a certain solution is measured to have a ph of 3. what is its concentration of h+?

Learning Objectives

• Ascertain pH.
• List pH values of common materials.
• Perform pH calculations for acidic and basic solutions.

Why is grapefruit juice acidic?

Grapefruit juice has a pH of somewhere betwixt 2.9-iii.3, depending on the specific product. Excessive exposure to this juice can cause erosion of tooth enamel and tin lead to tooth harm. The acids in grapefruit juice are carbon-based, with citric acrid existence one of the major constituents.

This compound has 3 ionizable hydrogens on each molecule which contribute to the relatively low pH of the juice. Another component of grape juice is malic acid, containing two ionizable hydrogens per molecule.

The pH Scale

Expressing the acidity of a solution past using the molarity of the hydrogen ion is cumbersome because the quantities are generally very modest. Danish scientist Søren Sørenson (1868-1939) proposed an easier arrangement for indicating the concentration of H ⁺ chosen the pH calibration. The messages pH stand for the power of the hydrogen ion. The pH of a solution is the negative logarithm of the hydrogen-ion concentration.

pH = -log[H ⁺ ]

In pure water or a neutral solution the [H ⁺ ] = one.0 × 10 ^-vii Thou. Substituting into the pH expression:

pH = -log[one.0 × 10 ^-vii ] = -(-7.00) = vii.00

The pH of pure water or any neutral solution is thus 7.00. For recording purposes, the numbers to the correct of the decimal point in the pH value are the significant figures. Since 1.0 × x ^-7 has two significant figures, the pH can be reported equally 7.00.

A logarithmic calibration condenses the range of acidity to numbers that are like shooting fish in a barrel to use. Consider a solution with [H ⁺ ] = 1.0 × 10 ^-4 M. That is a hydrogen-ion concentration that is 1000 times college than the concentration in pure h2o. The pH of such a solution is 4.00, a departure of but 3 pH units. Detect that when the [H ⁺ ] is written in scientific annotation and the coefficient is i, the pH is simply the exponent with the sign changed. The pH of a solution with the [H ⁺ ] = ane × ten ^-2 M is 2 and the pH of a solution with the [H ⁺ ] = 1 × x ^-10 Thousand is 10.

As nosotros saw earlier, a solution with the [H ⁺ ] higher than 1.0 × ten ^-seven is acidic, while a solution with the [H ⁺ ] lower than one.0 × 10 ^-7 is basic. Consequently, solutions whose pH is less than 7 are acidic, while those with a pH higher than vii are bones. Figure 1illustrates this relationship, along with some examples of diverse solutions.

Figure one. The pH values for several mutual materials.

Computing pH of Acids and Bases

Raising tropical fish

Many people savor having tropical fish in their homes or businesses. These brightly-colored creatures are relaxing to spotter, only practice crave a certain corporeality of maintenance in order for them to survive.

Tap water is ordinarily too alkaline when information technology comes out of the faucet, so some adjustments demand to be made. The pH of the water will alter over fourth dimension while it is in the tank, which means you lot need to test information technology every so oftentimes. Then you go to exist a pharmacist for your fish.

Calculating pH of Acids and Bases

Calculation of pH is simple when in that location is a ane × 10 ^power problem. Notwithstanding, in real life that is rarely the situation. If the coefficient is not equal to 1, a calculator must be used to find the pH. For example, the pH of a solution with [H ⁺ ] = 2.iii × 10 ^-5 M  can be found as shown below.

pH = -log[2.3 × 10 ^-5 ] = 4.64

When the pH of a solution is known, the concentration of the hydrogen ion can be calculated. The inverse of the logarithm (or antilog) is the 10 ^ten key on a estimator.

[H ⁺ ] = 10 ^-pH

For example, suppose that you have a solution with a pH of ix.14. To find the [H ⁺ ] use the 10 ^x central.

[H ⁺ ] = x ^-pH = x ^-9.14 = 7.24 × 10 ^-10 M

Hydroxide Ion Concentration and pH

Every bit nosotros saw earlier, the hydroxide ion concentration of whatsoever aqueous solution is related to the hydrogen ion concentration through the value of . We can apply that relationship to calculate the pH of a solution of a base.

Sample Problem: The pH of a Base

Sodium hydroxide is a stiff base. Find the pH of a solution prepared by dissolving 1.0 g of NaOH into enough h2o to make 1.0 Fifty of solution.

Step i: Listing the known values and plan the problem .

Known

• mass NaOH = 1.0 g
• molar mass NaOH = forty.00 g/mol
• book solution = 1.0 L
• Yard_w = 1.0 × 10^–14

Unknown

• pH of solution = ?

Starting time, convert the mass of NaOH to moles. Second, calculate the molarity of the NaOH solution. Because NaOH is a strong base and is soluble, the [OH ⁻ ] will exist equal to the concentration of the NaOH. Third, use to calculate the [H ⁺ ] in the solution. Lastly, calculate the pH.

Pace ii: Solve .

Pace 3: Remember nearly your result .

The solution is basic and and then its pH is greater than 7. The reported pH is rounded to two decimal places because the original mass and book has two meaning figures.

Summary

• The concept of pH is defined.
• pH values for several mutual materials are listed.
• Calculations of pH for acidic and bones solutions are described.

Practice

Read the material at the link below and answer the following questions:

http://staff.jccc.net/pdecell/chemical science/phscale.html

1. What is a buffer?
2. How much more than acidic is vinegar than grapefruit?
3. How much more basic is soapy water than milk of magnesia?

Comport out the requested calculations at the link below:

http://www.sciencegeek.net/APchemistry/APtaters/pHcalculations.htm

Review

1. What is one value of using pH instead of molar concentrations?
2. Is coffee an acidic or a bones substance?
3. If a material has a pH of 9.iii, is information technology acidic or basic?
4. What is the pH of a 4.5 × ten ^-three M Howdy solution?
5. What is the pH of a 3.67 × 10 ^-5 M NaBr solution?
6. If we take a weak base with a depression ionization constant, can nosotros assume that the [OH ^– ] in the solution is equal to the concentration of the base of operations?

Glossary

• pH: The negative logarithm of the hydrogen-ion concentration.

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Source: https://courses.lumenlearning.com/cheminter/chapter/the-ph-scale/

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