CH 15 Quiz

Calculate the hydrogen ion concentration in a solution of iced tea with lemon having a pH of 2.87?

1.3 x 10^-3 M We can use -log[H3O+]. to calculate the pH. Therefore we can use 10^-pH to calculate [H3O+] 10^-2.87 = 1.3 x 10^-3

The pH of a 0.095 M solution of an unknown monoprotic acid is 5.42. Calculate the Ka of the acid

1.5 x 10^-10 HA -> H+ + A- 0.095 0 0 -x. +x. +x 0.095-x x x ka = x^2 / 0.095 - x pH = 5.42 [H3O+] = 10^-5.42 = 3.8 x 10^-6 ka = (3.8 x 10)^2 / 0.095 - 3.8 x 10^-6 ka = 1.5 x 10^-10

What is the concentration of H+ in a 2.5 M HCl solution?

2.5 M HCl dissociates completely so: HCl + H2O -> Cl- + H3O+ I: 2.5 - 0 0 C: -2.5 - +2.5 +2.5 E: 0 - 2.5 2.5 [H3O+] = 2.5 M

Consider the weak acid CH3COOH (acetic acid). If a 0.048M CH3COOH solution is 5.2% ionized, determine the [H3O+] concentration at equilibrium.

2.5 x 10^-3 M CH3COOH + H2O -> CH3COO + H3O+ I 0.048 - 0 0 C -x - +x +x E. 0.048-x - x x percent ionization = ionized / total x 100 5.2 = x^2 / 0.048-x neglect one x and solve 5.2 /100 = x / 0.048 (5.2/100)(0.048) = x x = 2.5 x10^-3

The pOH of a solution is 10.40. Calculate the hydrogen ion concentration in the solution.

2.5 x 10^-4 M We can solve this two ways 1) 14 - 10.40 = 3.6 pH 10^-3.6 = 2.5 x 10^-14 [H3O+] 2) 10^-10.40 = 3.98 x 10^-11 [OH-} 1 x10^-14 / 3.98 x 10^-11 = 2.5 x 10^-4 [H3O+]

What is the pH of a 0.0055 M HA (weak acid) solution that is 8.2% ionized?

3.35 HA -> H+ + A- 0.0055 0 0 -x +x +x 0.0055-x x x 8.2 = x^2 / 0.0055 -x (100) neglect one x and solve (8.2/100)(0.0055) = x x = 4.51 x 10^-4 = [H3O+] -log (H3O+) = pH -log[4.51 x 10^-4] = 3.35

Calculate the H+ ion concentration in a 8.8x10^-4 M Ca(OH)2 solution

5.7 x 10^-12 M Ca(OH)2 + H2O(l) -> H3O+ + 2OH- I: 8.8x10^-4 - 0 0 C: -8.8x10^-4 - 8.8x10^-4 8.8x10^-4(2) E: 0 - 8.8x10^-4 0.00176 pOH = -log(0.00176) = 2.75448 pH = 14 - 2.75448 = 11.24 [H3O+]= 10^-11.24 = 5.7 x10^-12 Or you can also use: 1.4 x 10^-14 = [H3O+][OH-] 1.4x10^-14 / 0.00176 = 5.7 x 10^-12

When comparing acid strength of binary acids HX, as X varies within a particular group of the periodic table, which one of these factors dominates in affecting the acid strength?

Bond strength The weaker the bond strength, the more likely the acid is to dissociate. Thereby, making the acid stronger

Given the following ka values, which anion is the strongest base: H2CO3 = 4.2 x 10^-7 HCO3- = 4.8x10^-11 H2C2O4 = 6.5x10^-2 HC2O4- = 6.1 x 10^-5 H2PO4- = 6.2 x10^-4

CO3^2- Ka is the acid dissociation constant. Pka shows us how strong or weak the acid is. Lower pka is a strong acid, higher pka is a weak acid. ka and pka are related in: -log(ka) = pka Let's find the pka values: H2CO3 = 4.2 x 10^-7 = 6.38 HCO3- = 4.8x10^-11 = 10.32 H2C2O4 = 6.5x10^-2 = 1.19 HC2O4- = 6.1 x 10^-5 = 4.21 H2PO4- = 6.2 x10^-4 = 3.21 The strongest base will be the pka value that's the highest because the lower a pka value, the stronger the acid. Therefore the opposite must be true for bases. The strongest pka value is from the HCO3- acid. It's conjugate base will be CO3^2-

Identify the conjugate acid of HCO3^-

H2CO3 If we want to find the conjugate acid of HCO3- then we must treat it like the base Bases gain an H+ proton so we just need to add an H+ proton (by adding one, we increase the charge +1, that's why the final product will have no charge since -1 + 1 = 0 ) HCO3- -> H2CO3

The hydronium ion and the hydroxide ion, in that order are:

H3O+, OH- Hydronium ion can be expressed as H+ or as H3O+ Hydroxide ion can be expressed as OH- or as HO-

Which one of these statements about strong acids is true? Strong acids are very concentrated acids Strong acids are 100% ionized in water Strong acids produce solutions with a higher pH than weak acids All strong acids have H atoms bonded to electronegative oxygen atoms The conjugate base of a strong acid is itself a strong base

Strong acids are 100% ionized in water Justifying answers: A) Strong acids do not necessarily need to be very concentrated to be strong. B) The definition of a strong acid is that it will dissociate completely. C) Strong acids produce a lower pH because Hydronium concentration is related to pH in: -log[H3O+] = pH D) Not all strong acids are bonded to electronegative oxygen atoms for example HCl E) The conjugate base of a strong acid is actually a weak base

Hard water deposits (calcium carbonate) have built up around your bathroom sink. Which one of the following would be best to dissolve the deposit?

Vinegar (acetic acid) The Calcium carbonate is more basic. To neutralize it we need an acid.

Which of the following solutions is acidic?

[H3O+] > 7.0 x 10-7 M The larger the [H3O+] value, the lower the pH. Lower pH means greater acidity.

In the reaction HSO4^-(aq) + OH^-(aq) <=> SO4^2-(aq) + H2O(l), the conjugate acid-base pairs are

pair 1: HSO4^- and SO4^2- pair 2: H2O and OH- HSO4^-(aq) + OH^-(aq) <=> SO4^2-(aq) + H2O(l) HSO4^- -> SO4^2- HSO4^- loses its H+ atom so it acts as the acid SO4^2- would be the Conjugate Base OH- -> H2O OH- gains an H+ atom so it is the Base Therefore H2O is the Conjugate Acid