Name: strong acids, strong bases, and ph
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 3 min 22 s
Channel: JoVE

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Strong Acid and Base Solutions

Mocne kwasy całkowicie dysocjują w wodzie. Na przykład kwas azotowy dysocjuje całkowicie na jony hydroniowe i jony azotanowe. Ponieważ jony hydroniowe powstające w wyniku autojonizacji wody są znikome, stężenie jonów hydroniowych w wodzie jest równe stężeniu mocnego kwasu.
pH tych roztworów można określić za pomocą początkowego stężenia mocnego kwasu.
Na przykład w 0,10 molowym roztworze HCl HCl całkowicie zdysocjuje na jony hydroniowe i jony chlorkowe, a zatem stężenie jonów hydroniowych w roztworze również wyniesie 0,10 mola. Biorąc ujemny logarytm tego stężenia, pH roztworu jest równe jeden.
I odwrotnie, pH roztworu można wykorzystać do określenia stężenia jonów hydroniowych w roztworze. Na przykład dla roztworu o pH 3,60 jego stężenie jonów hydroniowych można określić, rozwiązując równanie 3,60 jest równe ujemnemu logarytmowi stężenia jonów hydroniowych.
Aby obliczyć stężenie, pomnóż obie strony przez ujemną, a następnie weź antylogarytm obu stron. Stężenie jonów hydroniowych jest równe 2,5 razy dziesięć do ujemnych czterech zębów trzonowych.
Silne zasady, które są wodorotlenkami metali z grupy pierwszej, takie jak wodorotlenek sodu i wodorotlenek potasu, dysocjują całkowicie w roztworze. Na przykład 0,20 molowy wodorotlenek sodu całkowicie zdysocjuje w wodzie i wytworzy 0,20 molowych jonów sodu i 0,20 molowych jonów wodorotlenku.
Jednak wodorotlenki metali z grupy drugiej, takie jak wodorotlenek baru i wodorotlenek wapnia, wytwarzają dwa mole jonów wodorotlenkowych na każdy mol zasady. Na przykład 0,020 molowy wodorotlenek wapnia całkowicie zdysocjuje w wodzie i wytworzy 0,020 molowych jonów wapnia i 0,040 molowych jonów wodorotlenku.
Tlenki jonów metali, takie jak tlenek sodu i tlenek wapnia, są również mocnymi zasadami. Ich jon tlenkowy reaguje z wodą i wytwarza jony wodorotlenkowe.
Stężenie jonów wodorotlenkowych można wykorzystać do obliczenia pOH i pH roztworu. Na przykład roztwór wodorotlenku potasu o wartości od pięciu do dziesięciu do ujemnych pięciu molowych ma taką samą ilość jonów wodorotlenkowych jak mocna zasada, a zatem ma pH 4,30.
Podobnie jak pH, pOH roztworu można również wykorzystać do określenia stężenia jonów wodorotlenkowych, rozwiązując równanie: pOH jest równe ujemnemu logarytmowi stężenia jonów wodorotlenkowych.
Ponieważ pH plus pOH jest równe 14, a pH pH wynosi 4,3, pH roztworu wynosi 9,7.

roztwory mocnych kwasów i zasad

Mocny kwas to związek, który całkowicie dysocjuje w roztworze wodnym i wytwarza stężenie jonów hydroniowych równe początkowemu stężeniu kwasu. Na przykład 0,20 M kwas bromowodorowy całkowicie zdysocjuje w wodzie i wytworzy 0,20 M jonów hydroniowych i 0,20 M jonów bromkowych.

<img alt="Eq1" src="/files/ftp_upload/11399/11399_Equation_1.png" style="height: 50px;" />

Z drugiej strony mocna zasada to związek, który całkowicie dysocjuje w roztworze wodnym i wytwarza jony wodorotlenkowe. Na przykład 0,015 M KOH, wodorotlenek metalu z grupy 1, ulegnie całkowitej dysocjacji i wytworzy 0,015 M OH- i 0,015 M K+.

<img alt="Eq2" src="/files/ftp_upload/11399/11399_Equation_2.png" style="height: 50px;" />

Wodorotlenki metali z grupy 2, takie jak wodorotlenek baru [Ba(OH)2] i wodorotlenek strontu [Sr(OH)2], są również mocnymi zasadami i zawierają dwa jony wodorotlenkowe. Powoduje to, że wytwarzają bardziej zasadowy roztwór w porównaniu z NaOH lub KOH w tym samym stężeniu. Na przykład 0,015 M Ba(OH)2 daje 0,015 M Ba+ i 0,030 M wodorotlenek.

<img alt="Eq3" src="/files/ftp_upload/11399/11399_Equation_3.png" style="height: 50px;" />

Ponieważ mocne kwasy i zasady ulegają całkowitej dysocjacji, stosunki molowe można wykorzystać do określenia ich stężeń hydroniowego i wodorotlenkowego, co z kolei można wykorzystać do obliczenia pH lub pOH roztworu. Na przykład 0,030 M roztwór HCl wytworzy 0,03 M jonów hydroniowych. Dlatego pH tego roztworu będzie

<img alt="Eq4" src="/files/ftp_upload/11399/11399_Equation_4.png" style="height: 135px;" />

Wartość pOH tego samego roztworu można określić za pomocą wzoru

<img alt="Eq5" src="/files/ftp_upload/11399/11399_Equation_5.png" style="height: 50px;" />

Ponieważ pH roztworu wynosi 1,52, jego pH można obliczyć jako

<img alt="Eq6" src="/files/ftp_upload/11399/11399_Equation_6.png" style="height: 50px;" />

Podobnie stężenie jonów wodorotlenkowych wytwarzanych przez mocne zasady można wykorzystać do określenia pOH roztworu za pomocą równania

<img alt="Eq7" src="/files/ftp_upload/11399/11399_Equation_7.png" style="height: 50px;" />

Powyższe równanie można również zastosować do określenia stężenia jonów wodorotlenkowych, gdy znane jest pOH. Na przykład, jeśli pOH roztworu wynosi 3,00,

<img alt="Eq8" src="/files/ftp_upload/11399/11399_Equation_8.png" style="height: 50px;" />

Mnożenie obu stron przez -1 daje

<img alt="Eq9" src="/files/ftp_upload/11399/11399_Equation_9.png" style="height: 50px;" />

Teraz weź antylog obu stron

<img alt="Eq10" src="/files/ftp_upload/11399/11399_Equation_10.png" style="height: 90px;" />

Zatem stężenie jonów hydroniowych w roztworze z pOH 3 wynosi 1,0 × 10-3 M. Podobną metodę można zastosować do określenia stężenia jonów hydroniowych w roztworze, jeśli znane jest jego pH.

Roztwory mocnych kwasów i zasad

Mocny kwas to związek, który całkowicie dysocjuje w roztworze wodnym i wytwarza stężenie jonów hydroniowych równe początkowemu ...

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strong acids, strong bases, and ph

Strong acids and strong bases change the pH of a solution by dissociating completely in water. A strong acid produces hydronium ions, which are H3O+ ions, and a strong base produces hydroxide ions, OH-. Because the dissociation is complete, the ion concentration can be found from the starting concentration and the molar ratio.

For example, 0.20 M hydrobromic acid dissociates fully in water. It produces 0.20 M hydronium ions and 0.20 M bromide ions. A 0.015 M KOH solution also dissociates completely. It produces 0.015 M OH- and 0.015 M K+.

Some group 2 metal hydroxides are also strong bases. Barium hydroxide, Ba(OH)2, and strontium hydroxide, Sr(OH)2, each contain two hydroxide ions. That means they create a more basic solution than NaOH or KOH at the same concentration. For example, 0.015 M Ba(OH)2 produces 0.015 M Ba+ and 0.030 M hydroxide.

The ion concentrations from strong acids and strong bases can be used to calculate pH and pOH. A 0.030 M HCl solution produces 0.03 M hydronium ions, so its pH can be found from that concentration. The same pH value can then be used to determine pOH. If the pH is 1.52, the pOH can be calculated from the relationship between them.

The same idea works for strong bases. The hydroxide ion concentration can be used to find pOH with the equation for pOH, and the equation can also be used in reverse when pOH is known. For example, if the pOH of a solution is 3.00, multiplying by -1 and taking the antilog gives a hydronium ion concentration of 1.0 × 10^-3 M. The same method can be used to find hydronium ion concentration when pH is known.

Strong Acids, Strong Bases, and pH

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Proton Transfer in Acids and Bases

Acids and bases can be understood through proton transfer. Early scientists described acids by their sour taste, their effect on dyes, and their reaction with limestone, which releases carbon dioxide. Robert Boyle also noted that acid solutions can lose these properties after contact with alkali, or base, solutions. The modern view developed step by step. Humphry Davy showed that hydrogen is the essential part of acids. Joseph Louis Gay-Lussac then described acids as substances that neutralize...

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pH and pOH in Water

pH and pOH show how hydronium and hydroxide ions behave in water and other aqueous solutions. These ion concentrations are linked by the ion product of water, K w , so when one goes up, the other goes down. Because ion concentrations can differ by huge amounts, a logarithmic scale is used to describe them. pH is defined from the hydronium ion concentration, [H3O+], and pOH is the matching p-function for hydroxide ion concentration. These two values are also connected through the K w...

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How Ka and Kb Show Acid-Base Strength

Brønsted-Lowry acid-base chemistry is based on proton transfer. That idea helps show how the strength of an acid is linked to the strength of its conjugate base, and vice versa. Acid and base strength is measured with ionization constants, Ka and Kb, which tell how far an ionization reaction goes. For the conjugate pair HA and A−, the acid ionizes in water and the base reaction can be written for the partner species. When the two reactions are added, they give the autoionization of water. The...

strong acid and base solutions

Strong acids and strong bases change the pH of a solution by dissociating completely in water. A strong acid produces hydronium ions, which are H3O+ ions, and a strong base produces hydroxide ions, OH-. Because the dissociation is complete, the ion concentration can be found from the starting concentration and the molar ratio. For example, 0.20 M hydrobromic acid dissociates fully in water. It produces 0.20 M hydronium ions and 0.20 M bromide ions. A 0.015 M KOH solution also dissociates...

weak acid solutions

Weak Acid Equilibrium in Water

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Weak Base pH and Kb Calculations

Weak base pH and Kb calculations show how partially reacting bases change water chemistry. Weak bases produce hydroxide ions when they dissolve by reacting with water molecules. Because the reaction only happens partly, these compounds are classified as weak bases. Weak bases are common in nature and in technology. Ammonia is one major example. Global production of ammonia is typically well over 100 metric tons each year. It is used as an agricultural fertilizer, a starting material for...

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Salt hydrolysis explains why some salt solutions are acidic, basic, or neutral. Salts are ionic compounds made of cations and anions. In water, either ion may react with water through an acid or base ionization reaction. The pH of the solution depends on the relative acid-base strength of the ions in the salt. Ammonium chloride is a good example of an acidic salt. When it dissolves, it separates into ammonium ions and chloride ions. The ammonium ion is the conjugate acid of ammonia, so it can...

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acid/base strengths and dissociation constants

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Acid and Base Strength in Water

Acid and base strength in water depends on how much a substance ionizes after it dissolves. If ionization is nearly complete, the substance is called strong. If only a small amount ionizes, it is called weak. Weak acids and weak bases are much more common than strong ones. The most common strong acids are HClO4, HCl, HBr, HI, HNO3, and H2SO4. The most common strong bases are LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. These strong acids and bases ionize essentially completely in water. <br...

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lewis acids and bases

Electron-Pair Reactions in Acid-Base Chemistry

Electron-pair reactions explain Lewis acid-base chemistry. In 1923, G. N. Lewis described acids and bases by how they accept or donate a pair of electrons. When that electron pair forms a coordinate covalent bond, one atom supplies both bonding electrons. This bond is also called a dative bond. A simple example is the reaction of water with a hydrogen ion to make a hydronium ion. Ammonia can also combine with a hydrogen ion to form an ammonium ion. In both cases, the reaction creates a Lewis...

key terms and concepts

Learn how strong acids and strong bases dissociate completely in water and how their ion concentrations are used to calculate pH and pOH.

Strong Acids, Strong Bases, and pH | JoVE K12

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Strong Acids, Strong Bases, and pH

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