Chemistry MCQs for NEET — Practice Questions with Answers

$ let the vol of acid left unused = V ml of 0.1 MH_2SO_4 $ $ \therefore V \times 0.1 \times 2 = 20 \times 0.5\times 1 $ $ V = 50 ml = 50 ml of .01 m H_2SO_4 $ $ Vol of acid used = 100 - 50 $ $ % N = { 1.4 \times 2 \times 50\times 0.1 \over 0.3 } = 46.6 $ $ %N in urea = { 28 \over 60} \times 100 = 46.6 $

Thiourea gives a blood red coloration when its Lassaigne extract is treated with alkali and ferric chloride. This is due to the formation of a complex between the thiourea and ferric ions, which results in the characteristic blood red color.

Lassaigne test for nitrogen involves the fusion of the organic compound with sodium, which converts nitrogen present in the compound into sodium cyanide ($NaCN$). Only $NaCN$ among the given options will form sodium cyanide, which can be detected by the formation of Prussian blue color when treated with iron(II) sulfate and then acidified.

In the Lassaigne test, p-aminobenzene sulphonic acid will give a blood red color due to the formation of ferric thiocyanate. This happens because the sulfur in the compound reacts with sodium to form sodium sulfide, which then reacts with iron(III) to form ferric thiocyanate, giving a blood red color.

The yellow color observed during the detection of phosphorus in an organic compound is due to the formation of ammonium phosphomolybdate, which has the chemical formula \((NH_4)_3PO_4 \cdot 12MoO_3\). This compound is a characteristic yellow precipitate that confirms the presence of phosphorus.

$ MW = { 108 \times 0.306 \over 0.216 } - 107 = 46 $

To find the molecular weight of the acid, we use the mass of the silver salt and the mass of silver obtained upon ignition. The tribasic acid forms a silver salt with 3 Ag atoms. The formula weight of silver (Ag) is 108 g/mol. The mass of silver in the salt is 0.648 g, which corresponds to 3 moles of Ag (since it's a tribasic salt). Therefore, the equivalent weight of the acid can be calculated as follows: \((1.026 / 0.648) imes 108 / 3 = 192\). Thus, the molecular weight of the acid is 192 g/mol.

Chromatography is a versatile technique used for the separation and purification of various substances. It can be used to purify solids, liquids, and gases. This is because chromatography relies on the differential partitioning between the mobile and stationary phases, making it effective for a wide range of substances.

The reagent $\text{cold, dilute, alkaline KMnO}_4$ (potassium permanganate) is used for the detection of unsaturation in alkenes. This reagent oxidizes the double bond in alkenes, resulting in the formation of diols (glycols). The reaction is accompanied by a color change from purple to brown due to the reduction of KMnO$_4$ to MnO$_2$, which helps in identifying the presence of unsaturation.

Beilstein’s test is used for the detection of halogens in an organic compound. In this test, a copper wire is heated in a flame until it stops producing a green flame. Then the wire is dipped into the organic compound and reheated in the flame. If a green flame reappears, it indicates the presence of halogen in the compound.