Q4. One mole of CoCl3·5NH3 is treated with excess AgNO3. What mass of AgCl precipitates? (Ag = 107.87, Cl = 35.45 g mol−1.)
The compound is [CoCl(NH3)5]Cl2, with two free chlorides, so 2 mol AgCl form (NCERT page 119). M(AgCl) = 107.87 + 35.45 = 143.32 g mol−1, so the mass is 2 × 143.32 = 286.64 g.
Q5. A 0.010 M solution of a cobalt(III) chloride–ammonia compound conducts like a 1 : 1 electrolyte. Which formula from NCERT Table 5.1 fits, and how many moles of AgCl would 0.020 mol of it give?
A 1 : 1 electrolyte has one ion of each sign: [CoCl2(NH3)4]Cl (green or violet; NCERT Table 5.1, page 119). It has one free chloride, so 0.020 mol gives 0.020 mol AgCl.
Q6. Why do the green and violet forms of CoCl3·4NH3 count as isomers?
They have the same empirical formula, both are [CoCl2(NH3)4]Cl and both give 1 mol AgCl, yet they have distinct properties, such as colour (NCERT page 119). The difference lies in how the two chlorides and four ammonias are arranged round the cobalt: they are the cis and trans forms of [CoCl2(NH3)4]+ (NCERT Fig. 5.3, page 125). Beyond the NCERT text: the green form is trans and the violet one cis (Wikipedia, “Alfred Werner”, which calls it purple).