By Painting, by galvanization, by tinning

6. (i) Explains the term ‘corrosion’?

(ii) Write the chemical reaction of corrosion of Iron?

(iii) Name two metals which corrodes easily?

(iv) Aluminum corrodes in moist air but is widely used is making utensils.

(v) what is galvanization and why do we use Zn for it?\

7. (i) What is rancidity? Where does it happen

(ii) what are anti oxidants? Why are they added fat and oil containing food to prevent from rancidity?

(iii) why do most items puffed with nitrogen.

Solution:

1. White precipitate of BaSO4 is obtained. Reaction will be as

Na₂SO₄ + BACl₂ ----------------à BaSO4 + 2NaCl

2. A is Zinc, B is ZnSO4 solutions C is H2gas and reactions will be

Zn (s) + H₂SO₄(d)-------------àZn SO₄(aq)+H₂(g)

3. A, B, C, and D are respectively-

CuSO4, 5 H2O, CuSO4, ZnSO4 (aq), Cu (s)

4. (i)Cr₂O₃ + 2Al ------à Al₂O3 + 2 Cr

(ii) This reaction is used in termite welding

5. (i) The process of slow destruction of metals when exposed to air, moisture and pollutant gases , in called as corrasim

(ii) Fe + 3H₂ + 2H₂O ------------à Fe₂O₃ x H₂O

(iii) Formation of green coating on copper and formation of thin layer of oxide on aluminum are example of corrosion.

(iv) Aluminum forms oxide layer on exposure to air, this oxide layer further checks corrosion.

(v) Galvanization is a process in which Zinc layer is applied on Iron. It is used to protect iron from rusting.

6. (i) The oxidative deterioration of oils and fats leading to stinking smell or stale taste is known as rancidity.

(ii) Anti Oxidants are those chemicals which an addition to fat and oil checks it from rancidityan addition of anti oxidants fatty food is protected from stale.

(iii) Nitrogen is filled in potato chips & other food to create anaerobic (air free atmosphere) which avoids rancidity.

Thursday, August 2, 2012

10th Chemical reaction and equation Practice Assesments

ASSIGNMENT : FIRST TERM (2012-2013) X SUBJECT : CHEMISTRY

CHAPTER : CHEMICAL REACTIONS AND EQUATIONS Max Marks: 55

A. Very short answer questions: (1 mark each) (1x 14= 14 marks)

1. What are reactants ?

2. What are products ?

3. What is the term used for symbolic representation of a chemical reaction ?

4. What does the + sign between the reactants indicate ?

5. How is the salt solution in water indicated in a chemical reaction /

6. Aluminium burns in chlorine to form aluminum chloride. Write a balanced equation for this reaction ?

7. Balance the following equation and add the state symbols :

Zn(s) + 2HCl(aq) → ZnCl₂ + H₂

8. Name the following reaction.

AB + CD → AD + BC

9. Aluminium metal displaces iron from ferric oxide (Fe₂O₂) giving aluminium oxide and iron. Which is more reactive, aluminium or iron ?

10. Identify from the following reaction : H₂S + Cl₂ → 2HCl + S

a. Component oxidized

b. Oxidizing agent

11. Give one example of a redox reaction which is also a combination reaction.

12. Which atom is reduced on burning an element in air.

13. When SO₂ gas is passed through saturated solution of H2S, the following reaction occurs

SO₂ + 2H₂S → 2 H₂O + 3S

In this reaction, which substance is oxidized and which one is reduced.

14. In the following reaction between lead sulphide and hydrogen peroxide

PbS(s) + 4H₂O(aq) → PbSO⁴(s) + 4H₂O(l)

a. Which substance is reduced ?

b. Which substance is oxidized ?

B. Short answer questions: (2 marks each) (2x4=8)

1. Write a chemical equation for each of the following reactions :

a. Zinc metal reacts with aqueous solution of hydrochloric acid to form zinc chloride solution and hydrogen gas.

b. When solid mercury (II) oxide is heated, liquid mercury and oxygen gas are produced.

2. H₂ + O → H₂O is a balanced chemical equation. It is considered to be incorrect. Why? 3. Write balance chemical equations to represent the following statements :

a. Carbon (coke) burns in air to form carbon dioxide gas.

b. A piece of sodium metal on putting in water forms caustic soda and hydrogen gas.

3. Write the balanced chemical equations for the following chemical reactions :

a. Aqueous solutions of sulphuric acid and sodium hydroxide react to form aqueous sodium sulphate and water.

b. Phosphorus burns in chlorine gas to form phosphorus penta chloride.

4. Magnesium is more reactive than copper or iron but iron is more reactive than copper.

a. A solution of magnesium sulphate is put into a copper pot.

b. A solution of copper sulphate is put into a iron pot.

c. A solution of magnesium sulphate is put into a iron pot.

Which of the above pots will get damaged? Why? What is this reaction called?

C. Short answer questions: (3 marks each)(3x 4= 12)

1. What are the three essentials of a chemical equation ?

2. Explainthe term reduction with examples.

3.A colourless lead salt, when heated, produces a yellow residue and brown fumes.

a. Name the lead salt.

b. Name the brown fumes.

c. Write a chemical equation of the reaction involved.

4. When a green iron salt is heated strongly, its colour finally changes to black and colour of burning sulphur is given out.

a. Name the iron salt.

b. Name the type of reaction that takes place during the heating of iron salt.

c. Write a chemical equation for the reaction involved.

D. Balance the following skeleton equation by hit and trial method : (2x6=12)

a. C₂H₄ + O₂ → CO₂ +H₂O

b. C₂H₂ + O₂ → CO₂ +H₂O

c. CH₄ + O₂ → CO₂ +H₂O

d. Al₂(SO₄)₃ + NaOH → Al(OH)₃ + Na₂SO₄

e. Cu₂S + O₂ → Cu₂O +S₂O

f. AlN + H₂O → Al(OH)₃ + NH₃

E Define: (1x9=9)

1. Rancidity 2. Combination reactions 3. Decomposition reactions 4. Double displacement reaction 5. Displacement reaction 6. Redox reaction 7. Corrosion 8. Oxidising agent 9. Reducing agent

Thursday, May 10, 2012

x Ch.1 Chemical reactions and equations key consents

1. Chemical reaction: A chemical reaction involves a chemical change in which substances react to form new substances with entirely new properties. Substances that react or take part in the reaction are known as reactants and the substances formed are known as products.
2. Physical change: If a change involves change in colour or state but no new substance is formed, then it is a physical change.
3. Chemical change: If a change involves formation of new substances, it is a chemical change.
4. Chemical equation: The symbolic representation of a chemical reaction is called a chemical equation.
5. Exothermic and endothermic reactions: If heat is evolved during a reaction, then such a reaction is known as exothermic reaction. If heat is absorbed from the surroundings, then such a reaction is known as endothermic reaction
6. Combination reaction: Combination reaction is a reaction in which two or more substances combine to give a single product.
7. Decomposition reaction: In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity
8. Displacement reaction: A reaction in which a more active element displaces less active element from its salt solution.
9. Reactivity series: The Reactivity series is a list of metals arranged in the order of decreasing reactivity. The most reactive metal is placed at the top and the least reactive metal is placed at the bottom.
10.Double displacement reaction: A chemical reaction in which there is an exchange of ions between the reactants to give new substances is called a double displacement reaction.
11.Precipitation reaction: An insoluble solid known as precipitate is formed during a double is placement reaction. Such reactions are also known as precipitation reactions.
12.Redox reaction: A reaction, in which oxidation and reduction takes place simultaneously is known as redox reaction.
13.Oxidation: Oxidation is a chemical process in which a substance gains oxygen or loses hydrogen.
14.Reduction: Reduction is a chemical process in which a substance gains hydrogen or loses oxygen.
15.During a chemical reaction, there is a breaking of bonds between atoms of the reacting molecules to give products.
16. A chemical reaction can be observed with the help of any of the following observations:
a) Evolution of a gas b) Change in temperature
c) Formation of a precipitate d) Change in colour e) Change of state
17. Skeletal chemical equation: A chemical equation which simply represents the symbols and formulae of reactants and products taking part in the reaction is known as skeletal chemical equation
for a reaction. For example: For the burning of Magnesium in the air, Mg + O2 → MgO is the skeletal equation.
18. Balanced chemical equation: A balanced equation is a chemical equation in which number of atoms of each element is equal on both sides of the equation i.e. number of atoms of an element on
reactant side = number of atoms of that element on the product side.
19. As per the law of conservation of mass, the total mass of the elements present in the products of a chemical reaction is equal to the total mass of the elements present in the reactants.
20. Decomposition reaction: In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity
Types of decomposition reactions:
a. Decomposition reactions which require heat are known as thermolytic decomposition reactions
b. Decomposition reactions which require light are known as photolytic decomposition reactions
c. Decomposition reactions which require electricity are known as electrolytic decomposition reactions

CBSE X Chemical Reaction and Equation Extra marks questions answers

1-mark Questions/ Answers

1. What happens when magnesium ribbon burns in air?

Ans. When magnesium ribbon burns in air, it combines with the oxygen to form magnesium oxide.

2Mg(s) + O2(g) ® 2MgO(s)

2. Name the gas evolved when zinc reacts with dil. HCl.

Ans. Hydrogen gas is evolved.

3. What is a chemical equation?

Ans. A chemical equation is a symbolic notation that uses formulae instead of words to represent a chemical equation.

4. On what chemical law, balancing of chemical equation is based?

Ans. Balancing of a chemical equation is based on the law of conservation of mass.

X Formative assessments Chemical reaction and equations

Q1. The given equation represents the reaction of sodium metal with water.

Sodium + Water Sodium hydroxide + Hydrogen

Which of the following chemical equations represents a complete balanced chemical equation for the given word equation?

A. 2Na(s) + H2O → 2NaOH(aq) + H2(g)
B. Na(s) + 2H2O → NaOH(aq) +2H2(g)

C. 2Na(s) + 2H3O → 2NaOH(aq) + 2H2(g)
D. 2Na(s) + 2H2O → 2NaOH(aq) + H2(g)

Q2. Identify the chemical equation which represents a complete balanced equation for the reaction of barium chloride with sodium sulphate to produce barium sulphate and sodium chloride.

A. BaCl2(aq) + Na2SO4 (aq) → BaSO4(s) + 2NaCl(aq)v

B. BaCl2(aq) + Na2SO4 (aq) → 2BaSO4(s) + 2NaCl(aq)

C. 2BaCl2(aq) + Na2 → SO4 (aq) 2BaSO4(s) + NaCl(aq)

D. BaCl2(aq) + Na2 → SO4 (aq) BaSO4(s) + NaCl(aq)

Q3. Ferric oxide reacts with aluminum to produce aluminum oxide and iron. The balanced chemical equation for the given reaction is
Fe2O3 + 2Al → Al2O3 + 2Fe

Which of the following substances is oxidized in the given reaction?

A. Al2O3
B. Fe2O3
C. A1
D. Fe

Q4. White silver chloride changes to grey in sunlight because of the formation of silver metal along with the evolution of chlorine gas. Identify the chemical equation that gives a correct representation of the process.

A. 2AgCl   → 2Ag + Cl2
B. AgCl →   Ag + Cl2
C. 2Ag + Cl2   → 2AgCl
D. Ag + Cl2   →   2AgCl

Q5. When copper oxide is treated with hydrogen gas copper is produced along with water. The balanced chemical equation for the given reaction is CuO + H2 → Cu + H2O Which substance is oxidized in the given reaction?

A. H2
B. Cu
C. H2O
D. CuO

Q6. The balanced chemical equation for the reaction of nitrogen with hydrogen to produce

Ammonia gas is-

A. N2(g) + H2(g) → 2NH3(g)
B. 2N2(g) + H2(g) → 2NH3(g)

C. N2(g) + 3H2(g) → 2NH3(g)
D. 2N2(g) + H2(g) → 2NH3(g)

Q7. Identify the chemical equation that correctly represents production of magnesium nitrideby burning magnesium metal in a pure nitrogen atmosphere from the following–

A. Mg3N2(s) ® Mg(g) + N2(g) B. Mg + N2 ® Mg3N2

C. 3Mg(g)N2(g) ®Mg3N2(g) D. Mg3N2 ® 3Mg + N2

Q8. Which of the following reactions represents a combination reaction?

A. CaO(s) + H2O(g) ® Ca(OH)2(aq) B. CaCO3(s) ® CaO(s) + CO2(g)

C. Zn + CuSO4(aq) ® ZnSO4(aq) + Cu(s) D. 2FeSO4(s) ® Fe2O3(s) + SO2(g) + SO3(g)

Q9. Which of the following reactions represents a double displacement reaction?

A. BaCl2(aq) + Na2SO4(aq) ® BaSO4(s) + 2NaCl(aq)

B. 2FeSO4(s) ® Fe2O3(s) + SO2(g) + SO3(g)

C. 2Pb(NO3)2(g) ® 2PbO(s) + 4NO2(g) + O2(g)

D. Zn(s) + 2AgNO3(aq) ®Zn(NO3)2(aq) + 2Ag(s)

Q10. The reaction: Fe2O3(s) + 2Al(s) ®Al2O3(s) + 2Fe(s) is an example of a–

A. combination reaction
B. double displacement reaction

C. decomposition reaction
D. displacement reaction

Q10. What happens when dilute hydrochloric acid is added to iron fillings?

A. Hydrogen gas and iron chloride are produced
B. Chlorine gas and hydroxide are produced

C. heat is absorbed, i.e. test tube becomes cold.
D. Iron salt and water are produced

Q. Write balanced chemical equations for the following word equations:

A. Calcium hydroxide + Carbon dioxide Calcium carbonate + Water