Question

Air at STP has a density of 1.292g/litre.What will be the weight of 6litre of air
at 20degree C at 755mm
​

Answer 1

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Let us write the given data first and solve the problem.

GIVEN:

❆ Density (d) = 1.292 g/L

❆ Volume of Air (v) =  6L

❆ Temperature (t) = 20°C = 20 + 273 = 293 K

Note:-

S.I unit of temperature is 'Kelvin' so we need to convert its value from °C to K . To do that just we need to add the +273 with given temperature.

❆ Pressure (P) = 755 mm of Hg = $\frac{755}{760}$  = 0.99 atm ≈ 1 atm

Note:-

Standard S.I unit of pressure is "atmospheric pressure".But here it is given mm of Hg so we need to divide the given value by 760 to obtain the resultant atm pressure value.

SOLUTION:

✧ Density = Mass/Volume

{Here Volume is given as standard S.T.P so we need to take it value as  22.4 L}

1.292 g/L × 22.4 L = Mass  {L and L will get cancelled}

Mass = 28.94 grams

✧ We need to use the gas formula to find the weight of 6L of air

PV = nRT

Here,

✯ P = Pressure

✯ V = Volume

✯ n = Number of moles

✯ R = Universal Gas constant = 0.0821 is its value

✯ T = temperature

1×6 = $\frac{weight}{G.M.W}$ ×0.0821×293

6  =  Weight/28.94 ×25.055

6 × 28.94 = weight × 25.055

173.64 = Weight × 25.055

173.64/25.055 = Weight

Weight = 7.218 grams

W ≈ 7.2 grams

Hence it weight will be 7.2 grams at 6L

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To calculate any values related to ideal gas, Then use ideal gas equation

PV = nRT

n can also be taken as w /G.M.W

Where

✯ P = Pressure

✯ V = Volume

✯ n = Number of moles

✯ R = Universal Gas constant

✯ T = temperature

Also u need to note the

✯ Mass × Volume = Density

With these formulas u can calculate any sum regarding to ideal gases.

Hope it helps

Thanks for asking:-)