Chemical Reactions and Equations Class 10 — Competency Based Questions

20 Questions | 56 Marks

A newly married couple noticed that the iron gate of their new house developed a reddish-brown coating after a few weeks of monsoon. They were concerned about the longevity of the gate.(a) Identify the process occurring on the iron gate. [1 mark](b) Write the chemical equation for this process. [1 mark](c) Name one method to prevent this process. [1 mark](d) The couple decided to paint the gate. Explain how painting prevents the process. 2marks

A student observed that during an experiment, a beaker containing a reaction mixture became hot.(a) What type of chemical reaction has occurred? [1 mark](b) Name the process of respiration in humans. Is it an exothermic or endothermic process? Justify. [2 marks](c) Give another example of this type of reaction other than burning of natural gas. 1mark

In Activity 1.2, when dilute hydrochloric acid is added to zinc granules, hydrogen gas is evolved.(a) Write the balanced chemical equation for this reaction. [1 mark](b) Identify the type of reaction. [1 mark](c) What observation would you make if this reaction were carried out in a test tube? [1 mark](d) If instead of zinc, copper is added to dilute hydrochloric acid, what will be the observation and why? 2marks

Read the following passage and answer the questions that follow:"Photosynthesis is a process by which green plants use sunlight, water and carbon dioxide to create their own food (glucose) and release oxygen. This process is vital for life on Earth."(a) Write the balanced chemical equation for photosynthesis. [2 marks](b) Is photosynthesis an exothermic or endothermic process? Justify your answer. [2 marks](c) Identify the type of reaction described in the passage. 1mark

Assertion (A): When silver chloride is exposed to sunlight, it decomposes to form silver and chlorine gas.Reason (R): This reaction occurs because light energy is absorbed, causing the decomposition.(a) If both A and R are true and R is the correct explanation of A.(b) If both A and R are true but R is not the correct explanation of A.(c) If A is true but R is false.(d) If A is false but R is true. 1mark

A laboratory assistant prepared a solution of calcium hydroxide by dissolving quicklime in water.(a) Write the chemical equation for the reaction that takes place. [1 mark](b) Name the common name for calcium hydroxide. [1 mark](c) What happens when this solution reacts with carbon dioxide gas from the air? Write the balanced chemical equation. [2 marks](d) Why is this reaction used for whitewashing? 1mark

Consider the following reaction:

F e_{2} O_{3} (s) + 2 A l (s) \to A l_{2} O_{3} (s) + 2 F e (l)

(a) Identify the type of reaction. [1 mark]
(b) Explain why this reaction is classified as such. [2 marks]
(c) Mention one use of this reaction. [1 mark]

Assertion (A): Addition of a solution of barium chloride to sodium sulphate solution produces a white precipitate.Reason (R): The formation of a precipitate indicates a double displacement reaction.(a) If both A and R are true and R is the correct explanation of A.(b) If both A and R are true but R is not the correct explanation of A.(c) If A is true but R is false.(d) If A is false but R is true. 1mark

A student accidentally dropped a piece of sodium metal into a beaker of water. The metal started burning and floated on the surface.(a) Name the metal. [1 mark](b) Write the balanced chemical equation for the reaction of this metal with water. [1 mark](c) State the nature of the product formed. [1 mark](d) Explain why the metal floats and burns. 2marks

Read the following passage and answer the questions that follow:"In a chemical reaction, a substance gains oxygen or loses hydrogen, it is said to be oxidised. If a substance loses oxygen or gains hydrogen, it is said to be reduced."(a) Identify the oxidising agent and the reducing agent in the reaction:

C u O (s) + H_{2} (g) \to C u (s) + H_{2} O (l)

. [2 marks](b) State what is oxidised and what is reduced in the above reaction. 2marks

Assertion (A): Respiration is considered an exothermic process.Reason (R): During respiration, glucose combines with oxygen to provide energy, which is released in the form of heat.(a) If both A and R are true and R is the correct explanation of A.(b) If both A and R are true but R is not the correct explanation of A.(c) If A is true but R is false.(d) If A is false but R is true. 1mark

A white solid compound 'X' dissolves in water to form a solution. When solutions of 'X' and 'Y' are mixed, a white precipitate 'Z' is formed. 'Y' is barium chloride solution.(a) Identify 'X' and 'Z'. [2 marks](b) Write the balanced chemical equation for the reaction. [1 mark](c) What type of reaction is this? 1mark

A student is asked to balance the chemical equation:

A l + H_{2} O \to A l_{2} O_{3} + H_{2}

. The student writes the coefficients as p, q, r, s respectively.(a) Determine the values of p, q, r, and s. [2 marks](b) What type of reaction is this? 1mark

Assertion (A): Decomposition reactions are opposite to combination reactions.Reason (R): In a combination reaction, two or more substances combine to form a single product, while in a decomposition reaction, a single substance breaks down to form two or more simpler substances.(a) If both A and R are true and R is the correct explanation of A.(b) If both A and R are true but R is not the correct explanation of A.(c) If A is true but R is false.(d) If A is false but R is true. 1mark

A chemist observes that when a solution of potassium bromide is mixed with silver nitrate solution, a pale yellow precipitate is formed.(a) Name the type of reaction that takes place. [1 mark](b) Write the balanced chemical equation for this reaction. [1 mark](c) Identify the precipitate formed. 1mark

A piece of metal 'M' was dipped in a solution of copper sulphate. After some time, the blue colour of the solution faded and the metal 'M' got coated with a reddish-brown layer.(a) Identify the metal 'M'. [1 mark](b) Write the balanced chemical equation for the reaction. [1 mark](c) Explain why the blue colour of the solution fades. 2marks

Read the following passage and answer the questions that follow:"To prevent the spoilage of food materials containing fats and oils, manufacturers often add antioxidants. These substances prevent oxidation, which causes rancidity."(a) What is rancidity? [1 mark](b) Name a gas commonly used by chips manufacturers to flush their packaging. Why is this gas used? [2 marks](c) Name a substance that can be added to food to prevent rancidity. 1mark

Assertion (A): A chemical equation must be balanced to satisfy the law of conservation of mass.Reason (R): In a chemical reaction, mass can neither be created nor destroyed.(a) If both A and R are true and R is the correct explanation of A.(b) If both A and R are true but R is not the correct explanation of A.(c) If A is true but R is false.(d) If A is false but R is true. 1mark

A student was asked to perform an experiment involving heating lead nitrate. The student observed the emission of brown fumes.(a) Write the balanced chemical equation for the decomposition of lead nitrate on heating. [2 marks](b) Name the brown fumes observed. [1 mark](c) What type of chemical reaction is this? 1mark

The reaction

C_{6} H_{12} O_{6} (a q) + 6 O_{2} (g) \to 6 C O_{2} (g) + 6 H_{2} O (l)

represents a biological process.(a) Name the biological process. [1 mark](b) Identify the type of chemical reaction. [1 mark](c) Is this reaction exothermic or endothermic? Justify. 2marks

Answers

(a) Corrosion (specifically rusting of iron). 1mark(b)

2 F e (s) + O_{2} (g) + 2 H_{2} O (l) \to 2 F e (O H)_{2} (s)

(or

4 F e (s) + 3 O_{2} (g) + 2 H_{2} O (l) \to 4 F e (O H)_{3} (s)

or simplified

2 F e + O_{2} + H_{2} O \to Reddish brown coating

) [1 mark](c) Painting, greasing, galvanizing, or making alloys. [1 mark](d) Painting creates a barrier between the iron gate and the atmospheric oxygen and moisture, thus preventing corrosion. [2 marks]

(a) Exothermic reaction. 1mark(b) Respiration is an exothermic process. This is because during respiration, glucose is broken down in the presence of oxygen to release energy, which is felt as heat. [2 marks](c) Burning of coal or formation of water from hydrogen and oxygen. [1 mark]

(a)

Z n (s) + 2 H C l (a q) \to Z n C l_{2} (a q) + H_{2} (g)

1mark(b) Displacement reaction. [1 mark](c) Effervescence (bubbles of gas) will be observed. [1 mark](d) No reaction will be observed because copper is less reactive than hydrogen and cannot displace it from dilute hydrochloric acid. [2 marks]

(a)

6 C O_{2} (g) + 6 H_{2} O (l) \overset{Sunlight}{\to} C_{6} H_{12} O_{6} (a q) + 6 O_{2} (g)

2marks(b) Photosynthesis is an endothermic process because it requires energy in the form of sunlight to occur. [2 marks](c) Combination reaction (or Redox reaction, but combination is more fitting for the simplified context of formation). [1 mark]

(a) If both A and R are true and R is the correct explanation of A. 1mark

(a)

C a O (s) + H_{2} O (l) \to C a (O H)_{2} (a q)

1mark(b) Slaked lime. [1 mark](c)

C a (O H)_{2} (a q) + C O_{2} (g) \to C a C O_{3} (s) + H_{2} O (l)

[2 marks](d) Calcium carbonate formed is a thin white layer that gives a shiny finish to the walls. [1 mark]

(a) Displacement reaction. 1mark(b) This reaction is a displacement reaction because aluminium, being more reactive than iron, displaces iron from its oxide. [2 marks](c) This reaction is used in welding railway tracks. [1 mark]

(a) If both A and R are true and R is the correct explanation of A. 1mark

(a) Sodium (Na). 1mark(b)

2 N a (s) + 2 H_{2} O (l) \to 2 N a O H (a q) + H_{2} (g)

[1 mark](c) The product formed is sodium hydroxide, which is an alkali. [1 mark](d) Sodium reacts vigorously with water, producing hydrogen gas, which ignites due to the heat generated, causing the metal to burn. Sodium is less dense than water, causing it to float. [2 marks]

(a) Oxidising agent: CuO; Reducing agent:

H_{2}

. 2marks(b)

H_{2}

is oxidised (gains oxygen), and CuO is reduced (loses oxygen). [2 marks]

(a) If both A and R are true and R is the correct explanation of A. 1mark

(a) 'X' is Sodium sulphate (

N a_{2} S O_{4}

). 'Z' is Barium sulphate (

B a S O_{4}

). 2marks(b)

N a_{2} S O_{4} (a q) + B a C l_{2} (a q) \to B a S O_{4} (s) + 2 N a C l (a q)

[1 mark](c) Double displacement reaction (specifically, a precipitation reaction). [1 mark]

(a) p=2, q=3, r=1, s=3. The balanced equation is

2 A l + 3 H_{2} O \to A l_{2} O_{3} + 3 H_{2}

. 2marks(b) Displacement reaction. [1 mark]

(a) If both A and R are true and R is the correct explanation of A. 1mark

(a) Double displacement reaction (specifically, a precipitation reaction). 1mark(b)

K B r (a q) + A g N O_{3} (a q) \to A g B r (s) + K N O_{3} (a q)

[1 mark](c) Silver bromide (AgBr). [1 mark]

(a) Iron (Fe). 1mark(b)

F e (s) + C u S O_{4} (a q) \to F e S O_{4} (a q) + C u (s)

[1 mark](c) Iron is more reactive than copper, so it displaces copper from copper sulphate solution. As copper ions (

C u^{2 +}

) are removed from the solution, the blue colour of the copper sulphate fades. [2 marks]

(a) Rancidity is the condition where food substances containing fats and oils develop an unpleasant smell and taste due to their oxidation. 1mark(b) Nitrogen (

N_{2}

). It is used because it is unreactive and prevents the oxidation of the chips. [2 marks](c) Antioxidants like BHA (Butylated hydroxyanisole) or BHT (Butylated hydroxytoluene). [1 mark]

(a) If both A and R are true and R is the correct explanation of A. 1mark

(a)

2 P b (N O_{3})_{2} (s) \overset{Heat}{\to} 2 P b O (s) + 4 N O_{2} (g) + O_{2} (g)

2marks(b) Nitrogen dioxide (

N O_{2}

). [1 mark](c) Decomposition reaction (thermal decomposition). [1 mark]

(a) Respiration. 1mark(b) Redox reaction (or Exothermic reaction, as it releases energy). [1 mark](c) This reaction is exothermic because energy is released during the process. [2 marks]

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Chemical Reactions and Equations — Competency Based Questions

Competency based questions

Answers

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