WBBSE Solutions For Class 10 Physical Science And Environment Chapter 3 Chemical Calculations

WBBSE Class 10 Physical Science Question Answer In English

Chapter 3 Chemical Calculations MCQs

Question 1. Which of the following contains the least number of molecules?

1. 1.12 LSO₂ at STP
2. 1 gm-mole SO₂
3. 32g SO₂
4. 4 x 1023 molecules of SO₂

Answer: 1. 1.12 L SO₂ at STP.

Question 2. Who put forward the law of conservation of mass?

1. Cannizzaro
2. Lavoisier
3. Dolton
4. Ge Lusaka

Answer: 2. Lavoisier.

Read And Learn More: WBBSE Solutions For Class 10 Physical Science And Environment

Question 3. No. of atoms present in 3.7g. mole of nitrogen is :

1. 4.45 x 1024
2. 6.023 x 1024
3. 1.204 x 1024
4. 3.023 × 1023

Answer: 1. 4.45 × 1024.

Question 4. The balanced equation for the chemical equation :

Ag₂ SO₄ + BaCl_{2 →} BaSO₄+ AgCl is:

1. Ag₂ SO₄ + BaCl₂ = BaSO₄ + AgCl
2. Ag₂ SO₂+ BaCl₂ = BaSO₄ + 2AgCl
3. Ag₂ SO₄ + 2BaCl₂= 2BaSO₄ + AgCl

Answer: 2. Ag₂ SO₂+ BaCl₂ = BaSO₄ + 2AgCl

Question 5. The balanced equation for the chemical equation :

FeCl₃ + SnCl_{2  →} FeCl₂ + Sn Cl₄ is :

1. Fecl₃ + 2 SnCl₂ = FeCl₂ + 2SnCl₄
2. 2FeCl₄ + SnCl₂ = 2FeCl₂+ SnCl₄
3. 3FeCl₃ + SnCl₂ = 3 FeCl₂ + SnCl₄

Answer: 2.  2FeCl₄ + SnCl₂ = 2FeCl₂+ SnCl₄

Question 6. NaOH + HCl = NaCl + H₂O; the type of reaction is :

1. Substitution reaction
2. Addition reaction
3. Neutralization reaction

Answer: 3. Neutralization.

Class 10 Physical Science Solution WBBSE

Question 7. Ammonium cyanate changes to urea on heating is an example of :

1. Decomposition reaction
2. Direct combination reaction
3. Rearrangement reaction

Answer: 3. Rearrangement reaction.

Question 8. The chemical equation provides :

1. Some information
2. All information
3. No information

Answer: 1. Some information.

Question 9. The balanced equation for the chemical equation

MnO₂ + HCl → MnCl₂ + Cl₂ + H₂O is:

1. MnO₂ + 2HCl = 2MnCl₂ + Cl₂ + H₂O
2. 2MnO₂ + HCI = 2MnCl₂ + Cl₂ +H₂O
3. MnO₂+3HCI = MnCl₂+ 3Cl₂ + 2H₂O
4. MnO₂ + 4HCI = MnCl₂+ Cl₂+2H₂O

Answer: 4. MnO₂ + 4HCI = MnCl₂+ Cl₂+2H₂O

Class 10 Physical Science Solution WBBSE

Question 10. N₂ + O₂ = 2NO – Q Cal; this reaction is :

1. Endothermic
2. Exothermic
3. Rearrangement
4. Decomposition

Answer: 1. Endothermic.

Question 11. Which of the following one takes part in a chemical reaction?

1. Electron
2. Proton
3. Iron
4. Positron

Answer: 1. Electron.

Question 12. NH₃ + HCI = NH₄Cl; it is a type of chemical reaction :

1. Substitution
2. Direct combination
3. Addition reaction
4. Rearrangement

Answer: 2. Direct combination.

Question 13. 27g of Al will react completely with how many grams of oxygen?

1. 8g.
2. 16g.
3. 32g.
4. 24g.

Answer: 4. 24g.

Question 14. The reaction in which two or more reactants combine directly forming molecules of new substances is called :

• Direct combination
• Neutralization reaction
• Addition reaction
• Decomposition

Answer: 1. Direct combination

Question 15. Calcium pyrophosphate is represented by the formula Ca₂P₂O₇. The molecular formula of ferric pyrophosphate is :

1. Fe2 (P₂O₇)⁴
2. Fe2 (P₂O₇)
3. Fe (P₂O₇)³
4. Fe 4 (P₂O₇)³

Answer: 4. Fe 4 (P₂O₇)³

Class 10 Physical Science Solution WBBSE

Question 16. The chemical formula of a particular compound represents :

1. The size of its molecule
2. The shape of its molecule
3. The total number of atoms in a molecule
4. The number of different types of atoms in a molecule

Answer: 4. The number of different types of atoms in a molecule.

Question 17. The formula which represents the simple ratio of atoms in a compound is called :

1. Empirical formula
2. Molecular formula
3. Rational formula
4. Structural formula

Answer: 1. Empirical formula.

Question 18. If 0.5 mole of BaCl₂ is mixed with 0-2 mol of Na₃PO⁴, the maximum number of mol of Ba₃ (PO₄)² that can be formed of:

1. 0.7
2. 0.5
3. 0.30
4. 0.10

Answer: 4. 0.10.

Question 19. 2.76 g. of silver carbonate on being strongly heated yields residue weighting:

1. 2.4 8g
2. 2.15g
3. 2.32g
4. 2.64g

Answer: 3. 2.32g.

Question 20. The reaction in which molecule or molecules of a compound break down into comparatively simpler molecules in the presence of heat or electricity is called :

1. Decomposition
2. Direct combination
3. Double composition
4. Neutralization reaction

Answer: 1. Decomposition.

Question 21. The balanced equation for the chemical equation :

2KCI0_{3 →} KCI +O₂

1. 2KCIO₃ = 2KCI + 3O₂
2. KCIO₂ = KCI + 2O₂
3. 4KCIO₃  = 2KCI + 2O₂

Answer: 1. 2KCIO₂ = 2KCI + 3O₂

Class 10 Physical Science Solution WBBSE

Question 22. Fe+ S = FeS; it is a type of chemical reaction :

1. Decomposition reaction
2. Displacement reaction
3. Combination reaction
4. Dis placement reaction

Answer: 3. Combination reaction.

Question 23. 1 amu = _________ g.

1. 1.6605 10^-24 g
2. 1.660059 × 10^-23 g
3. 1.66 x 10^-11 g
4. 1.65 x 10^-21 g

Answer: 1. 1.6605 10^-24 g

Question 24. 2SO₂ +O₂…. 2SO₃ ; What type of reaction is it?

1. Reversible type of reaction
2. Oxidation-reduction type of reaction
3. Redox type of reaction

Answer: 1. Reversible type of reaction.

Question 25. A + B² = A² + B is an example of what type of reaction?

1. Oxidation-reduction type of reaction
2. Reversible type of reaction
3. Redox type of reaction

Answer: 1. Oxidation – reduction type of reaction.

Question 26. CuO+H₂ = Cu + H₂O is an example of what type of reaction?

1. Redox type of reaction
2. Oxidation-reduction type of reaction
3. Reversible type of reaction

Answer: 1. Redox type of reaction.

Question 27. Ag NO₃ + NaCl = AgCl + NaN0₃ is an example of what type of reaction?

1. Double decomposition type of reaction
2. Direct combination type of reaction
3. Substitution type of reaction

Answer: 1. Double decomposition type of reaction.

Question 28. What is the percentage of water in blue vitriol?

1. 36.07 %
2. 36.77%
3. 49.07 %
4. 55.77%

Answer: 1. 36.07%.

Class 10 Physical Science WBBSE

Question 29. 49g H₂SO₄ = ________ mole.

1. 0.55 mol
2. 0.5 mol
3. 0.15 mol
4. 0.1 mol

Answer: 2. 0.5 mol.

Question 30. The weight of oxygen obtained on heating 24.5g KCIO₃ is :

1. 19.6 g
2. 29.6g
3. 9.6 g
4. 10.6g

Answer: 3. 9.6g.

Question 31. How much hydrogen is produced when steam is passed over 28kg of red hot iron?

1. 1.33 kg
2. 2.33 kg
3. 3.33 kg
4. 0.33 kg

Answer: 1. 1.33 kg.

Question 32. How much CaO is obtained from 10 kg? CaCO₃ ?

1. 5.6 kg.
2. 6.6 kg
3. 7.6 kg
4. 3.6 kg

Answer: 1. 5.6 kg.

Question 33. NH₄CNO (R) CO (NH₂)₂; What type of chemical reaction is it?

1. Rearrangement reaction
2. Substitution reaction
3. Addition reaction

Answer: 1. Rearrangement reaction.

Question 34. In a balanced chemical equation, what sign needs to be placed instead of the arrow sign?

1. Greater than sign
2. Smaller than sign
3. Equal to sign

Answer: 3. Equal to sign.

Question 35. Calcium carbonate contains what percentage of calcium?

1. 40%
2. 60%
3. 50%
4. 75%

Answer: 1. 40%.

Class 10 Physical Science WBBSE

Question 36. Zn + NaOH → H₂ + ________.

1. Na₂ ZnO₄
2. Na₂ ZnO₂
3. Na₂ ZnO₂
4. NaZn 0₃

Answer: 2. Na₂ ZnO₂

Question 37. CO + Cl₂ = COCl₂What type of reaction is it?

1. Rearrangement
2. Substitution
3. Addition

Answer: 3. addition.

Question 38. 2Mg + O₂ = 2MgO; What type of chemical reaction is it?

1. Neutralization reaction
2. Substitution reaction
3. Direct combination type of chemical reaction

Answer: 3. Direct combination type of chemical reaction.

Question 39. Molecular formula = _______ × empirical formula.

1. n
2. m
3. t
4. y

Answer: 1. n

Question 40. Atomic mass = Equivalent weight x _________.

1. Volume
2. Mass
3. Valency
4. Velocity

Answer: 3. Valency.

Chapter 3 Chemical Calculations Very Short Answer Type Questions

Question 1. State a limitation of a chemical equation.
Answer: A reaction whether exo-thermic or endo-thermic is not known from a chemical equation.

Question 2. Give an example of an addition reaction.
Answer: Carbon monoxide reacts with chlorine to form carbonyl chloride (COCL₂) is an example of an addition reaction.

Question 3. What is the molecular weight of ammonium phosphate?
Answer: 149.

Question 4. How much CaCO₃ will react with dil HCI to produce 22g CO₂?
Answer: 50g.

Question 5. How much potassium chlorate is to be heated to produce as much oxygen as required to burn 6g, of carbon completely?
Answer: 40.83g

WB Class 10 Physical Science Question Answer

Question 6. Give an example of a thermal decomposition type of reaction.
Answer: Calcium carbonate on heating decomposes into calcium oxide and carbon dioxide is an example of a thermal decomposition type of reaction.

Question 7. What is the mole number of a substance?
Answer: \(\text { Mole number of a substance }=\frac{\text { Wt. of the substance in gram }}{\text { Gram-molecular weight of the substance }}\)

Question 8. How many grams of limestone are needed to get 48g? CO₂?
Answer: 109.09g.

Question 9. How much quantity of silver chloride (AgCI) can be obtained from 1.0g silver nitrate?
Answer: 0.0844g.

Question 10. Balance the following reaction: Fe + H₂O (R) Fe₃O₄ + H₂
Answer: Balanced equation of \(\)

Question 11. Give an example of a substitution reaction.
Answer: Chlorine reacts with methane (CH₄ ) to form successively CH₃CI, CH₂Cl₂, CHCI₃ and ultimately CCI₄ in the presence of sunlight is an example of a substitution reaction.

\(\mathrm{CH}_4+\mathrm{Cl}_2 \stackrel{\text { Sunlight }}{\longrightarrow} \mathrm{CH}_3 \mathrm{Cl}+\mathrm{HCl}\) ⇒ \(\mathrm{CH}_3 \mathrm{Cl}+\mathrm{Cl}_2 \stackrel{\text { Sunlight }}{\longrightarrow} \mathrm{CH}_2 \mathrm{Cl}_2+\mathrm{HCl}\)

\(\mathrm{CH}_2 \mathrm{Cl}_2+\mathrm{Cl}_2 \stackrel{\text { Sunlight }}{\longrightarrow} \mathrm{CHCl}_3+\mathrm{HCl}\) ⇒ \(\mathrm{CH}_2 \mathrm{Cl}_3+\mathrm{Cl}_2 \stackrel{\text { Sunlight }}{\longrightarrow} \mathrm{CCl}_4+\mathrm{HCl}\)

Question 12. Give an example of a polymerization type of chemical reaction.
Answer: \(\mathrm{n}\left(\mathrm{CH}_2=\mathrm{CH}_2\right) \rightarrow\left(-\mathrm{CH}_2-\mathrm{CH}_2-\right) \mathrm{n}\)

Question 13. Give an example of is isomerization type of chemical reaction.
Answer: \(\mathrm{NH}_4 \mathrm{CNO} \rightarrow \mathrm{NH}_2 \mathrm{CONH}_2 \text { (Urea) }\)

Question 14. Write the relation between molecular weight and vapor density.
Answer: Molecular = 2 x vapor density.

WB Class 10 Physical Science Question Answer

Question 15. What is the atomic mass unit?
Answer: It is the quantity of mass equal to [latexl\frac{1}{12}[/latex]th of the mass of a carbon atom (12C)

l amu 1.6605 × 10^-24 g.

Question 16. What is solubility?
Answer: The amount of solute in grams that can be dissolved in 100 grams of a solvent to form a saturated solution at a definite temperature is called solubility.

Question 17. What is a gram’s atomic mass?
Answer: It is the atomic mass of an element expressed in grams.

Question 18. What is normality (N)?
Answer: It is the number of gram equivalents of solute dissolved per liter of a solution.

Question 19. Give an example of the catalytic type of chemical reaction.
Answer: \(\mathrm{N}_2+3 \mathrm{H}_2 \mathrm{Fe} \rightleftharpoons \mathrm{MO} 2 \mathrm{NH}_3\)

Question 20. What is atomic mass?
Answer: It is the average relative mass of an atom of an element as compared to the mass of a carbon atom (12C) taken as 12.

WB Class 10 Physical Science Question Answer Chapter 3 Chemical Calculations Fill In The Blanks

Question 1. KCIO₃ → KCI + _________.
Answer: O₂.

Question 2. The law of conservation of mass is shown to be ________ equation.
Answer: Valid.

Question 3. Fe + CuSO₄= Cu + FeSO₄; it is a _________reaction.
Answer: substitution.

Question 4. CuO + H₂ = Cu + H₂O; it is an ________ reaction.
Answer: oxidation-reduction.

Question 5. There are many
Answer: limitations.

Question 6. Zn + NaOH → H₂ + __________.
Answer: Na₂ ZnO₂.

Question 7. mg + CO₂→  _______ + C
Answer: MgO.

Question 8. 49g H₂SO₄ = ________ mole.
Answer: 0.5 mol.

Question 9. Calcium carbonate contains _______ % calcium.
Answer: 40.

WB Class 10 Physical Science Question Answer

Question 10. Molecular formula = n x ________.
Answer: Empirical formula.

Question 11. A symbolic chemical reaction may be called a chemical equation only when it is balanced by putting the least numerals as formulae in it.
Answer: Coefficients.

Question 12. CO + Cl₂ = COCl₂ : This is a ________
Answer: Reaction.

Question 13. Chemical reaction means a permanent ________ between the atoms or radicals of the combining substances.
Answer: Rearrangement.

Question 14. In a balanced chemical equation _______ sign is placed instead of the arrow sign.
Answer: Equal.

Question 15. MnO₂ + HCl → MnCl₂ + _______ + H₂O.
Answer: Cl₂

Question 16. From a chemical equation, the time required for the completion of the reaction is not ________.
Answer: Known.

Question 17. From a chemical equation, the time required for the _______ of the reaction is not known.
Answer: Completion.

Question 18. If the reactants and products are gaseous then at the same temperature and pressure the ratio in ______ is known.
Answer: Volumes.

Question 19. 12g carbon combines with 32g oxygen producing ________ liter of carbon dioxide at NTP.
Answer: 22.4

Question 20. The empirical formula is the formula of a compound that gives the ______ whole number ratio of the atoms of various elements present in one molecule of the compound.
Answer: Simple.

Question 21. The molecular formula is the formula of a compound that gives the _______ number of the atoms of various elements present in one molecule of the compound.
Answer: Actual.

Question 22. The percentage of an element in a chemical compound is the number of parts by weight of its present _______ in parts by weight of the compound.
Answer: 100.

Question 23. The weight of oxygen obtained on heating 24.5g KCIO₃ is
Answer: 9.6 g.

WBBSE Solutions Guide Class 10

Question 24. Decomposition or analysis is a process where a compound ________ into a simpler substance.
Answer: Splits.

Question 25. The empirical formula of a compound is HO and its molecular weight is 34. Therefore its molecular formula is __________.
Answer: H₂O₂.

Question 26. A chemical equation is one where the formulae of the ________ of a chemical reaction are connected with plus (+) signs in one set and those of the products are similarly connected in another set.
Answer: Reactants.

Question 27. In the double decomposition process, two different compounds, react chemically to produce two new compounds by mutual ________ radicals.
Answer: Interchange.

Question 28. NaOH + HCl = NaCl + H₂O₂; the type of reaction is
Answer: Neutralisation reaction.

Question 29. 27g of Al will react completely with _________ g of oxygen?
Answer: 24g.

Question 30. _______ takes part in a chemical reaction.
Answer: Electron.

Question 31. N₂ + O₂ 2NO – Q cal; this reaction is ________.
Answer: Endothermic.

Question 32. Mag + H₂SO₄ = _______ + H₂.
Answer: MgSO₄.

WBBSE Solutions Guide Class 10 Chapter 3 Chemical Calculations Short Answer Type Questions

Question 1. What are the limitations of chemical formulas?
Answer:

Limitations of chemical formula

1. If fails to convey whether the elements in a molecule are present in the form of atoms or ions.
2. It does not tell anything about the binding force that holds atoms in a molecule together.
3. It does not tell us about the arrangement of various atoms with respect to one another within the molecule.

Question 2. What is the limiting reactant?
Answer:

Limiting reactant: The reactant that is completely used and determines the amount of product formed is known as limiting reactant.

Question 3. Define reactants in a chemical reaction.
Answer:

Reactants:

The substances with which a chemical reaction is started are called the reactants.

Question 4. What is the percent yield?
Answer:

Percent yield: Percent yield which is the ratio of the actual yield to the theoretical yield multiplied by 100.

Question 5. What is meant by decomposition reaction?
Answer:

Decomposition: When a molecule of a substance is broken down or decomposed in a chemical reaction to form two (or more) new substances in the presence of heat or electricity. It is called decomposition.

Example:

Calcium carbonate on heating decomposes into calcium oxide and carbon dioxide. \(\mathrm{CaCO}_3 \stackrel{\text { heat }}{\longrightarrow} \mathrm{CaO}+\mathrm{CO}_2\)

Electricity is passed through acidulated water hydrogen and oxygen are produced due to the decomposition of water. 2H₂O = 2H₂+O₂

Class 10 Physical Science Solution WBBSE

Question 6. What is meant by addition reaction?
Answer:

Addition reaction: The reaction in which one reactant molecule directly combines with other molecules of reactant forming new molecules of the product without leaving any part of the molecules of reactants is known as an addition reaction.

Example:

 

 

 

 

 

 

Question 7. What is the structural formula?
Answer:

Structural formula: A formula that gives the actual arrangement of the different atoms in the molecule or shows how the different atoms in the molecule are linked together is called a structural or a graphic formula of the compound.

Question 8. What do you mean by a chemical reaction?
Answer:

Chemical reaction: Any chemical change in matter that involves the transformation of matter into a new substance or new substance is termed a chemical reaction.

Question 9. What are mass volume relationship problems?
Answer:

Mass volume relationship problems: In this type of problem. mass or volume of one of the reactants or products is calculated from the volume or mass of other substances.

Question 10. Define products in a chemical reaction.
Answer:

Products: The substances formed as the result of the chemical reaction are called the products.

Question 11. What is the percentage of an element?
Answer:

Percentage of an element: The percentage of an element in a chemical compound is the number of parts by weight of it present in 100 parts by weight of the compound.

Class 10 Physical Science Solution WBBSE

Question 12. Define double decomposition reaction.
Answer:

The reaction in which the constituent of the molecules of reactants change their position and form molecules of new substances is called.
Double decomposition

Example: AgNO₃ + NaCl = AgCl + NaNO₃

Question 13. What is the molecular formula?
Answer:

Molecular formula: It is the formula of a compound that gives the actual number of atoms of various elements present in one molecule of the compound.

Question 14. Define oxidation-reduction type reaction.
Answer:

Oxidation-reduction reaction: The chemical reaction in which a chemical species loses electrons (s) is an oxidation reaction and the reaction in which a chemical species gains electrons (s) is called an oxidation-reduction reaction.

Question 15. What is the empirical formula?
Answer:

Empirical formula: It is the formula of a compound that gives the simple whole number ratio of the atoms of various elements in one molecule of the compound.

Question 16. What are mass-mass relationship problems?
Answer:

Moss-moss relationship problems: In this type of problem, the moss of one of the reactant products is to be calculated if that of the other reactant products is given.

Question 17. What are volume-volume relationship problems?
Answer:

Volume-volume relationship problems: In this type of problem, the volume of one of the reactants or products is to be calculated from the volume of some other reactant and product.

Question 18. What is a theoretical yield?
Answer:

Theoretical yield: The theoretical yield of a product is the maximum yield obtainable as calculated on the basis of the amount of limiting reactant used.

Class 10 Physical Science Solution WBBSE

Question 19. Define direct combination reaction.
Answer:

Direct combination: The reaction in which two or more reactions combine directly forming molecules of a new substance is called direct combination.

Example:

Burning magnesium wire reacts directly with oxygen forming new molecules of magnesium oxide. 2Mg +O₂ = 2MgO

Question 20. What is meant by the acid-base reaction on neutralization reaction?
Answer:

Acid-base reaction or neutralization reaction: In this reaction, an acid reacts with a base forming salt and water. An equivalent amount of an acid neutralizes an equivalent amount of a base. This is known as a neutralization reaction.

Example:

\(\underset{\text { (acid) }}{\mathrm{HCl}}+\underset{\text { base }}{\mathrm{NaOH}}=\underset{\text { (salt) }}{\mathrm{NaCl}}+\underset{\text { (water) }}{\mathrm{H}_2 \mathrm{O}}\)

Question 21. Define Chemical equation.
Answer:

Chemical equation: A brief representation of a chemical reaction by using symbols of atoms of the elements and formulae of molecules of reactants and products maintaining the balance in between is known as a chemical equation.

It reveals both the qualitative and quantitative aspects of a chemical change.

Question 22. Define substitution reaction.
Answer:

Substitution reaction: It is a chemical reaction in which one atom or molecule of a compound is replaced by another atom or molecule of another substance.

Example: Zn + CuSO₄ = ZnSO₄ + Cu.

Question 23. What is meant by rearrangement reaction?
Answer:

Rearrangement reaction: A reaction where a compound changes by internal arrangement of its atoms into another substance with different properties but having the same composition is known as a rearrangement reaction.

Example:

Ammonium cyanate changes to urea on heating.

 

 

 

 

 

Question 24. Why is a chemical equation called a balanced equation?
Answer:

A chemical equation must be balanced because, from the law of conservation of mass, the total reacting mass of the reactants must be equal to the total mass of the products.

Question 25. What is meant by ‘The vapor density of SO₂ is 32′?
Answer:

The vapor density of SO₂ is 32 under the same conditions of temperature and pressure, a certain volume of SO₂ is 32 times heavier than the same volume of hydrogen.

Class 10 Physical Science Solution WBBSE

Question 26. Write the significance of a chemical equation.
Answer:

The chemical equation signifies

1. The names of the reactants and the products our products formed as a result of chemical reactions.
2. The relative number of atoms and molecules of the reactants taking part and also the product in a chemical reaction.
3. Weight-weight, weight-volume, and volume-volume relations amongst the reactants and products are obtained from a chemical equation.

Question 27. What is the substitution reaction? Write an example.
Answer:

Substitution reaction: An atom or group in a molecule is replaced by another atom or group.

Example: CuSO₄ Fe = FeSO₄ + Cu.

Question 28. Write the relation between normal density and vapor density.
Answer:

At STP, normal density vapor density x 0.08.

Question 29. State the law of conservation of mass in chemical reactions.
Answer:

Law of conservation of mass in chemical reaction. In a chemical change, the total mass of the reaction is equal to the total mass of the products. Matter can neither be created nor destroyed.

Question 30. Short Note-Double decomposition.
Answer:

Double decomposition: Two compounds exchange their cations and anions to produce new compounds.

PbSO₄ + Na₂CO₄ = PbCO₃ + Na₂SO₄

Question 31. What are the classification of problems based upon the chemical reactions?
Answer:

The classifications of the problem based on the chemical reactions

• Mass-Mass relationship problems
• Mass-volume relationship problems
• Volume-volume relationship problems

Class 10 Physical Science WBBSE

Question 32. Short Note-Problems based on chemical equation.
Answer:

Problems based on chemical equation: The problems based upon chemical equation may be classified as :

• Mass-mass relationship problems – In this type of problem, the mass of one of the reactant products is to be calculated if that of the outer reactant products is given.
• Mass-volume relationship problems – In this type of problem, the mass or volume of one of the reactants or products is calculated from the volume or mass of other substances.
• Volume-volume relationship problems. In this type of problem, the volume of one of the reactants or products is to be calculated from the volume of some other reactant or product.

Question 33. Write the relation between molecular weight and vapor density.
Answer:

Molecular weight = 2 x Vapour density.

Question 34. Define-chemical equation.
Answer:

Chemical equation: Balancing the number of atoms of reactants and products, the representation of a chemical reaction in short by symbol and formula is called a chemical equation.

Question 35. Write the partial elimination of the limitations
Answer:

• (s), (i) or (g) may be written respectively for solid, liquid, and gaseous reactants and products.
• For exothermic reaction (4H) and for endothermic reaction (+ 4H) may be written.
• Temperature pressure and catalyst may be written on the arrow of the arrowheel equation.

\(\begin{aligned}
& \mathrm{CaCO}_3(\mathrm{~S}) \stackrel{\text { heat }}{\longrightarrow} \mathrm{CaO}(\mathrm{s})+\mathrm{CO}_2(\mathrm{~g}) \uparrow \\
& \begin{aligned}
\mathrm{C}(\mathrm{s})+\mathrm{O}_2(\mathrm{~g}) \rightarrow & \mathrm{CO}_2(\mathrm{~g}) \uparrow \mathrm{CO}_2(\mathrm{~g}) \uparrow+(4 \mathrm{H}) \\
& +(4 \mathrm{H})
\end{aligned}
\end{aligned}\)

Question 36. Short Note-Addition reaction.
Answer:

Addition reaction: When two molecules combine chemically with the detachment of any part, the reaction is called an addition reaction, Generally unsaturated compounds are given this reaction.

CO + Cl₂ = COCl₂

Question 37. Write an example of a balanced equation.
Answer:

An example of a balance equation: CaCO₃ + 2HCI = CO₂ + CaCl₂ + H₂O

Class 10 Physical Science WBBSE

Question 38. Write the limitations of a chemical equation.
Answer:

The limitations of the chemical equation :

• The physical states of the reactants and products
• The reaction condition (i.e. temperature, pressure, and catalyst if required)
• Whether the reaction is exo thermic or endo thermic in nature.
• The concentration of the reactants

Question 39. \(\text { Prove, vapour density }=\frac{\text { Molecular weight of gas }}{\text { molecular weight of hydrogen }}\)
Answer:

\(\begin{aligned}
\text { Vapour density of gas (D) } & =\frac{\mathrm{n} \text { molecules of gas }}{\mathrm{n} \text { molecules of hydrogen }} \\
& =\frac{\text { weight of } 1 \text { molecule of gas }}{\text { weight of } 1 \text { molecules of hydrogen }} \\
& =\frac{\text { molecular weight of mass }}{\text { molecular weight of hydrogen }}
\end{aligned}\)

 

Question 40. Short Note Direct combination reaction.
Answer:

Direct combination reaction: The direct combination reaction takes place as soon as the reactants come into indirect contact. Sometimes heat, light, pressure, or catalyst is necessary to start the reaction.

Example: The reaction between Mg and O₂ starts with the application of heat.

2Mg +O₂= 2MgO

Question 41. Short Note-Decomposition reaction.
Answer:

Decomposition reaction: By this reaction, a compound is changed to different substances. This reaction is conducted by heat or electricity CaCO₃ on heating decomposed calcium oxide (CaO) and carbon dioxide (CaO) and carbon dioxide (CaO) and carbon dioxide (CO₂)

CaCO₃ = CaO + CO₂

Acidified water on electrolysis is decomposed to form H2 and O₂.

2H₂O=2H₂ ↑ +O₂↑

Question 42. State Avogadro’s law’
Answer:

Avogadro’s law: ‘Under the same conditions of temperature pressure, equal volumes of all gases contain the same number of molecules.

Class 10 Physical Science WBBSE Chapter 3 Chemical Calculations Broad Answer Type Questions

Question 1. What steps should be followed to solve a problem based on the chemical equation by the weight-weight method?
Answer:

The following steps are followed :

• First, write down the complete balanced chemical equation.
• The molecular weight of the reactants and products is to be calculated from their respective formulae by adding the atomic weights of the concerned elements.
• The unknown weight of the substance asked for in the question is to be calculated from the calculated weight in the equations
• The same units are to be used for all quantities.

Question 2. What is the information available from the formula CaCO₃?
Answer:

The formula CaCO₃ conveys the following information :

• It stands for calcium carbonate.
• It tells that calcium carbonate is composed of calcium, carbon, and oxygen elements.
• It represents a molecule of calcium carbonate.
• It represents that a molecule of calcium carbonate is made up of one atom each of calcium and carbon and three atoms of oxygen.
• It stands for 100 parts by weight of calcium carbonate i.e. its molecular weight and signifies that the ratio of calcium, carbon, and oxygen by weight in it is 40:12:48.

Question 3. What is meant by the balancing of a chemical equation? Why it is necessary?
Answer:

Balancing of a chemical equation: It means making both sides of the equation equal with respect to the kind and number of the atoms of the elements involved.

Balancing of a chemical equation is necessary: Due to the conservation of mass and indestructibility of matter, no atoms can be created or destroyed in a chemical reaction Hence, The same kind of atoms in the same numbers must be present on both sides of the chemical equation.

Question 4. Write the following as balanced equations.

Cu+HNO₃ → Cu (N0₃) + O₂

Pb (N0₃)₂ → PbO + NO₂ + O₂

Al + NaOH + H₂O → NaAlO₂ + H₂

CuO + NH₃ → Cu + N₂ + H₂O

Answer:

Balanced equations are:

3Cu + 8HNO₃ = 3Cu (NO₃)₂  + 2NO – 4H₂O

2Pb (NO₃)₂  = 2pb0+ 4NO₂ +O₂

2Al + 2NaOH + 2H₂O = 2NaAIO₂ + 3H₂

2NH₃ +3CuO = 3Cu + 2n₂ + 3H₂0

Question 5. What are the limitations of a chemical equation?
Answer:

Limitation of a chemical equation :

Under what conditions a chemical reaction occurs i.e. pressure, temperature, catalyst are not-known.

• A reaction whether exothermic or endothermic is not known from a chemical equation.
• The chemical equations cannot provide information about the completion of the reaction or the attainment of equilibrium.
• A chemical equation does not give any idea about the reversibility of the reaction.
• From the chemical equation, the time required for the completion of the equation is not known.
• A reaction whether slow or fast is not known from the equation.
• The equation does not provide information regarding the nature of the reactants and products viz. solid, liquid, or gas.

Question 6. Balance the equation KCI0₃ → KCI + O₂ by trial and error method.
Answer:

KCI0₃ KCI + O₂: It is seen that the number of atoms of oxygen on the left-hand side is 3 whereas in the right-hand side it is 2. To equalize the number of atoms of oxygen on both sides it requires to multiply KCIO₃ by 2 and oxygen by 3.

2KCIO₃ → KCI +30₂ SO as to balance this equation if KCI is multiplied by then the equation is proper balance the equation if KCI is multiplied by 2 then the equation is proper. balanced.

2KCIO₃ = 2KCI + 30₂

Question 7. What information is obtained from the chemical equations?
Answer:

A chemical equation gives the following information:

1. Qualitative informations:

• From the chemical equation, the naming of elements and compounds taking part in the reaction and also the products are known.
• From the chemical equation, the symbols and the formulae of the reactants and products are also known.

2. Quantitative information:

• A number of atoms or molecules of the reactants and products involved in the reaction are known.
• How many parts of elements and compounds take part in the reaction and production is also known.
• If the reactants and products are all gaseous then at the same temperature and pressure. The ratio in volumes is known.

Question 8. Explain the method of balancing a chemical equation by trial and error method.
Answer:

Balancing of a chemical equation by trial and error method :

• In the method, the proper numbers are put before reactants and products so that the number of atoms on both sides is equal.
• In doing so, we must be cautious to see that all the reactants and products exist as molecules and not as atoms as the free existence of atomic is not possible.

Class 10 Physical Science WBBSE

Question 9. What is the method of writing chemical equations?
Answer:

Method of writing chemical equation :

Initially, the symbols of atoms of elements and formulae of molecules of reactants and products are written.

• Symbols and formulae of the reactants are written on the left side and those for products are on the right side. An arrow (→) is placed between reactants and products. For more than one reactants and product a plus sign (+) is to be given between the reactants and also between the products.
• The number of atoms of the reactants on the left-hand side must be equal to the number of atoms of the products on the right-hand side so as to maintain the law of conservation of mass. To equalize both sides, proper multiplication is required so that the number of atoms on both sides are same.
• Now the equation is expressed by replacing the arrow sign with a sign of equal (=).

Question 10. What information is obtained from the equation: 3H₂ + N₂ = 2NH₂
Answer:

The following information is obtained from the equation: 3H₂+N₂ = 2NH₂

Qualitative information: The reactants are hydrogen and nitrogen, and ammonia is the product.

Quantitative information :

• Three molecules of hydrogen combine with one molecule of nitrogen to produce two molecules of ammonia.
• Three volumes of hydrogen and one volume of nitrogen combine to produce two volumes of ammonia at the same temperature and pressure and their ratio is 3:1:2.
• Three moles of hydro and one mole of nitrogen combine chemically to produce two moles of ammonia.

Question 11. What information is obtained from the equation? C + O₂ = CO₂
Answer:

The following information is obtained from an equation: C + O₂= CO₂

Qualitative informations :

• From the above equation, it is known that carbon combines with oxygen producing carbon dioxide.
• Their respective symbols and formulas are also known

Quantitative information:

• One carbon atom combines with one oxygen molecule producing one carbon dioxide molecule.
• Hence the total number of atoms on the left-hand side is (1+2) = 3 and the number of atoms on the right-hand side is also 3.
• One gram-atom carbon reacts with one gram-molecule of oxygen giving rise to one gram-molecule of carbon dioxide.
• 12g carbon combines with 32g oxygen yielding 44g carbon dioxide.
• Hence, the total mass on the left-hand side (12+32) g = 44g is equal to the total mass on the right-hand side 44g. It proves the law of conservation of mass.
• Again 12g carbon combines with 32g oxygen producing 22.4 litre of carbon dioxide at STP.

Question 12. How many grams of oxygen evolve when 122.5g potassium chlorate is heated? (Given K = 39, CI = 35.5 0 = 16)
Answer:

The balanced equation is : \(\begin{array}{ll}
2 \mathrm{KClO}= & 2 \mathrm{KCl}+3 \mathrm{O}_2 \\
2(39+35.5+3 \times 161 \mathrm{~g} & 3[2 \times 16] \mathrm{g} \\
=245 \mathrm{~g} & =96 \mathrm{~g}
\end{array}\)

By heating 245g KCIO₃ 96g O₂ is obtained

∴ By heating 122.5g KCIO₃ \(\frac{96 \times 122.5}{245} \mathrm{~g}\) is obtained.

Physics Class 10 WBBSE

Question 13. 2.6g zinc is treated with excess dil H₂SO₄ How many grams of oxygen combine with the evolved hydrogen?
Answer:

The balanced equation for the production of hydrogen is:

\(\underset{65 \mathrm{~g}}{\mathrm{Zn}}+\mathrm{H}_2 \mathrm{SO}_4=\mathrm{ZnSO}_4+\underset{(2 \times 1) \mathrm{g}=2 \mathrm{~g}}{\mathrm{H}_2}\)

So, 65g of Zinc produces 2g of hydrogen

∴ 2-6 Zinc produces \(\frac{2 \times 2.6}{65} \mathrm{~g}=0.089\) hydrogen

Now, the reaction where hydrogen and oxygen combine is: 2H₂ + O₂ = 2H₂O

So, 4g hydrogen combined with 32g oxygen

0.08g hydrogen combined with \(\frac{32 \times 0.08}{4} \mathrm{~g}=0.64 \mathrm{~g}\)

Question 14. What is the observed loss in weight of 5g? calcium carbonate when it undergoes thermal decomposition?
Answer:

The balanced equation is : \(\begin{aligned}
& \mathrm{CaCO}_3=\mathrm{CaO}+\mathrm{CO}_2 \\
& (40+12+16 \times 3) \mathrm{g}(12+16 \times 2) \mathrm{g} \\
& =100 \mathrm{~g} \quad=44 \mathrm{~g} \\
&
\end{aligned}\)

Loss in weight in the weight of CO₂ that escapes 100g CaCO₃ produces 44g CO₂

∴ 5g CaCO₃ produces \(\frac{44 \times 5}{100} \mathrm{~g}=2.2 \mathrm{gCO}_2\)

Question 15. What is the percentage of ammonia in that quantity of ammonium chloride that can produce 5g? ammonia?
Answer:

The balanced equation is :

\(\begin{aligned}
& 2 \mathrm{NH}_4 \mathrm{Cl}+\mathrm{CaO}=2 \mathrm{NH}_3+\mathrm{CaCl}_2+\mathrm{H}_2 \mathrm{O} \\
& 2[14+1 \times 4+35.5)_{\mathrm{g}} 2[14+1 \times 3]_{\mathrm{g}} \\
& =107 \mathrm{~g}
\end{aligned}\)

So, 34g ammonia is obtained from 107g NH₂CI.

Question 16. What weight of potassium chlorate of 96% purity will yield 4.8g oxygen on complete thermal decomposition? (Given, K = 39, CI = 35.5, O = 16)
Answer:

The balance equation is: 2KCIO₃ (245g) = 2KCI + 3O₂(96g)

∴ 96g oxygen is obtained from 245g KCIO₂ of 100% purity.

∴ 4.8g oxygen is obtained from \(\frac{245 \times 4.8}{96} \mathrm{~g}\)

Let x gram of 96% purity contain 12.25g KCIO₃ of 100% parity

∴ \(\frac{96}{100} \times 12.56 \text { or, } x=\frac{12.25 \times 100}{96}=12.76 \text { (approx) }\)

So, the required quantity of KCIO₃ = 12.76g

Physics Class 10 WBBSE

Question 17. On strong heating, limestone decomposes into quicklime and carbon dioxide. How much quantity of limestone will produced on complete decomposition, 30g of quicklime by the above reaction?
Answer:

The balanced equation is: \(\begin{array}{ll}
\mathrm{CaCO}_3=\mathrm{CaO}+\mathrm{CO}_2 & \\
(40+12+3 \times 16) \mathrm{g} & {[40+16] \mathrm{g}} \\
=100 \mathrm{~g} & =56
\end{array}\)

So 56g, CaO is obtained by the complete decomposition of 100g CaCO₃

∴ 30g CaO is obtained by the complete decomposition of \(\frac{100 \times 30}{56} \mathrm{~g} \mathrm{CaCO}_3=53.6 \mathrm{~g} \mathrm{CaCO}_3\)

Thus 53.6g of limestone will have to be decomposed.

Question 18. How many grams of magnesium metal will give 1.2g hydrogen in a complete reaction with dilute H₂SO₄ (Mg= 24, H = 1) The balanced equation is:
Answer:

\(\begin{aligned}
\mathrm{Mg}+\mathrm{H}_2 \mathrm{SO}_4= & \mathrm{Mg} \mathrm{SO}_4+\mathrm{H}_2 \\
24 \mathrm{~g} & (1 \times 2) \mathrm{g}=2 \mathrm{~g}
\end{aligned}\)

So 2g H₂ is obtained from 24g Mg

∴ 1.2g H₂ is obtained from \(\frac{24 \times 1.2}{2} \mathrm{~g} \mathrm{Mg}=14.4 \mathrm{gMg} .\)

So, 14.4g will be required

Question 19. Calculate the number of moles in 1.5 gm of ammonia.
Answer:

We know, number of mole = \(\frac{\text { Mass given }}{\text { gram molecular mass }}\)

\(\begin{aligned}
& =\frac{1.5}{1.7} \\
& =0.88
\end{aligned}\)

Question 20. The vapor density of a gas is 40. Calculate the volume of 20 gm of this gas at 27°C and 950 mm pressure.
Answer:

The molecular weight of the gas = 2 x vapor density

= 2 × 40 = 80

The volume of 80 gm of gas at S.T.P. is 22.4 Lit

The volume of 10 gm of gas at S.T.P.

\(=\frac{22.4 \times 10}{80}=2.8 \mathrm{Lit}\)

Let the volume of this 2.8 liter of gas at 27°C and 950 mm pressure be V Litre

\(\frac{\mathrm{V} \times 950}{273+27}=\frac{2.8 \times 760}{273}\)  ⇒V = 7.79 Litre

Hence the volume of the gas at 27°C and 950 pressure is 4.9 Litre.