CHEMICAL REACTIONS AND EQUATIONS CLASS X

YOU SHOULD KNOW THE SYMBOLS AND VALENCY OF DIFFERENT ELEMENT.

MONOATOMIC IONS +CHARGE

+1Charge	+2 Charge	+3Charge	+4 Charge
HYDROGEN-H SODIUM-Na POTASSIUM-K CUPROUS-Cu MERCUROUS-Hg SILVER-Ag	CUPRIC-Cu BARIUM-Ba CALCIUM-Ca MERCURIC-Hg COBALT-Co NICKEL-Ni IRON(FERROUS)-Fe MAGNESIUM-Mg MANGANESE-Mn ZINC-Zn LEAD(II)	ALUMINIUM-Al IRON(FERRIC)-Fe CHROMIUM-Cr	LEAD(IC)-Pb

MONOATOMIC NEGATIVE IONS

-1CHARGE	-2CHARGE	3-CHARGE
FLUORIDE-F CHLORIDE-Cl BROMIDE-Br IODIDE-I HYDRIDE-H	SULPHIDE-S OXIDE-O	PHOSPHIDE-P NITRIDE-N

POLYATOMIC IONS

POSITIVELY CHARGED		NEGATIVELY CHARGED
+1CHARGE	-1 CHARGE	-2 CHARGE	-3 CHARGE
AMMONIUN-NH₄⁺	HYDROXIDE-OH BICARBONATE-HCO₃ _NITRATE-NO₃ _ACETATE-CH₃COO	CARBONATE-CO₃ _SULPHITE-SO3 _SULPHATE-SO4 _{CHROMATE-CrO4} _{DICHROMATE-Cr2 O7}	PHOSPHATE-PO₄ PHOSPHITE-PO₃ BORATE-BO₃ PHOSPHIDE-P NITRIDE-N

SABITABRATA MANDAL

,KV AFS,BKP

5/4/16

Balance equations "by inspection" with these steps:

Check for diatomic molecules.

Balance the metals (not Hydrogen).

Balance the non metals (not Oxygen).

Balance oxygen.

Balance hydrogen.

The equation should now be balanced, but recount all atoms to be sure.

Reduce coefficients (if needed).

Balancing Equations

Balance the following chemical equations.

H2S04

Fe2(SO4)3

C2H6

H2O

CO2

KOH

H3PO4

K3PO4

H2O

SnO2

H2O

NH3

H2O

KNO3

H2CO3

K2CO3

HNO3

B2Br6

HNO3

B(NO3)3

HBr

BF3

Li2SO3

B2(SO3)3

LiF

(NH4)3PO4 +

Pb(NO3)4

Pb3(PO4)4

NH4NO3

10.

SeCl6

SeO2

Cl2

Writing Equation Word Problems

Name __________ ____________________ #________

Use the following chemical reactions to write a complete balanced chemical equation. For each chemical compound write the correct chemical formula, and then balance the final equation. Once complete identify the type of reaction in each equation as either a double displacement, single displacement, decomposition or synthesis.

1) Potassium Chloride + Silver Nitrate yields Potassium Nitrate + Silver Chloride

2) Aluminum Hydroxide + Sodium Nitrate yields Aluminum Nitrate + Sodium Hydroxide

3) Iron Metal + Copper ( II) Sulfate yields Iron ( II) Sulfate + Copper Metal

4) Aluminum Metal + Copper ( II) Chloride yields Aluminum Chloride + Copper Metal

5) Potassium Bromide yields Potassium Metal + Bromine Gas

6) Calcium Carbonate yields Calcium Oxide + Carbon Dioxide Gas

7) Zinc Metal + Oxygen Gas yields Zinc Oxide

8) Chlorine Gas + Sodium Metal yields Sodium Chloride

9) Aluminum Sulfate + Barium Chloride yields Aluminum Chloride + Barium Sulfate

10) Beryllium Fluoride + Magnesium Metal yields Magnesium Fluoride + Beryllium Metal

11 Sodium Bicarbonate yields Sodium Carbonate + Carbon Dioxide + Water
CHAPTER 1

Chemical reactions and equations

• Characteristics of chemical reactions

Chemical reactions are the process in which new substances with new properties are formed.

Ref activity 1.1, 1.2, and 1.3.

Each notable change which takes place as a result of 0chemical reactions are known as characteristics of chemical reactions.

They are

a. Evolution of gas (Dil HCl+Zn)- H2 (gas)

b. Formation of precipitate Pb(NO3)2 +KI-yellow ppt

c.Change in colour -citric acid +KMnO4

d.Change in temperature –quicklime + water.

e.Change in state –wax is burned-CO2(g) and H2O(l) are formed.

• Chemical Equation.

A complete chemical equation represents the reactants, products and their physical states symbolically.

In a chemical reaction ,substances are changed into other substances .An equation is a representation a chemical reaction. It shows the reactants and the products formed.

• Writing a chemical equation.

1. An equation can be written in words this is called word equation.

Ex – Magnesium + Oxygen Magnesium Oxide.

Heat

Calcium Carbonate Calcium oxide + Carbon dioxide .

Zinc + Hydrochloric acid Zinc chloride + hydrogen.

2. An equation can be written with formulae or symbols of reactants products. Which is usually meant by a chemical equation.

3. All the reactants and products are represented by their symbols and formulae.

Zn + HCl ZnCl2 + H2

This is said to be a skeletal equation.

4. The skeleton equation is balanced.

Zn +2HCl ZnCl2 + H2.

• Balancing of a chemical equation

All chemical equation must be balanced .The law of conservation of matter states that “matter can neither be created nor destroyed.” According to this law ,the total mass of the reactants should be equal to the total mass of the products: or the number of atoms of each element should be equal on either side of the balanced chemical equation.

Note: You are not allowed to change the formula of a substance in an equation, when balancing the equation.

Step :- 1 .Write down the chemical reaction in word equation .Keeping the reactants on the left hand side and product on the right hand side.

Step :- 2.Substitute the word equation with respective symbols and formulae.

Step :- 3. Balance the equation starting with a compound which has maximum number of atoms by putting the smallest possible number. Do not alter the formulae to balance the equation.

Step :- 4. make the equation more informative by representing physical state of substances. Eg. (s)-solid, (l) - liquid ,(g) -gas , Solution in water -(aq) .

and reaction conditions such as temperature ,pressure,catalyst etc. above or below the arrow mark.

CO(gas) + 2H2 (g) 340atm 3000c CH3OH (l)

ZnO + CrO3 (methanol)

(Catalyst)

A balanced chemical equation express the relative amounts of the reactants and products involved in the reaction. This relative amount may be in grams, kilograms etc, or in moles. The quantitative information of the reactants and the products that a chemical equation provides is of immense utility in making calculations.

2KClO3 2KCl + 3O2

Quantitative information

2 moles of KClO3 on decomposition yield 2 moles of KCl and 3 moles of oxygen that is (2 ×122.6 units) of KClO 3 gives (2× 74.6 units) of KCl + (3 ×52 units) of oxygen.

A precipitate insoluble is a sparingly soluble substance formed during the reaction. (ppt)

• Types of chemical reactions

1.Chemical Combination.

A Chemical reaction in which two or more substances (reactants) combine to form a single new substance (product) as a combination reaction.

CaO + H2O Ca(OH)2 .(Activity 1.2)

Quick lime Slaked lime

Try to write few more examples of combination reaction.

2. Chemical decomposition

A chemical reaction in which in a single compound breaks down to produce 2 or more simpler substances is called a decomposition reaction.

It can be carried out by applying heat, light

or electricity. These provide energy which break up a compound into 2 or more simpler compound.

Heat

CaCO3 (s) CaO(s) + CO2 (g)

Limestone

When a substance decomposes on heating , it is called thermal decomposition.

2FeSO4(s) heat Fe2O3 (s) +SO2 (g) +SO3 (g)

Decomposition

Pale Green Brown

a. FeSO4 .7H2O (pale green) loses 7 molecules of H2O when heated and becomes white colour .

b. On further heating white anhydrous FeSO4 decomposes to ferric oxide (brown color) and SO2 and SO3 (smell of S is observed).

Activity 1.6 (N.C.E.R.T)

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

Lead nitrate is a colour less compound.

Brown fumes of NO2 gas are evolved which fills the boiling tube .

The gas becomes colourless when it reaches the mouth of the test tube as NO2 changes into NO (Colourless).

Activity 1.7 - Electrolysis of water.

Electricity

2H2O(l) Decomposition 2H2 (g) + 02 (g)

Activity 1.8

sunlight

2AgCl(s) decomposition 2Ag (s) + Cl2 (g).

sunlight

2AgBr(s) 2Ag(s) + Br2 (g)

White Grey

Digestion of food in the body is an example of decomposition reaction.

• Displacement reaction

A chemical reaction in which a more reactive element displaces a less reactive element from its compound is called displacement reaction .These reactions occur in solution.

Activity 1.9 (ncert)

Fe(s) + CuSO4 (aq) FeSO4 (aq) +Cu (s)

Zn(s) + CuSO4 (aq) ZnSO4 (aq) +Cu (s)

Pb(s) + CuCl2 (aq) PbCl2 (aq) + Cu (s)

• Double displacement reaction

A reaction in which there is a mutual exchange of ions between the reactants is called double displacement reaction.

Activity 1.10 (NCERT)

Na2SO4 (aq) + Bacl2 (aq) BaSO4 (s)+ 2NaCl (aq)

White ppt

Pb(NO3)2 (aq) + 2KI (aq) 2KNO3 (aq) +PbI2 (Yellow)

ppt

These two reactions can also be called as precipitation reaction.

• Oxidation and reduction

Oxidation –is a process of addition of oxygen to a substance or removal of hydrogen from a substance.

Reduction – is a process of addition of hydrogen to a substance or removal of oxygen from a substance.

Activity 1.11(NCERT)

Cu +O2 2CuO-oxidation of copper-to-copper oxide.

CuO + H2 Cu + H2O. Reduction of CuO to Cu.

Reactions in which one reactant gets oxidized while the other gets reduced are called oxidation- reduction reaction or redox reaction.

Illustrations.

Reduction

H2S + SO2 2H2O + 3S

¬¬¬¬ Oxidation

OXIDATION AND REDUCTION IN TERMS OF ELECTRON TRANSFER.

2Mg +O2 2MgO

Mg Mg2+ + 2e

O+ 2e O2-

Mg2+ +O2 MgO.

During this reaction, Mg loses two electrons to form a positive ion and oxygen gains those two electrons to form negative ion .thus, oxidation is defined as loss of electron and the reduction as gain of electrons.

• A reaction may be accompanied by liberation or absorption of heat reactions during which heat is liberated are said to be exothermic & those during which heat is absorbed are called to be endothermic.

Example- Exothermic

CH4 (g) + O2 (g) CO2 (g) + 2H2O (g) + Heat

C6H12O6 (aq) + 6O2 6CO2 + 6H2O + Heat(energy)(Respiration)

Endothermic

CaCO3 (s) + Heat CaO(s) + CO2(g)

Oxidation and reduction reaction which occur simultaneously are termed as redox reactions. Redox reactions include process such as burning, rusting respiration etc.

Effects of oxidation reactions in everyday life.

1)Corrosion of metals

2) Rancidity of food.

Corrosion: Is a process in which metal are eaten up gradually by the action of the air, moisture or a chemical (such as an acid) on their surface.

Ex; Rusting of IRON (iron gets corroded with red brown flaky substance (rust).

4Fe + 3O2 + 2H2O – 2Fe2O3 2H2O(Hydrated iron Oxide-Rust)

Black coating on silver, green coatings on copper metal are the other example of corrosion.

Effects Of corrosion

1. Weakens the metal.

2. Economic loss to the country.

Rancidity

The condition produced by the aerial oxidation of fats and oils in foods mark by unpleasant smell and taste is called as rancidity.

Rancidity foils the food material prepared on fats oils which have been kept for a long time and makes them unfit for eating.

Rancidity can be prevented

a. By adding antioxidants to food containing Fats and oils. Anti oxidants are actually reducing agents. The two common antioxidants used in foods to prevent the development of Rancidity are BHA (Butylated Hydroxy-Anisole) and BHT (Butylated Hydroxy-Toluene).

b. It can be prevented by packaging fat and oil containing foods in nitrogen gas.

c. It can be delayed refrigerating the food.

d. It can be retarded by storing food in air tight containers.

e. It can be retarded by storing food away from light.

Question bank

1 mark

1. Write chemical equation for the thermal decomposition of mercury oxide.

2HgO (s)  2Hg (l) + O2 (g)

2. Complete the following equation.

HCl(aq)

2Al(s) 2AlCl3 (aq) + 3H2 (g)

3. Why should magnesium ribbon cleaned before burning in air.

To remove the protective layer of basic magnesium carbonate from the surface of the magnesium ribbon.

4. Name the solid product obtained when AgCl is exposed to sunlight.

Silver- (grey powder)

5. When a colourless lead salt is heated a reddish brown gas is liberated name the gas.

NO2

6. Define the law on which the balancing of chemical equation is based. Law of conservation of energy.

7. Give an example of an oxidation reaction which is also a combination reaction.

2H2 + O2 2H2O

8. Name the substance in the following reaction.

PbS + 4H2O2 PbSO4 + 4H2O

Lead Hydrogen Lead Water

sulphide peroxide sulphate

9. What are antioxidants?

They are often added to fat containing food to prevent rancidity due to oxidation.

10. Why is respiration considered to be an exothermic reaction?

As it releases heat energy.

2 Mark question

1. Translate the following statements into chemical equation and then balance.

Barium chloride reacts with aluminum sulphate to give aluminum chloride and a precipitate of barium sulphate.

2. State two characteristics of the chemical reaction which occurs on adding KI to PbNO3 solution.

3. Give two examples from everyday life situation where redox reactions are taking place.

4. Write a chemical equation showing electrolytic decomposition.

5. What is a balanced chemical equation?

3 mark question

1. Why is photosynthesis considered as endothermic reaction . Explain with an equation?

2. Balance the following chemical equation;

• HNO3 + Ca(OH)2 Ca (NO3)2 + H2O

• NaOH + H2SO4 Na2SO4 + H20

• BaSO4 + KCl BaCl2 + K2SO4

3. What is exothermic and endothermic reaction. Explain with examples?

4. How can we make chemical equation more informative?

5. What happens when? Explain with chemical equation.

a) A piece of Zn is dipped in CuSO4 solution (aq).

b) Calcium oxide is added to water.

c) Potassium chlorate is strongly heated.

6. How would you distinguish between oxidation and reduction?

Oxidising agent and reducing agent.

7. Show by an example the oxidation and reduction reaction taking place simultaneously

8. Why decomposition reactions are called the opposite of combination reaction? Write equation for these reactions

9. What are the different types of decomposition reactions?

10. Identify the oxidising and the reducing agent in the following equation.

CuSO4 (aq) + Fe FeSO4 (aq) + Cu (s)

SHORT ANSWER QUESTIONS

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

i) Hydrogen + Chlorine Hydrogen chloride

ii) Magnesium oxide + Carbon Magnesium+Carbon monoxide.

iii) Sodium + Water Sodium hydroxide + Hydrogen

iv) Barium chloride + Aluminium sulphate Barium sulphate + Aluminium chloride

Ans. The balanced equations are written for the symbol equations and not for word

Equations.

i) H2 + Cl2 2HCl

ii) MgO + C Mg + CO

iii) 2Na + 2H2O 2NaOH + H2

iv) 3BaCl2 + Al2(SO4)3 3BaSO4 + 2AlCl3

2. Write the balanced equations with physical state symbols for the following reactions:

i) solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride

ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride (in water) and water.

Ans. The symbol equations in balanced form for the reactions are :

i) BaCl2 (aq) + Na2SO4 (aq) BaSO4(s) + 2NaCl (aq)

white ppt.

ii) NaOH(aq) + HCl(aq) NaCl(aq) +H2O(l)

3. On mixing the solutions of lead (II) nitrate and potassium iodide prepared in water

Write the chemical reaction involved in the balanced form

i) What is the colour of the precipitate? Name the precipitate.

Ans. i) Balanced chemical equation for the reaction is

Pb(NO3)2(aq)+2KI(aq) PbI2(s) + KNO3(aq)

Yellow ppt

ii) The precipitate is of lead iodide(PbI2) and is yellow in colour.

4.Identify the substance oxidized and substance reduced in the following reactions:

i) ZnO + C Zn + CO

ii) 2Na(s) + O2(g) 2Na2O(s)

iii) CuO (s) + H2(g) Cu(s) + H2 (g)

Ans. i) C is oxidized to CO and ZnO is reduced to Zn

ii) Na is oxidized to Na2O and O2 is reduced.

iii)H2 is oxidized to H2O and CuO is reduced to Cu.

5.What is a balanced chemical equation? Why should the chemical equation be balanced?

Ans. An equation in which the atoms of different elements on both sides of the equation are equal, is known as balanced equation. The equation should be balanced to fulfill the requirement of the law of conservation of mass.

6.What do you mean by exothermic and endothermic reactions? Give examples.

Ans. Exothermic reaction is a chemical reaction in which a certain amount of energy as heat is released. For example,

CH4(g) +2O2(g) CO2(g) + 2H2O(l) + Heat

Endothermic reaction is a chemical reaction in which a certain amount of energy as heat is absorbed. For example,

N2(g) + O2(g) 2NO(g) – heat

7.Why is respiration considered as exothermic reaction?

Ans. Respiration occurs in the cells and is accompanied by the combustion of glucose producing carbon dioxide and water with the liberation of energy (heat). The reaction is exothermic because heat energy is released.

8.Write the balanced equations for the following skeleton 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

Ans. a) 2HNO3 + Ca(OH)2 -------- Ca(NO3)2 + H2O

b)2 NaOH + H2SO4 ------ NaSO4 + 2H2O

c)NaCl + AgNO3 -------- AgCl + NaNO3

d)BaCl2 + H2SO4 ------ BaSO4 + 2 HCl

9.Why is decomposition reaction called opposite of combination reaction? Write equations for these reactions.

Ans. In a combination reaction, reactant molecules combine to form a new substance. In the decomposition reaction, reverse happens. Here, the reactant molecules break into new substances. For example,

H2(g) + Cl2(g) ------ 2HCl (g) (Combination reaction)

CaCO3(s) ------ CaO(s) + CO2 (g) (Decomposition reaction)

10.Write equations for each decomposition reaction where energy is supplied in the form of heat, light and electricity.

Ans. i) MgCO3 + heat---- MgO + CO2

ii) 2AgCl + light-------- 2Ag + Cl2

iii) 2NaCl + electricity------- 2Na + Cl2

11.What is the difference between displacement and double displacement reactions?

Ans. In a displacement reaction, one element takes the place of another in a compound. For example,

Fe(s) + CuSO4 (aq) ------- FeSO4 (aq) + Cu(s)

In a double displacement reaction, one component each of both the reacting molecules exchange to form the products. For example,

HCl (aq) + NaOH (aq) ----- NaCl (aq) + H2O (l)

12.What do you mean by precipitation reaction? Explain giving examples.

Ans. In a precipitation reaction, one of the products formed during the reaction does not go in solution and gets settled at the bottom of the container (beaker or test tube). It is known precipitate. For example,

AgNO3(aq) + NaCl (aq) -------- AgCl(s) + NaNO3 (aq)

(White ppt.)

BaCl2 (aq) + Na2SO4 (aq) --------- BaSO4 (s) + 2NaCl (aq)

White ppt

13.Which type of the reactions are represented by the following equations?

a) CaO + CO2 -------- CaCO3

b) Mg + CuSO4 -------- MgSO4 + Cu

c) CH4 + 2O2 --------CO2 + 2H2O + heat

d) NH4NO2 ------- N2 + 2H2O

Ans. a) Combination reaction

b)Displacement reaction

c)Combustion reaction

d) Decomposition reaction

14.What happens when :

CO2 (g) is bubbled through lime water (i) in small amount (iii) in excess?

Ans. i) Solution becomes milky due to the formation of calcium carbonate which is insoluble in water(i.e., ppt).

Ca(OH)2 (aq) + CO2(g)-------- CaCO3 (s) + H2O(l)

(Milky)

White ppt

ii) Milkiness disappears because calcium carbonate changes to calcium hydrogen carbonate which is soluble in water.

CaCO3 (s) + H2O (l)+ CO2¬(g) ------ Ca(HCO3)2 (aq)

(Soluble)

15.Which of the following statements about the reaction given below are incorrect?

2PbO(s) + C(s) -------- 2Pb(s) + CO2(g)

a)Lead is getting reduced

b)Carbon dioxide is getting oxidized

c)Carbon is getting oxidized

d)Lead oxide is getting reduced

i) a and b(ii) a and c(iii) a, b, and c(iv) all are incorrect

Ans. i) a and b are both incorrect

Pb is getting oxidized to PbO in the backward reaction.CO2 is getting reduced to C in the backward reaction.

16.Fe2O3 + 2Al ------- Al2O3 + 2Fe .

The above reaction is an example of :

a)combination reaction

b) double displacement reaction

c)decomposition reaction

d) displacement reaction

Ans . d) It is an example of displacement reaction.

17.What happens when dilute hydrochloric acid is added to iron filings. Tick the correct answer.

i. Hydrogen gas and iron chloride are produced

ii. Chlorine gas and iron hydroxide are produced

iii. No reaction takes place

iv. Iron salt and water are produced

Ans. a) Iron chloride and hydrogen gas are produced according to the reaction

Fe(s) + 2 HCl(dil.) --------- FeCl2(aq) + H2(g)

18.A solution of CuSO4 was kept in an iron pot. After a few days, the pot developed some holes in it. How will you account for this?

Ans. Iron lies above copper in the activity series. So, Fe is more reactive than Cu.Therefore, a chemical reaction has taken place between iron from iron pot and copper sulphate solution. We can also say that iron has displaced copper from the CuSO4 solution.

Fe(s) + CuSO4(aq) ---------- FeSO4 (aq) + Cu(s)

Since iron has taken part in the reaction, holes will appear in the iron pot after a few days.

19.A silver spoon is kept immersed in an aqueous copper sulphate solution. What change will take place?

Ans. No change will take place and the silver spoon will remain unaffected. Moreover blue colour of copper sulphate will also not fade. This is because of the reason that no chemical reaction takes place between silver and copper sulphate solution as silver is less reactive than Cu because silver is placed below copper in the activity series.

20.Why does copper not liberate hydrogen on reacting with dilute sulphuric acid?

Ans. copper is placed below hydrogen in the activity series. Therefore, it can not lose electrons to H+ ions of the acid to reduce into H 2 gas.

21.A, B and C are three elements which undergo chemical reaction according to following equations.

A2O3 + 2B ---------- B2O3 + 2A

3CSO4 + 2B -------- B2(SO4)3 + 3C

3CO + 2A -------- A2O + 3C

Answer the following questions.

a) which element is most reactive?

b) Which element is the least reactive?

Ans. a) The most reactive element is ‘B’ as it has displaced both ‘A’ and ‘C’ compounds

b) The least reactive element is ‘C’ as it has been replaced by both ‘A’ and ‘B’.

22.A solution of the substance ‘X’ is used for white washing.

a.Name the substance ‘X’ and write its formula

b.Write the reaction of the substance ‘X’ with water.

Ans. a) The substance ‘X’ is calcium oxide (also called quick lime)

a) It formula is CaO

CaO(s) + H2O(l) --------- Ca(OH)2 (s)

Calcium hydroxide

23.In the refining of silver, the recovery of silver from silver nitrate solution is displacement by copper metal. Write down the reaction involved.

Ans. 2AgNO3 (aq) + Cu (s) ---------- Cu(NO3)2 (aq) + 2 Ag(s).

BIOLOGY, EDUCATION

MANDALSIR

CHEMICAL REACTIONS AND EQUATIONS CLASS X

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