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Acids & Bases |
Acids are sour in taste with pH below 7 where as Bases
are bitter in taste with pH above 7. They change the colour of Indicators |
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Indicators |
Litmus: Turns Red in Acid and Blue in Base Phenolphthalein: Remains colourless in Acid and
turns Pink in Base Turmeric: Remains Yellow colour in Acid and
changes to Orange-Red in base Methyl Orange: It turns Red in Acid and Yellow
in Base China Rose: Turns Pink in Acid and Green in base |
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Olfactory Indicators |
These Indicators change their odour in an Acid or a Base
e.g. Vanilla, Onion, Clove |
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Chemical properties of Acids and Bases |
Acid + Metal -> Salt + Hydrogen Acid + Metal Carbonate -> Salt + CO2 + H2O Acid + Base -> Salt + Water |
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More about Acids & Bases |
Acids and Bases conduct electricity in aqueous
solutions, Acids generate H+ ions and Bases generate OH- ions in
an aqueous solution (Water) Acid should be slowly added to water with constant
stirring as it is exothermic reaction |
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pH |
pH means Potenz of Hydrogen. It measures the Concentration
of H+/OH- ions produced. pH of 0-6-9 is Acid, 7 is neutral, 7.1 – 14 is Basic |
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Some naturally occurring Acid |
Vinegar: Acetic Acid, Orange/Lemon: Citric Acid Tamarind: Tartaric Acid Nettle: Methanoic Acid Tomatoes: Oxalic Acid Apples: Malic Acid |
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Sodium Hydroxide |
Formula: NaOH, also called Caustic Soda or Lye. Used to
make soaps, detergents, paper etc |
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Calcium Hypo Chloride |
Formula: CaOCl2, also called Bleaching Powder. Used in
bleaching, disinfecting water, oxidizing agent |
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Sodium Bi Carbonate |
Formula: NaHCO3, also called Baking Soda. Used to make
baking Powder, in Antacids |
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Sodium Carbonate |
Formula: Na2CO3, also called Washing Soda. Used in
glass, soap industry, Make Borax, to remove hardness of water |
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Water of Crystallization |
Fixed number of Water molecules present in one formula
unit of a salt. Example: Washing Soda: Na2SO4 has 10 molecules of Water Copper Sulphate: CuSO4 has 5 molecules of water Gypsum: CaSO4 has 2 molecules of water |
Q. You have been provided with three test tubes. One of them contains distilled water and other two contain acidic and basic solution. If you are given only red litmus paper, how will your identify the contents of each test tube?
Ans: When we dip the red litmus paper into the test tubes, the colour changes to blue in test tube containing Basic solution.
The colour changes to Purple in distilled water.
The colour will not change in acidic solution.
Q. Why should Curd and sour substances not be kept in brass and copper vessels?
Ans: Curd and sour substances contains acid which reacts with brass and copper vessels to produces toxic substances.
Q. Which gas is usually liberated when an acid reacts with metal? Illustrate with an example. How will you test the presence of this gas?
Ans: When an acid reacts with metal, hydrogen gas is produced.
E.g
Mg + HCl ___> MgCl2 + H2
When burning incense stick is bought near the gas, It produces "Pop" sound.
Q. A metal compound A reacts with dilute HCl to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction, if one of the compounds formed is calcium chloride.
Ans:
The Metal Compound A is calcium carbonate and the gas produced is Carbon dioxide.
The reaction is as follows;
CaCO3 + HCl ____> CaCl2 + H2O + CO2
Q. Why do HCl, HNO3 etc show acidic characters in aqueous solutions while as solutions of compounds like alcohol and glucose do not show acidic character ?
Ans: HCl, HNO3 dissociate in aqueous solution to form H+ ions, hence show acidic characters. Where as Alcohol, Glucose do not form H+ ions.
Q. Why does an aqueous solution of an acid conduct electricity?
Ans: An aqueous solution of acid contains H+ and other anions . Hence it conducts electricity.
Q. Why does dry HCl gas not change colour on dry litmus paper.
Ans: Dry HCl gas is a covalent compound. It does not dissociate to form H+ ions.
Hence, no change in colour of dry litmus paper.
Q. While diluting an acid, why is it recommended that the acid should be added to water and not water to acid?
Ans: Adding water to acid is an exothermic reaction. Acid must be slowly added to water and stirred.
If water is added to acid, the heat generated causes mixture to splash and break glass container due to heat as well.
Q. How is concentration of hydronium ions (H3O+) affected when a solution of acid is diluted?
Ans: When a solution of acid is diluted, the concentration of hydronium ions (H3O+) decreases.
Q. How is concentration of hydroxide ions (OH-) affected when excess base is dissolved in the solution of sodium hydroxide?
Ans: We know that hydroxide ions (OH-) are produced when a base is dissolved in water.
When excess base is dissolved is a solution of sodium hydroxide, the concentration of hydroxide ions will increase.
Q. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which of these is basic?
Ans: pH is negative logarithm of hydrogen ion concentration. Therefore Solution with lower pH has more hydrogen ions.
So, Solution A has more hydrogen ion concentration.
Q. Under what soil conditions do you think a farmer would treat the soil of his fields with quick lime (Calcium oxide) or slaked lime ( Calcium hydroxide) or chalk (Calcium carbonate) ?
Ans: If the soil becomes acidified and pH is less than 7 due the use of Pesticides, fertilizers and insecticides, the farmer would treat soil with quick lime, slaked lime or chalk.
Q. What is common name of the compound CaOCl2 ?
Ans: CaOCl2 is named as Bleaching powder.
Q. Name the substance which on treatment with chlorine yields bleaching powder.
Ans: Dry slaked lime.
Q. Name the sodium compound which is used for softening hard water.
Ans: Washing soda is used for softening hard water.
Q. What will happen if a solution of Sodium hydrocarbonate is heated? Give the equation of reaction involved.
Ans: When the solution of Sodium hydrocarbonate is heated, it decomposes into sodium carbonate, water and carbon dioxide.
NaHCO3 ____> Na2CO3 + H2O + CO2
Sod. Hydrocarbonate Sod. Carbonate
Q. Write an equation to show reaction between Plaster of Paris and water.
Ans: Plaster of Paris reacts with water to form gypsum.
CaSO4. 1/2 H2O + H20 ____> CaSO4.2H20
POP Gypsum
Q. Write equation and then balance equations for the reaction taking place when:
a. Dilute Sulphuric acid reacts with zinc granules
Ans: Zn + H2SO4 ____> ZnSO4 + H2
b. Dilute hydrochloric acid reacts with magnesium ribbon.
Ans: Mg + 2 HCl _____> MgCl2 + H2
c. Dilute sulphuric acid reacts with aluminium powder.
Ans:
d. Dilute sulphuric acid reacts with iron filings.
Ans: H2SO4 + Fe ____> FeSO4 + H2
Q. Why does distilled water not conduct electricity, where as rain water does?
Ans: Rain water contains impurities in form of ions and salts due to which it conducts electricity. However distilled water does not contain ions.
Q. Why do acids not show acidic behaviour in the absence of water?
Ans: Acid reacts with water to form hydrogen ions (H+ ions) due to which it shows acidic behaviour.
However in absence of water, acids do not dissociate to form Hydrogen ions.
Q. Equal lengths of magnesium ribbon are taken in test tube A and B. Hydrochloric acid is added to test tube A, while acetic acid is added to test tube B. In which test tube will the fizzing occur more vigorously and why?
Ans: Fizzing will occur more vigorously in test tube A as hydrochloric acid is more strong acid than acetic acid.
Q. Fresh milk has the pH of 6. What do you think the pH will change as it turns into curd? Explain your answer.
Ans: As the curd is more acidic than milk due to presence of lactic acid. Hence, pH will be less than milk.
Q. A milkman adds a very small amount of baking soda to fresh milk.
A. Why does he shift the pH of fresh milk from 6 to slightly alkaline?
Ans: The milk man shifts the pH to alkaline to stop formation of curd and stop milk from spoiling.
B. Why does this milk take a long time to set as curd?
Ans: The milk to which baking soda is added takes long time to set as curd because lactic acid produced reacts with baking soda to form salt.
Q. Plaster of paris should be stored in moisture proof container. Explain why?
Ans: This is because plaster of paris reacts with water to form hard mass called gypsum.
CaSO4. 1/2 H2O + H20 ____> CaSO4.2H20
POP Gypsum
Q. What is neutralization reaction? Give two examples.
Ans: Neutralization is a reaction of acid with base to form salt and water.
Examples:
HCl + NaOH ____> NaCl + H2O
HNO3 + KOH ____> KNO3 + H20
Q. Give two important uses of Washing Soda?
Ans: Washing Soda is Na2CO3.
Its uses are:
1. It is used to make glass
2. It is used to make soap
3. It is used to soften hard water.
Q. Give two important uses of Baking Soda?
Ans: Baking soda is NaHCO3.
Its uses are:
1. It is used to make baking powder.
2. It is used as antacid.
Q. Give important uses of plaster of paris?
Ans: Plaster of paris is CaSO4. 1/2H2O
Uses:
It is used to make statues, models etc
It is used to treat fractures in bones.
It is used as fire proof material.
Q. Give chemical name of bleaching powder? Give its uses.
Ans: Bleaching powder is CaOCl2.
Uses:
It is used to bleach textiles.
It is used in paper industry.
It is used as oxidizing agent.
Q. What is baking powder? How does it cause cakes to become fluffy.
Ans: Baking powder is mixture of Sodium bicarbonate and tartaric acid or citric acid.
When baking powder is heated it produces carbon dioxide which causes cakes to become fluffy.
Q. Why Citric acid is added to baking powder?
Ans: Citric acid is added to baking powder to neutralize effect of sodium bicarbonate.
Otherwise the bread or cake will taste bitter.
Q. Explain the difference between Acids and Bases.
Ans:
Q. What is neutralization? Give practical applications of neutralization reaction?
Ans: Neutralization is the reaction of Acid plus Base to form Salt.
Acid + Base _____> Salt + Water
E.g. HCl + NaOH ____> NaCl + H2O
Practical Applications:
1. Removal of acidity in soil by adding slaked lime.
2. Antacid tablets taken in case of stomach acidity.
3. Sting of wasps neutralized by rubbing with acetic acid and sting of ants, bees neutralized by rubbing with base.
Q. What is meant by water of crystallization?
Ans: Water of crystallization is the fixed number of water molecules in some salts.
Such salts are also called hydrated salts.
On heating, these salts loose water of crystallization and become amorphous a d change colour.
Examples:
CuSO4. 5H2O (Copper sulphate penthydrate)
Na2CO3.10H2O (Sodium carbonate decahydrate)
Q. What happens when a metal reacts with dil. HCl or Dil. H2SO4?
Ans: When a metal reacts with Dil. HCl or H2SO4, It forms Salt and Hydrogen gas.
Metal + Acid ____> Salt + Hydrogen
Q. What happens when acid reacts with a metal carbonate?
Ans: When an acid reacts with metal carbonate, Carbon dioxide is produced.
Example,
MgCO3 + HCl ____> MgCl2 + H20 + CO2
Q. Name two metals which displace hydrogen from dil. Acids and two metals which will not?
Ans: Zinc (Zn), Magnesium (Mg) displaces hydrogen from dilute acids.
Copper (Cu), Silver (Ag) will not displace Hydrogen from dilute acids.
Q. How can pH change cause tooth decay? How can tooth decay be prevented?
Ans: If the pH in mouth falls below the normal. It indicates presence of bacteria.
These bacteria cause tooth decay.
Tooth decay can be prevented by use of toothpastes which are basic in nature.
Q. Write down a note on Aqua Regia.
Ans: Aqua Regia is the mixture of Hydrochloric acid and Nitric acid in the proportion of 3:1. Aqua Regia dissolves metals like gold and silver in it
Q. What is an alkali? Write down two properties of alkali.
Ans: Alkali is a base which is dissolved in water.
Properties: i. It has pH of above 7 ii. It turns litmus paper blue
Q. The indicators which turn red in acid solution are:
a. Turmeric and litmus b. Phenolphthalein and Litmus
c. Litmus and Methyl orange d. Phenolphthalein and methyl orange
Ans: c. Litmus and Methyl orange
Q. The Property which is common between Vinegar and Curd is:
a. Sweet taste b. Tasteless c. Bitter taste d. Sour taste
Ans: d. Sour taste
Q. The indicator which produces a pink colour in an alkaline solution is:
a. Methyl orange b. Turmeric powder c. Phenolphthalein d. Litmus paper
Ans: c. Phenolphthalein
Q. One of the following is not an organic acid. This is
a. Ethanoic acid b. Formic acid c. Citic acid d. Carbonic acid
Ans: d. Carbonic acid
Q. The property which is not shown by acid is:
a. They have sour taste b. They feel soapy
c. They turn litmus red d. Their pH is < 7
Ans: b. They feel soapy
Q. The number of molecules of water of crystallization present in washing soda crystal is:
a. Five b. Two c. Ten d. Seven
Ans: c. Ten
Q. What are amphoteric oxides? Give two examples
Ans: Amphoteric oxides are the oxides which have a tendency to react with both acid and base to form salt and water are known as amphoteric oxides. Examples: Al2O3, ZnO
Q. Bee stings can be treated with?
A. Vinegar B. Potassium hydroxide C. Sodium hydrogen carbonate D. Lemon Juice
Ans: C. Sodium hydrogen carbonate
Q. The acid produced naturally in our stomach is:
a. Acetic acid b. Citric acid c. Hydrochloric acid d. Sulphuric acid
Ans: c. Hydrochloric acid
Q. Zinc reacts with H2SO4 to give;
a.) N2 b.) O2 c.) H2 d.) Cl2
Ans:-- H2
Q. pH of pure water is;
a.) 7 b.) 6 c.) 8 d.) 9
Ans:-- 7
Q. The acid present in stomach is;
a.) HCl b.) H2SO4 c.) HNO3 4.) CH3COOH
Ans:-- HCl
Q. Which of the following types of medicines is used for treating indigestion?
a.) Antibiotic b.) Analgesic
c.) Antacid d.) Antiseptic
Ans:-- Antacid.
Q. pH of base solution is;
a.) 7 b.) >7 c.) <7 d.) 1
Ans:-- >7
Q. The formula of lime stone is;
a.) CaO b.) Ca(OH)2 c.) CaCO3 d.) CaSO4
Ans:-- CaCO3
Q. Na2O reacts with water to give;
a.) NaCl b.) NaOH
c.) Na2CO3 d.) NaHCO3
Ans:-- NaOH
Q. The formula of Plaster of Paris is;
a.) CaSO4 b.) CaSO4. 2H2O
c.) CaSO4. 3H2O
d.) CaSO4.H2O
Ans:-- CaSO4.2H2O
Q. which of the following phenomenon occur when a small amount of acid is added to water?
a.) Ionisation b.) Dilution
c.) Neutralisation d.) Salt formation
Ans:-- Ionisation.
Q. Our body works within the pH range of;
a.) 7.0 - 7.8 b.) 7.6 - 7.9
c.) 7.2 - 7.5 d.) 7.0 - 7.5
Ans:-- 7.2 - 7.5
Q. What is the pH of blood?
Ans:-- 7.3
Q. Sting of Nettle plant contains;
a.) Methanoic acid b.) Citric acid
c.) Oxalic acid d.) Tartaric acid
Ans:-- Methanoic acid
Q. Which of the following is acidic in nature?
a.) Lime juice b.) Lime water
c.) Antacid d.) Human blood
Ans:-- Lime juice.
Q. A solution turns red litmus solution blue. Its pH is likely to be;
a.) 1 b.) 4 c.) 5 d.) 10
Ans:-- 10
Q.. Calcium phosphate is present in tooth enamel, its nature is;
a.) basic b.) acidic
c.) neutral d.) amphoteric
Ans:-- basic.
Q. A solution reacts with crushed egg shells to give a gas that turns lime water milky. The solution contains;
a.) NaCl b.) HCl c.) LiCl d.) KCl
Ans:-- HCl
Ans: Universal indicator is a mixture of many indicators that gives different colours at different pH values.
A. Strong acid B. Strong base
C. Weak acid D. Weak base
Ans: B. Strong base
Q. pH value of weak acids ranges from
A. 0 -3 B. 7 -10 C. 5-7 D. 12 -14
Ans: C. 5-7
Q. Which among the following is a weak acid?
A: HCl B. Acetic acid
C. H2SO4 D. HNO3
Ans B. Acetic acid
Q. The reaction between H+ ions given by the acid with OH- ions given by the base to form water, is called
A. Crystillization B. Condensation
C. Neutralization D. Both B and C
Ans: C. Neutralization
Q. Strong bases when dissolved in water
A. Dissociate completly into ions
B. Give large amounts of OH- ions in solution
C. Dissociate incompletely and give less ions
D. Both A and B
Ans: D. Both A and B
Q. Name the substance which on treatment with chlorine yields bleaching powder.
Ans: When Calcium hydroxide is treated with chlorine, it forms bleaching powder.
Q. Reaction between an acid and a base to form a salt is called
A. Saponification
B. Neutralization
C. Sublimation
D. None of these
Ans: B. Neutralization
Q. The salt derived from strong acid and strong base forms a solution having a pH value,
A. More than 7
B. Less than 7
C. Equal to 7
D. Between 7 and 14
Ans: C. Equal to 7
Q. Which among the following is an example of salt?
A. Sulphuric acid
B. Pottasium hydroxide
C. Hydrogen chloride
D. Pottasium nitrate
Ans: D. Pottasium nitrate
Q. Which salt among following is used in fire extinguishers?
A. Sodium carbonate
B. Sodium bicarbonate
C. Calcium carbonate
D. None of these
Ans: B. Sodium bicarbonate
Q. The solution of salt is having pH value less than 7, the salt has been derived from
A. A weak acid and a weak base
B. A strong acid and a strong base
C. A weak acid and a strong base
D. A strong acid and a weak base
Ans: D. A strong acid and a weak base
Q. Another name of baking soda:
Ans: Sodium Bicarbonate.
Q. Another name of Caustic soda;
Ans: Sodium hydroxide.
Q. Another name of Washing soda
Ans: Sodium carbonate.
Q. Formula of Plaster of Paris;
Ans: CaSO4.2H2O
Ans: Sodium Carbonate also called Washing Soda is used for softening hard water.
Its formula is Na2CO3.
Q. Human body works within the PH range of:
A. 1.0 to 7.0 B. 7.0 to 14 C. 7.0 to 7.8 D. 7.8 to 9.8
Ans: C. 7.0 to 7.8
Hint: This question is factually incorrect. It probably is talking about blood with works in the range of 6.8 to 7.8. Some body parts have low pH such as Skin which has pH as low as 5.0
Q. There is a solution that turns red litmus blue. The pH of that solution is likely to be
A. 1 B. 5 C. 4 D. 10
Ans: 10
Q. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solutions would reverse the change?
A. Baking Soda B. Lime C. Ammonium hydroxide D. Hydrochloric acid
Ans: D. Hydrochloric acid
Q. Which of the following gives the correct increasing order of acid strength?
Water (H2O) , Acetic Acid (CH3COOH), Hydrochloric Acid (HCl)
Ans: Hydrochloric acid is more acidic than Acetic acid which is more acidic than water.
Q. The pH value of a solution is lower, when:
A. The hydronium ion concentration is higher
B. the Hydronium ion concentration is lower
C. the hydroxide ion concentration is higher
D. the hydronium ion concentration is equal to hydroxide ion concentration
Ans: A. The hydronium ion concentration is higher
Q. Which of the following statements are correct about an
aqueous solution of an acid and of a base?
a. Higher the pH, Stronger the acid b. Higher the pH, weaker the acid
c. Lower the pH, stronger the base d. Lower the pH, Weaker the base
e. Both B and C
Ans: Both B and C
Q. Three solutions A, B and C when tested with universal
indicator showed pH as 5, 1 and 13 respectively. Based on the observation,
Choose the correct statement from the following:
a. A is strong acid
and B is weak acid b. A
is weak acid, C is weak base
c. Both A and B are strong acids d. B is strong acid, C is
strong base
Ans: d. B is strong acid, C is strong base
Q. Which of the following phenomena occur, when a small
amount of acid is added to water,
i. Ionisation ii.
Neutralization iii. Dilution iv. Both A and C
Ans: iv. Both A and C (Both Ionization and Dilution)
(A) Methanoic acid (B) Oxalic acid (C) Citric acid (D) Carbonic acid
Ans: (A) Methanoic acid
Q. Bee sting contains which acid:
(A) Ethanoic Acid (B) Formic Acid (C) Oxalic Acid (D) Citric Acid
Ans: B. Formic Acid
Q. Name the acid present in Tamarind:
(A) Oxalic Acid B. Acetic Acid C. Tartaric Acid D. Methanoic Acid
Ans: C. Tartaric Acid
Q. Which of the following types of medicine is used for treating acidity in stomach ?
(A) Antibiotic (B) Antacid (C) Analgesic (D) Antiseptic
Ans: (B) Antacid
