Chemistry chapter 1

Cu + 2AgNO3 → Cu(NO3)2 + 2Ag

A precipitation reaction occurs when two solutions are mixed, resulting in the formation of an insoluble solid (precipitate).

Example 1: AgNO3 + NaCl → AgCl(s) + NaNO3

Example 2: BaCl2 + Na2SO4 → BaSO4(s) + 2NaCl

Oxidation is the gain of oxygen or the loss of hydrogen.

Example 1: 2Mg + O2 → 2MgO (magnesium oxidizing)

Example 2: C + O2 → CO2 (carbon oxidizing)

Reduction is the loss of oxygen or the gain of hydrogen.

Example 1: CuO + H2 → Cu + H2O (copper oxide reducing)

Example 2: Fe2O3 + 3H2 → 2Fe + 3H2O (iron oxide reducing)

The element 'X' is copper (Cu), and the black coloured compound formed is copper(II) oxide (CuO).

Milk undergoes a chemical change due to bacterial action, leading to spoilage and the formation of sour milk.

The iron undergoes oxidation, resulting in rust formation, which is a chemical change.

Fermentation is a chemical reaction where sugars in grapes are converted into alcohol and carbon dioxide by yeast.

Cooking food involves chemical changes such as the breakdown of proteins and carbohydrates, altering the food's flavor and texture.

Digestion involves chemical reactions where enzymes break down food into simpler substances that can be absorbed by the body.

Respiration is a chemical reaction where glucose is oxidized to produce energy, carbon dioxide, and water in living organisms.

A chemical reaction is a process where the identity and nature of substances change, resulting in the formation of new substances.

Burning magnesium ribbon produces a bright light and forms magnesium oxide, indicating a chemical reaction has occurred.

Observations that indicate a chemical reaction has taken place include:

• Change in state
• Change in colour
• Evolution of a gas
• Change in temperature

The reaction of magnesium with oxygen can be represented as a word-equation:

Magnesium + Oxygen → Magnesium oxide

This shows the reactants and the product of the reaction.

In the reaction of magnesium burning in oxygen, the reactants are magnesium and oxygen, and the product is magnesium oxide.

A word-equation simplifies the description of a chemical reaction by showing the change of reactants to products in a concise format, using an arrow to indicate the direction of the reaction.

A chemical equation represents a chemical reaction using chemical formulae instead of words. For example, the reaction of magnesium and oxygen can be represented as Mg + O₂ → MgO.

A chemical equation is considered balanced if the number of atoms of each element is the same on both sides of the equation (LHS and RHS).

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction, meaning the total mass of reactants must equal the total mass of products.

Since the number of atoms is the same, the equation is balanced.

The skeletal chemical equation for the burning of magnesium in air is represented as Mg + O₂ → MgO.

To balance the equation Fe + H₂O → Fe₃O₄ + H₂, you need to ensure that the number of atoms of each element is equal on both sides, adjusting coefficients as necessary.

Draw boxes around each formula and do not change anything inside the boxes while balancing the equation.

1 atom of iron (Fe) is present in the reactants.

There is 1 oxygen atom in the reactants (in H₂O).

The compound with the maximum number of atoms should be balanced first, which in this case is Fe₃O₄ because it contains 4 oxygen atoms on the products side.

To balance the oxygen atoms, place a coefficient of '4' in front of H₂O, making it 4 H₂O, to equalize the 4 oxygen atoms in Fe₃O₄.

There are 8 hydrogen atoms present in the reactants (in 4 H₂O).

The final balanced equation is Fe + 4H₂O → Fe₃O₄ + 4H₂.

Iron is the third element that needs to be balanced.

The method used is called the hit-and-trial method, where trials are made to balance the equation using the smallest whole number coefficients.

The physical states are represented by the notations: (g) for gaseous, (l) for liquid, (aq) for aqueous, and (s) for solid states.

The physical state of water is indicated by the notation (g), showing that water is used in the form of steam.

Reaction conditions such as temperature, pressure, and catalysts can be indicated above and/or below the arrow in the equation.

A magnesium ribbon should be cleaned before burning in air to remove any oxide layer that may have formed on its surface. This ensures that the magnesium can react more efficiently with oxygen during combustion, leading to a more vigorous reaction and brighter flame.

The balanced equation is: H2(g) + Cl2(g) → 2HCl(g)

The balanced equation is: 3BaCl2(aq) + Al2(SO4)3(aq) → 3BaSO4(s) + 2AlCl3(aq)

The balanced equation is: 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

The balanced equation is: BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)

The balanced equation is: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

A combination reaction is a type of chemical reaction where two or more reactants combine to form a single product. An example is the reaction of calcium oxide with water to form calcium hydroxide: CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat

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

C(s) + O₂(g) → CO₂(g)

2H₂(g) + O₂(g) → 2H₂O(l)

The process is called respiration, represented by the equation: C₆H₁₂O₆(aq) + 6O₂(aq) → 6CO₂(aq) + 6H₂O(l) + energy.

The decomposition of vegetable matter into compost is an example of an exothermic reaction.

A decomposition reaction is a type of chemical reaction where a single reactant breaks down into simpler products. In the case of ferrous sulphate crystals (FeSO₄), when heated, they decompose to form ferric oxide (Fe₂O₃), sulphur dioxide (SO₂), and sulphur trioxide (SO₃). The heating causes the crystals to lose water and change color, indicating the reaction has occurred.

The thermal decomposition of calcium carbonate (CaCO₃) produces calcium oxide (CaO), also known as quick lime, and carbon dioxide (CO₂) gas. This reaction is significant in various industries, particularly in the manufacture of cement.

When lead nitrate is heated, it emits brown fumes of nitrogen dioxide (NO₂). This is a characteristic observation of the thermal decomposition of lead nitrate.

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

Bubbles are formed at both electrodes, displacing water in the test tubes.

White silver chloride turns grey due to the decomposition into silver and chlorine gas.

2AgCl(s) → 2Ag(s) + Cl2(g)

The decomposition reactions of silver bromide are caused by light energy.

The substance 'X' used for whitewashing is calcium hydroxide, and its formula is Ca(OH)₂.

The reaction of calcium hydroxide with water is:

Ca(OH)₂ + H₂O → Ca(OH)₂ (aqueous)

The amount of gas collected in one test tube is double because the reaction produces two moles of gas for every mole of reactant consumed. The gas collected is ammonia (NH₃).

Cleaning the iron nails with sandpaper removes any oxidation layer or impurities, ensuring better contact with the copper sulfate solution for a more accurate reaction.

The intensity of the blue color in test tube B will be less than in test tube A, indicating that the iron nails in test tube B have reacted with the copper sulfate, displacing the copper ions.

The iron nail becomes brownish in color, and the blue color of the copper sulfate solution fades due to the formation of iron sulfate and the displacement of copper.

This reaction is known as a displacement reaction.

A white insoluble substance known as a precipitate is formed when sodium sulfate and barium chloride are mixed.

The chemical equation is:

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

Zinc and lead are more reactive elements than copper, which allows them to displace copper from its compounds.

The reaction between SO₄²⁻ and Ba²⁺ produces a white precipitate of BaSO₄ and sodium chloride remains in the solution.

The precipitate formed is yellow, and the compound precipitated is lead(II) iodide (PbI₂).

The balanced chemical equation is:

2KI + Pb(NO₃)₂ → PbI₂ + 2KNO₃

Yes, the reaction between lead(II) nitrate and potassium iodide is a double displacement reaction.

When copper powder is heated in the presence of oxygen, it forms black copper(II) oxide (CuO).

When hydrogen gas is passed over heated copper(II) oxide, it is reduced to copper, and water is produced.

A substance is said to be oxidized if it gains oxygen during a reaction.

A substance is said to be reduced if it loses oxygen during a reaction.

Oxidation-reduction reactions are also known as redox reactions.

Magnesium is being oxidised when it burns in air, forming magnesium oxide as a white substance.

Corrosion is the process where metals are attacked by substances around them, leading to damage. For example, iron rusts, forming a reddish-brown powder, which causes significant damage to iron objects.

Rancidity occurs when fats and oils are oxidised, changing their smell and taste. It can be prevented by adding antioxidants and storing food in airtight containers.

Oxidation of fats and oils leads to rancidity, which alters the taste and smell of the food.

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

A chemical equation must be balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on both the reactant and product sides.

In a combination reaction, two or more substances combine to form a new single substance.

Decomposition reactions are the opposite of combination reactions; in a decomposition reaction, a single substance decomposes to give two or more substances.

Exothermic reactions are characterized by the release of heat along with the products.

Endothermic reactions are characterized by the absorption of energy.

In a displacement reaction, an element displaces another element from its compound.

In double displacement reactions, two different atoms or groups of atoms (ions) are exchanged.

Precipitation reactions produce insoluble salts.

Oxidation is the gain of oxygen or loss of hydrogen, while reduction is the loss of oxygen or gain of hydrogen.

The incorrect statements are: (a) Lead is getting reduced, (b) Carbon dioxide is getting oxidised, and (c) Carbon is getting oxidised. Therefore, the answer is (iii) (a), (b) and (c).

The reaction Fe₂O₃ + 2Al→ Al₂O₃ + 2Fe is an example of a combination reaction.

Hydrogen gas and iron chloride are produced.

A balanced chemical equation has equal numbers of each type of atom on both sides of the equation. Balancing is necessary to obey the law of conservation of mass, ensuring that matter is neither created nor destroyed in a chemical reaction.

The balanced equation is: N₂(g) + 3H₂(g) → 2NH₃(g)

The balanced equation is: 2H₂S(g) + 3O₂(g) → 2H₂O(g) + 2SO₂(g)

The balanced equation is: 3BaCl₂(aq) + Al₂(SO₄)₃(aq) → 2AlCl₃(aq) + 3BaSO₄(s)

The balanced equation is: 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)

Exothermic reactions release heat (e.g., combustion of fuels), while endothermic reactions absorb heat (e.g., photosynthesis).

Respiration is considered exothermic because it releases energy in the form of heat when glucose is broken down in the presence of oxygen.

Decomposition reactions involve breaking down a compound into simpler substances, while combination reactions involve forming a compound from simpler substances. For example:

• Decomposition: 2H₂O(l) → 2H₂(g) + O₂(g)
• Combination: 2H₂(g) + O₂(g) → 2H₂O(l)

2HgO(s) → 2Hg(l) + O2(g) (upon heating)

2AgBr(s) → 2Ag(s) + Br2(g) (upon exposure to light)

2H2O(l) → 2H2(g) + O2(g) (electrolysis)

Displacement reactions involve one element replacing another in a compound, while double displacement reactions involve the exchange of ions between two compounds.

Example of Displacement Reaction: Zn + CuSO4 → ZnSO4 + Cu

Example of Double Displacement Reaction: Na2SO4 + BaCl2 → BaSO4 + 2NaCl

We apply paint on iron articles to prevent corrosion by creating a protective barrier that keeps moisture and oxygen away from the iron surface.

Oil and fat containing food items are flushed with nitrogen to prevent oxidation and rancidity, which can spoil the food and affect its taste and safety.

Corrosion is the gradual destruction of materials, usually metals, by chemical reactions with their environment.

Example: Rusting of iron: 4Fe + 3O2 + 6H2O → 4Fe(OH)3

Rancidity is the process by which fats and oils become spoiled due to oxidation, leading to off-flavors and odors.

Example: Rancid butter develops a sour smell and taste due to the breakdown of fats.