10th acid base and salt solved model sample paper

Question (1): Define the terms: Acid, alkali and salt.

Answer:  An acid is a compound, which releases hydronium ions (H₃O⁺) as the only positive ions in solution. 
An alkali is a compound, which releases hydroxyl ions (OH^-) as the only negative ions in solution. 
A salt is one of the products of neutralization between an acid and a base; water being the only other product. 
OR
 A salt gives positive ions other than H⁺ ion and negative ions other than OH^- ion in solution.

Question (2): Identify the number of replaceable hydrogen ions (H⁺) in the following acids: HCl, CH₃COOH, H₂SO₄, H₃PO₄.

Answer:  HCl = 1    CH₃COOH = 1       H₂SO₄ = 2     H₃PO₄ = 3.

Question (3): What is a neutralization reaction?

Answer:  Neutralization is essentially a chemical reaction between H₃O⁺ ions of an acid with OH^- ions of the base, to give undissociated molecules of water.

Question (4): What are strong and weak acids? Give one example of each?

Answer:  A strong acid is one, which is almost completely dissociated in solution. Examples: Dilute nitric acid, dilute sulphuric acid and dilute hydrochloric acid. 
A weak acid ionized in solution (degree of dissociation is >30%). Examples: Acetic acid, carbonic acid and sulphurous acid.

Question (5): Why is acetic acid called a weak acid though there are 4 'H' atoms in the molecule?

Answer:  Acetic acid is called a monobasic acid because only one of the 4 'H' atoms of the acid is released as H⁺ ion in solution.

Question (6): How does a strong acid differ from a concentrated acid?

Answer:  The strength of an acid depends upon its dissociation power whereas concentration depends on water content in the acid.

Question (7): Name a salt of a strong acid HNO₃ and a weak base like NH₄OH. Represent the reaction that takes place.

Answer:  The salt that results due to the above reaction is Ammonium nitrate (NH₄NO₃). The reaction is represented as:  HNO₃         +             NH₄OH         -------->     NH₄NO₃    

Question (8): What is the action of Na₂CO₃ solution on litmus and why?
Examples:  K⁺Ca²⁺PO^3- (Potassium calcium phosphate) , Na⁺K⁺SO₄^2- (Sodium potassium sulphate).

Question (9): Name the following:

Answer:   1) Two non-hydrated crystalline salts are: sodium chloride (NaCl) and potassium nitrate (KnO₃)

Question (10): Name the salts of sulphuric acid.

Answer:  The salts of sulphuric acid are bisulphate and sulphate. Examples: NaHSO₄, KHSO₄ and Na₂SO₄.

Question (11): Define the term "pH"; what does" pH" stand for?

Answer:  The term "pH" is defined as the negative logarithm of H⁺ ion concentration of a given solution; the concentration being expressed as moles per litre. Mathematically pH = - log [H⁺] 'pH' stands for: Power of hydrogen ion concentration, 'p' for power and 'H' for H⁺ ion concentration.

Question (12): What is 'pH' scale? Explain briefly.

Answer:  The strength of an acid or a base is expressed in terms of hydronium ion concentration. This is expressed on a scale known as 'pH' scale. It is a 14 point scale; i.e., it has values ranging from 0 to 14, indicating the value of negative logs of H⁺ ion concentration of the solution. Some important benchmark values in the pH scale are: pH = 7 indicates neutral solutions e.g., aqueous solutions. pH > 7 to 14 indicates alkaline solutions and pH < 7 to 0 indicate acidic solutions

Question (13): What is the 'pH' of pure water and that of rain water? Explain the difference.

Answer:  The pH of pure water is seven. Rain water is slightly acidic because as rain drop fall, the carbon dioxide in the air dissolves with drops to form very weak carbonic acid. Accordingly, rain water has a pH that is slightly below 7.

Question (14): What is the pH of solution 'A' which liberates CO₂ gas with a carbonate salt? Give the reason?

Answer:  The pH of solution 'A' is lesser than 7. Carbonates salts react with acids (A) to liberate CO₂ gas.

Question (15): What is the pH of solution 'B' which liberates NH₃ gas with an ammonium salt? Give reason?

Answer:  The pH of solution 'B' is lesser than 7 because 'B' is an alkali as it liberates NH₃ gas. Question (16): How do you increase or decrease the pH of pure water? 
Answer:  By adding a few drops of alkali to pure water, it's pH increases; and by adding a few drops of an acid decreases the pH of pure water.

Question (17): What are indicators?

Answer:  Indicators are chemicals that show whether the given solution is acidic or basic, by the sudden change of color.

Question (18): Name the common acid-base indicators used in the laboratory with their color change.

Answer:  The three common indicators used in the laboratory are:

Question (19): What is a universal indicator? What is its advantage?

Answer:  A universal indicator is a mixed indicator of organic chemicals which not only shows whether the given solution is acidic or basic, but also shows the approximate pH values by giving a wide particular colour for a specific value of pH.

Question (20): What is the action of litmus on ferric chloride solution and why?

Answer:  An aqueous solution of FeCl₃ salt undergoes hydrolysis and releases H⁺ ions from the stronger acid HCl formed. Hence, the resulting solution is acidic and turns blue litmus turns red.

Fecl₃    +   3 H₂O          ------------->    Fe (OH)₃    + 3 H Cl

HCl -------------------------> H⁺      +   Cl ^-
Question (21): 1) Name a strong base and a weak base. 2) Name a hydrated salt.

Answer:  1) A strong base is sodium hydroxide (NaOH) and a weak base is ammonium hydroxide (NH₄OH). 

Question (22): What is the action of NaHSO₄ solution on litmus and why?

Answer:  Blue litmus turns red in NaHSO₄ solution due to the release of H⁺ ions along with Na⁺ ions. Thus, NaHSO₄ is an acid salt.

Question (23): Though NaHSO₄ solution releases H⁺ ions, why is it not called an acid?

Answer:  NaHSO₄ solution is not called an acid because an acid should release only H⁺ ions as positive ions and not any other positive ions. But NaHSO₄ is solution releases H⁺ ions as well as Na⁺ ions also as positive ion.

Question (24): Define the term ' normal salt ' with examples.
Answer:  A normal salt is produced when all the replaceable 'H' atoms of an acid are completely replaced by a metal or NH₄ group, during neutralization with a base. Examples: NaCl, K₂CO₃and (NH₄)₃PO₄.

Question (25): Define the term 'acid salt' with examples.

Answer:  An acid salt is formed when the available 'H' atoms of an acid are only partially replaced by a metal, during neutralization with a base, and hence there are still 'H' atoms present in the salt that are available for replacement.  Examples: NaHSO₄, NaHCO₃, Na₂HPO₄and NaH₂PO₄

Question (26): Define the term 'basic salt' with an example.

Answer:  A basic salt is formed by the incomplete neutralization of a base with an acid or partial replacement of hydroxyl radicals of a diacidic base or a triacidic base with an acid radical. Example: Zn(OH)Cl, Cu(OH)NO₃.

Question (27): Define a double salt. Give some examples.

Answer:  A double salt is formed between two simple salts by crystallization from a saturated solution of a mixture of the two. 
Examples   
K₂SO_4.Al₂(SO₄)₃.24H₂O ( potash Alum),

(NH₄)₂ Al₂(SO₄)₃.24H₂O (Ammonium Alum)                      
FeSO₄(NH₄)₂ SO₄.6H₂O (Mohr’s Salt)

Question (28): Define mixed salt giving some examples.

Answer:  Mixed salts contain more than one acid radical or basic radical other than H⁺ and OH^- ions.

Ca²⁺(OCl)^-Cl^- [Bleaching powder (Calcium chloro hypochlorite)]

Question 29: How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?

Ans. : When an acid is diluted, the concentration of hydronium ions (H₃O⁺) per unit volume decreases. This means that the strength of the acid decreases.

Question (30): What happens if NaOH is added to ferrous ammonium sulphate solution and warmed? What is the inference?

Answer:  When NaOH is added to ferrous ammonium sulphate solution and warmed, both ferrous ion and ammonium ion separate and exhibit their individual properties. A green precipitate of Fe(OH)₂ is formed and the smell of NH₃ gas from (NH₄)⁺ ion is observed. Hence it is an example of the formation of a double salt.

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X: Acids, Bases and Salts : Model Test paper For CBSE Examinations

Model Test paper For CBSE Examinations

ACID, BASE AND SALTS

Time: 2 hrs                                       M.M 40

General Instructions

1. All questions are compulsory.

1. Write chemical equations wherever required.

1. Draw neat and clean diagrams.

1. Question no. 01 to 10 carries 01 marks each.

1. Question no. 11 to 14 carries 02 marks each.

Question no. 15 to 18 carries 03 marks each.

Question no. 19 to 20 carries 05 marks each.

Que. 1 Why does distilled water not conducts electricity, whereas rainwater does?

Que. 2 Fresh milk has a pH 6. How do you think the pH will change as it becomes sour?

Que. 3 What is alkalis?

Que. 4 How is concentration of hydroxide ions (OH^-) affected when excess of base is dissolved in a solution of sodium hydroxide?

Que.  5 What is acid rain? How does it affect our aquatic life?

Que.  6 What happens during a bee sting? What is its remedy?

Que.  7 Two solutions X and Y are tested with universal indicator. Solution X turns orange whereas solution Y turns red. Which of the solution is a stronger acid?

Que.  8 Why does dry HCI gas not change the colour of the dry litmus paper?

Que.  9 Three solutions A, B and C have pH, values of 6, 4 and 10 respectively. Which of the solution is highly acidic?

Que.  10 Why should curd and sour substances not be kept in brass and copper vessels?

Que.  11 State Arrhenius Concept of acids and bases. Giving reason, select a strong acid and a weak base from amongst the following substances:

H₂CO₃, HNO₃, NaOH, NH₄OH

Que.  12 Sate the chemical property in each case on which the following uses of baking soda are based.

(i) as an antacid.

(ii) as a constituent of baking powder

Que.  13 What happens when

(i) plaster of Paris is heated to 473 K? (ii) plaster of Paris is mixed with water?

Que.  14 What happens when

(a) solid sodium hydrogen carbonate is heated,

(b) chlorine gas is passed through dry slaked lime,

Que.  15 (i) Why are acids not stored in meal containers? Containers made from which material are safe to store acids.

(ii) Explain why does dry hydrochloric acid not conduct electricity but its aqueous

solution conducts electricity.

(iii) Why are commercial samples of bleaching powder not completely soluble in water?

Que.  16  A metal compound ‘X’ reacts with dilute hydrochloric acid to produce gas (Y). The gas (Y) evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. Write names of X & Y.

Que.  17 Explain the pH change as the cause of tooth decay. How can tooth decay caused by pH change be prevented?

Que.  18 Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCI) is added to test tube A, while acetic acid (CH3 COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?

Que.  19 Write one activity to show the reaction of acids with metal Carbonates/Bicarbonates salts.

Or

Compounds like alcohol and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.

Que.  20 Identify the compounds of calcium which is yellowish white powder and is used for disinfecting drinking water. How is it manufactured? White the chemical equation for the reaction involved. What happens when it is left exposed to air?

Or

What happens when

(i) Aluminium metal reacts with dilute HCI?

(ii) Potassium oxide is dissolved in water?

(iii) Sodium hydroxide reacts with sulphuric acid completely?

Give equation for the chemical reactions involved.

                                                                                                Prepared by:

                                                                                                Sinha Sir

Solved example for 10th class Science Acid , Base and salt

1. A milkman adds a very small amount of baking soda to fresh milk

Ans: A milkman adds a very small amount of baking soda to fresh milk to increase alkalinity of milk that prevent to set as curd

2. Why do acids not show acidic behaviour in the absence of water?

Answer : In absence of water, acids do not dissociate H - So, they do not show acidic behaviour.

3. Alcohols and Glucose contain hydrogen but are not categorized as acids.

Answer: Alcohols and Glucose does not dissociate into ions on dissociation. So, the are not an acid.

4. Plaster of Paris should be stored in a moisture-proof container. Explain why?

Answer : Plaster of Paris easily absorbs water and forms hard gypsum. Thus, if Plaster of Paris is not kept in a moisture-proof container, then all Plaster of Paris will get converted into gypsum.

Ca SO4 .1/2 H2O + 3/2 H2O ------> CaSO4 . 2H2O ( gypsum)

5. Why is calcium sulphate hemihydrates called 'Plaster of Paris'?

Answer: A big source of this substance is at Montmartre in Paris. So it is called as Plaster of Paris.

6. Equal lengths of the magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occur more vigorously and why?

Answer : Since HCl is strong acid and CH3COOH is a weak acid so being HCl a strong acid , dissociate more so that In test tube A, fizzing occur more vigorously.

7. Name a solution reacts with crushed egg-shells to give a gas that lime-water milky.


Answer H Cl , H Cl + CaCO3 ----> CaCl2 + Co2 + H2O

In this reaction carbon di oxide is given off that tumn lime water milky

8. Why does distilled water not conduct electricity, whereas rain water does.

Answer : Distilled water does not dissociate into ions. So it doe snot conduct electricity. Rain water has dissolved CO2 in it which form carbonic acid.

CO2 + H2O ----> H2CO3 This carbonic acid dissociate into ions.

H2CO3 + 2H2O-------à (H3O+)2 + CO3-2

These ions are responsible for electrical conductivity of rain water.

9. What is aqua-regia ?

Answer : A mixture (acid) of HCl and HNO3. Formed by mixing 3 moles of HCl and 1 mole of HNO3 i.e in the ratio 3:1.

This is one of the few acids that can dissolve metals like gold and platinum and use by gold smith . FIrst discovered by the famous muslim scientist Jabir-bin-Haiyan(known as the father of chemistry). It is a highly-corrosive fuming yellow liquid.

The name "Aqua Regia" is latin for "Royal Water". It was so named because it could dissolve the royal noble metals.Aqua regia works to dissolve gold, even though neither constituent acid will do so alone because, in combination, each acid performs a different task. Nitric acid is a powerful oxidizer, which will actually dissolve a tiny (virtually undetectable) amount of gold, forming gold ions.

 The hydrochloric acid provides a ready supply of chloride ions, which react with the latter, thus taking the gold out of the solution. This allows further oxidation of gold to take place, and so the gold is dissolved.

10. Name the sodium compound which is used for softening hard water.

Answer : Hard water is water that has high mineral content .Hard water has high concentrations of Ca2+ and Mg2+ ions. Washing soda i.e., sodium carbonate (Na2CO3). is used for softening hard water.

It precipitates calcium and magnesium ions out of hard water.

11. Why should curd and sour substances not be kept in brass and copper vessels?

Answer : Curd and sour substances contain acids. Acids reacts with metals to give salt and hydrogen gas. So, if such substances are kept in copper container, the acid will react and the container will be corroded.

12. What is efflorescence?

Answer: Efflorescence is the loss of water (usually as evaporation to air) in an aqueous solution of salts, leaving behind crusts of solid salt crystals, called efflorescent salts

13.Explain the term olfactory indicator.

Ans. Substances whose odour changes in acidic or basic medium are called olfactory indicator. e.g. Eucalyptus (nilgiri) Oil, Onion & clove extract.

14. What is universal indicator? Does  Mg(OH)₂  react with sodium hydroxide? If not, why?

Ans. Universal indicator is a mixture of several indicators which gives different colours at different pH values of the pH scale.

Mg(OH)₂ does not react with sodium hydroxide as both are bases having the same negative radical i.e. OH-

15.Why is Plaster of Paris written as CaSO4. ½ H2O ? How is it possible to have half a water
molecule attached to CuSO4? 

Ans. The actual formula of Plaster of Paris is 2CaSO4.H2O which means that one molecule of
H2O is associated with two molecules of CaSO4. The formula for simplicity is written as CaSO4.
½H2O.

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10th class Chemistry chapter 1. Chemical change

Chemistry Adda

1. Chemical reactions- Chemical changes or chemical reactions are the changes in which one or more new substances are formed.

2. Chemical Equations – Representation of a chemical reaction in terms of symbols and formulae of the reactants and products is known as chemical equation.

3. Balanced Chemical equation – The chemical equation in which the no. of atoms of different elements is same on both sides of the arrow is called balanced chemical equation.

4. The chemical reactions can be classified into different types such as

(a) Combination reactions- The reactions in which two or more substances combine to form a new substance are called combination reactions. For example,

2Mg(s) + O2 (g) → 2 MgO (s)

(b) Decomposition reactions – The reactions in which a single compound breaks up into two or more simpler substances are called decomposition reactions. For example,

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

The decomposition of a substance on heating is known as thermal decomposition. The decomposition of a substance by passing electric current through it is known as electrolysis.

For example, when electric current is passed through acidified water, it decomposes into hydrogen and oxygen. Electric current

2H2O (l) → 2H2 (g) + O2 (g)

Certain compounds when exposed to light undergo decomposition. For example, Silver chloride when exposed to sunlight turns grey due to its decomposition into silver and chlorine. Sunlight 2AgCl(s) → 2Ag(s) + Cl2 (g)

The decomposition of a substance by absorbing light energy is called photolysis or photochemical decomposition.

(c) Displacement Reactions- The chemical reactions in which a more reactive element displaces a less reactive element from a compound are known as displacement reactions.

 For Example,

(i) Zn(s) + CuSO4 (aq) → ZnSO4 (aq) + Cu(s)

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

(d) Double Displacement Reactions- The chemical reactions in which compounds react to form two different compounds by mutual exchange of ions are called double displacement reactions. These reactions take place in solution. Two common types of double displacement reactions are precipitation reactions and neutralization reactions.

(i) Precipitation reaction : In precipitation reactions, aqueous solution of two salts are mixed whereby some salts precipitate due to mutual exchange of ions between the two salts. For example

AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3

(ii) Neutralization reaction: In this type of reaction an acid reacts with a base to form salt and water by exchange of ions. NaOH (aq) + HCl (aq) → NaCl (aq) + H2O

(e) Redox reaction : If a substance gains oxygen or looses hydrogen during a reaction it is oxidized. On the other hand if a substance loses oxygen or gains hydrogen during a reaction, it is reduced. Both oxidation and reduction take place simultaneously and hence these are called redox reaction. Oxidation

ZnO               +            C       →    Zn + CO

Reduction           Oxidation

Cl2                    +        H2S          → 2HCl + S

Reduction

(f) Exothermic reaction and endothermic reaction : On the basis of energy changes during chemical reaction, they can be classified as

(i) Exothermic reaction- A chemical reaction in which heat energy is produced is called exothermic reaction .For e.g. (i) C (s) + O2 → CO2 (g) + Heat

(ii) Endothermic reaction- A chemical reaction in which heat energy is absorbed is called endothermic reaction. CaCO3 + Heat → CaO + CO2

5. Effects of some oxidation reaction in everyday life:

(a) Corrosion – The process of slow conversion of metals into their undesirable compounds due to their reaction with moisture and other gases present in the atmosphere is called corrosion of metals. Some common examples of corrosion are rusting of iron, formation of green layer on the surface of copper, tarnishing of silver etc. Formation of brown layer on the surface of iron is called rusting of iron. Formula of rust is Fe2O3.xH2o. Rusting of iron is a serious problem.

 (b) Rancidity- The taste and odour of food materials containing fat and oil changes when they are left exposed to air for a long time. This is known as rancidity. Rancidity is caused due to oxidation of fat and oil present in food materials. Rancidity can be prevented by using various methods such as by adding antioxidants to the food materials, storing food in air tight container and by flushing out air with some inert gases like nitrogen.

Extrascore science Acid Base and Salt Solved question class 10th

For CBSE Student: CPS and SDV

1. Match the important chemicals given in Column (A) with the chemical formulae given in Column (B)

Column (A)                       Column (B)

(a) Plaster of Paris                (i) Ca(OH)2

(b) Gypsum                          (ii) CaSO4.1/2 H2O

(c) Bleaching Powder           (iii) CaSO4.2H2O

(d) Slaked Lime                    (iv) CaOCl2

2. Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.

3. What happens when nitric acid is added to egg shell?

4. How would you distinguish between baking powder and washing soda by heating?

5. Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water turns it milky. Identify A, B and C.

6. In one of the industrial processes used for manufacture of sodium hydroxide, a gas X is formed as by product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y giving the chemical equation of the reactions involved.

7. What are strong and weak acids? In the following list of acids, separate strong acids from weak acids.  Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.

8. When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilized in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.

9.Why aqueous solution of sodium carbonate is basic in nature?

10.Why is an aqueous solution of ammonium chloride acidic in nature?

Answer

1. (a)— (ii) (b)— (iii) (c)— (iv) (d)— (i)

2. The acid present in ant sting is methanoic acid (formic acid). The chemical formula is HCOOH. To get relief one should apply any available basic salt e.g., baking soda (NaHCO3) on it.

3. Egg shells contain calcium carbonate. When nitric acid is added to it, carbon dioxide gas is evolved. The reaction can be given as CaCO3 + 2HNO3 → Ca (NO3)2 + H2O + CO2

4. The chemical formula of baking powder is sodium hydrogen carbonate (NaHCO3). Whereas, that of washing soda is sodium carbonate (Na2CO3.10H2O)Sodium hydrogencarbonate on heating gives CO2 gas which will turn lime water milky whereas no such gas is obtained from sodium carbonate.

2NaHCO3 ---Heat→ Na2CO3 + H2O + CO2

Na2CO3.10H2O -Heat→ Na2CO3 + 10H2O

5. Baking powder (NaHCO3), salt A is commonly used in bakery products. On heating it forms sodium carbonate (Na2CO3), B and CO2 gas, C is evolved. When CO2 gas is passed through lime water it forms calcium carbonate (CaCO3), which is slightly soluble in water making it milky
A – NaHCO3 B – Na2CO3 C - CO2

6. In the manufacture of sodium hydroxide, hydrogen gas and chlorine gas (X) are formed as by–products. When chlorine gas (X) reacts with lime water, it forms calcium oxychloride (bleaching powder) Y. The reactions are

2NaCl (aq) + 2H2O(l) ---> 2NaOH (aq) + Cl2 (g) + H2(g)
X ---------> Cl2 (Chlorine gas)

Ca (OH)2 (s) + Cl2 (g) --------> CaOCl2 (s) + H2O
Y —> Calcium oxy chloride (bleaching powder)

7. In aqueous solutions strong acids ionize completely and provide hydronium ions. On the other hand weak acids are partially ionized and an aqueous solution of same molar concentration provides a much smaller concentration of H3O+ ions.

Strong acids — Hydrochloric acid, sulphuric acid, nitric acid
Weak acid — Citric acid, acetic acid, formic acid

8. When zinc reacts with dilute solution of strong acid, it forms salt and hydrogen gas is evolved.
Zn + 2HCl ------> ZnCl2 + H2
When a burning splinter is brought near the mouth of the test tube, the gas burns with a pop sound.

9.Ans: Sodium bicarbonate is an amphoteric compound. Aqueous solutions are mildly alkaline due to the formation of carbonic acid and hydroxide ion:
NaHCO3 + H2O → H2CO3 + OH− 

10.A basic component is the one that produces hydroxide (OH-) ions when dissolved in water. In aqueous solution of ammonium chloride, ammonium ions (NH4+) first associate with H2O and form ammonia and hydroxide ions.
NH4Cl + H2O = NH4+ + HCl
NH4+ + H2O = NH3 + OH-
Since ammonium ions produce hydroxide ions, NH4+ are considered to be the basic components.

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CBSE Acid base and salt Short type Questions with solution for 10

Chemistry Adda  VERY SHORT QUESTIONS ANSWER

Q.1. Name two natural indicators.

Ans. Litmus solution, beet-root extract and turmeric solution.

Q.2. Name the acid present in vinegar and lemon.

Ans. In vinegar acetic acid is present and in lemon it is citric acid.

 Q.3. What is an Alkali. 

Ans. The base that dissolves in water is called alkali.

Q.4. What is the colour of methyl orange in acidic solution.

Ans. The colour of methyl orange is pink in acidic solution.

Q.5. In a solution phenolphthalein turns pink. What is the nature or solution?

Ans. The solution is basic.

Q.6. Hydrogen ion concentration of an acid is 1×10-2 mol/L, what is its pH.

Ans. Its pH is 2.

Q.7. pH of one solution is 7, is it acidic basic or neutral.

Ans. Solution with pH no 7 is neutral.

Q.8.Which has a higher pH value, 1M HCl or 1M NaOH

solution. Ans. 1M NaOH solution has higher pH value.

Q.9. Name two strong and two weak acids.

Ans. Strong acid: Hydrochloric acid and Nitric acid. Weak acid: Acetic acid and carbonic acid.

 Q.10. Name the gas formed when sodium hydroxide reacts with zinc.

Ans. Hydrogen gas is formed when NaOH reacts with zinc.

Q.11. What is bleaching powder?

Ans. Bleaching powder is a mixture of CaOCl2 .Ca(OH)2 .CaCl2 .2H2O.

Q.12. Write the chemical formula for washing soda.

Ans. Chemical formula for washing soda is Na2CO3.10H2O.

Q.13. Write the chemical name of baking soda.

 Ans. Its chemical name is sodium hydrogen carbonate.

Q.14. Write one domestic use of sodium carbonate. 

Ans. It is used as a cleansing agent.

Q.15. What happens when gypsum is heated at 373 K.

Ans. When gypsum is heated at 373 K .it changes to plaster of paris. 

CaSO4. 2H2O → CaSo4. ½ H2O +1 ½ H2O 

Gypsum                              Plaster of Paris

Q.16. Doctors use paste of a white substance in water to maintain a 
fractured bone in its place. Identify the substance and write its chemical formula.

Ans. Name of the compound: Plaster of Paris.

Acids Bases and Salts

2 and 3 Marks questions

Q 1.What are indicators ? Name some common indicators

Ans. Indicators are substances that undergo definite color change in acids and bases solution. Some common indicators are – Litmus solution, methyl orange, phenolphthalein etc.

Q.2. What are alkalis? Write three examples.

Ans. The bases which dissolve in water to give OH- ions in solution are called alkalis, such as- NaOH, KOH, Ca(OH)2.

Q3. While diluting the acid, why is it recommended that acids should be added to water and not water to acid?

Ans. Mixing of water and acid is a highly exothermic process. When water is added to acid , due to small amount of water, evolved heat will change it to vapour and acid will spill out and may cause injury. So it is advised to mix acid to water and not water to acid.

Q4. Write the composition of baking powder. What will happen if tartaric acid is not added to it?

Ans. Baking powder is a mixture of sodium bicarbonate and tartaric acid. This acid neutralizes sodium carbonate formed on decomposition of baking soda. If tartaric acid is not present in baking powder‘, the food materials such as cake will taste bitter due to the presence of sodium carbonate.

Q5. What isBleaching powder? How is it prepared and write its two uses.

Ans. Bleaching powder is Calciumoxychloride and its formula is CaOCl2. It is prepared by passing chlorine gas through slaked lime.

Ca(OH)2+Cl2 CaOCl2+Cl2

Two uses of bleaching powder-

1. It is used to disinfect water

2. It is used to bleach cotton and paper

Q.6. A student working in the laboratory added some water to a syrupy liquid taken in a tube. The tube immediately cracked and the liquid which escaped out of it, produced blisters on the skin of the student. What actually happened?

Ans. The syrupy liquid was concentrated sulphuric acid. On adding water, large amount of heat is released. For this reason the tube cracked and the acid produced blisters on the skin.

Q.7. The pH of rain water collected from two cities A and B was found to be 6 and 5 respectively. Water of which city is more acidic? Find out the ratio of hydrogen ion concentration in the two samples of the rain water.

Ans. Rain water with pH 5 obtained from city B is more acidic than the rain water of city A. The ratio of hydrogen ion concentration can be calculated as below: For city

A: pH= -log[H+]=1

6= -log[H+]

Log[H+]= -6

[H+]= 10^-6

Similarly,

for city B,

we can have [H+]=10^-5

Ratio of [H+] of samples

= 10^-6/10^-5

= 1/10

Q.8. A compound X of sodium is commonly used for making crispy pakoras. It is also used for curing acidity in the stomach. Identify ‗X‘. What is its formula? State the reaction that takes place when it is heated.

Ans. The compound X is baking soda, a constituent of baking powder. Its chemical name is sodium hydrogen carbonate and its formula is NaHCO3.

On heating this compound gives CO2 gas.

2NaHCO3 (s) ------> Na2CO3 + H2O + CO2 


Q.9. Dry hydrogen chloride gas does not turn blue litmus whereas hydrochloric acid does. Give one reason.

Ans. In the dry state, hydrogen chloride (HCl) does not release H+ ions. Therefore, it cannot behave as an acid. When dissolved in water, it forms hydrochloric acid. It dissociates to give H+ ion in solution and behaves as an acid. HCl (aq) -----> H+ (aq) + Cl- (aq)

Q.10. Why is Plaster of Paris written as CaSO4. ½ H2O ? How is it possible to have half a water molecule attached to CuSO4?

Ans. The actual formula of Plaster of Paris is 2CaSO4.H2O which means that one molecule of H2O is associated with two molecules of CaSO4. The formula for simplicity is written as CaSO4. ½H2O.

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