Chapter-1 Chemical reactions and equations

Explanation:

Magnesium is a highly reactive metal. When it is stored, it reacts with oxygen to form a layer of magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned with sand paper for removing this layer so that the metal which is underlying can be exposed to air.​

Explanation:

(i) H2 + Cl2 → 2HCl

(ii) 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3

(iii) 2Na + 2H2O → 2NaOH + H2↑

Explanation:

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

(ii) NaOH (aq) + HCl(aq) → NaCl(aq) + H2O(l)

Explanation:

(i) The substance which has a  solution in water used for whitewashing is calcium oxide (or quicklime). Its formula is CaO. Quicklime or burnt lime, also known as calcium oxide (CaO), is a chemical substance that is frequently used. At room temperature, it is a crystalline solid that is white, caustic, and alkaline. The commonly used term "lime" refers to inorganic materials that contain calcium and are mostly composed of carbonates, oxides, and hydroxides of silicon, magnesium, aluminum, and iron.

ii) CaO + H2O (l) → Ca(OH)(aq)

  Calcium oxide         Calcium hydroxide

     (Quick lime)                (slaked lime)

Explanation:

Two parts of hydrogen and one part of oxygen make up water (H2O). As a result, the ratio of hydrogen to oxygen created during the electrolysis of water is 2:1. During electrolysis, hydrogen is supplied to one test tube while oxygen is sent to the other, resulting in a gas collection that is two times as large in one test tube as the other.

Explanation:

Because iron is more reactive than copper and so displaces copper from the solution, the colour of copper sulphate changes from blue to pale green when an iron nail is kept in it.

An empirical technique for forecasting displacement reaction products and metal reactivity with water and acids in replacement processes and ore extraction is the metal activity series. Metals are included in the activity series table in decreasing order of relative reactivity. The metals at the top are more reactive than the less reactive metals at the bottom.

Fe(s) + CuSO4(aq)       →    FeSO4(aq)     +     Cu(s)

Iron        Copper Sulphate       Iron sulphate          Copper

                 (Blue colour)             (Green colour)

Therefore, the blue colour of the copper sulphate solution disappears and the green colour appears.

Explanation:

 Pb(NO3)2 (aq)  +     2KI (aq)         →          PbI2 (s)         +   2KNO3(aq)

Lead Nitrate  Potassium Iodide            Lead Iodide         PotassiumNitrate

We get a precipitate of lead iodide and a solution of potassium nitrate when we mix aqueous solutions of lead nitrate and potassium iodide. Ion exchange will occur between the reactants in a double displacement reaction. The cations Pb2+ and K+ will exchange their anions NO3- and I- in this reaction, forming new compounds PbI2 and KNO3. An illustration of a double displacement reaction is this.

Explanation:

When oxygen is given to a substance, it is said to be oxidised, but when oxygen is removed, it is said to be reduced. Hence, in order to check for oxidation and reduction, we must examine the addition or removal of oxygen.

(i) Sodium (Na) will be oxidised as it gains oxygen and oxygen will get reduced. Na changes to Na2 O. As a result, oxygen was introduced, and Na was oxidised and reduced.

(ii) Copper oxide (CuO) gets reduced to copper (Cu) while hydrogen (H2) gets oxidised to water (H2O). CuO changes to Cu hence oxygen is removed from CuO. Hence, CuO is reduced and H2 is oxidised.

Explanation:

If oxygen is introduced to a substance, it is said to have undergone oxidation.

It loses electrons in the process.

If oxygen is removed from a substance or if electrons are added, the substance is said to be reduced.

Lead oxide loses oxygen in the process to produce elemental lead. Hence, lead oxide rather than the lead is being reduced. As a result, assertion (a) is untrue.

The carbon atom also receives the addition of oxygen. So, rather than carbon dioxide, carbon is being oxidised. The byproduct of carbon's oxidation is carbon dioxide. Thus, claim (b) is untrue.

Explanation:

A displacement response is the one that is being described.

Here Aluminum is a comparatively highly reactive metal than Fe. Therefore Al will replace Fe from its oxide. This type of chemical reaction in which one of the elements replaces another is called a displacement reaction. Here less reactive metal is replaced by more reactive metal. Because there is just one displacement happening, it is referred to as a single displacement response. Displacement reaction is used in both nonmetals and metals.

Explanation:

Iron chloride and hydrogen gas are created. The iron fillings displace the chlorine from hydrogen chloride to cause the next reaction. Below is the response:

2HCl + Fe → FeCl2 + H2

Iron (II) chloride and hydrogen gas are created when the iron replaces the hydrogen in hydrochloric acid. One displacement reaction has occurred here.

Option (A): The production of hydrogen gas and iron chloride is the correct response.

Explanation:

A balanced chemical equation is one in which each element's number of atoms on each side of the chemical equation is equal.

The conservation of mass principle states that matter cannot be created or destroyed. Hence, in a chemical reaction, the total mass of the reactants and the total mass of the products should be equal. It implies that each element should have an equal number of atoms on both sides of a chemical equation. Thus, chemical equations should be balanced for this reason.

Explanation:

(a) 3H2 (g) + N2 (g) → 2NH3 (g)

(b) H3S (g) + 3O2 (g) → SO2 (g) + 2H2O(l)

(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 ↓(s)

(d) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

Explanation:

(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O

(b) 2NaOH + H2SO4 → Na2SO4 + 2H2O

(c) NaCl + AgNO3 → AgCl + NaNO3

(d) BaCl2 + H2SO4 → BaSO4 + 2HCl

Explanation:

(a) Ca (OH)2 + CO2 → CaCO3 + H2O

(b) Zn + 2AgNO3 → Zn(NO3)2 + 2 Ag

(c) 2Al + 3 CuCl2 → 2AlCl3 + 3 Cu

(d) BaCl2 + K2SO4 → BaSO4 + 2KCl

Explanation:

(a) 2KBr (aq) + BaI2(aq) → 2KI(aq) + BaBr2(s)

Type: Double displacement reaction

(b) ZnCO3 (s) → ZnO (s) + CO2 (g)

Type: Decomposition reaction

(c) H2 (g) + Cl2 (g) → 2HCl(g)

Type: Combination reaction

(d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

Type: Displacement reaction

Explanation:

Exothermic reactions: The Reactions in which heat is given out along with the products are called exothermic reactions. When energy is released as heat or light, the reaction is exothermic. An exothermic reaction releases energy into the environment as opposed to an endothermic process, which absorbs energy from its surroundings. The change in enthalpy (H) in an exothermic reaction will be negative.

Example :

(i) C (s) + O2 (g) → CO2 (g) + Heat (ii) N2 (g) + 3H2 (g) → 2NH3 (g) + Heat 

Endothermic reactions: In every chemical process, energy is involved. When new bonds form in products, energy is produced. Reactant bonds are broken using energy. As new bonds form in the products of some chemical reactions, known as exothermic reactions, more energy is produced than is required to break bonds in the reactants. In contrast, endothermic reactions are the opposite. Endothermic reactions release more energy when new bonds form in the products than is required to break bonds in the reactants.

Example : 

(i) C (s) + 2S (s) → CS2 (l) – Heat  (ii) N2 (g) + O2 (g) → 2NO(g) – Heat

Explanation:

Life needs energy to survive. Our bodies get their energy from the food that we eat. Large food molecules are broken down during digestion into smaller molecules like glucose. In the cells, glucose and oxygen mix to produce energy. Respiration is the unique name for this combustion reaction. It is an exothermic process since energy is released throughout the entire procedure. As a result, respiration is viewed as an exothermic reaction.

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

Explanation:

Decomposition reactions are those in which a chemical disintegrates into two or more other components. To continue, these processes will need an energy source. They are said to be the reverse of combination reactions since they release energy while combining two or more chemicals to create a new compound.

Examples of decomposition reactions are

ZnCO3 → ZnO + CO2

CaCO3 + Energy → CaO + CO2

2HgO → 2Hg + O2

Explanation:

A chemical process known as thermal decomposition occurs when a single component is heated and decomposes into two or more simple compounds.

2KClO3 + Heat → 2KCl + 3O2

A substance is transformed into simple substances by a chemical process called photo breakdown when it is exposed to light (photons).

2AgCl → 2Ag + Cl2

When an electric current is passed through a compound's aqueous solution, electrolytic breakdown will take place.

2H2O→ 2H2 + O2

Explanation:

A displacement reaction occurs when a more reactive substance pushes a less reactive one out of its salt solution; a double displacement reaction occurs when two compounds exchange ions.

A displacement reaction only involves one displacement, however, a double displacement reaction involves two displacements between the molecules, as the name suggests.

Example:

Displacement reaction

Mg + 2HCl → MgCl2 + H2

Double displacement reaction

2KBr + BaI2 → 2KI + BaBr2

Explanation:

Cu(s)    +   2AgNO3(aq) → Cu(NO3)2(aq)   +   2Ag(s)

Copper   Silver Nitrate    Copper Nitrate    Silver

Explanation:

In a double displacement reaction, the ions are exchanged between the compounds when two solutions containing soluble salts are mixed. One of these compounds settles to the bottom of the container when it has solidified and is insoluble in water. This substance is referred to as a precipitate, and the associated reaction is known as a precipitation reaction. Some illustrations of precipitation reactions include

CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)

2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)

Explanation:

The Easy way of understanding oxidation and reduction is in terms of the gain and loss of oxygen.Oxidation is the gain of oxygen whereas Reduction is the loss of oxygen.

(a)Oxidation: The substance is known to be oxidised and the reaction is known as an oxidation reaction when oxygen is introduced to some element or compound and hydrogen is removed during a chemical reaction.

Example:

2Cu + O2 = 2CuO (Cu is oxidised to CuO)

S(s) + O2(g) =  SO2(g) (Addition of oxygen to sulphur)

(b)Reduction: A substance is said to be reduced and a reaction is known as a reduction reaction when oxygen is taken out of an element or molecule and hydrogen is supplied. Example:

ZnO + C = Zn + CO ( ZnO is reduced to Zn).

CuO + H2 = Cu + H2O (CuO is reduced to Cu).

Explanation:

Copper's response to air:

1. Copper (cu) is an atomic number 29 chemical element.

2. It truly occurs naturally in pure form as a native element.

3. Copper naturally has a brown colour, but it also reacts with oxygen to produce copper oxide, which is a dark black colour.

4. In essence, copper metal heats up when exposed to air.

5.It will undergo oxidation to produce copper oxide, which is dark in colour.

6. This entire process is actually a redox reaction in which the oxygen is reduced and the copper is oxidised to copper oxide.

7.Reaction: 2Cu(s)               +                          O2(g)      →          2CuO(s)

(Shiny brown in colour)                             (Black in colour)

As a result, a glossy brown element called "X" that turns black when heated in air is actually copper, and the black compound that results from heating copper is copper.

Explanation:

An iron oxide coating known as rust develops chemically on iron things. Iron things become poisonous and lose their aesthetic appeal as a result of rust.

Rust can only form in the presence of iron, water, and oxygen. Despite being a complicated process, the chemical formula is

Iron is painted to avoid rusting so that the iron layer cannot come into touch with the environment and react with oxygen to generate iron oxide, preventing the development of rust.

Oiling the iron items is another approach to stop it from happening so that air and water don't come into touch with each other. Linseed oil aids in rust removal from iron articles. Any acrylic paint works to keep iron from rusting.

Explanation:

Due to its inert nature, nitrogen does not readily interact with these chemicals. On the other hand, oxygen will cause food ingredients to react and get rancid. As a result, nitrogen gas is flushed within the bags used to pack food items to remove any remaining oxygen. Food items containing oil and fat won't go rancid if oxygen isn't present inside the pack.

Explanation:

Corrosion:

Metals undergo a natural process called corrosion that erodes their strength and limits their ability to sustain other structures. As a refined metal is changed into a more stable chemical state, such as an oxide, hydroxide, sulphate, or sulphide, corrosion occurs. Its capacity to perform its intended job is slowed by corrosion, which causes chemical or electrochemical reactions with the molecules in the fluid (gas or liquid) that surrounds it. The presence of microbiological organisms can also cause corrosion.

The rusting of iron or steel is a common example of corrosion. The oxidation of iron into iron oxide is the primary cause of corrosion. The surfaces have a reddish powdered deposit on them.

 Rancidity:

The oxidation of the fats and oils that are often found in food is the only cause of rancidity. Both complete and partial oxidation are possible. Foods that have gone rancid provide an incredibly bad flavour and odour. Oxidative rancidity is the term for rancidity that results from the oxidation of unsaturated fatty acids into aldehydes and ketones. Additional types of rancidity include hydrolytic rancidity, in which triglycerides are hydrolyzed to produce an unpleasant odour, and microbiological rancidity, in which fats are broken down utilising enzymes.

There are numerous varieties that make food unpalatable and harmful to our bodies. Meat spoilage is a common example of rancidity. Some of the poly-unsaturated fats in the meat will continue to deteriorate and turn rancid even after being immediately chilled. It is always preferable to eat meat right away after purchasing it.