how to calculate pH value

One of the calculations of PH is the commonly used H+ concentration to represent the acidity and alkalinity of the solution. When [H+] is less than 1mol L-1, for the convenience of use, the negative logarithm of the hydrogen ion concentration is commonly used, that is, -lg[H+] to represent the solution The acidity, and called pH, that is, pH = -lg [H +]. [H+]·[OH-]=Kw in the aqueous solution of any substance, Kw=1×10-14 at room temperature. [H+]=[OH-]=10-7mol L-1 in pure water, then pH= -lg[H+]=7. In other neutral solutions [H+]=[OH-]=10-7mol L-1, the pH is also 7; in acidic solutions [H+]>[OH-], the pH<7; in alkaline solutions [ H+]<[OH-], its pH>7. The negative logarithm of the hydroxide ion concentration can also be expressed as pOH, then the pH of the solution + pOH = 14, pH=14 - pOH. The key to calculating the pH of a solution is to correctly calculate the [H+] of various solutions, the specific calculation is as follows: Example 1 Calculate the pH of 0.01mol·L-1 hydrochloric acid solution. Solution Hydrochloric acid is a strong electrolyte, and it is completely ionized in water [H+]=0.01mol·L-1pH=-lg[H+]=-lg 0.01=2 Answer The pH of the solution is 2. Example 2 Calculate the pH of c=0.1mol·L-1 acetic acid solution (degree of ionization α=1.34%). Acetic acid solution is partial ionization of weak electrolyte in water [H+]=α·C=1.34%×0.1 =1.34×10-3(mol·L-1) pH= -lg[H+]=-lg 1.34×10-3= 2.87 Answer The pH of the solution is 2.87. Example 3 Calculate the pH of c(NaOH)=0.1mol·L-1 sodium hydroxide solution. Solve NaOH as a strong electrolyte and fully ionize in water [OH-]=0.1mol L-1 pH= -lg[H+]=-lg10-13=13 Another algorithm: pH=14-pOH=14-(-lg[ OH-])=14-1=13 The pH of the sodium hydroxide solution is 13. Example 4 The pH of a certain solution is 5. Calculate the concentration of H+ and OH- in this solution. Solution pH=5=-lg[H+] [H+]=10-5（mol·L-1） Answer The concentration of H+ in this solution is 10-5mol·L-1, and the concentration of OH- is 10-9mol·L- 1 pH Calculation II 1. The pH of a simple acid-base solution is from pH= -lg[H+], only [H+] is required. (1) Monobasic strong acid: [H+]=C acid Binary strong acid: [H+]=2C acid Weak acid: [H+]=Cα, then find the pH. (2) Monobasic strong base [OH-]=C base, binary strong base: [OH-]=2C base, 2. Dilution of strong acid and strong base (1) The pH increases during the dilution process of strong acid, and the [H+] of the diluted solution can be calculated first, and then the pH. (2) When the pH decreases after dilution with a strong base, the [OH-] in the solution after dilution should be calculated first, and then [H+] to obtain the pH. (3) For extremely dilute solutions, the ionization of water should be considered. The pH of the acid solution cannot be greater than 7, and the pH of the alkaline solution cannot be less than 7. 3. Mixing of strong acid and strong alkali solutions in equal volume: If the pH difference is more than 2 units, 'pH mixed = pH small + 0.3' If the pH difference is 1 unit, 'pH mixed = pH small + 0.26' (2) Two strong bases are mixed : When mixing equal volumes: If the pH difference is more than 2 units, 'pH mixing = pH big -0.3' If the pH difference is 1 unit, 'pH mixing = pH big -0.26' (3) Strong acid and strong alkali solution mixing: If it is just right And, the solution pH=7. Then ask for [H+] to mix, and then ask for pH.