✓ Board-verified
Science · 2025 · 4 marks
CBSE 2025 · Region 3 · Set 1 · Q37
'A' and 'B' are two salts used for washing purposes. Salt 'A' is used for bathing also. Four test tubes I, II, III and IV as mentioned below are…
'A' and 'B' are two salts used for washing purposes. Salt 'A' is used for bathing also. Four test tubes I, II, III and IV as mentioned below are taken. I. Rain water + solution of salt 'A' II. Rain water + solution of salt 'B' III. Tubewell water + solution of salt 'A' IV. Tubewell water + solution of salt 'B' The test tubes are shaken one by one almost identically for the same time and the lengths of foam formed in each test tube is noted.
(a)
In which one of the four test tubes is the foam formed the minimum ?
(b)
Differentiate between salt A and salt B.
(c)(i)
What are esters ? What happens when an ester reacts with an alkali (say sodium hydroxide) ? Give chemical equation for the reaction.
OR
(c)
(ii)
What is the cause of hardness of water ? Sometimes it is observed that while bathing foam is formed with difficulty and an insoluble substance is formed. Name this substance and write the cause of its formation.
Marking-scheme solution
(a)(III)
/ Tubewell water + Solution of Salt A
(b)
| Salt A | Salt B |
| Soap | Detergent |
| Na/K salt of long chain carboxylic acids | sodium salt of sulphonic acids or ammonium salts with chloride or bromide ions. |
| Does not form lather with hard water | Forms lather even with hard water |
(i)
Esters are sweet smelling substances used in making perfumes and flavoring agents. / Formed when alcohol and carboxylic acid react in presence of acid to form ester.
It is converted back to alcohol and a salt of carboxylic acid.
\[\mathrm{CH}_{3} \mathrm{COOC}_{2} \mathrm{H}_{5} + \mathrm{NaOH} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} + \mathrm{CH}_{3} \mathrm{COONa}
\]
(ii)
Presence of Ca and Mg salts in water
Scum
Soap reacts with calcium and magnesium salts to form insoluble substance.
All Carbon and its Compounds questions2025 question paperNCERT solutions: Carbon and its CompoundsPractice Carbon and its Compounds →
More from Carbon and its Compounds
- The number of single and double bonds present in a molecule of benzene (C_6 H_6) respectively, are:2024
- Which one of the following hydrocarbons is different from the others?2024
- Draw two different possible structures of a saturated hydrocarbon having four carbon atoms in its molecule. What are these two structures of the…2022
- Hydronium ions are formed by the reaction between:2023
- The number of electrons in the outermost shell of the atom of a non-metal can be:2023
- (i) Butane had both Carbon - Carbon bonds as well as Carbon - Hydrogen bonds. Draw its structural formula and state the number of (1) C-H bonds and…2023
- The melting and boiling points of carbon compounds are generally low and they are largely non-conductors of electricity. State two conclusions based…2024
- Select the correct option(s) in the following table:2023
CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.