Acids and Bases Flashcards

Question

Measuring Acidity: pH

Answer 1

pH = -log([H3O+]) - exponent on 10 with a positive sign pH < 7 is acidic; pH > 7 is basic pH = 7 is neutral

Answer 2

Another way of expressing the acidity/basicity of a solution is pOH. – pOH = −log[OH–] * If you know pOH, then you can determine [OH–]. – [OH–] = 10−pOH – pOHwater = −log[10−7] = 7 * pOH < 7 is basic; pOH > 7 is acidic; pOH = 7 is neutral. * pH + pOH = 14.00 at 25 °C.

Answer 3

Another way of expressing the strength of an acid or base is through its pK. * Acid: pKa = −log(Ka), Ka = 10−pKa – The stronger the acid, the smaller the pKa. * Larger Ka = smaller pKa – Because pKa is −log(Ka) * Base: pKb = −log(Kb), Kb = 10−pKb – The stronger the base, the smaller the pKb. * Larger Kb = smaller pKb

Answer 4

Another way to measure the strength of an acid is to determine the percentage of acid molecules that ionize when dissolved in water; this is called the percent ionization. – The higher the percent ionization, the stronger the acid. [H3O]+equil × 100 = percent ionization [HA]init

Answer 5

There are two sources of H3O+ ions in an aqueous solution between a strong acid and water: – The H+ ion from the dissociation of the strong acid and the H+ ion produced by the autoionization of water * There are two sources of OH− ions in an aqueous solution between a strong base and water: * The OH– ion from the dissociation of the strong base and the OH– ion produced by the autoionization of water * For a strong acid or base, the contribution of either the [OH–] ions and/or [H+] ions produced from the autoionization water is negligible

Answer 6

There are six strong acids: Five are monoprotic and one is diprotic. – Monoprotic: HCl, HBr, HI, HClO4, and HNO3 – Diprotic: H2SO4 * For a monoprotic strong acid, the acid concentration equals the hydronium concentration. – [H3O+] = [HAcid] – Example: 0.10 M HCl has [H3O+] = 0.10 M and pH = 1.00 * For H2SO4, the first ionization is the most significant, but the second ionization cannot generally be ignored. – In such cases, the [H3O+] contributed from the second step is added to the [H3O+] produced in the first step. * Example: 0.10 M H2SO4 has [H3O+] = 0.11 M and pH = 0.96

Answer 7

Generally, you can ignore the contribution of the weaker acid to the [H3O+]equil. * For a mixture of a strong acid with a weak acid, the complete ionization of the strong acid provides more than enough [H3O+] to shift the weak acid equilibrium to the left so far that the weak acid’s added [H3O+] is negligible. * For mixtures of weak acids, you generally need to consider only the stronger for the same reasons, as long as one is significantly stronger than the other and their concentrations are similar.

Answer 8

Hydroxide compounds are strong bases. – Examples: KOH, NaOH, Ca(OH)2 * Ionic bases (soluble) are almost 100% dissociated into OH– ions --Strong electrolyte

Answer 9

For a strong mono hydroxyl ionic base, the [BOH] = [OH−]. – Example: 0.10 M KOH has [OH–] = 0.10 M * To find the pH of a mono hydroxyl ionic base, first find the pOH and then determine the pH. – Example: * 0.10 M KOH has 0.10 M [OH–] ions. * pOH = –log [OH–] or pOH = –log [0.10], so pOH is 1.00. * pH + pOH = 14.00, so pH + 1.00 = 14.00; thus, the pH is 13.00. * For strong poly hydroxyl ionic base compounds, the [OH–] is equal to number of OH– ions in the base. – Example: * 0.10 M Ca(OH)2 has [OH−] = 0.20 M and pH = 13.30. * pOH = –log [OH–] or pOH = –log [0.20], so pOH is 0.70. * pH + pOH = 14.00, so pH + 0.70 = 14.00; thus, the pH is 13.30

Answer 10

Weak electrolyte – Most of the weak base molecules do not accept H+ ions from water. * Examples of common weak bases: ‒ Ammonia, NH3 ‒ Amines (organic bases) ‒ Carbonates, such as sodium carbonate,Na2CO3, and sodium bicarbonate, NaHCO3 * Finding the pH of a weak base solution is similar to finding the pH of a weak acid using ICE.

Answer 11

Base strength is measured by the size of the equilibrium constant when it reacts with H2O. :Base + H2O (l) OH− + H:Base+ * The equilibrium constant is called the base ionization constant, Kb. Keep in mind that only base dissociation can give rise to [OH-] and only acid dissociation can give rise to [H+] – The larger the Kb, the stronger the base.

Answer 12

When Kb > Ka, the solution is basic. * When Kb < Ka, the solution is acidic. * When Kb >> Ka, the solution is neutral or nearly neutral

Answer 13

Because polyprotic acids ionize in steps, each H has a separate Ka value. – Ka1 > Ka2 > Ka3 * Generally, the difference in Ka values is great enough so that the second ionization does not happen to a large enough extent to affect the pH. – Most pH problems just use the first ionization. – [A2−] = Ka2 as long as the second ionization is negligible

Answer 14

Lewis acid–base theory focuses on transferring an electron pair. – Lone pair bond – Bond lone pair * It does NOT require H atoms to be classified as an acid. * The electron donor is called the Lewis base. – It is electron rich chemical species. – It is often referred to as a nucleophile. * The electron acceptor is called the Lewis acid. – It is electron deficient chemical species. – It is often referred to as an electrophile

Answer 15

Lewis acids are electron deficient species, due either to being attached to electronegative atom(s) in a bond or as a result of not having a complete octet. * They must have an empty orbital willing to accept the electron pair. – Examples: * H+ has an empty 1s orbital. * B in BF3 has an empty 2p orbital and an incomplete octet. – Many small, highly-charged metal cations have empty orbitals they can use to accept electrons. * Atoms that are attached to highly electronegative atoms and/or have multiple bonds can be designated as Lewis acids

Answer 16

A Lewis base species has electrons it is willing to give away to or share with another atom that is deficient in electrons. * A Lewis base must have a lone pair of electrons on it that it can donate. * Anions are better Lewis bases than neutral atoms or molecules. – Example: N: < N:− * Generally, the more electronegative an atom, the less willing it is to be a Lewis base. – Example: O: < S:

Answer 17

The Lewis base donates a pair of electrons to the acid. * This donated pair of electrons generally results in a covalent bond forming. H3N: + BF3 H3N—BF3 * The product that forms is called an adduct. * Arrhenius and Brønsted–Lowry acid–base reactions are also Lewis acid–base reactions

Acids and Bases Flashcards

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