Question

Small quantities of hydrogen can be prepared by the addition of hydrochloric acid to zinc. A sample of 195 mL of hydrogen was collected over water at 25°C and 753 torr. What mass of hydrogen was collected? (Pwater = 24 torr at 25°C)

Answer 1

Answer:

mass of hydrogen collected is 0.016 gram

Explanation:

Given values:

For calculating mass we have to find the number of moles first  

Ideal gas equation   PV =nRT

Volume= 195 ml

Pressure: 753 torr =0.99 atm

Temperature: 25+273= 298 Kelvin

Ideal gas constant R= 0.0821 Latm/molK

Number of moles n= ?

So n=  PV/RT

Adding the values  

n= = (753 torr)(1 atm/760 torr)(195 mL)(1 L/1000 mL)/(0.0821 L·atm/mol·K)(273 K)

n = 0.007897 moles of H₂

Now mass of hydrogen collected = number of moles x Molar mass of H₂

                                                     = 0.007897 x 2  

                                                        = 0.0157 g H₂

Now mass of hydrogen collected is 0.016 gram (rounding the amount)