An analytical chemist wants to determine the value of $x$ in the formula of hydrated cobalt(II) chloride, ${CoCl}_2\cdot x{H}_{2}O$. They weigh a sample of the hydrated crystals, heat them in a crucible to drive off all the water of crystallisation, and then reweigh the remaining anhydrous cobalt(II) chloride until a constant mass is reached.

The equation representing the thermal decomposition is:

$${CoCl}_2\cdot x{H}_{2}O\to {CoCl}_2+x{H}_{2}O$$

The chemist records the following results:

• Mass of dry hydrated crystals before heating = $11.90g$
• Mass of anhydrous crystals after heating to a constant mass = $6.50g$

Use these results to determine the value of $x$ in the formula of ${CoCl}_2\cdot x{H}_{2}O$.

[$M_r$ values: ${CoCl}_2=130$, $H_{2}O=18$]