0.0136 g + 2.70 × 10-4 g - 4.21 × 10-3 g = ? how many digits to the right of the decimal point should be used to report the result?

You should use 5 digits to the right of the decimal point.

Explanation:

To be precise in the mathematical operation you have to conserve all significant digits .

Replace the scientific notation for its equivalent in decimal notation:

2.70 x 10-4 g = 0.00027  g

4.21 x 10-3  g = 0.00421  g

Then, compute the addition and subtraction :

0.01360  g

+  

0.00027  g

-  

0.00421  g

0.00966 g = 9.66 x 10-3 g

That means you should use 5 digits to the right of the decimal point, which are the biggest amount of digits necessary to represent  2 of the numbers involved in the mathematical operation.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.