CHEMISTRY (Part-VIII) (Railway)

Total Questions: 50

21. Recipitation reactions occur when cation of one reactant and anion of second reactant, found in an aqueous solution, combine to form: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) A soluble ionic solid
(2) An insoluble acid
(3) An soluble acid
(4) An insoluble ionic solid

Correct Answer: (4) An insoluble ionic solid

Solution:

A precipitation reaction occurs when the cations of one reactant and the anions of a second reactant found in aqueous solutions combine to form an insoluble ionic solid.
For example, magnesium ions combine with carbonate ions to form ppt of magnesium carbonate.

Mg²⁺ (aq) + CO₃⁻² (aq) → MgCO₃ (s)

22. The term 'triads' was used by: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) John Newlands
(2) Johann Wolfgang Dobereiner
(3) Henry Moseley
(4) Mendeleev

Correct Answer: (2) Johann Wolfgang Dobereiner

Solution:Dobereiner classified the elements into triads (group of three).
• He made the groups such that the atomic mass of the middle element was the average atomic mass of the other two elements.
• Li, Na, K is an example of Dobereiner's triad. Here, the average atomic mass of Li and K is equal to the atomic mass of Na.

23. Saturated carbon compounds are normally: [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) less stable than unsaturated compounds
(2) having electrostatic force of attraction
(3) less reactive than unsaturated compounds
(4) having a double bond between carbon atoms

Correct Answer: (3) less reactive than unsaturated compounds

Solution:The saturated hydrocarbons have single covalent bond between the C atoms that is strong and hard to break.
• The unsaturated hydrocarbons have double and triple bonds that are very weak and can be broken down easily while taking part in a reaction to form different compounds.
• This implies unsaturated hydrocarbons are more reactive than saturated hydrocarbons.

24. Which of the following is produced when baking powder is heated? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) Carbon dioxide and sodium carbonate is produced.
(2) Carbon monoxide and sodium salt of tartaric acid is produced.
(3) Carbon monoxide and sodium carbonate is produced.
(4) Carbon dioxide and sodium salt of tartaric acid is produced.

Correct Answer: (4) Carbon dioxide and sodium salt of tartaric acid is produced.

Solution:Sodium bicarbonate (baking soda) decomposes on heating to form sodium carbonate, carbon dioxide, and water.
• The chemical reaction involved is:
• 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

25. What happens when aqueous silver nitrate is added to sodium chloride solution? [RRB Group 'D' CBT Exam, 19.09.2022 (Shift-III)]

(1) No precipitate of silver chloride is produced.
(2) White precipitate of silver chloride is produced.
(3) Brown precipitate of silver chloride is produced.
(4) Yellow precipitate of silver chloride is produced.

Correct Answer: (2) White precipitate of silver chloride is produced.

Solution:When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed along with sodium nitrate solution.
• The reaction takes place as:
AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)
• This reaction is an example of double displacement reaction.

26. Which of the following explanations regarding the given reaction is correct? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

(1) Iron displaces copper because iron is less reactive than copper.
(2) Iron displaces copper because the atomic number of iron is less than copper.
(3) Iron displaces copper because iron is more reactive than copper.
(4) Iron displaces copper because the atomic mass of iron is less than copper.

Correct Answer: (3) Iron displaces copper because iron is more reactive than copper.

Solution:Iron displaces copper because iron is more reactive than copper.
• As iron is placed higher in reactivity series than copper, iron readily displaces copper from copper sulphate solution to form iron sulphate and copper.
• It is an example of displacement reaction.

27. A compound with molecular formula C₃H₄ belongs to the homologous series of _______. [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

(1) alkene only
(2) alcohol
(3) alkane only
(4) alkyne only

Correct Answer: (4) alkyne only

Solution:The alkynes comprise a series of carbon and hydrogen-based compounds that contain at least one triple bond.
• This group of compounds is a homologous series with the general molecular formula of CₙH₂ₙ₋₂, where n equals any integer greater than one.
• The first four members of the alkyne series are Ethyne (C₂H₂), Propyne (C₃H₄), Butyne (C₄H₆), and Pentyne (C₅H₈).

28. Which of the following is a hydrate of sodium carbonate containing ten molecules of water of crystallisation? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

(1) Bleaching Powder
(2) Baking soda
(3) Washing soda
(4) Baking powder

Correct Answer: (3) Washing soda

Solution:Sodium carbonate (Na₂CO₃), commonly known as Washing soda, is Sodium carbonate with ten (10) molecules of crystallisation Water (H₂O).
• Thus, Washing soda is Sodium carbonate decahydrate (Na₂CO₃·10H₂O).

29. Which of the following reactions produces water insoluble salts? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

(1) Addition reaction
(2) Catalytic reaction
(3) Precipitation reaction
(4) Displacement reaction

Correct Answer: (3) Precipitation reaction

Solution:A precipitation reaction produces an insoluble solid as a result of the reaction of two dissolved chemicals in a solution.
• In such a reaction, two aqueous solutions react to produce a precipitate (an insoluble salt).
Example: NaCl (aq) + AgNO₃ (aq) → AgCl (s) + NaNO₃ (aq)

30. What is the trend for the atomic number while moving across a period in the modern periodic table? [RRB Group 'D' CBT Exam, 20.09.2022 (Shift-I)]

(1) The atomic number decreases by one unit.
(2) The atomic number increases by two units.
(3) The mass number increases by one unit.
(4) The atomic number increases by one unit.

Correct Answer: (4) The atomic number increases by one unit.

Solution:The atomic number increases by one unit.

• The atomic number increases from moving left to right across a period.
• This is because as we move across a period from left to right, the number of protons increases in the subsequent elements.
• The elements in the periodic table are arranged in order of increasing atomic number.

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