PH & Concentration Help - Problem Solving

In summary, the conversation discussed two problems. The first problem involved translating a voltage reading from a pH electrode into pH values using the Nernst equation. The second problem was about preparing a solution with specific concentrations of Ca and C ions. The person providing help recommended using the Nernst equation and converting the natural log to a log base 10. The conversation ended with the person asking for help with the second problem.
  • #1
kawaiitora
3
0
Hi,

I need some help with a few problems. Thanks!

(1) You have a pH Electrode that reports a voltage in
mV, which is proportional to the hydrogen ion concentration
in solution. You also have pH buffers at known pH of say
4, 7 and 10. What do you do to translate the mV reading
into pH values for any given solution with pH between
4 and 10?

(2) You have DI water plus CaCl2 and NaHCO3 salts.
What do you do to prepare a solution with Ca concentration
of 10 mmol/l and total C concentration of 2 mmol/l?
 
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  • #2
Hi there kawaiitora and welcome to PF,

What are your thoughts on the problems?
 
  • #3
Thanks for the quick reply. Sorry, I forgot about that.

(1) I'm thinking that I should use the Nernst equation, but I'm not sure which variation would be the best.

(2) For this one, I'm really not sure how to start. would I need to make up a molecular equation first?
 
  • #4
No problem, let's take each problem in turn.

Question One

You should first start with the basic Nernst Equation;

[tex]E = E^{\theta} - \frac{RT}{nF}\cdot\ln Q[/tex]

Now, how many moles of electrons much be transferred to balance the charge on Q (which in this case is the hydrogen ion)? If we also assume standard conditions we have sorted the [itex]\frac{RT}{nF}[/itex] coefficient. Now, the next thing you should do is convert the natural log into a log to the base 10; this involves a little bit of mathematics but is petty straight forward. Next, you will want to express Q in terms of hydrogen ion concentration or activity. After which, all is plain sailing :smile:. Can you go from here?
 
  • #5
Yep. Thanks, Hootenanny! Now, I need some help with the second problem...
 

1. What is the relationship between pH and concentration?

The pH of a solution is a measure of its acidity or basicity. It is related to the concentration of hydrogen ions (H+) in the solution. As the concentration of H+ increases, the pH decreases, making the solution more acidic. Conversely, as the concentration of H+ decreases, the pH increases, making the solution more basic.

2. How do you calculate pH from concentration?

To calculate pH from concentration, you can use the equation pH = -log[H+]. This means you take the negative logarithm of the concentration of hydrogen ions to determine the pH of a solution. For example, if the concentration of H+ is 0.001 mol/L, the pH would be 3.

3. What is the difference between pH and pOH?

pH and pOH are both measures of a solution's acidity or basicity, but they are related to different components. pH measures the concentration of H+ ions, while pOH measures the concentration of OH- ions. The two are related by the equation pH + pOH = 14. A solution with a pH of 7 is neutral, while a solution with a pH less than 7 is acidic and a solution with a pH greater than 7 is basic.

4. How does changing the concentration of a solution affect its pH?

The concentration of a solution directly affects its pH. As the concentration of H+ ions increases, the pH decreases, making the solution more acidic. Conversely, as the concentration of H+ ions decreases, the pH increases, making the solution more basic. This relationship is described by the pH scale, where each whole number change in pH represents a 10-fold change in concentration.

5. How do you use pH and concentration to prepare a solution of a specific pH?

To prepare a solution of a specific pH, you need to determine the concentration of H+ ions needed for that pH. Then, you can use this concentration to calculate the amount of acid or base needed to achieve the desired pH. For example, to prepare a solution of pH 4, you would need a concentration of 0.0001 mol/L of H+ ions. This can be achieved by diluting a stronger acid solution or using a weaker acid solution.

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