Acids
What is: HCl produces hydrogen/hydronium ions only in the presence of water?
Dry hydrogen chloride gas does not change dry blue litmus, but its aqueous solution turns blue litmus red. Explain why.
What are zinc and hydrogen; Zn + 2HCl → ZnCl₂ + H₂?
A metal reacts with dilute hydrochloric acid to form zinc chloride and a gas that burns with a pop. Identify the metal and gas, and write the balanced equation.
What is CO₂; Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂, and Ca(OH)₂ + CO₂ → CaCO₃ + H₂O?
A white powder reacts with dilute HCl with brisk effervescence. The gas turns limewater milky. Name the gas and write both balanced equations if the powder is sodium carbonate.
What is: HNO₃ is a strong oxidising agent; magnesium and manganese are the exceptions with very dilute HNO₃?
Most metals liberate hydrogen with dilute acids, yet nitric acid usually does not. State the NCERT reason and name the two metals that can release hydrogen with very dilute HNO₃.
What is: dilution is highly exothermic and may cause splashing; H₃O⁺ concentration decreases and pH increases?
Concentrated acid is added slowly to water while stirring, never water to concentrated acid. Explain the danger and state what happens to H₃O⁺ concentration and pH on dilution.
What is sodium hydroxide; NaOH(aq) → Na⁺(aq) + OH⁻(aq)?
A compound used in soap manufacture dissociates in water to produce Na⁺ and OH⁻ ions. Name it and write its dissociation equation.
What is: water enables the base to furnish mobile OH⁻ ions?
Why does a base such as sodium hydroxide show its basic character only in aqueous solution?
What are sodium hydroxide, sodium zincate and hydrogen; Zn + 2NaOH → Na₂ZnO₂ + H₂?
Zinc reacts with a strong base despite being a metal. Name the base and products, and write the balanced equation given in Class 10 NCERT.
What are Ca(OH)₂ + CO₂ → CaCO₃ + H₂O, followed by CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂?
Passing CO₂ through limewater first makes it milky, but excess CO₂ removes the milkiness. Explain with two equations.
What are CaO, Ca(OH)₂ and CaCO₃; each neutralises excess soil acidity?
A farmer has acidic soil and chooses between quicklime, slaked lime and limestone. Give the formula of each and explain why all can correct the soil.
What is sodium chloride, NaCl?
This common salt is the raw material for sodium hydroxide, baking soda, washing soda and bleaching powder. Name it and give its formula.
What are sodium carbonate, carbon dioxide and water; 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O?
On heating baking soda, a salt used in glass and soap industries forms. Name all products and write the balanced equation.
What is washing soda; 10H₂O represents water of crystallisation; it is used to remove permanent hardness of water or in glass/soap/paper industries?
Name Na₂CO₃·10H₂O, state why the ‘10H₂O’ is important, and give one use besides cleaning clothes.
What is bleaching powder, CaOCl₂; Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O?
A chlorine-smelling powder used to disinfect drinking water is made by passing chlorine over dry slaked lime. Identify it and write the preparation equation.
What is plaster of Paris, CaSO₄·½H₂O; CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O?
A white powder for fractured-bone casts is obtained by heating gypsum at 373 K. Name it, give its formula, and write the equation for its setting with water.
What is litmus?
I am born from lichen. Acid paints me red, while a base paints me blue. Name me.
What is phenolphthalein?
I am colourless with acids but turn pink in bases; turmeric cannot copy my colourless disguise. Who am I?
What is methyl orange?
In acid I am red, in base I am yellow, and orange lies between my two costumes. Who am I?
What is turmeric?
A golden kitchen powder stays yellow in acid but becomes reddish-brown in a base. Identify me.
What is an olfactory indicator; onion?
I reveal no colour at all: my familiar smell remains in acid but disappears in a base, and cutting me may bring tears. What type of indicator—and which example—am I?
What is: bacteria convert food sugars into acids; basic toothpaste neutralises the excess acid?
Tooth enamel begins to corrode below pH 5.5. Explain how mouth bacteria cause this and why basic toothpaste helps.
What is: HCl turns blue litmus red; NaOH turns red litmus blue; NaCl changes neither?
A student must distinguish dilute HCl, NaOH and NaCl using only red and blue litmus. Give the observations that identify all three.
What are chlorine at the anode, hydrogen at the cathode and NaOH in solution; 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂?
Electrolysis of brine is called the chlor-alkali process. Name the products at the anode and cathode and the product left in solution, with the overall equation.
What are A = NaHCO₃ (baking soda), B = Na₂CO₃ (sodium carbonate), and C = Na₂CO₃·10H₂O (washing soda)?
Compound A is used in cakes and antacids. Heating A gives B, used to remove permanent hardness; crystallising B gives C with ten water molecules. Identify A, B and C.
What are Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂; NaHCO₃ + HCl → NaCl + H₂O + CO₂; the gas turns limewater milky due to CaCO₃ formation?
A student adds dilute HCl separately to sodium carbonate and sodium hydrogen carbonate. Both release the same gas. Write both balanced equations, name the gas test, and explain the observation in limewater.