Kerala SSLC · Chemistry · Class 10
Acids, Bases and Salts: Important Questions with Answers
These are 10 important multiple-choice questions from the Kerala SSLC Chemistry chapter “Acids, Bases and Salts” (Kerala SCERT syllabus). Each one shows the correct answer and a short explanation of why it is right. Try answering before you read the answer. ExamSummary has 10 practice questions on this chapter in total.
Q1.When turmeric indicator is added to a solution, it changes color from yellow to reddish-brown. What does this indicate about the nature of the solution?
- A)The solution is acidic.
- B)The solution is basic.
- C)The solution is neutral.
- D)The solution contains salt only.
Answer: B) The solution is basic.
Turmeric is a natural indicator that remains yellow in acidic and neutral solutions. It turns reddish-brown specifically in the presence of a basic solution due to the change in pH.
Q2.During the dilution of a strong acid with water, which of the following safety precautions must be followed to prevent accidents?
- A)Add water to the acid quickly while stirring.
- B)Add acid to water slowly while stirring continuously.
- C)Mix equal amounts of acid and water without stirring.
- D)Pour the acid into a dry container first.
Answer: B) Add acid to water slowly while stirring continuously.
Diluting acid is an exothermic process that releases a large amount of heat. Adding acid to water allows the heat to dissipate safely, whereas adding water to acid can cause splashing and burns due to sudden boiling.
Q3.Plaster of Paris is obtained by heating gypsum at approximately 373 K. What is the chemical formula of Plaster of Paris?
- A)CaSO4 · 2H2O
- B)CaSO4 · 1/2H2O
- C)CaSO4
- D)Ca(OH)2
Answer: B) CaSO4 · 1/2H2O
Gypsum has two water molecules per formula unit. When heated to 373 K, it loses three-fourths of its water of crystallization to form calcium sulphate hemihydrate, known as Plaster of Paris.
Q4.Tooth decay begins when the pH of the mouth drops below which critical value?
- A)pH 5.5
- B)pH 7.0
- C)pH 9.0
- D)pH 3.0
Answer: A) pH 5.5
Enamel on teeth starts to corrode when the environment becomes too acidic. A pH level below 5.5 creates conditions where bacteria produce enough acid to dissolve the calcium phosphate in tooth enamel.
Q5.Why does an aqueous solution of hydrochloric acid conduct electricity?
- A)Because it contains only molecules.
- B)Because it dissociates into ions.
- C)Because it is a non-polar solvent.
- D)Because it produces hydrogen gas.
Answer: B) Because it dissociates into ions.
Electrical conductivity in solutions requires charged particles to move freely. HCl dissociates into hydrogen ions (H+) and chloride ions (Cl-) in water, allowing the flow of electric current.
Q6.Which of the following reactions represents a neutralization reaction used to treat indigestion caused by excess stomach acid?
- A)Zn + HCl → ZnCl2 + H2
- B)NaOH + HCl → NaCl + H2O
- C)CaCO3 + HCl → CaCl2 + H2O + CO2
- D)MgO + H2O → Mg(OH)2
Answer: B) NaOH + HCl → NaCl + H2O
Neutralization involves the reaction between an acid and a base to form salt and water. Magnesium hydroxide or sodium bicarbonate acts as an antacid (base) to neutralize hydrochloric acid in the stomach.
Q7.What happens when baking soda (Sodium Bicarbonate) is heated strongly?
- A)It melts without changing chemically.
- B)It decomposes to form sodium carbonate, water, and carbon dioxide.
- C)It reacts with oxygen to form sodium oxide.
- D)It turns into a liquid acid.
Answer: B) It decomposes to form sodium carbonate, water, and carbon dioxide.
Thermal decomposition of sodium bicarbonate occurs upon heating. This reaction produces sodium carbonate along with the release of water vapor and carbon dioxide gas.
Q8.Bleaching powder is widely used for disinfecting drinking water supplies. What is its common chemical name?
- A)Calcium Carbonate
- B)Calcium Oxychloride
- C)Calcium Sulphate
- D)Sodium Chloride
Answer: B) Calcium Oxychloride
Bleaching powder is chemically known as Calcium Oxychloride (CaOCl2). It is prepared by the action of chlorine on dry slaked lime and acts as a strong oxidizing agent.
Q9.If a few drops of phenolphthalein are added to a colourless solution and it turns pink, what is the likely pH range of the solution?
- A)Less than 7
- B)Exactly 7
- C)Greater than 7
- D)Between 4 and 6
Answer: C) Greater than 7
Phenolphthalein is an acid-base indicator that is colourless in acidic and neutral solutions. It turns pink only when exposed to a basic solution, indicating a pH greater than 7.
Q10.Washing soda is used to remove permanent hardness from water. What is the chemical formula of washing soda?
- A)NaHCO3
- B)Na2CO3 · 10H2O
- C)CaCO3
- D)NaOH
Answer: B) Na2CO3 · 10H2O
Washing soda is the decahydrate form of sodium carbonate. Its formula includes ten water molecules attached to the crystal lattice, distinguishing it from baking soda which lacks these waters of crystallization.