Edexcel A Level Chemistry:復習筆記5.2.2 pH
Defining pH
- The acidity of an aqueous solution depends on the number of?H+?ions in solution
- The?pH?is defined as:
pH = -log[H+]
-
- where [H+] is the concentration of hydrogen ions in mol dm–3
- Similarly, the?concentration?of?H+?of a solution can be calculated if the pH is known by rearranging the above equation to:
[H+] = 10-pH
- The pH scale is a logarithmic scale with base 10
- This means that each value is 10 times the value below it. For example, pH 5 is 10 times more acidic than pH 6.
- pH values are usually given to 2 decimal places
- The relationship between concentration is easily seen on the following table
pH & [H+] Table
pH & Hydrogen Ion Concentration
Worked Example
pH and H+?calculations
Question 1:?Find the pH when the hydrogen concentration is 1.60 x 10-4?mol dm-3
Question 2:?Find the hydrogen concentration when the pH is 3.10
Answer
Answer 1:
The pH of the solution is:
pH? = -log[H+]
= -log 1.6 x 10-4
= 3.80
Answer 2:
The hydrogen concentration can be calculated by rearranging the equation for pH
pH? ?= -log[H+]
[H+] = 10-pH
= 10-3.10
= 7.94 x 10-4?mol dm-3
Worked Example
Powers of 10
10.0 cm3?of an aqueous solution of an acid of pH = 1.0 is mixed with 990.0 cm3?of distilled water. What is the pH of the final solution?
A.??1
B.??2
C.??3
D.??10
Answer
The correct option is?C.
-
- The total volume after dilution is 1000.0 cm3?so the concentration of H+?has been?reduced?by a factor of 100 or 10-2, which means an increase of 2 pH units
- The final solution is therefore?pH 3
轉載自savemyexams
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