Science Olympiad Test: Acids, Bases and Salts- 1 - Class 10 MCQ

Acids change the colour of the litmus solution from blue to red. They have a sour, vinegar-like flavour and are sticky to the touch. Bases, on the other hand, change the colour of the red litmus solution to blue. They have a bitter taste, similar to baking soda, and are slippery to the touch.

Lemon juice and coffee are both acidic solutions. Lemon juice has a pH of 2, and coffee has a pH of 5.

When a glass rod dipped in the ammonia solution is brought near HCl gas, a dense white fume of ammonium chloride is formed.
This is because ammonia reacts with the fumes of HCl to give ammonium chloride.
NH_3​ + HCl → NH₄​Cl

When a small amount of acid is added to water, a concentrated acid turns into dilute acid. This process is called dilution of acid. A dilute acid is also called an aqueous solution in which acid releases hydronium ions (H⁺) and undergoes ionisation. 
HCl(aq) → H⁺(aq) + Cl⁻(aq)

Molar concentration of HCl acid solution = 0.02/2L = 0.01 mol L^–1
= 10^–2 mol L^–1  
pH = – log [H⁺]
pH = – log (10^–2)
pH = 2 log 10
pH = 2

 A, B, C and D have pH 3,4,6 and 8. The solution with highest acidic strength is 6.

Option (C):- (ii) only

• Electrical conductivity is the ability of an electrolyte to carry a current.
• Electrolyte is actually a medium which contains ions and because of the movement of those charged ions when placed in an electric field, there would be conduction of electricity.
• Electric current flows only in a closed circuit that would be formed here by the joining of two iron nails (which are the good conductor of electricity in the NaOH solution) with the bulb , battery and switch through the connecting wires.
• NaOH is a strong base and furnishes strong Na+ and OH- ions which would be responsible for the electrical conductivity.
• 

Citric acid is not a mineral acid but an organic acid present in citrus fruits

Na₂CO₃.10H₂O is efflorescent and loses 9 water molecules on exposure to air to give Na₂CO₃.H₂O.

Most metal oxides are insoluble in water but few of them, such as Na₂O and CaO dissolve in water to form alkalies and not salt and acid. Mainly group I and group II metals react with water to form hydroxides. Other metals such as iron, chromium, etc do not react with water.