When repeated measurements of the same quantity are very close to one another they are

When repeated measurements of the same quantity are very close to one another they are termed as precise measurements.

Explanation:

An experiment is repeated two to three times and the outcomes were checked to have similar values to attain precision of the measurements. The accuracy and precision are the important in attaining correct measurements.

The accuracy is the closest true value obtained from the measuring instrument. But to get precise results, the measurements were taken repeatedly and then analyzed whether the values obtained are similar or varying significantly.

If the repeatedly measured values are very close to one another that means the measured quantities are precisely taken. All the values are precise in nature.

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