Chemistry (CDS-Solved Paper)

When magnesium carbonate (MgCO₃) reacts with hydrochloric acid (HCl), the product will be magnesium chloride (MgCl₂) water (HO₂) and carbon dioxide (CO₂).
MgCO₃(s) + 2HCl → MgCl₂ (aq)+ H₂O(l) + CO₂(g) ↑
Above two reactants when taken in a flask at room temperature, they will
produce bubbles of CO₂ (carbon dioxide) gas.
After that, CO₂ reacts with lime water to form calcium carbonate (CaCO₃), which is white and does not dissolve in water. Thus, causing the lime water turns milky.
[Lime water → Lime water is the common name for a diluted solution of calcium hydroxide (Ca(OH)₂). It is clear and colourless.]
Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

(i) Reaction between magnesium and hydrochloric acid
When magnesium reacts with hydrochloric acid, they produce hydrogen (H₂) gas.
(ii) Reaction between copper and dilute nitric acid
(iii) Reaction between calcium carbonate and hydrochloric acid
Calcium carbonate reacts with hydrochloric acid which cannot produce hydrogen (H₂)
gas.
(iv) Reaction between zinc and nitric acid
When zinc reacts with nitric acid, they also cannot produce hydrogen (H₂) gas.
Note Nitric acid is an oxidising agent which produces oxides of nitrogen on reacting with metal. It do not produces hydrogen gas.

C₇H₇NO₂
Number of carbon atoms = 7
Number of hydrogen atoms = 7
Number of nitrogen atoms = 1
Number of oxygen atoms = 2
An oxygen molecule O₂ contains 2 oxygen atoms. Total number of
molecules = 7 + 7 + 1 + 2 = 17. So, 17 atoms are present in a molecule of the compound.

Alkanes are saturated hydrocarbons. This means that they contain only carbon and hydrogen atoms bonded by single bonds only.
●The general formula for an alkane is CₙH₂ₙ₊₂.
● In this formula, n = number of carbon.

(i) Diamond→ It has a crystalline lattice. In diamond, each carbon atom undergoes sp3 hybridisation and linked to four other carbon atoms. The structure extends in space and produces a rigid three-dimensional network of carbon atom.
In this structure, directional covalent bonds are present throughout the lattice. There are no free electrons, in the structure of diamond. Therefore, it is a very poor electric conductor.

(ii) Graphite Graphite has layered structure. Its layers are held by van der Waals’ forces. Each layer is composed of planar hexagonal rings of carbon atoms. Electrons are mobile in graphite, therefore graphite conducts electricity. It is a good electric conductor than diamond.