Given a barometric pressure of 754.5 mmHg , calculate the pressure of gas sample (a) as indicated by the manometer. 

Given a barometric pressure of 754.5 mmHg , calculate the pressure of gas sample (b) as indicated by the manometer. 

Answer:

1) we can see that

difference in height of mercury = 2 cm

now

1 cm = 10 mm

so

difference in height of mercury column = 2 x 10 = 20 mm

so

pressure difference = 20 mm Hg

now

looking at the figure

we can say that

Patm > Pgas

so

Patm - Pgas = 20 mm Hg

given

Patm = 754.5 mm Hg

so

Pgas = Patm - 20

Pgas = 754.5 - 20

Pgas = 734.5 mm Hg

so

the pressure of gas is 734.5 mm Hg

2)

we can see that

difference in height of mercury = 6.5 cm

now

1 cm = 10 mm

so

difference in height of mercury column = 6.5 x 10 = 65 mm

so

pressure difference = 65 mm Hg

now

looking at the figure

we can say that

Pgas > Patm

so

Pgas - Patm = 65 mm Hg

given

Patm = 754.5 mm Hg

so

Pgas = Patm + 65

Pgas = 754.5 + 65

Pgas = 819.5 mm Hg

so

the pressure of gas is 819.5 mm Hg