# Questions tagged [ph]

pH (or the potential of hydrogen) is a scale used to measure how acidic or basic an aqueous solution is.

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### Difference in pH of water and rainwater

In my textbook (Olmsted and Williams 4th ed) it is given that pH of pure water is 7, pH of unpolluted rain water is between 5-6 and pH of acid rain is between 4-5. It is obvious that pH for acid ...
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### Difference in calculated pH and the real pH of a phosphate buffer?

I'm from Colombia and I joined this site to ask a question that I could not solve yet. I am calculating the amounts to prepare a phosphate buffer with two salts. I want to prepare a buffer system with ...
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### Why is the pKa of the thiol group in N-acetylcysteine higher then the pKa of the thiol group in cysteine?

I understand why cysteine has a $\mathrm pK_{\mathrm a}$ of 8.3. But the $\mathrm pK_{\mathrm a}$ of thiol in N-acetylcysteine is 9.27. Since there is an acetyl group attached to the nitrogen, doesn't ...
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### No indicator is suitable when titrating weak acid with weak alkali

This was a statement in my book: A solution of a weak acid cannot be titrated with a weak base using an indicator to find the end-point because the pH change is too gradual close to the equivalence ...
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### pKa of phenols using UV-Vis spectroscopy

I have done an experiment where I dissolved four different substituted phenols in acidic, basic, and buffer solutions, and recorded the UV-Vis spectra for each. I'm supposed to pick a wavelength where ...
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### Could we reach a pH of 4.9 by blowing through straws?

According to Wikipedia's article on Breathing: The permanent gases in gas we exhale are 4% to 5% by volume more carbon dioxide and 4% to 5% by volume less oxygen than was inhaled. If I started ...
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### pH of a buffer made with boric acid and potassium dihydrogen borate

The Problem Calculate the pH of a buffer that is $\pu{0.200M}$ $\ce{H3BO3}$ and $\pu{0.122M}$ $\ce{KH2BO3}$. The $K_\mathrm{a}$ for $\ce{H3BO3}$ is $7.3\times10^{-10}$ What I Tried For each of ...
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### How can I choose an indicator for determining the concentration of a base using its pKb values?

I have a base $\ce{M(OH)_{3}}$ having 3 $\mathrm{p}K_{\mathrm{b}}$ values as, $$\mathrm{p}K_{\mathrm{b}_{1}} = 0.5\\ \mathrm{p}K_{\mathrm{b}_{2}} = 3.7\\ \mathrm{p}K_{\mathrm{b}_{3}} = 7.7\\$$ If a ...
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### Which pH indicator will give a dramatic color change with small changes in the amount of carbon dioxide dissolved in water?

I want to do a demonstration for students where they take a capped syringe and change the volume above a solution of seltzer water. The amount of carbon dioxide dissolved will vary, hopefully ...
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### Calculating pH for titration of weak base with strong acid

Calculate the pH at the equivalence point for the titration of $\pu{0.130 M}$ methylamine ($\ce{CH3NH2}$) with $\pu{0.130 M}$ $\ce{HCl}$. The $K_\mathrm{b}$ of methylamine is ${5.0 \cdot 10^{–4}}$. ...
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### Why is ionic strength (mu) calculated differently for these 2 examples?

In the following examples; I don't understand why $\ce{Na_3PO_4}$ is a much more complicated process when calculating $\mu$ compared to $\ce{NaH_2PO_4}$ and $\ce{Na_2HPO_4}$. Specifically, I don't ...
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### Is this problem about acid-base titration wrong?

I wouldn't post mere 'problems' here normally, but I will hopefully be starting to give chemistry education to some 10-11-12th graders and I want to make sure that it is not I that has a problem but ...
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### Investigating a factor affecting buffer capacity

I'm preparing for an experiment to investigate some factor affecting buffer capacity. At the moment, I'm looking at using a $\ce{NH_3}$ ($2\,\mathrm{M}$) $+$ $\ce{NH_4Cl}$ buffer, but I'm not sure ...
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### Dissolving Tylenol Science Experiment - why is it fastest in distilled water?

My son has a science experiment for class to dissolve Tylenol (325mg acetaminophen) in 3 different solutions (125 mL volume each): Distilled water Vinegar (1 part white vinegar to 4 parts water) Salt ...
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### How does pH affect the degradation of ascorbic acid (vitamin C)?

I know that vitamin C degrades over time (as I understand through oxidation). However, I am having trouble understanding how changing the pH of the solution in which the vitamin C is affects the rate ...
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### How to calculate the amount of citric acid to neutralise the pH within wastewater?

We have an effluent tank, with a consent to discharge at between 5.5 - 11 pH, the tank holds 100000 liters of dirty water. When the pH reaches 10.5 we add citric acid to bring the pH down. How ...
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### What happens when 0.02 mole NaOH is added to a buffer solution?

I am asking this question for my son. (This question is related but we still have our confusions.) We have one liter buffer solution of 4.74 pH which contains 0.1 mole $\ce{CH_3COOH}$ and 0.1 mole ...
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### Why does pKw first decrease but eventually increase when temperature rises?

I understand the initial decrease in pKw. $\ce{Heat + H2O (l) <=> H+ (aq) + OH- (aq)}$ Temperature increases, reaction shifts to the right, so $\ce{H+} \text{ and } \ce{OH}$ ...
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### Slow acidification process

I'm trying to find a substitute of Glucono delta-lactone (GDL). This food additive is usually used to produce silk tofu. Because of its slow hydrolysis the pH decreases very smoothly, which results in ...
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### Why does dissolving a salt in water get a high pH?

I dissolved some sodium carbonate in water and I measured the $\mathrm{pH}$. It turned out to be 11. I don't really understand why dissolving it in water increased the $\mathrm{pH}$. I mean, I know ...
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### What is the physical quantity/magnitude of pH?

I have a database to classify variables/parameters in water resources as follows: Variable: Precipitation (P); Quantity: Length; Units of measurement: mm (millimeters). Following the example, what ...
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### What is the correct pH value of weak and strong alkalis? [closed]

In the book titled fundamental chemistry for Cambridge O level, it states at page 149, Ammonia solution with a pH of 11.1 is a weak alkali and that's why it shows much lower conductivity of 0.50 ...
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### How can pKas differ across similar protons of the same atom?

For example, citric acid has three acidic protons, all of which are carboxylic acids. Despite being part of the same functional groups, they all have very different pKas. Why (and how?) is this?
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### How to calculate the pH of a buffer after HCl was added?

A buffer is made from $50~\mathrm{mL}$ of $1.0~\mathrm{M}$ benzoic acid, $K_a = 6.3\cdot10^{-5}$, and $50~\mathrm{mL}$ of $1.0~\mathrm{M}$ sodium benzoate. a) Calculate the pH of this buffer For this ...
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### What is the pH of kvass?

I know that it is less than 7.0, but would be nice to know exact value of pH of natural fermented kvass (not soda-like counterfeit). Another aspect is to know if kvass is more gentle than Cola (pH=2.5)...
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### Why does hydrogen phosphate act as a base?

Let's look at question c: a) Write a balanced equation for the reaction. $$\ce{2 NaOH + H3PO4 -> Na2HPO4 + 2 H2O (l)}$$ b) When some crystals of $\ce{Na2HPO4}$ were dissolved in water, ...
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### pH of sodium metasilicate anhydrous vs pentahydrate when dissolved in water

I'm not a chemist and don't remember much chemistry from school, so please forgive a naive question (I've read the Wikipedia article on sodium silicate though). I'm researching this topic to make ...