Acids and Bases Flashcards by monica atherton

What is a Brønsted acid and base in terms of protons and hydrogen ions

Acid = proton donor, release H+
Base = proton acceptor, attract H+

How well did you know this?

Not at all

Perfectly

What does Brønsted acid-base equilibria involve

Transfer of protons

How well did you know this?

Not at all

Perfectly

Equation that related pH and H+

pH = -log10[H+]
[H+] = 10^-pH

How well did you know this?

Not at all

Perfectly

What is Ka

An equilibrium constant for the dissociation of an acid

How well did you know this?

Not at all

Perfectly

What is the equation for Kw in pure water

Kw = [H+]^2

How well did you know this?

Not at all

Perfectly

Equation for pKa

pKa = -log10Ka

How well did you know this?

Not at all

Perfectly

What does it mean when acids and bases dissociate in water

Break up into positively and negatively charged ions

How well did you know this?

Not at all

Perfectly

What dissociates the most and why

Strong acids = releasing all H+ ions
Strong bases = ionise completely
Weaker bonds dissociate more

How well did you know this?

Not at all

Perfectly

What happens to the equilibrium if you add more acid or base in acid + base = salt + water

Position of equilibrium shifts right
(opposite happens if you add more salt or water)

How well did you know this?

Not at all

Perfectly

What does the dissociation of water equation look like

H2O <–> H+ + OH-

How well did you know this?

Not at all

Perfectly

What is a conjugate acid-base pair

A conjugate acid-base pair is two species that are different from each other by an H+ ion

How well did you know this?

Not at all

Perfectly

what is Kc

the equilibrium constant, measured using products and reactants in either the gaseous or aqueous state

How well did you know this?

Not at all

Perfectly

What is Kw

Kw i= autoprolysis constant of water
(at 25 degrees Celsius)
Is always = 1.0 x 10^-14.

How well did you know this?

Not at all

Perfectly

What is the Kc and Kw equation for the dissociation of water

Kc = [H+][OH-] / [H2O]

Kw = [H+][OH-]

How well did you know this?

Not at all

Perfectly

Why is [H2O] not shown in the Kw expression

[H2O] is almost constant

How well did you know this?

Not at all

Perfectly

What is a pH scale a measure of

Hydrogen ion concentration in a solution
measured in mol dm-3

How well did you know this?

Not at all

Perfectly

What is the equation for strong acid ionisation

HA (aq) -> H+ (aq) + A- (aq)

How well did you know this?

Not at all

Perfectly

What is the equivalence point

where the amount of acid neutralises the alkali or vice versa

How well did you know this?

Not at all

Perfectly

Kc equations

Kc x H2O = [H2O][OH-]

How well did you know this?

Not at all

Perfectly

Strong base ionisation equation

BOH (aq) → B+ (aq) + OH- (aq)

Strong base equations:

[H+] = Kw/[OH-}

[H+] = 1 x 10^-14 / [OH-]

pH = -log[H+] = -log (Kw (1 x 10^=14) / [OH-])

Calculate the pH of 0.15 mol dm-3 sodium hydroxide, NaOH

[H+] = Kw ÷ [OH-]

[H+] = (1 x 10-14) / 0.15 = 6.66 x 10-14

pH = -log[H+]

  = -log 6.66 x 10-14  = 13.17

Calculate the hydroxide concentration of a solution of sodium hydroxide when the pH is 10.50

Step 1: Calculate H concentration
[H+]= 10-pH

[H+]= 10-10.50

[H+]= 3.16 x 10-11 mol dm-3

Step 2: Rearrange the ionic product of water

Kw = [H+] [OH-]

[OH-]= Kw ÷ [H+]

Step 3: Find the concentration of hydroxide ions

Kw is 1 x 10-14 mol2 dm-6,

[OH-]= (1 x 10-14) ÷ (3.16 x 10-11)

[OH-]= 3.16 x 10-4 mol dm-3

What is Ka

Dissociation constant for a weak acid

Equation for Pka

pKa = -log10Ka

Ka equation

Ka = [H+][A-] / [HA]

What are you looking for when you are calculating: pH Ionic product of water Weak acid dissociation constant Weak acid pH

pH = -log10[H+] Ionic product of water = Kw = [H+][OH-] Equation for pKa = -log10 Ka Weak acid pH = Ka = [H+][A-] / [HA]

What does the higher or lower the value of Ka mean

higher the value of Ka the more dissociated the acid and the stronger it is The lower the value of Ka the weaker the acid

How to find the pH of weak acids step by step

1) Write Ka for weak acid ( Ka = [H+]^2 / [HA] ) 2) Rearrange equation and substitute to find [H+]^2 3) Square root the number to find [H+] 4) Substitute [H+] into pH ( pH = -log10 [H+] )

How to find concentration of weak acids step by step

1) Substitute pH into pH equation to calculate [H+] ( [H+]=10^-pH ) 2) Write an expression for Ka 3) Rerrange to give concentration ( [H+]^2 / Ka ) 4) Substitute Ka and [H+] into equation

Find Ka of weak acids step by step

1) Use pH of acid to find [H+] 2) Write an expression for Ka 3) Substitute values for [H+] and [A-]

Step by step calculating Ka

1) Concert pKa to Ka ( Ka = 10^-pKa ) 2) Write Ka expression 3) Rerrange to give [H+]^2 4) Square root it 5) Substitute [H+] into pH equation and solve

How to calibrate pH meter

1) Rinse probe with distilled water, shake off excess, place in standard buffer solution, record pH reading in table 2) Repeat solutions of other concentrations, rinsing the probe between each step 3) Plot graph of recorded pH against pH of buffer

What is Kw When going from [OH-] to [H+]

Kw = [H+][OH-]

As temperature increases, what happens to pH?

pH drops because water dissociated more so there are more H+

How to find the equivalence point in a titration graph?

In the middle of the graph where the line is completely straight going up

How to find the half equivalence point?

Half neutralised So distance between straight line going up, half of it

What is the half equivalence point

PH = pKa

Pure weak acid equation by itself

Ka = [H+]^2 / [HA]

describe how the student would carry out a titration to obtain a pH curve

1) Use pH probe to measure the initial pH of ammonia solution 2) Add Hcl acid 2cm^3 at a time 3) Stir mixture 4) Record pH after each addition 5) Reduce size portions when close to the end point 6) Repeat until acid in excess 7) Plot a graph of the results

Explain why [H2O] is not shown in the Kw expression

[H2O] is very large compared to [H+ ] and [OH-]

Explain why the value of Kw increases as the temperature increases

Equilibrium is endothermic so shifts to the right to oppose temperature increase

Explain why water is neutral at 50 °C

[H+] = [OH–]

Suggest why the pH probe is washed with distilled water between each of the calibration measurements.

To wash off any residual solution/substance (which could interfere with the reading)

Explain why the volume of sodium hydroxide solution added between each pH measurement is smaller as the end point of the titration is approached.

To wash off any residual solution/substance (which could interfere with the reading)

How do you know if the indicators are suitable in the titration

All will have a colour change/pH range within the steep/vertical part of the titration curve

State the meaning of the term weak acid.

partially dissociates (in water to form H+ ions)