Sig Fig & Acids - pH Change & NaOH Effects

  • Thread starter Dooh
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In summary, when performing logarithms in an equation, only numbers and decimal points are counted as significant figures. Therefore, if a problem requires 2 significant figures, the answer should be rounded to 1.0. In terms of adding NaOH to an acetic acid solution, the concentration of hydrogen ions will decrease because the hydrogen and hydroxide ions will neutralize each other to form water, resulting in a drop in pH. When determining significant figures, it is important to use the least amount found in the problem. In logarithmic answers, only numbers after the decimal point are considered significant figures. Therefore, 1.0 would be considered two significant figures. The presence of logarithms in base 10 does not affect the number
  • #1
Dooh
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It has to do with sig fig. Froom what i know, when performing log in an equation, only the numbers are the decimal point are counted as sig figs. So if i have 0.1 M of acid, to find the ph, it would be : -log(0.1) = 1; since sig figs have to be AFTER the decimal point, is the correct answer 1.0?

Also, if NaOH were added to an acetic acid solution, will the concentration of the hydrogen ion increase or decrease? and WHy?
 
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  • #2
Depends on the requirements of the problem.If the problem's asking for 2 sig digs,then "1.0" should do it.

What's your thought or your guess for the second part and on what grounds...?

Daniel.
 
  • #3
Well the problem didnt specifically asked for a certain amount of sig fig, the number of sig fig in answer depends on the problem itself, we have to use the least amount of sig fig that is found in the problem.

As for the other one, i first had down the concentration will decrease because the hydrogen and hydroxide ion will neutralize each other and form water, but i wasnt sure if that was right.
 
  • #4
The pH definitely drops.Since the pH is the conc.of protons,it means you're right.

Daniel.
 
  • #5
Thanks, back to the sig fig problems, shouldn't 1.0 be considered 1 sig fig? since in a log answer, only the numbers after the decimal point is counted as a sig fig.
 
  • #6
Nope,two sig digs.And the presence of logarithms in base 10 is of no relevance.

Daniel.
 

Related to Sig Fig & Acids - pH Change & NaOH Effects

1. What are significant figures and why are they important in scientific calculations?

Significant figures are the digits in a number that are known with certainty, plus one estimated digit. They are important in scientific calculations because they indicate the precision and accuracy of a measurement or calculation. Significant figures help ensure that the final result is not more precise than the original data.

2. How do you determine the number of significant figures in a measurement?

In a measurement, all non-zero digits are considered significant. Zeros between non-zero digits are also significant. Leading zeros (zeros to the left of the first non-zero digit) are not significant. Trailing zeros (zeros to the right of the last non-zero digit) are significant if there is a decimal point present, but not significant if there is no decimal point. Scientific notation can also be used to indicate the number of significant figures.

3. What is pH and how does it relate to acid and base strength?

pH is a measure of the acidity or basicity (alkalinity) of a solution. It is defined as the negative logarithm of the hydrogen ion concentration. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is basic. The lower the pH, the stronger the acid, and the higher the pH, the stronger the base.

4. How does the addition of NaOH affect the pH of a solution?

Sodium hydroxide (NaOH) is a strong base, meaning it dissociates completely in water to form hydroxide ions. When added to a solution, it increases the concentration of hydroxide ions and decreases the concentration of hydrogen ions, resulting in a higher pH. The more NaOH added, the more the pH increases.

5. How do you calculate the change in pH when adding a strong acid or base to a solution?

The change in pH when adding a strong acid or base can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid. Alternatively, you can use a pH meter to directly measure the change in pH.

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