hmmmm let me think about that
most events like the rising and setting of the sun were used a natural measurement of time until recently.
solar time, which is based on the motion of the sun, is not the only way of measuring time, however. one might keep track of the regular appearance of the full moon. that event occurs once about every 29.5 solar days. the time between appearances of new moons, then, could be used to define a month.
one also can use the position of the stars for measuring time. the system is the same as that used for the sun, since the sun itself is a star. all other stars also rise and set on a regular basis.
although any one of these systems is a satisfactory method for measuring some unit of time, such as a day or a month, the systems may conflict with each other. it is not possible, for example, to fit 365 solar days into 12 or 13 lunar months exactly. this problem creates the need for leap years
i abbreviated most of it but there is a ton more at this link if you still need more.
we know we will need a balanced equation with masses and molar masses, so let’s gather all the information in one place.
m_r: 127.91 253.81
2hi ⟶ h₂ + i₂
(a) calculate the moles of hi
n = 506 g hi × (1 mol hi/127.91 g hi)
n = 3.955 mol hi
(b) calculate the moles of i₂
the molar ratio is (1 mol i₂/2 mol hi)
n = 3.955 mol hi × (1 mol i₂/2 mol hi)
n = 1.978 mol hi
(c) calculate the mass of i₂
m = 1.978 mol i₂ × (253.81 g i₂/1 mol i₂)
m = 502 g i₂
explanations: - as per the significant figures rule, in multiplication and division, we go with least number of sig figs.
4.03 has three sig figs where as 0.0000035 has two sig figs only, the zeros in this number are not sig figs as they are just holding the place values. as the least number of sig figs here is two, the answer needs to be reported with two sig figs only.