Question (1 Viewer)

[Dumbarse]

A small amount of pure sodium metal is dropped into 1.2L of water. The reaction is summarised in the following equation.

2 Na(s) +2 H2O(l) ---> 2 NaOH(aq) + H2(g)

The gas collected occupied a volume of 4.68L at 25 degrees celcius and 1 atm. pressure

a) Calculate the amount in moles of gaseous product

b) Calculate the final pH of the water

 

[spice girl]

Originally posted by Dumbarse
A small amount of pure sodium metal is dropped into 1.2L of water. The reaction is summarised in the following equation.

2 Na(s) +2 H2O(l) ---> 2 NaOH(aq) + H2(g)

The gas collected occupied a volume of 4.68L at 25 degrees celcius and 1 atm. pressure

a) Calculate the amount in moles of gaseous product

b) Calculate the final pH of the water

1 mole gas occupies 24.47L at SLC

#moles H2 = 4.68/24.47 = whatever that is

[OH-] = 2 * #H2 (from above equation)
= 2 * 4.68/24.47 = whatever that is

pH = 14 - (-log([OH-])) = whatever that is.

 

[BlackJack]

a) 24.47L per mole @ SATP...

Therefore, 4.68L / 24.47 L/mol
= .1913 mol

b) looking at equation,
mol NaOH = 2*mol H2
= 0.3825...

divide by L of water

0.3188... mol L-1

convert to pOH... -log10 (conc.)
= 0.4965
pH = 14- pOH
=13.5

That should be right...

 

[Dumbarse]

Originally posted by BlackJack
a) 24.47L per mole @ SATP...

Therefore, 4.68L / 24.47 L/mol
= .1913 mol

b) looking at equation,
mol NaOH = 2*mol H2
= 0.3825...

divide by L of water

0.3188... mol L-1

convert to pOH... -log10 (conc.)
= 0.4965
pH = 14- pOH
=13.5

That should be right...

ohh so why does the concentration of NaOH equal the concentration of the OH- ions??

so if i had that H2SO4 had a concentration of 2mol/L could i work out the concentration of H30+ ions just by saying there are 2 H's so the conc would be 4 mol/L ??

 

[McLake]

Originally posted by Dumbarse



ohh so why does the concentration of NaOH equal the concentration of the OH- ions??

so if i had that H2SO4 had a concentration of 2mol/L could i work out the concentration of H30+ ions just by saying there are 2 H's so the conc would be 4 mol/L ??

H2SO4 + H2O --> H3O+ + HSO4-
HSO4- + H2O <-> H3O+ + SO4-

so H2SO4 gives two lots of H3O+, so yes 4M ...