$\pu{1.20 g}$ of hydrated tin chloride decompose to form $\pu{1.01 g}$ of anhydrous tin chloride on heating. Calculate the value of $x$ given

$$\ce{SnCl2.xH2O -> SnCl2 + x H2O}$$

I done it and came out with $1.666477009$ using:

  • $M(\ce{H}) = 1.008$
  • $M(\ce{O}) = 15.999$
  • $M(\ce{Cl}) = 35.45$
  • $M(\ce{Sn}) = 118.710$

This is a "challenge" question set by my chemistry teacher (GCSE Chemistry), but I won't see any of my teachers for another 2 weeks so I would really like someone to help check if I done this right.


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  • 2
    $\begingroup$ How did you get that value? (Also it has way to many significant figures.) $\endgroup$ – MaxW Apr 5 at 22:35
  • $\begingroup$ In addition to the issue with sigfigs, it would be nice to see units. Plain numbers are rarely meaningful in natural sciences. $\endgroup$ – andselisk Apr 6 at 0:09

1.20g of hydrated tin chloride decompose to form 1.01g of anhydrous tin chloride on heating. Calculate the value of x

1.20 Stannous chloride hydrate = 1.01 anhydrous stannous chloride

So 1.20 - 1.01 = 0.19 grams of water

Moles of anhydrous stannous chloride

$$\dfrac{1.01}{189.60} = 0.0053270$$

Moles of water

$$\dfrac{0.19}{18} = 0.01065$$

ratio of stannous chloride to water

$$\dfrac{0.01056}{0.0053270} = 1.982 \ce{->[rounding]} = 2.0$$

So the formula is $\ce{SnCl2\cdot2H2O}$

Notice that I carried some extra digits in the intermediate calculations but rounded the final result to two significant figures since the grams of water only has two significant figures.

  • 1
    $\begingroup$ With respect to using "moles", "number of moles" etc. instead of amount of substance you might want to check out a recent Meta post:) $\endgroup$ – andselisk Apr 5 at 23:47
  • $\begingroup$ Yes I know about IUPAC's moving to amount of substance but to me it seems stupid, after all I am calculating moles. $\endgroup$ – MaxW Apr 6 at 0:04
  • $\begingroup$ Ehhm, technically speaking, it's amount (physical quantity) you are calculating. Mole is a unit, and units are not to be calculated. $\endgroup$ – andselisk Apr 6 at 0:08
  • 1
    $\begingroup$ Terrorists only understand negotiation done the Korben Dallas way. Terminologists are more like inventors and preservers of the uniform language so that the people could still understand each other and keep up building the tower of Babel regardless of the "god's will" (I bet conspiracy theory adepts will also read between the lines:) ). $\endgroup$ – andselisk Apr 6 at 6:44
  • 1
    $\begingroup$ @andselisk - Made a note to myself. Do not fool with the master blaster. $\endgroup$ – MaxW Apr 6 at 14:28

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