Suppose that a series of measurements have shown that the mean mass of an object is 122.4g with
deviation of 1.3 g. how many significant figures are justified in the mean and how would you report the
most probable mass of the object? explain.

Explanation:

If the deviation is 1.3 g the true measurement will be within the interval 122.4g - 1.3g to 122.4g + 1.3g:

Hence, only the first two digits, hundreds and tens places, are certain. The ones digit is uncertain.

Since, the signficant figures include the certain digits plus one uncertain digit, you should report the number with three significant figures: 2 certain digits + 1 uncertain digit.

The most probable mass of the object would be the mean which is 122.4, which must be rounded to three significant figures, i.e 122 g.

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2