Chemical Reactions and Equations
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Questions and Answers

Why should a magnesium ribbon be cleaned before burning in air?

A magnesium ribbon should be cleaned before burning in air to remove any oxide layer that might be present on its surface. This layer can interfere with the combustion process and prevent the ribbon from burning brightly. The cleaning ensures a more vigorous reaction.

Write the balanced equation for the following chemical reactions: Hydrogen + Chlorine → Hydrogen chloride

H₂ + Cl₂ → 2HCl

Write the balanced equation for the following chemical reactions: Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃

Write the balanced equation for the following chemical reactions: Sodium + Water → Sodium hydroxide + Hydrogen

<p>2Na + 2H₂O → 2NaOH + H₂</p> Signup and view all the answers

Write a balanced chemical equation with state symbols for the following reactions: Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.

<p>BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)</p> Signup and view all the answers

Write a balanced chemical equation with state symbols for the following reactions: Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

<p>NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)</p> Signup and view all the answers

A solution of a substance 'X' is used for whitewashing. (i) Name the substance 'X' and write its formula. (ii) Write the reaction of the substance 'X' named in (i) above with water.

<p>(i) The substance 'X' is calcium hydroxide (Ca(OH)₂). (ii) The reaction of calcium hydroxide with water is Ca(OH)₂(s) + H₂O(l) → Ca(OH)₂(aq) + Heat</p> Signup and view all the answers

Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

<p>The gas collected in larger quantities in the test tube is hydrogen (Hâ‚‚). This is because during the electrolysis of water, hydrogen gas is produced twice as much as oxygen gas.</p> Signup and view all the answers

Why does the iron nail become brownish in colour and the blue colour of copper sulphate solution fades?

<p>The iron nail becomes brownish due to the formation of a layer of iron(II) sulphate (FeSOâ‚„) on its surface. This is because the copper ions from the blue copper sulphate solution displace iron ions from the iron nail, resulting in the formation of iron(II) sulphate. The blue colour of the copper sulphate solution fades as the copper ions are replaced by iron(II) ions.</p> Signup and view all the answers

Give an example of a double displacement reaction other than the one given in Activity 1.10.

<p>An example of a double displacement reaction is the reaction between lead nitrate (Pb(NO₃)₂) and potassium iodide (KI) which forms a yellow precipitate of lead iodide (PbI₂) and potassium nitrate (KNO₃) in solution. The balanced equation for this reaction is Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq).</p> Signup and view all the answers

Identify the substances that are oxidised and the substances that are reduced in the following reactions: (i) 4Na(s) + O₂(g) → 2Na₂O(s) (ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)

<p>(i) Sodium is oxidised as it gains oxygen, and oxygen is reduced as it gains electrons. (ii) Copper oxide is reduced as it loses oxygen, and hydrogen is oxidised as it gains oxygen.</p> Signup and view all the answers

Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

<p>The blue colour of the copper sulphate solution changes because the iron displaces copper from the copper sulphate solution, resulting in the formation of iron(II) sulphate which is a greenish colour.</p> Signup and view all the answers

What is the difference between displacement and double displacement reactions? Write equations for these reactions.

<p>In a displacement reaction, one element replaces another element in a compound. For example, Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s) In a double displacement reaction, the ions of two reactants switch places to form two new compounds. For example, AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)</p> Signup and view all the answers

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

<p>The reaction involved in the refining of silver is: Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)</p> Signup and view all the answers

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

<p>A precipitation reaction is a chemical reaction that produces an insoluble solid, known as a precipitate, when two solutions are mixed. For example, when barium chloride solution (BaCl₂) is added to a solution of sodium sulphate (Na₂SO₄), a white precipitate of barium sulphate (BaSO₄) forms: BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)</p> Signup and view all the answers

Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation (b) Reduction

<p>(a) Oxidation is the gain of oxygen or loss of hydrogen. For example: 2Mg(s) + O₂(g) → 2MgO(s) In this reaction, magnesium gains oxygen and is oxidised. Another example is the combustion of methane: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) Here, methane (CH₄) gains oxygen and is oxidised. (b) Reduction is the loss of oxygen or gain of hydrogen. For example: CuO(s) + H₂(g) → Cu(s) + H₂O(l) In this reaction, copper oxide (CuO) loses oxygen and is reduced. Another example is the reduction of iron oxide by carbon monoxide (CO) Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g) Here, iron oxide (Fe₂O₃) loses oxygen and is reduced.</p> Signup and view all the answers

A shiny brown coloured element ‘X' on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

<p>The element ‘X’ is copper (Cu). The black coloured compound formed is copper oxide (CuO).</p> Signup and view all the answers

Why do we apply paint on iron articles?

<p>Iron is a reactive metal that easily corrodes in the presence of moisture and oxygen, forming rust. Paint provides a protective layer to prevent direct contact of the metal with the atmosphere, thereby slowing down or preventing corrosion.</p> Signup and view all the answers

Oil and fat containing food items are flushed with nitrogen. Why?

<p>Oil and fat containing food items are flushed with nitrogen to prevent the oxidation of fats and oils, a process known as rancidity. Oxidation can cause the food to become stale, develop unpleasant odors, and lose nutritional value. Nitrogen is an inert gas that does not react with fats and oils, preventing this oxidation.</p> Signup and view all the answers

Explain the following terms with one example each. (a) Corrosion (b) Rancidity

<p>(a) Corrosion refers to the gradual deterioration of a material, typically a metal, due to chemical reactions with its environment. Rusting of iron is an example of corrosion. (b) Rancidity is the spoilage of fats and oils due to oxidation, leading to unpleasant taste and smell. For example, when butter or oil is left exposed to air for a prolonged period, it becomes rancid and develops a bad odor and a bitter taste.</p> Signup and view all the answers

Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

<p>Decomposition Reactions: (a) Heat: CaCO₃(s) → CaO(s) + CO₂(g) (b) Light: 2AgCl(s) → 2Ag(s) + Cl₂(g) (c) Electricity: 2H₂O(l) → 2H₂(g) + O₂(g)</p> Signup and view all the answers

Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO₂(g) (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced.

<p>The incorrect statements are (b) and (c). Carbon dioxide (COâ‚‚) cannot be further oxidised, as it is already in its highest oxidation state (+4). Carbon (C) is oxidised, as it goes from an oxidation state of 0 to +4 in carbon dioxide (COâ‚‚).</p> Signup and view all the answers

Flashcards

Chemical Reaction

A change in the nature and identity of a substance, indicating a new substance has been formed.

Reactants

The substances that undergo a chemical change in a reaction, reacting with each other to form new substances.

Products

The new substances formed during a chemical reaction.

Combination Reaction

A process where a single product is formed from two or more reactants.

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Decomposition Reaction

A reaction where a single reactant breaks down into two or more simpler products.

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Exothermic Reactions

Chemical reactions that release heat energy during the process.

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Endothermic Reactions

Chemical reactions that absorb heat energy from their surroundings.

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Displacement Reaction

A reaction where one element displaces another from its compound.

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Double Displacement Reaction

A reaction where two different atoms or groups of atoms (ions) exchange places.

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Precipitation Reaction

A reaction that produces an insoluble solid, called a precipitate.

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Oxidation

The gain of oxygen or the loss of hydrogen during a chemical reaction.

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Reduction

The loss of oxygen or the gain of hydrogen during a chemical reaction.

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Balanced Chemical Equation

A chemical equation where the number of atoms of each element is the same on both sides of the equation.

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Chemical Equation

A short and concise way to represent a chemical reaction using chemical formulae.

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Corrosion

The gradual destruction of a metal due to a reaction with substances in its environment, like moisture or acids.

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Rancidity

The process of fats and oils becoming rancid due to oxidation, changing their smell and taste.

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Antioxidants

Substances that prevent or slow down oxidation.

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Digestion

The process where food is broken down into simpler substances, releasing energy.

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Respiration

The process where glucose combines with oxygen to provide energy for cells. It is an exothermic reaction.

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Oxidation of Metals

A combination reaction where a metal combines with oxygen to form its oxide.

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Reduction of Metal Oxides

A decomposition reaction where a metal oxide is reduced to the metal by removing oxygen.

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Precipitation Reaction

A chemical reaction that produces a precipitate, an insoluble solid.

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Exothermic Reaction

A reaction where heat is released during the process.

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Endothermic Reaction

A reaction where heat is absorbed during the process.

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Chemical Formula

The chemical formula for a substance that represents the types and numbers of atoms present in its molecule.

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Physical State

The physical state of a substance, such as solid, liquid, or gas.

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State Symbol

A symbol used in chemical equations to represent the physical state of a substance.

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Left-Hand Side (LHS) of a Chemical Equation

The reactants are written on the left-hand side (LHS) of the arrow.

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Right-Hand Side (RHS) of a Chemical Equation

The products are written on the right-hand side (RHS) of the arrow.

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Arrow in a Chemical Equation

The arrow in a chemical equation represents the direction of the reaction.

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Study Notes

Chemical Reactions and Equations

  • Chemical reactions involve changes in the nature and identity of substances.
  • Chemical reactions can be observed through changes in state, color, temperature, and formation of gases.
  • Chemical reactions involve breaking and forming bonds between atoms.
  • Chemical reactions have reactants (substances undergoing change) and products (new substances created).

Activity 1.1

  • Magnesium ribbon burns in air to form magnesium oxide.
  • This reaction involves a change of state and color and can be observed through exothermicity.
  • Observation of a change during reaction can help determine if a chemical process has occurred.

Activity 1.2

  • Lead nitrate and potassium iodide react in a test tube, generating a change in the solution.

Activity 1.3

  • Zinc granules react with dilute hydrochloric/sulfuric acid, forming a gas (hydrogen) and releasing energy.
  • This reaction is observed by noting the gas formation and/or temperature change.

1.1 Chemical Equations

  • Word equations represent chemical reactions using words instead of symbols.
  • Chemical equations show reactants and products using their formulas.
  • Equations contain symbols like: +, →, (s), (l), (g), (aq) - these signify reactants, products, solid, liquid, gas, and aqueous respectively.
  • Chemical equations must balance, maintaining the same number of atoms for each element both on the product and reactant sides.

1.1.2 Balanced Chemical Equations

  • The law of conservation of mass states that mass cannot be created or destroyed during a chemical reaction.
  • This means balancing chemical equations is a necessary detail that needs to satisfy this equation in order to be a valid chemical equation.
  • Balancing maintains the same number of atoms of each element on both sides.

1.2 Types of Chemical Reactions

  • Combination reaction: Two or more reactants forming a single product. -Example: Formation of water from hydrogen and oxygen
    • Example: Formation of calcium hydroxide from calcium oxide and water.
  • Decomposition reaction: A single reactant breaking down into two or more products. -Example: Decomposition of ferrous sulphate at heat. -Example: Decomposition of lead nitrate at heat.

1.2.3 Displacement Reaction

  • One element replaces another in a compound.
  • Example: Iron replacing copper in copper sulphate solution.
  • Example: Zinc replacing copper in copper sulphate solution.

1.2.4 Double Displacement Reaction

  • An exchange of ions occurs between two compounds.
  • Example: Formation of barium sulphate precipitate by mixing sodium sulphate and barium chloride solutions.

1.2.5 Oxidation and Reduction (Redox) Reactions

  • Oxidation: Gain of oxygen or loss of hydrogen in a chemical reaction. -Example: Copper reacting with oxygen to form copper(II) oxide
  • Reduction: Loss of oxygen or gain of hydrogen in a chemical reaction.
  • Example: Copper(II) oxide reacting with hydrogen to form copper.

Questions

  • Questions on chemical reactions are provided for self-assessment.

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Test your knowledge on chemical reactions and their equations with this engaging quiz. Explore various activities that illustrate different chemical processes and the changes that occur during these reactions. Understand how substances interact to form new products through observable changes.

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