Chemistry Test-21

Allergy in the body is caused by the production of histamine.

An allergic reaction occurs due to the hypersensitivity of the immune system to a harmless substance known as an allergen. Antibodies are produced by the B-lymphocyte cells which destroy the allergens. Destruction of allergens by the antibodies causes the release of a chemical substance into the bloodstream called histamine.  The release of histamine in a large amount causes swelling of body tissues (inflammation), itching, enlargement of blood vessels and causes bronchospasm.

Methane cannot be prepared byWurtz andKolbe's electrolytic methods.

Wurtz reaction: \(RX +2 Na + XR \rightarrow R - R +2 NaX\)

Kolbe's electrolysis: \(2 RCOOK +2 H _{2} O \rightarrow R - R +2 CO _{2}+2 KOH + H _{2}\)

In kolbe process - senderens reaction \(R-R\) forms as a product so methane can not be formed by these methods.

The larger the atom, the lesser the electronegativity, since the electrons being farther away from the nucleus, experience a lesser force of attraction. So, the atomic size increases down the group while electronegativity decreases. Across a period, electronegativity increases from left to right while atomic radius decreases. So, Electronegativity increases across a period and decreases down the group.

An oxidising agent is the one which oxidises other substances (by removal of hydrogen or addition of oxygen) and itself gets reduced(addition of hydrogen or removal of oxygen).

\(\mathrm{CuO}+\mathrm{H}_{2} \stackrel{\text { heat }}{\longrightarrow} \mathrm{Cu}+\mathrm{H}_{2} \mathrm{O}\)

In above reaction, cupric oxide \((\mathrm{CuO})\) acts as an oxidising agent as it oxidises hydrogen \(\left(\mathrm{H}_{2}\right)\) to form water \(\left(\mathrm{H}_{2} \mathrm{O}\right)\) and copper \((\mathrm{C u})\).

So, the hydrogen is getting oxidised in the given reaction.

In glycerol, there are three −OH group present, whereas in propanol only one −OH group is present. So, in glycerol, these produce a great deal of intermolecular hydrogen bonding than the intermolecular hydrogen bond present in propanol.

Hence, because of extensive intermolecular H -bonding as compare to propanol because of the large number of OH groups, the boiling point of glycerol is more than propanol.

The non-proteinaceous substance, which certain enzymes require for their activity are called co-enzymes.The non-proteinaceous substance, which certain enzymes require for their activity are called coenzymes. Coenzymes are organic molecules that are required by certain enzymes to carry out catalysis. They bind to the active site of the enzyme and participate in catalysis but are not considered substrates of the reaction. They function as intermediate carriers of electrons, specific atoms or functional groups that are transferred in the overall reaction.

\(\mathrm{Ag}\) does not displace hydrogen from dil. \(\mathrm{HCl}\).

Metals such as copper, silver, gold and platinum are less reactive than hydrogen. Hence, they cannot displace hydrogen from dil. \(\mathrm{HCl}\).

Dry cell convert chemical energy to electrical energy.

An electrical cell internally converts stored chemical energy into electrical potential energy, allowing a current to flow from the positive terminal round to the negative one via an external circuit

There is a potential difference between the terminals of a cell:

• Positive or Higher
• Negative or Lower

The electrical cells are of two types:

Primary cells: The chemical reactions are irreversible in these types of cells. These types of cells are discarded after use as they cannot be recharged.

• Examples: Simple voltaic cells, Daniel cell, and dry cell.

Secondary cells: The chemical reactions are reversible in these types of cells and they can be recharged after use.

• Examples: Li-H Battery, Li-ion Battery(Used in Mobile phones).

So, dry cell convert chemical energy to electrical energy.

As the branching increases, the surface area decreases. As a result, the magnitude of van der Waal's forces of attraction decreases and hence the boiling decreases.

Now, \(2-\)methylpentane has the largest surface area and hence has the highest boiling point. Further because of two branches on the same carbon, \(2, 2\) dimethylbutane has lower surface area and hence lower boiling point that \(2,3-\) dimethylbutane. Thus, the overall order of decreasing boiling points is:

\(2-\)methylbutane \((333 K )>2,3\)-dimethylbutane \((331 K )>2,2\)-dimethylbutane \((323 K )\).