amnahaa
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Hi guys!

I was wondering if you were able to help me with these questions?
Calculate the pH if the following weak acids:
a) 0.10 mol dm^3 NH4Cl
pKa (NH4+)= 9.25
Calculate the pH of the solution formed when:
a) 20cm^3 of 0.10moldm-3 HCl is added to 30cm^3 of 0.04moldm-3 NaOH
b)100cm^3 of water is added to 25cm^3 of 0.50moldm-3 KOH
c) 15cm^3 of 0.5moldm-3 H2S04 is added to 100cm^3 of 0.75moldm-3 KOH

Any help would be appreciated
Thank you!
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amnahaa
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flowerscat
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Calculate the pH of the solution formed when:
a) 20cm^3 of 0.10moldm-3 HCl is added to 30cm^3 of 0.04moldm-3 NaOH

1. Write a balanced equation for the reaction between HCl and NaOH
2. Calculate the moles of each one
3. Figure out which moles are in excess
4. Convert the excess moles back to concentration (using the NEW volume of 50 cm3)
5. If HCl is in excess - the molar ratio of HCl to H+ is 1:1, so find pH by simply substituting HCl concentration in the pH = -log[H+] equation
6. If NaOH is in excess, use the Kw expression to find H+ and then find pH. OH- conc = NaOH conc (1:1 ratio)


a) 0.10 mol dm^3 NH4Cl, pKa (NH4+)= 9.25

1. Convert pKa back to Ka (=10-pKa)
2. Use Ka = [H+]2/[HA] expression
3. [HA] = 0.10
4. Rearrange to find [H+]2, then square root to find [H+]
5. Use this value to find pH
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amnahaa
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(Original post by flowerscat)
Calculate the pH of the solution formed when:
a) 20cm^3 of 0.10moldm-3 HCl is added to 30cm^3 of 0.04moldm-3 NaOH

1. Write a balanced equation for the reaction between HCl and NaOH
2. Calculate the moles of each one
3. Figure out which moles are in excess
4. Convert the excess moles back to concentration (using the NEW volume of 50 cm3)
5. If HCl is in excess - the molar ratio of HCl to H+ is 1:1, so find pH by simply substituting HCl concentration in the pH = -log[H+] equation
6. If NaOH is in excess, use the Kw expression to find H+ and then find pH. OH- conc = NaOH conc (1:1 ratio)


a) 0.10 mol dm^3 NH4Cl, pKa (NH4+)= 9.25

1. Convert pKa back to Ka (=10-pKa)
2. Use Ka = [H+]2/[HA] expression
3. [HA] = 0.10
4. Rearrange to find [H+]2, then square root to find [H+]
5. Use this value to find pH
Thank you so much youre a life saver !
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username3477548
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(Original post by amnahaa)
Hi guys!

I was wondering if you were able to help me with these questions?
Calculate the pH if the following weak acids:
a) 0.10 mol dm^3 NH4Cl
pKa (NH4+)= 9.25
Calculate the pH of the solution formed when:
a) 20cm^3 of 0.10moldm-3 HCl is added to 30cm^3 of 0.04moldm-3 NaOH
b)100cm^3 of water is added to 25cm^3 of 0.50moldm-3 KOH
c) 15cm^3 of 0.5moldm-3 H2S04 is added to 100cm^3 of 0.75moldm-3 KOH

Any help would be appreciated
Thank you!
is this a gcse question?
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amnahaa
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A level Don't worry!
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amnahaa
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(Original post by vix.xvi)
is this a gcse question?
A level
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flowerscat
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(Original post by flowerscat)Calculate the pH of the solution formed when:
a) 20cm^3 of 0.10moldm-3 HCl is added to 30cm^3 of 0.04moldm-3 NaOH

5. If HCl is in excess - the molar ratio of HCl to H+ is 1:1, so find pH by simply substituting HCl concentration in the pH = -log[H+] equation
6. If NaOH is in excess, use the Kw expression to find H+ and then find pH. OH- conc = NaOH conc (1:1 ratio)

Just to Clarify:

5. If HCl is in excess - the molar ratio of HCl to H+ is 1:1, so find pH by simply substituting (EXCESS) HCl concentration in the pH = -log[H+] equation

6. If NaOH is in excess, use the Kw expression to find H+ and then find pH. OH- conc = (Excess) NaOH conc (1:1 ratio)
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amnahaa
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(Original post by flowerscat)
(Original post by flowerscat)Calculate the pH of the solution formed when:
a) 20cm^3 of 0.10moldm-3 HCl is added to 30cm^3 of 0.04moldm-3 NaOH

5. If HCl is in excess - the molar ratio of HCl to H+ is 1:1, so find pH by simply substituting HCl concentration in the pH = -log[H+] equation
6. If NaOH is in excess, use the Kw expression to find H+ and then find pH. OH- conc = NaOH conc (1:1 ratio)

Just to Clarify:

5. If HCl is in excess - the molar ratio of HCl to H+ is 1:1, so find pH by simply substituting (EXCESS) HCl concentration in the pH = -log[H+] equation

6. If NaOH is in excess, use the Kw expression to find H+ and then find pH. OH- conc = (Excess) NaOH conc (1:1 ratio)
It turned out that HCl was in excess thank you so much for your help!
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flowerscat
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(Original post by amnahaa)
It turned out that HCl was in excess thank you so much for your help!
Glad to have helped
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