Class 11th

1.17. 15 ppm means 15 parts per million i.e.15 in 10⁶

So, % by mass = 15/10⁶ x 100 = 15 x 10^-4 = 1.5 x 10^-3%

Molality = No. of moles of solute/Mass of solvent in kg

Percent by mass = 1.5 x 10^-3 % means 100 g of the sample contain 1.5 x 10^-3 g chloroform.

So, 1000 g or 1 kg of the sample will contain 1.5 x 10^-3 x 1000/100 = 1.5 x 10^-2 g chloroform.

Molar mass of chloroform = 12 + 1 + (3 x 35.5) = 119.5 g/mol

Therefore, molality = 1.5 x 10^-2 /119.5 = 1.26 x 10^-4m.

1.16. Significant figures are meaningful digits which are known with certainty plus one which is estimated or uncertain. The uncertainty in the experimental or the calculated values is indicated by mentioning the number of significant figures

1.15. micro = 10^–6, deca = 10, mega = 10⁶, giga = 10⁹, femto = 10^–15

Hydrolysis of aikyltrichlorosilanes gives cross-linked silicones.

Due to inert pair effect, elements of group 14 exhibit oxidation states of +2 and +4. Thus, option (b) is correct.

Thermodynamically the most stable form of carbon is graphite, i.e., option (b) is correct.

In B₂H₆, B is sp³-hybridized. Therefore, option (c) is correct.

Boric acid is polymeric due to the presence of H-bonds. Therefore, option (b) is correct.

Borax is a salt of a strong base (NaOH) and a weak acid (H₃BO₃), therefore, it is basic in nature, i.e., option (c) is correct.

Laboratory preparation of carbon monoxide:

Formic acid is dehydrated with concentrated sulphuric acid at 373 K.

HCOOH → H₂O + CO↑

Commercial preparation of CO:

Steam is passed over hot coke.

C + H₂O → CO + H₂

Laboratory preparation of carbon dioxide:

Calcium carbonate reacts with dilute HCl to form carbon dioxide.

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

Industrial preparation of carbon dioxide:

Limestone is heated to produce carbon dioxide.

CaCO₃ →→CaO + CO₂