The acidic behaviour of acids is due to the presence of hydrogenil(H⁺)ions in them. They produce hydrogen ions in the presence of water. Water is a polar solvent and this property of water helps in weakening the bond between the ions and makes them soluble. Hence, acids and bases produce ions in aqueous solutions.
It may be noted that a dry Hel gas or a solution of hydrogen chloride in organic, nonpolar solvents like toluene or benzene do not show acidic properties. This is because hydrogen chloride does not undergo ionization in toluene.
The reason why Hel splits into H⁺ and CI^- ions in presence of water lies in the fact that water molecules, being polar, pull the H⁺ and Cl ^- ions apart and thus, the bond in Hel is broken

(i) Identify the wrong statement.

(ii) If the pH of a solution is 8, then its [H⁺] ion is

(iii) In terms of acidic strength, which one of the following is in the correct increasing order?

(iv) Which of the following compounds does not give H⁺ ions in aqueous solution?

(v) Four solutions labelled as P, Q, Rand Shave pH values 1, 9, 3 and 13 respectively.
Which of the following statements about the given solutions is incorrect?

A compound, X of sodium forms a white powder. It is a constituent of baking powder and is used in some antacids. When heated it gives a compound, Y which is anhydrous and absorbs water to become a hydrated salt. When this salt is kept in open air, it loses water molecules in a process called efflorescence. When dissolved in water it forms a strong base and a weak acid, Z.
(i) What is the compound, X?

(ii) The compound, Y is

(iii) What is the nature of the solution formed by dissolving Y in water?

(iv) Identify the compound, Z.

(v) Sodium carbonate is a basic compound because it is a salt of a

Sodium chloride obtained from sea water or from lakes contains many impurities such as sulphates of sodium and magnesium along with chlorides of calcium and magnesium. The chlorides of calcium and magnesium are particularly undesirable on account of their deliquescent nature.
For its purification, common salt is dissolved in minimum quantity of water to get a saturated solution from which insoluble impurities are filtered off. Then hydrogen chloride gas is passed through the saturated solution and the crystals of pure NaCl separate out. The soluble impurities remain in the mother liquor. The crystals are filtered, washed and dried.
(i) Select the correct statement regarding salt NaCl.

(ii) Nature of aqueous solution of common salt is

(iii) In the given series of reactions, Y and Z respectively are
²

(iv) Which of the following compounds is alkaline in aqueous medium?

(v) Some statements regarding salt NaCI are given below
(I) It is prepared by chlor-alkali process
(II) It is a white crystalline substance
(III) It also exists in the form of rocks and is called rock salt
(IV) It is a neutral salt, pH value of NaCI is 7

Chemically, Plaster of Paris (POP) is calcium sulphate hemihydrate, i.e., containing half molecule of water of crystallisation. It is represented by the formula, CaSO_{4 ·}1/2H₂O. Half molecule of water of crystallisation means that one water molecule is shared by two formula units of CaSO_4. Hence, we also represent its formula as (CaSO₄)_2·H₂O. The name, plaster of Paris, was given to this compound because for the first time, it was made from gypsum which was mainly found in Paris.
(i) The difference of water molecules in gypsum and plaster of Paris is

(ii) Plaster of Paris hardens by

(iii) Which of the following statements is incorrect?

(iv) Select the incorrect statement with respect to gypsum

(v) Plaster of Paris is obtained by

pH is quite useful to us in a number of ways in daily life. Some of its applications are:
Control of pH of the soil: Plants need a specific pH range for proper growth. The soil may be acidic, basic or neutral depending upon the relative concentration of H⁺ and OH^-. The pH of any soil can be determined by using pH paper. If the soil is too acidic, it can be corrected by adding lime to it. If the soil is too basic, it can be corrected by adding organic manure which contains acidic materials
Regaining shine of a tarnished copper vessel by use of acids: A copper vessel gets tarnished due to formation of an oxide layer on its surface. On rubbing lemon on the vessel, the surface is cleaned and the vessel begins to shine again. This is due to the fact that copper oxide is basic in nature, which reacts with the acid (citric acid) present in lemon to form a salt (copper citrate) which is washed away with water. As a result, the layer of copper oxide is removed from the surface of the vessel and the shining surface is exposed
(i) When black copper oxide placed in a beaker is treated with dilute HCl, its colour changes to

(ii) P is an aqueous solution of acid and Q is an aqueous solution of base. When these two are diluted separately, then

(iii) Which of the following acids is present in bee sting?

(iv) Sting of ant can be cured by rubbing the affected area with soap because

(v) The pH of soil X is 7.5 while that of soil Y is 4.5. Which of the two soils, should be treated with powdered chalk to adjust its pH?

Baking powder produces carbon dioxide on heating, so it is used in cooking to make the batter spongy. Although, baking soda also produces CO₂ on heating, but it is not used in cooking because on heating, baking soda produces sodium carbonate along with carbon dioxide. Sodium carbonate, thus, produced, makes the taste bitter. Baking powder is the mixture of baking soda and a mild edible acid. Generally, tartaric acid is mixed with baking soda to make baking powder. When baking powder is heated, NaHCO₃ decomposes to give CO₂ which makes bread and cake fluffy. Tartaric acid helps to remove bitter taste due to formation of sodium tartrate.
\(2 \mathrm{NaHCO}_{3}+ \ \ \mathrm{C}_{4} \mathrm{H}_{6} \mathrm{O}_{6} \quad \longrightarrow \quad 2 \mathrm{CO}_{2}+2 \mathrm{H}_{2} \mathrm{O}+\mathrm{Na}_{2} \mathrm{C}_{4} \mathrm{H}_{4} \mathrm{O}_{6}\)
Baking soda         Tartaric acid            Carbon dioxide               Sodium tartrate
(i) On passing excess CO₂ gas in aqueous solution of sodium carbonate, the substance obtained is

(ii) When sodium hydrogen carbonate is added to acetic acid, it evolves a gas. Which of the following statements are true about the gas evolved?
(I) It turns lime water milky
(II) It extinguishes a burning splinter
(III) It dissolves in a solution of sodium hydroxide
(IV) It has a pungent odour

(iii) Select the correct statement regarding sodium hydrogen carbonate.

(iv) Acetic acid was added to a solid X kept in a test tube. A colourless and odourless gas was evolved. The gas was passed through lime water which turned milky. It was concluded that

(v) Which of the following statements are correct regarding baking soda?
(I) Baking soda is sodium hydrogen carbonate
(II) On heating, baking soda gives sodium carbonate
(III) It is used for manufacture of soap
(IV) It is an ingredient of baking powder

Bleaching powder is also known as chloride of lime. It is a solid and yellowish white in colour. Bleaching powder can be easily identified by the strong smell of chlorine. When calcium hydroxide (slaked lime) reacts with chlorine, it gives calcium oxychloride (bleaching powder) and water is formed. Aqueous solution of bleaching powder is basic in nature. The material to be bleached is first passed through solution of NaOH to remove greasy matter. Then it is passed through aqueous solution of bleaching powder and very dil. HCI solution. HCI reacts with bleaching powder to liberate nascent oxygen which bleaches material.
(i) Bleaching powder is used as

(ii) Bleaching powder is also known as

(iii) Bleaching powder gives smell of chlorine because it

(iv) Select the correct statement(s) regarding bleaching powder.

(v) Identify the product 'X' in the given reaction \(\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{Cl}_{2} \longrightarrow X+\mathrm{H}_{2} \mathrm{O}\)

The preparation of washing soda is carried out through following steps:
Step-I: Manufacture of sodium hydrogen carbonate:\(\mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}+\mathrm{NH}_{3}+\mathrm{CO}_{2} \longrightarrow \ \mathrm{NaHCO}_{3}+ \ \mathrm{NH}_{4} \mathrm{Cl}\)
                                                    Sodium hydrogen carbonate
Step-II: Thermal decomposition of sodium hydrogen carbonate: When dry crystals of sodium hydrogen carbonate are heated strongly, they decompose to form anhydrous sodium carbonate (soda ash). \(2 \mathrm{NaHCO}_{3(s)} \longrightarrow \mathrm{Na}_{2} \mathrm{CO}_{3(s)}+\mathrm{CO}_{2(g)}+\mathrm{H}_{2} \mathrm{O}_{(g)}\)
Step-III: Recrystallisation of sodium carbonate: Sodium carbonate thus obtained is recrystallised to form crystals of washing soda.\(\mathrm{Na}_{2} \mathrm{CO}_{3(s)}+ 10 \mathrm{H}_{2} \mathrm{O}_{(l)} \longrightarrow \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}_{(s)}\)
Anhydrous                                              Washing soda 
sodium carbonate
(i) Some of the uses of washing soda are given below:
(I) It is used for removing permanent hardness of water
(II) It is used in glass industry
(III) It is used in paper industry
(IV) It is used in the manufacture of sodium compounds such as borax
Select the correct option regarding uses of washing soda

(ii) What products will be formed along with water when sodium carbonate reacts with dilute hydrochloric acid? 

(iii) Chief raw materials for the manufacture of washing soda are

(iv) What is the action of sodium carbonate on litmus paper?

(v) What products will be obtained when solution of sodium carbonate and slaked lime is heated?

"Indicator is a chemical compound which is added to the solution in very small amount to detect its acidic or basic nature:" As they show colour change in acidic and basic medium, they are also called acid-base indicators. In other words, "an acid-base indicator is that substance which possesses one colour in acidic medium and a different colour in alkaline medium:''
Indicators, basically, are coloured organic substances either extracted from plants (natural indicators) or synthesised in the laboratory (synthetic indicators). A few common acid base indicators are: Litmus, phenolphthalein, methyl orange etc. In addition to these there are some naturally occurring substances which have different smell in acidic and basic medium. These substances are called olfactory indicators.
(i) Which one of the following will turn red litmus blue?

(ii) A solution turns blue litmus red. The pH of the solution is probably

(iii) A solution in test tube 'A' turns red litmus blue, evolves hydrogen gas on reaction with zinc and does not react with sodium carbonate. Whereas, solution in test tube 'B' turns blue litmus red, liberates hydrogen gas on reaction with zinc and evolves carbon dioxide gas with sodium carbonate. Identify 'A' and 'B'

(iv) Select the incorrect option

(v) Which one of the following can be used as an acid-base indicator by visually impaired student?

Acids turn blue litmus red but have no effect on red litmus. Bases turn red litmus blue but have no effect on blue litmus. The sample in which phenolphthalein remains colourless while methyl orange changes to pink/ red are acids while the samples in which phenolphthalein colour changes to pink and methyl orange changes to yellow are bases. Some observations of different sample solutions in litmus, phenolphthalein and methyl orange indicator are given in the table.

(i) Which of the following substances does not turn red litmus solution to blue?

(ii) Phenolphthalein's colour in basic medium is ___________but in acid it is ___________ .

(iii) Which of the following acids are edible?
(I) Citric acid
(II) Tartaric acid
(III) Hydrochloric acid
(IV) Carbonic acid.

(iv) The colour of methyl orange in neutral solution is

(v) Which of the following cannot act as an indicator?

A girl met with an accident and his leg fractured. She went to orthopedics doctor for treatment. On examination, the doctor mixed the white power in water and applied to her leg along with the cotton and gauze. After a while, it turned into white, solid, hard mass. He said that it would support her fractured bone in the right position.
(i)  After treatment, the doctor repacked the white powder back into moisture proof, airtight container. Why?
(a)  The fungus growth will occur in open
(b) The powder would react to moisture and turn into solid mass
(c) The powder with react to sunlight and turn into solid mass
(d) To prevent the stealing of the powder as it is very expensive
(ii) What is 'white, solid hard mass' called as?
(a) Talcum powder                          (b) Paris of Plaster
(c) Plaster of Paris                          (d) Copper sulphate
(iii) The graph shows the porosity and expansion of plaster with respect to water content

At what temperature, the reaction would occur?

(iv) The reaction involved in the formation of white mass is:

(v) Study the following reaction and choose the correct option:
\(\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}+\frac{3}{2} \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{CaSO}_{4} \cdot 2 \mathrm{H}_{2} \mathrm{O}\)
(a) Reactant is calcium hemihydrate, product is Gypsum
(b) Reactant is Gypsum, product is calcium hemihydrate
(c) Reactant is Gypsum, product is calcium sulphate hemihydrate
(d) Reactant is calcium sulphate hemihydrate, product is Gypsum

Ajay wanted his house to be white washed. He bought 10 kg of quicklime from the market. Before mixing all 10 kg, he took one beaker and took small quantity of quicklime in a beaker then he added some water, he observed that the water started boiling even when it was not being heated and he touch the beaker carefully. The beaker feels to be quite hot

(i) What is formed when water is added to quicklime.
(a) CaCO₃    (b) CaO    (c) Ca(OH)₂    (d) NaOH
(ii)  The nature of the product formed is:
(a) Acidic    (b) Basic    (c) Neutral    (d) Both (a) and (b)
(iii) The chemical reaction between quicklime and water is characterised by :
(a)  evolution of hydrogen gas
(b)  formation of slaked lime precipitate
(c) change in temperature of mixture
(d) change in colour of the product
The chemical reaction between quicklime (CaO) and water is characterized by change in temperature of mixture. The reaction is exothermic (heat is liberated) and a hissing sound is heard. The product is slaked lime (calcium hydroxide).
(iv) Which of the following statements is correct about the above reaction based on your observations?
I.    It is an endothermic reaction.
II.    It is an exothermic reaction
III.    The pH of the resulting solution will be more than seven.
IV.    The pH of the resulting solution will be less than seven.
(a) I and II    (b) II and III    (c) I and IV    (d) III and IV
It is an exothermic reaction because heat is given out. The resulting compound is Ca(OH)₂ which is basic in nature. So the pH of the resulting solution will be more than seven.
(v)  Which of the following is not an endothermic reaction ?
(a) CaCO₃ → CaO + CO₂
(b) 2H₂O → 2H₂ + O₂
(c) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(d) C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
During respiration, glucose combines with oxygen in the cells of our body to form carbon dioxide and water alongwith the production of energy.

Respiration is an exothermic process because energy is produced during this process

Whenever a solution has a pH of less than 7, it will be an acidic solution. For example, a solution having a pH of 4 will be acidic in nature (or it will be an acid). Please note that more acidic a solution is, the lower will be its pH. For example, a solution of pH 1 is much more acidic than another solution of pH 4. In other words, a solution of pH 1 will be a much more stronger acid than another acid having pH 4 (see the figure). The solutions having pH of 0, 1, 2 and 3 are usually considered to be strong acids. And the solutions having pH of 4, 5 and 6 are considered to be weak acid solutions. It is clear that the acidity of a substance is related to its pH. Strongly acidic substances have a very low pH. In fact, lower the pH, the stronger the acid.
(i)  A solution turns red litmus blue. Its pH is likely to be :
(a) 1    (b) 4    (c) 5    (d) 10
(ii)  The pH values of six solutions A to F are given below :
A = 0, B = 11, C = 6, D = 3, E = 13, F = 8
Which of the above solutions are acids
(a) A, C, D    (b) A, B, C    (c) A, C, D, F    (d) A, C, D, E
(iii) Fresh milk has a pH of 6. When milk changes into curd, the pH value will :
(a) become 7                      (b) become less than 6
(c) become more than 7    (d) remain unchanged
(iv)  The pH values of three acids A, B and C having equal molar concentrations are 5.0, 2.8 and 3.5 respectively.
Arrange these acids in order of the increasing acid strengths.
(a) A, C, B    (b) B, C, A    (c) A, B, C    (d) C, B, A
"Lesser the pH, stronger the acid.“
Considering the above statement, the order of increasing acidic strength is A < C < B
(v)  A beaker of concentrated hydrochloric acid has a pH of 1. What colour will full range universal indicator turn if it is added to this beaker?
(a) red    (b) blue    (c) pink    (d) no change in colour

A group of students measured the pH of some substances they found in their homes. Their results are given in the following table :

(i) Which solution is the most acidic?
(a) Apples    (b) Vinegar        (c) Lemon Juice    (d) Black Coffee
(ii) Which solution is the most alkaline?
(a) Household ammonia                 (b)  Washing soda
(c) Baking soda                              (d)  Toothpaste
(iii) Which solutions are neutral?
(a) Salt                 (b) Sugar
(c) Milk                 (d) Both (i) and (ii)
(iv) What will be the litmus test if the solution is basic?
(a) Red litmus will turn to blue
(b) Blue litmus will turn to red
(c) No change in colour
(d) It will change into orange pink.
(v) Arrange the following in order of the increasing basic strengths.
Baking soda, Toothpaste, Household ammonia, Washing soda
(a) Baking soda, Toothpaste, Household ammonia, Washing soda
(b) Baking soda, Toothpaste, Washing soda, Household ammonia
(c) Washing soda, Baking soda, Toothpaste, Household ammonia
(d) Baking soda, Household ammonia, Toothpaste, Washing soda
Higher the pH, the stronger the base