Problem 2

A sample of 2.3793 g of a crystallohydrate of the type

\ce{M_xA_y . z H2O}

(where M is a metal) reacted with an excess of

\ce{SOCl2}

. The gaseous products were absorbed in an aqueous solution containing barium chloride, hydrochloric acid and hydrogen peroxide. Small carried-over amounts of

\ce{SOCl2}

had been frozen out. The mass of the deposited precipitate was 14.004 g and contained 13.74 mass % of sulphur. In another experiment, 1.1896 g of the initial hydrate was dissolved in water and made up to 100 cm

^3

. One fifth of this solution required 10 cm

^3

of 0.2 M

\ce{AgNO3}

solution for complete precipitation (yielding 0.28664 g of precipitate). (a) Calculate the formula of the crystallohydrate. (b) Given that the hydrate can contain at most 7 moles of water per mole of hydrate, name another hypothetical hydrate that is ruled out by this limit.

Step 4 of 4: Ruled-out alternative

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\ce{YCl3 . 9H2O}\ (z = 9 > 7)

Analysis

For $v=3$ , $\ce{MCl3 . 9H2O}$ would give $M(\ce{M}) \approx 88.4$ g mol $^{-1}$ (yttrium, Y), but it has $z = 9 > 7$ moles of water, so the 7-mole limit rules it out.