1. Home
  2. Chemistry
  3. Acid-base equilibria
  4. Ph and poh

14.2 Ph and poh  (Page 3/8)

<< Chapter < Page
  Chemistry     Page 3 / 8
Chapter >> Page >

Calculation of poh

What are the pOH and the pH of a 0.0125- M solution of potassium hydroxide, KOH?

Solution

Potassium hydroxide is a highly soluble ionic compound and completely dissociates when dissolved in dilute solution, yielding [OH − ] = 0.0125 M :

pOH = −log [ OH − ] = −log 0.0125
= − ( − 1.903 ) = 1.903

The pH can be found from the pOH:

pH + pOH = 14.00
pH = 14.00 − pOH = 14.00 − 1.903 = 12.10

Check your learning

The hydronium ion concentration of vinegar is approximately 4 × 10 −3 M . What are the corresponding values of pOH and pH?

Answer:

pOH = 11.6, pH = 2.4

Got questions? Get instant answers now!

The acidity of a solution is typically assessed experimentally by measurement of its pH. The pOH of a solution is not usually measured, as it is easily calculated from an experimentally determined pH value. The pH of a solution can be directly measured using a pH meter ( [link] ).

This figure contains two images. The first, image a, is of an analytical digital p H meter on a laboratory counter. The second, image b, is of a portable hand held digital p H meter.
(a) A research-grade pH meter used in a laboratory can have a resolution of 0.001 pH units, an accuracy of ± 0.002 pH units, and may cost in excess of $1000. (b) A portable pH meter has lower resolution (0.01 pH units), lower accuracy (± 0.2 pH units), and a far lower price tag. (credit b: modification of work by Jacopo Werther)

The pH of a solution may also be visually estimated using colored indicators ( [link] ).

This figure contains two images. The first shows a variety of colors of solutions in labeled beakers. A red solution in a beaker is labeled “0.10 M H C l.” An orange solution is labeled “0.10 M C H subscript 3 C O O H.” A yellow-orange solution is labeled “0.1 M N H subscript 4 C l.” A yellow solution is labeled “deionized water.” A second solution beaker is labeled “0.10 M K C l.” A green solution is labeled “0.10 M aniline.” A blue solution is labeled “0.10 M N H subscript 4 C l (a q).” A final beaker containing a dark blue solution is labeled “0.10 M N a O H.” Image b shows pHydrion paper that is used for measuring pH in the range of p H from 1 to 12. The color scale for identifying p H based on color is shown along with several of the test strips used to evaluate p H.
(a) A universal indicator assumes a different color in solutions of different pH values. Thus, it can be added to a solution to determine the pH of the solution. The eight vials each contain a universal indicator and 0.1- M solutions of progressively weaker acids: HCl (pH = l), CH 3 CO 2 H (pH = 3), and NH 4 Cl (pH = 5), deionized water, a neutral substance (pH = 7); and 0.1- M solutions of the progressively stronger bases: KCl (pH = 7), aniline, C 6 H 5 NH 2 (pH = 9), NH 3 (pH = 11), and NaOH (pH = 13). (b) pH paper contains a mixture of indicators that give different colors in solutions of differing pH values. (credit: modification of work by Sahar Atwa)

Key concepts and summary

The concentration of hydronium ion in a solution of an acid in water is greater than 1.0 × 10 −7 M at 25 °C. The concentration of hydroxide ion in a solution of a base in water is greater than 1.0 × 10 −7 M at 25 °C. The concentration of H 3 O + in a solution can be expressed as the pH of the solution; pH = −log H 3 O + . The concentration of OH − can be expressed as the pOH of the solution: pOH = −log[OH − ]. In pure water, pH = 7.00 and pOH = 7.00

Key equations

  • pH = −log [ H 3 O + ]
  • pOH = −log[OH − ]
  • [H 3 O + ] = 10 −pH
  • [OH − ] = 10 −pOH
  • pH + pOH = p K w = 14.00 at 25 °C

Chemistry end of chapter exercises

Explain why a sample of pure water at 40 °C is neutral even though [H 3 O + ] = 1.7 × 10 −7 M . K w is 2.9 × 10 −14 at 40 °C.

In a neutral solution [H 3 O + ] = [OH − ]. At 40 °C,
[H 3 O + ] = [OH − ] = (2.910 −14 ) 1/2 = 1.7 × 10 −7 .

Got questions? Get instant answers now!

The ionization constant for water ( K w ) is 2.9 × 10 −14 at 40 °C. Calculate [H 3 O + ], [OH − ], pH, and pOH for pure water at 40 °C.

Got questions? Get instant answers now!

The ionization constant for water ( K w ) is 9.311 × 10 −14 at 60 °C. Calculate [H 3 O + ], [OH − ], pH, and pOH for pure water at 60 °C.

x = 3.051 × 10 −7 M = [H 3 O + ] = [OH − ]
pH = −log3.051 × 10 −7 = −(−6.5156) = 6.5156
pOH = pH = 6.5156

Got questions? Get instant answers now!

Calculate the pH and the pOH of each of the following solutions at 25 °C for which the substances ionize completely:

(a) 0.200 M HCl

(b) 0.0143 M NaOH

(c) 3.0 M HNO 3

(d) 0.0031 M Ca(OH) 2

Got questions? Get instant answers now!

Calculate the pH and the pOH of each of the following solutions at 25 °C for which the substances ionize completely:

(a) 0.000259 M HClO 4

(b) 0.21 M NaOH

(c) 0.000071 M Ba(OH) 2

(d) 2.5 M KOH

(a) pH = 3.587; pOH = 10.413; (b) pH = 0.68; pOH = 13.32; (c) pOH = 3.85; pH = 10.15; (d) pH = −0.40; pOH = 14.4

Got questions? Get instant answers now!

What are the pH and pOH of a solution of 2.0 M HCl, which ionizes completely?

Got questions? Get instant answers now!

What are the hydronium and hydroxide ion concentrations in a solution whose pH is 6.52?

[H 3 O + ] = 3.0 × 10 −7 M ; [OH − ] = 3.3 × 10 −8 M

Got questions? Get instant answers now!

Calculate the hydrogen ion concentration and the hydroxide ion concentration in wine from its pH. See [link] for useful information.

Got questions? Get instant answers now!

Calculate the hydronium ion concentration and the hydroxide ion concentration in lime juice from its pH. See [link] for useful information.

[H 3 O + ] = 1 × 10 −2 M ; [OH − ] = 1 × 10 −12 M

Got questions? Get instant answers now!

The hydronium ion concentration in a sample of rainwater is found to be 1.7 × 10 −6 M at 25 °C. What is the concentration of hydroxide ions in the rainwater?

Got questions? Get instant answers now!

The hydroxide ion concentration in household ammonia is 3.2 × 10 −3 M at 25 °C. What is the concentration of hydronium ions in the solution?

[OH − ] = 3.1 × 10 −12 M

Got questions? Get instant answers now!

Questions & Answers

how do you get the 2/50
Abba Reply
number of sport play by 50 student construct discrete data
Aminu Reply
width of the frangebany leaves on how to write a introduction
Theresa Reply
Solve the mean of variance
Veronica Reply
Step 1: Find the mean. To find the mean, add up all the scores, then divide them by the number of scores. ... Step 2: Find each score's deviation from the mean. ... Step 3: Square each deviation from the mean. ... Step 4: Find the sum of squares. ... Step 5: Divide the sum of squares by n – 1 or N.
kenneth
what is error
Yakuba Reply
Is mistake done to something
Vutshila
Hy
anas
hy
What is the life teble
anas
hy
Jibrin
statistics is the analyzing of data
Tajudeen Reply
what is statics?
Zelalem Reply
how do you calculate mean
Gloria Reply
diveving the sum if all values
Shaynaynay
let A1,A2 and A3 events be independent,show that (A1)^c, (A2)^c and (A3)^c are independent?
Fisaye Reply
what is statistics
Akhisani Reply
data collected all over the world
Shaynaynay
construct a less than and more than table
Imad Reply
The sample of 16 students is taken. The average age in the sample was 22 years with astandard deviation of 6 years. Construct a 95% confidence interval for the age of the population.
Aschalew Reply
Bhartdarshan' is an internet-based travel agency wherein customer can see videos of the cities they plant to visit. The number of hits daily is a normally distributed random variable with a mean of 10,000 and a standard deviation of 2,400 a. what is the probability of getting more than 12,000 hits? b. what is the probability of getting fewer than 9,000 hits?
Akshay Reply
Bhartdarshan'is an internet-based travel agency wherein customer can see videos of the cities they plan to visit. The number of hits daily is a normally distributed random variable with a mean of 10,000 and a standard deviation of 2,400. a. What is the probability of getting more than 12,000 hits
Akshay
1
Bright
Sorry i want to learn more about this question
Bright
Someone help
Bright
a= 0.20233 b=0.3384
Sufiyan
a
Shaynaynay
How do I interpret level of significance?
Mohd Reply
It depends on your business problem or in Machine Learning you could use ROC- AUC cruve to decide the threshold value
Shivam
how skewness and kurtosis are used in statistics
Owen Reply
yes what is it
Taneeya
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
<< Chapter < Page Page > Chapter >>
Practice Key Terms 5

Read also:

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chemistry' conversation and receive update notifications?

Ask