(1) Mass of gas is measured by determining the wt. of empty container and then container filled wet gas and then taking their difference which will give mass of gas.

No of molar = masses gram/molar mass

(2) The volume of gas is equal to volume of container is which gas is present. 25’ SI unit is m³.

Other unit are         1 m³ = 10³ dm³ = 10⁶ cm³

                                    1 ml = 1 cm³

1 litre = 10³ cm³ = 1 dm³ = 10^-3 m³

(3) Pressure:- The atmospheric pressure is measured by barometer. The height of Hg – column above the level of Hg is dish is measure of atmospheric pressure at that place.

The pressure of gas is measured by manometer.

Manometer is of 2 types:-

Pressure = Force/Area = ((A x h x ρ) x g/A)

Where A → Area of cross section

h → height to which Hg – rises

ρ → density of Hg             g → acceleration due to gravely

(A x h x ρ) = mass of mercury     so P = ρ h g

Standard or Normal atmospheric pressure is

1 atm = 76 cm = 760 mm or 760 torr

Now unit of P uses is ‘bar’

1 bar = 0.987 atm

1 atm = 101325 Pa or non^-2 or kg m^-1s^-2

1 bar = 10⁵ Pa

Temperature is measured on 3 difference scales

(i) Centigrade or Celsius scale (ii) Fahrenheit scale

(iii) Kelvin scale

0^°C = 273.15 k

Relation between – ^°C & F

^°C = 5/9 (°F – 32)