I'm stuck on this question, I've tried a few different methods but I can't get to the mark scheme answer. Please could someone help me
Here is the question:
This question involves calculations about two strong acids and one weak acid. All measurements were carried out at 25 °C. 3 –3 (a) A 25.0 cm sample of 0.0850 mol dm hydrochloric acid was placed in a beaker and 100 cm3 of distilled water were added. Calculate the pH of the new solution formed. Give your answer to 2 decimal places.
ohhhhh, that's how you do it! I just have one teeny tiny question, if we add 100cm^2 of water, isn't there a dilution factor of 5 how come the number of moles of HCl doesn't change?
As far as I know the number of moles doesn’t change if the volume increases, the moles are still in there, just in a larger volume. The concentration only changes which is what you had to work out.
Say you have 5g (imagine it as moles) of sugar in 100cm3 of water, you have 5 moles of sugar solution. If you increase the volume by adding 900cm3, you still have 5g, or 5 moles, just in a larger volume
ohhhhh, that's how you do it! I just have one teeny tiny question, if we add 100cm^2 of water, isn't there a dilution factor of 5 how come the number of moles of HCl doesn't change?
As far as I know the number of moles doesn’t change if the volume increases, the moles are still in there, just in a larger volume. The concentration only changes which is what you had to work out.
Say you have 5g (imagine it as moles) of sugar in 100cm3 of water, you have 5 moles of sugar. If you increase the volume by adding 900cm3, you still have 5g/moles, but in a larger volume
an easy way is: original H+ conc x old volume/new volume = new H= conc. then you can plug this into the orginal -logH+ to find the pH. of course this is only for monobasic acids and units for both volumes have to be the same. and you can also use this for all the acid and base dilution questions. i got 1.77? is that correct
I'm stuck on this question, I've tried a few different methods but I can't get to the mark scheme answer. Please could someone help me
Here is the question:
This question involves calculations about two strong acids and one weak acid. All measurements were carried out at 25 °C. 3 –3 (a) A 25.0 cm sample of 0.0850 mol dm hydrochloric acid was placed in a beaker and 100 cm3 of distilled water were added. Calculate the pH of the new solution formed. Give your answer to 2 decimal places.
an easy way is: original H+ conc x old volume/new volume = new H= conc. then you can plug this into the orginal -logH+ to find the pH. of course this is only for monobasic acids and units for both volumes have to be the same. and you can also use this for all the acid and base dilution questions. i got 1.77? is that correct
That’s an easy way too! Yep, you’re right 1.77 is the pH 😊
As far as I know the number of moles doesn’t change if the volume increases, the moles are still in there, just in a larger volume. The concentration only changes which is what you had to work out.
Say you have 5g (imagine it as moles) of sugar in 100cm3 of water, you have 5 moles of sugar solution. If you increase the volume by adding 900cm3, you still have 5g, or 5 moles, just in a larger volume
Hi again! @cciaran, I needed some help with a maths question and was wondering whether you'd be able to help? Thank you!