1.

100 mL of HCl gas at 25^@ C and 740 mm pressure was dissolved in 1 L of water. What will be the pH of solution. (Given, vapour pressure of H_2 O at 25^@ C is 23.7 mm.)

Answer»

`2.012`
`3.241`
`2.414`
`3.021`

Solution :Givenvapourpressureof water ` =23.7` mm
`:. P_(HCI _("DRY"))=( 740-23.7 )/( 760) atm= 0.9425 ` atm
`V=100/1000= 0.1 L ,T= 25+ 273= 298K`
` therefore ` Mole of ` HCI` i.e.,`""^(n)HCI = (W) /(m ) =(PV )/(RT)= ( 0.9425 xx 0.1 )/( 0.0821 xx 298)`
`thereforen= 3.85 xx 10^(-3)`
Nowmolarityof HCI= noof molesdissolved in 1 L ofsolution
`= (3.85 xx 10^(-3) )/( 1 ) ` ( V in litre )
` therefore[H^+] = 3.85xx 10^(-3)M`
` thereforepH =- LOG[H^+] =- log ( 3.85 xx 10^(-3))`
`pH =2.414`


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