How fast should you heat the melting point sample?
a. heat slowly until you get close to the expected temperature.
b. as slowly as possible.
c. as fast as possible.
d. heat quickly until you get close to the expected temperature.

Option a.

Explanation:              

The transformation of a solid into liquid is a slow process, hence a rate of heating too fast, near the melting point of the sample, will not give the right time to the crystals of the sample to absorb the heat and to melt in the outside and the inside, leading to wrong results in all cases. If we heat to fast, the melting point range will be too broad and will be misleading, resulting in values of the range more hight than the theoric ones.  

A rate of 1 °C/min or 2 °C/min is the most appropriate to approach the melting point of the sample. Since it is too slow, from preventing the experiment taking forever it is recommended to start the experiment at a high heating rate until it reaches 20 °C below the melting point, and then, turn the heating rate down to 1 °C/min or 2 °C/min.      

Therefore, the correct answer is a: near the melting point of the sample, we must heat slowly until it reach the expected temperature.

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given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g