(a) A compound 'A' is used in soda-lime fire-extinguisher and decomposes on heating to form compound 'B'. Compound 'B' is used for removing permanent hardness of water. Identify 'A' and 'B'. (b) Write chemical formula of Plaster of Paris. At what temperature gypsum is heated to obtain Plaster of Paris?
Common salt and the chemicals made from it
High importanceUsually 2 marks a paper · mostly case-based questions and very short answers · asked in 3 of the last papers
Notes are being written
The board questions below are real and complete — they come from the CBSE papers themselves. The written notes for this topic are still being prepared.
Board questions on this topic
6 from the CBSE papers we hold — the exact wording the board used.
[Case: Seawater contains many dissolved salts; common salt is separated from these, deposits of solid rock salt (brown due to impurities) are mined like coal, and common salt is an important raw material for chemicals of daily use.] Write balanced chemical equations to show the products formed during electrolysis of brine.
[Case: Seawater/common salt/rock salt as raw material for chemicals of daily use.] List two uses of any one product obtained during electrolysis of brine.
[Case: Seawater/common salt/rock salt as raw material for chemicals of daily use.] A mild non-corrosive basic salt 'A', used for faster cooking, is strongly heated to produce a compound 'B', that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated.
(i) A compound 'X' which is prepared from gypsum has the property of hardening when mixed with proper quantity of water. Identify 'X' and write its chemical formula. (ii) State the difference in chemical composition between baking soda and baking powder.
Select washing soda from the following:
- (a) NaHCO_3
- (b) Na_2CO_3.5H_2O
- (c) Na_2CO_3.10H_2O
- (d) NaOH