Topic 12
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
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What are bronsted-Lowry acids
• Acids are proton donors • When mixed with water they dissociate into H+ ions
What are Bronstead-lowry bases
• Bases are proton acceptors • Which will mix with water to dissociate into OH- ions
What are strong acids?
• Strong acids/bases will always dissociate completely into OH- or H+ ions • Where the forward reaction is favoured strongly
What are weak acids?
• Strong acids/bases will partially completely into OH- or H+ ions • Where the backwards reaction is favoured
What are conjugate pairs?
Acids and Bases that are linked by the transferring of a proton from one to the other
What is a conjugate base?
The conjugate base is a base that has lost a proton
What is a conjugate acid?
A conjugate acid is an acid that has gained a proton
How are conjugate pairs formed?
• HA will lose an electron to A • Meaning that A becomes A- • HA becomes BH+
How do you find the pH of a solution from H+ concentration?
How do you find the H+ from pH?
What does the p in pH mean?
• p means POTENTIAL • if you ever see p its -log(rest of symbol) • pKA = -log(Ka)
What is Ka (explanation + formula)?
• Acidic dissociation constant • Indicated the extent of dissociation • The equilibrium constant for the dissociation of a weak acid at 298K
What is pKa?
• pKa is used to compare the Ka between different acids • As Ka values are generally too small • -log[Ka]
What does Ka tell you?
• Indicated the extent of dissociation • High Ka • Acid has almost fully dissociated • Meaning its strongly acidic • The equilibrium lies to the right (more $H^+$) • Low Ka • Acid partially dissociated • Meaning its a weak acid • The equilibrium lies to the left (more $HA_{aq}$)
What assumptions are made when writing the equilibrium for weak acids?
• The concentration of $HA_{aq}$ is the same at the start and is the same at the equilibrium • The concentration of HA = $A^-$ • Due to small amounts of dissociation
What are the steps for calculating Ka?
• Write the ionic equation for the dissociation of the acid • Write the equilibrium expression • Determine conc of H+,A-, HA • Use the equation to find Ka
How do you calculate Ka from mass and pH?
• Calculate moles of acid in the solution • Calculate the concentration of acid from moles giving you [HA] • Use 10^{-pH} to calculate [H+] concentration • Use the Ka equation to calculate Ka
How do you calculate Ka from a practical measuring pH?
• Accurately weigh the acid and dissolve it in a small volume of deionised water in a beaker • Transfer the solution to a 250cm3 volumetric flask. wash the beaker several times and pour the washings into the flask. make up to the mark with deionised water • Invert the flask several times • Take a sample from the solution and place it in a small beaker • Measure the pH of the solution using a calibrated pH metre
What is Kw and what does it tell you?
• Ionic product of water • The equilibrium constant for the dissociation of water at 298K • 1×10^{-14} mol^2}dm{-6}
What is the Kw expression with the simplified versions?
What is pKw?
• pKw is used to compare the Kw between different acids • As Kw values are generally too small • -log[Kw]
How do you find the pH from Kw?
How do you prove the pH of water is 7?
How can the relative strengths of acids/bases be determined?
• Can be determined by measuring pH • Of equimolar aqueous solutions of acids/bases • At the same Temperature
