Agrain of sand is made up of 1.38 × 10-3 grams of oxygen and 0.00122 grams of silicon. what is the total weight, in grams, of the grain of sand?

               2.6 × 10⁻³ g   (Or)    0.0026 g

                 Mass of Oxygen  =  1.38 × 10⁻³ g

                 Mass of Silicon  =  0.00122 g  =  1.22 × 10⁻³ g

The total weight of grain of sand is calculated by adding the masses of Oxygen and Silicon as,

                        Total Weight  =  Mass of Oxygen + Mass of Silicon

Putting values,

                            Total Weight  =  1.38 × 10⁻³ g + 1.22 × 10⁻³ g

                            Total weight  =  2.6 × 10⁻³ g

Or,

                            Total weight  =  0.0026 g

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm