//M0//QN1//SUB//DL0

Glucose or Sucrose are soluble in water but cyclohexane or benzene (simple six membered ring compounds) are insoluble in water. Explain.

//X

A glucose molecules contains five –OH groups while a sucrose molecule contains eight –OH groups. Thus, glucose and sucrose undergo extensive H–bonding with water. Hence, these are soluble in water. But, cyclohexane and benzene do not contain –OH groups. Hence, they can not undergo H–bonding with water and as a result, they are insoluble in water.

//M0//QN2//SUB//DL0

What are the expected products of hydrolysis of lactose?

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Lactose is composed of b–D–galactose + b–D–glucose, thus on hydrolysis it gives b–D–galactose and b–D–glucose.
C12H22O11 + H2O → C6H12O6 + C6H12O6
Lactose b–D–galactose b–D–glucose

//M2//QN3//SUB//DL0

How do you explain the absence of aldehyde group in the penta-acetate of D-glucose?

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D–glucose reacts with hydroxylamine (NH2OH) to form an oxime because of the presence of aldehyde (–CHO) group of carbonyl carbon. This happens as the cyclic structure of glucose forms an open chain structure to give an oxime. But penta acetate of
D–glucose does not react with NH2OH. This is because penta acetate does not form an open chain structure.

//M2//QN4//SUB//DL0

The melting points and solubility in water of amino acids are generally higher than that of the corresponding halo acids. Explain.

//X

Both acidic (Carboxyl) as well as basic (amino) groups are present in the same molecule of amino acids.
In aqueous solutions, the carboxyl group can lose a proton and the amino group can accept, thus giving rise to a dipolar ion known as zwitter ion.
Due to this dipolar behaviour, they have strong electrostatic interactions within them and with water.
But halo acids do not exhibit such dipolar behaviour. For this reason the melting points and the solubility of amino acids in water is higher than those of the corresponding halo-acids.

//M1//QN5//SUB//DL0

Where does the water present in the egg go after boiling the egg?

//X

When an egg is boiled, the proteins present inside the egg gets denatured and coagulate. After boiling the egg the water present in it is absorbed by the coagulated protein through H-bonding.

//M1//QN6//SUB//DL0

Why cannot vitamin C be stored in our body?

//X

Vitamin C cannot be stored in our body because it is water soluble. As a result it is readily excreted in the urine.

//M1//QN7//SUB//DL0

What products would be formed when a nucleotide form DNA containing thymine is hydrolysed?

//X

When a nucleotide for the DNA containing thymine is hydrolyzed, thymine b–D–2 deoxyribose and phosphoric acid are obtained as products.

//M1//QN8//SUB//DL0

When RNA is hydrolysed, there is no relationship among the quantities of different bases obtained. What does this fact suggest about the structure of RNA?

//X

A DNA molecule is double-stranded in which the pairing of bases occurs. Adenine (A) always pairs with thymine (T) while cytosine (C) always pairs with guanine (G). So on hydrolysis of DNA, the quantity of adenine produced is equal of that of thymine (T) and Adenine (A). Similarly, the quantity of cytosine (C) is equal to that of guanine (G). But when RNA is hydrolysed there is no relationship among the quantities of the different bases obtained. Hence, RNA is single stranded.
Class 12 Chemistry (Part 2) 021