Question
How will you distinguish between conc. HCl and conc. $H_2SO_4?$
✓
Answer
Conc. HCl and Conc. $H_2SO_4:$
| S.No. | Conc. HCl | Conc. $H_2SO_4$ |
| 1. | Addition to silver nitrate : When conc. HCI is added to silver nitrate white ppt. of silver chloride are formed. $AgNO _3+ HCl \longrightarrow AgCl + HNO _3$ White ppt. of silver chloride dissolve in excess of ammonium hydroxide. |
Addition to copper : Conc. Sulphuric acid is added to copper and heated. Sulphur dioxide, which is colourless gas with the smell of burnt sulphur is evolved. $ Cu +2 H _2 SO _4 \longrightarrow CuSO _4+2 H _2 O + SO _2 $ $SO _2$ gas turns $K _2 Cr _2 O _7$ paper green. |
| 2. | A glass rod dipped in conc. HCl is brought in contact with ammonia gas, curdy white fumes of ammonium chloride is seen around the glass rod. | Glucose when conc. Sulphuric acid $\underset{\text { blue }}{ CuSO _4 \cdot 5 H _2 O } \xrightarrow{\text { conc } \cdot H _2 SO _4} CuSO _4+\underset{\text { white }}{5 H _2 O }$ |
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→$( H =1 ; C =12 ; Cl =35.5)$
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(c) Decomposition by acid
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