CBSE Class 10 Science Chapter 2: Acids, Bases and Salts NCERT Solutions

Acids turn blue litmus red, while bases turn red litmus blue. The pH scale measures the acidity or basicity of a solution. A pH value less than 7 indicates an acidic solution, a pH of 7 indicates a neutral solution, and a pH value greater than 7 indicates a basic solution.

Since the given solution turns red litmus blue, it indicates that the solution is basic. Among the given options, only pH 10 is greater than 7, signifying a basic nature. Therefore, the pH of the solution is likely to be 10.

Eggshells are primarily composed of calcium carbonate (CaCO_3). When an acid reacts with a carbonate, it produces a salt, water, and carbon dioxide gas (CO_2). Carbon dioxide gas is known to turn lime water (calcium hydroxide solution) milky due to the formation of a white precipitate of calcium carbonate.

The reaction is as follows:

CaCO_{3(s)} + 2HCl_{(aq)} \longrightarrow CaCl_{2(aq)} + H_2O_{(l)} + CO_{2(g)}

The gas produced, CO_2, turns lime water milky: Ca(OH)_{2(aq)} + CO_{2(g)} \longrightarrow CaCO_{3(s)} + H_2O_{(l)}

Since the solution reacts with eggshells to produce a gas that turns lime water milky, the solution must contain an acid. Among the given options, HCl (hydrochloric acid) is an acid. NaCl and KCl are salts.

Therefore, the solution contains HCl.

This problem involves a neutralization reaction between sodium hydroxide (NaOH), a base, and hydrochloric acid (HCl), an acid. The balanced chemical equation for this reaction is:

NaOH_{(aq)} + HCl_{(aq)} \longrightarrow NaCl_{(aq)} + H_2O_{(l)}

This equation shows that one mole of NaOH reacts with one mole of HCl. This implies that the volumes of equimolar solutions of NaOH and HCl required for complete neutralization are in a direct ratio.

We are given that 10 mL of NaOH solution is completely neutralized by 8 mL of HCl solution. This means that the concentration of HCl is such that 8 mL of it is equivalent to 10 mL of NaOH in terms of neutralization capacity.

Now, we need to find the amount of the same HCl solution required to neutralize 20 mL of the same NaOH solution. Since the volume of NaOH is doubled (from 10 mL to 20 mL), and the concentration of both solutions remains the same, the volume of HCl required will also be doubled to achieve complete neutralization.

Amount of HCl required = 2 × (Amount of HCl required for 10 mL NaOH)

Amount of HCl required = 2 × 8 mL = 16 mL

Therefore, 16 mL of the HCl solution will be required to neutralize 20 mL of the NaOH solution.

Indigestion is often caused by an excess of acid in the stomach. Medicines that are used to treat indigestion are called antacids. Antacids are typically mild bases that neutralize the excess acid in the stomach, providing relief.

• Antibiotics are used to kill or inhibit the growth of bacteria.
• Analgesics are pain relievers.
• Antacids are used to neutralize stomach acid.
• Antiseptics are used to prevent the growth of microorganisms on living tissues.

Therefore, antacid is the type of medicine used for treating indigestion.

These reactions involve the reaction of dilute acids with active metals, which typically produce a salt and hydrogen gas.

1. Reaction of dilute sulphuric acid with zinc granules:

   Word equation: Sulphuric acid + Zinc → Zinc sulphate + Hydrogen

   Balanced chemical equation:

   H_2SO_{4(aq)} + Zn_{(s)} \longrightarrow ZnSO_{4(aq)} + H_{2(g)}

2. Reaction of dilute hydrochloric acid with magnesium ribbon:

   Word equation: Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen

   Balanced chemical equation:

   2HCl_{(aq)} + Mg_{(s)} \longrightarrow MgCl_{2(aq)} + H_{2(g)}

3. Reaction of dilute sulphuric acid with aluminium powder:

   Word equation: Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen

   Balanced chemical equation:

   3H_2SO_{4(aq)} + 2Al_{(s)} \longrightarrow Al_2(SO_4)_{3(aq)} + 3H_{2(g)}

4. Reaction of dilute hydrochloric acid with iron filings:

   Word equation: Hydrochloric acid + Iron → Iron(III) chloride + Hydrogen

   Balanced chemical equation:

   6HCl_{(aq)} + 2Fe_{(s)} \longrightarrow 2FeCl_{3(aq)} + 3H_{2(g)}

   Note: Iron can form both Iron(II) chloride (FeCl_2) and Iron(III) chloride (FeCl_3). With dilute HCl, Iron(III) chloride is typically formed under these conditions.

To prove that compounds like alcohols and glucose, which contain hydrogen, are not acids, we can conduct an experiment to test their electrical conductivity in aqueous solution. Acids ionize in water to produce hydrogen ions (H^+), making their solutions electrically conductive. Alcohols and glucose do not ionize significantly in water and thus do not conduct electricity well.

Activity:

1. Take a 100 mL beaker and fit two nails onto a cork that can be placed inside the beaker.
2. Connect these nails to the two terminals of a 6-volt battery using connecting wires. Include a bulb and a switch in the circuit.
3. Pour some dilute hydrochloric acid (HCl) into the beaker, ensuring the nails are immersed in the acid.
4. Close the switch. Observe if the bulb glows.
5. Empty the beaker, clean it, and repeat the experiment by pouring dilute glucose solution into the beaker and closing the switch. Observe the bulb's glow.
6. Finally, repeat the experiment with an alcohol solution (like ethanol) in the beaker and observe the bulb's glow.

Observations:

• When dilute HCl is in the beaker, the bulb glows brightly. This indicates that the HCl solution conducts electricity, meaning it contains ions.
• When glucose solution is in the beaker, the bulb does not glow, or glows very dimly. This indicates that the glucose solution does not conduct electricity well, meaning it does not contain a significant concentration of ions.
• Similarly, when alcohol solution is in the beaker, the bulb does not glow. This indicates that the alcohol solution does not conduct electricity well.

Conclusion:

The glowing of the bulb in the HCl solution demonstrates that HCl dissociates into ions (H^+ and Cl^-) in water, which allows electric current to pass through. The fact that the bulb does not glow in glucose and alcohol solutions shows that these compounds do not dissociate into ions in water. Therefore, although they contain hydrogen atoms, they do not exhibit acidic properties because they do not produce H^+ ions in solution.