What does it mean when a sample has a higher melting point range than its literature value?

The previous answerers are WRONG.

IMPURITIES in a solid LOWER the melting point, and also spread out the range / make it broader (5-10 deg instead of 1-2, for example).

Reasons you might get a HIGHER measured mp than the literature value include:
* Miscalibration of the thermometer
* Heating the sample too fast
* (Rarely) The literature value is wrong or was acquired using
a wet sample.
* Melting point not being performed at 1 atm (the previous guy
is right about that point...)
* Wrong/different compound being measured.

You can see, it's usually an experimental error. Even mixed melting points are usually lower than lit values for pure materials.
it means that it contains impurities
it means either it is under pressure like in pressure cooker bp of water is higher . or it has some impurities in it ,like salt dissolved in water.
One or more of several things:

(1) The thermometer is faulty,
(2) The sample is impure,
(3) The literature is wrong (unlikely, but possible), or
(4) something I haven't thought of.

I'd say the most common cause is probably #2. Impurities generally raise the b.p. and lower the m.p. so that the liquid phase temperature-range is widened.
Depending on the impurity material, it could Lower or Higher the melting point, in your case it is making it higher.

Also, the literature value is obtained under strict lab conditions. Your experiment may have some unisolated variables, such as calibration of temperature measurement equipment and also you will have 'errors'.

If you allow for your absolute error, re-check your results and see what you end up with.

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