[help] using indicators to test pH of coke (2 Viewers)

[haloeshorns]

how do i use indicators to test the pH of substances which are already coloured such as coke?

 

[kathrynso]

You're probably best off using a pH meter for those sorts of substances

 

[kloudsurfer]

how do i use indicators to test the pH of substances which are already coloured such as coke?

We used lemonade for that reason.

 

[xiao1985]

if you insist on using coke, dilute it 10 or 50 times... it makes the colour lighter and colour of the indicator would be easier to see...

 

[nys-j]

if you insist on using coke, dilute it 10 or 50 times... it makes the colour lighter and colour of the indicator would be easier to see...

yeah if you have to use a coloured indicator rather than a pH meter, i'd dilute it heaps, and use an indicator with a really obvious colour change - eg. goes clear; or changes from clear to a colour and avoid ones that go from dark red to dark blue sorta thing.
good luck

 

[wrxsti]

Methly Orange...

 

[xiao1985]

you will need a mixture of indicators imho... one indicator tells you too big of a range to be useful...

 

[haloeshorns]

if i dilute it wont that change the pH since the pH of water is 7?

 

[Forbidden.]

if i dilute it wont that change the pH since the pH of water is 7?

yeh adding any amount of water changes the pH because you change the H⁺ and OH^- concentrations in amounts of molL^-1

 

[airie]

yeh adding any amount of water changes the pH because you change the H⁺ and OH^- concentrations in amounts of molL^-1

Uhh, no. As long as you add deionised water, you don't change the pH. Dilution is common technique in measuring the pH of a solution.

 

[nys-j]

if i dilute it wont that change the pH since the pH of water is 7?

no. stuff dissociates into its ions in water, n pH is a measure of the H+ in the solution, H+ is an ion, adn the amount present stays the same, so its all ok.

yeh adding any amount of water changes the pH because you change the H<SUP>+</SUP> and OH<SUP>-</SUP> concentrations in amounts of molL<SUP>-1</SUP>

pH is H+ ions present in the solution, so when ur doing ur calculations dont base it on the total volume of water added, base it on the original amount. Cause the amount of H+ present in the original amount is the same amount present once its been diluted 10 times.

 

[xiao1985]

unfortunately, even adding deionised water, pH will change

pH = -log [H+]

concentration of H+ will change if you add more volume of water... if we neglect the self ionisation of water, the number of moles of H+ will not however... which means it is still possible to find the pH before dilution....

 

[Forbidden.]

unfortunately, even adding deionised water, pH will change

pH = -log [H+]

concentration of H+ will change if you add more volume of water... if we neglect the self ionisation of water, the number of moles of H+ will not however... which means it is still possible to find the pH before dilution....

i was pretty sure adding 90 mL distilled water to 10mL HCl affected pH, because it was a question given to me in an exam, and I got it wrong somehow.

 

[xiao1985]

i was pretty sure adding 90 mL distilled water to 10mL HCl affected pH, because it was a question given to me in an exam, and I got it wrong somehow.

it would affect the pH... if you neglect the self ionisation of water, the pH would (in your case) rise by 1 (since pH is a log scale)

 

[elseany]

it'll change because the pH is a measure of the CONCENTRATION of H+ ions. by adding water were increasing the volume of the solution and hence the concentration of any present H+ ions. but as far as changing the amount of H+ ions, as far as i know thats negligible so we just ignore it, at the hsc level anyway.

 

[fishbulb]

Why not use red cabbage indicator strips. Just get the red cabbage juice and soak it in thin cardboard strips, let it dry, and dip it in the coke.