Question

2. When a basic solution is dissolved in water, how and why does the concentration of H ⁺ions change in the solution? ( two reasons)

3. What is the difference in H+ ion concentration between a solution that is pH 4 and a solution that is pH 8?   If a solution has a pH of 6, express the concentration of H⁺ in moles/liter.

9. How are two monosaccharides joined to form a disaccharide? How are disaccharides digested?

Answer 1

2

When a basic solution is added in water the overall concentration of OH^- ions in the water increase. This happens because a basic solution has excess OH^- ions. The H⁺ (or more accurately hydronium ions H₃O⁺) in the water then react with the excess OH^- ions forming water. This ultimately leads to a decrease in the hydrogen ion concentration and the increase in pH from 7 to a greater value.

Thus, the water does not remain neutral and becomes basic in nature.

This can also be understood using the theory of self-protolysis or self ionization of water. In pure form, water deprotonates to become a hydroxide ion, OH⁻. The hydrogen nucleus, H⁺, immediately protonates another water molecule to form hydronium ion, H₃O⁺. Whenever there is an influx of hydrogen ion or hydroxide ion, the pH of water will change due to reverse of the above reactions taking place.

3

Formula for calculating pH is:

pH = -log[H+]

So for calculating concentration of Hydrogen ion, equation will be

[H⁺] = 10^-pH moles/litre

Now the H⁺ concentration at pH 4 will be

[H⁺] = 10^-4 moles/litre or 10^-4 M

Concentration of H⁺ at pH 8 will be 10^-8 moles/litre

Thus, we see that there is a difference of 10⁴ degrees between the concentration of hydrogen ions at pH 4 and pH 8. This can also be understood by another means.

Hydrogen ion concentration is a measurement using log. This means that there is a difference of 10 degrees between successive pH values. Thus the difference between pH 4 and pH 8 will be 10 X 10 X 10 X 10 = 10000 times. Thus, there are 10⁴ times more hydrogen ion when pH is 4, rather than when it is pH 8.

H⁺ concentration at pH 6 will be

[H⁺] = 10^-6 moles/litre or 10^-6 M or 1M

9

Disaccharides form when two monosaccharides undergo a dehydration reaction also known as condensation reaction. In this process hydroxyl group of one monosaccharide combines with the hydrogen of another monosaccharide, releasing a molecule of water and forming a covalent bond.

Glucose + Glucose ------> Maltose + Water

The digestion of disaccharide takes place in the small intestine. Disaccharides are digested and break into monosaccharides (glucose) with the help of various enzymes like maltase, lactase, sucrase.

• Maltose is converted into Glucose + Glucose with the help of enzyme Maltase
• Lactose is converted into Glucose + Galactose with the help of enzyme Lactase.
• Sucrose is converted into Glucose + Fructose with the help of enzyme Sucrase or invertase.