Chemical Reactions and Equations

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.

H₂ + Cl₂ → 2HCl

3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃

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

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

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

<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

<p>The gas collected in larger quantities in the test tube is hydrogen (H₂). 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

<p>The iron nail becomes brownish due to the formation of a layer of iron(II) sulphate (FeSO₄) 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

<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

<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

<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

<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

<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

<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

<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

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

<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

<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

<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

<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

<p>The incorrect statements are (b) and (c). Carbon dioxide (CO₂) 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 (CO₂).</p> Signup and view all the answers