Search found 17468 matches

Sun Aug 21, 2011 12:54 pm
Forum: *Titrations & Titration Calculations
Topic: Tiration of weak acid with strong base
Replies: 1
Views: 475

Re: Tiration of weak acid with strong base

Answer: In the example I did we calculated the pH at the stoichiometric point of the titration of 25.00 ml of 0.100 M HCOOH(aq) with 0.150 M NaOH(aq). Note that we have a weak acid and a strong base so the stoichiometricpoint will be above pH 7. AT STOICHIOMETRIC POINT: # MOLES OH- ADDED = # MOLES ...
Sun Aug 21, 2011 12:53 pm
Forum: *Titrations & Titration Calculations
Topic: Tiration of weak acid with strong base
Replies: 1
Views: 475

Tiration of weak acid with strong base

Question: I have a question regarding titrations of a weak acid with a strong base. As an example, we had a known molarity of NaOH (titrant) reacting with HCOOH of a specific molarity and volume. I understand that the # of moles of HCOOH=# moles of NaOH=# moles of HCOO- (conj base of HCOOH). Howeve...
Sun Aug 21, 2011 12:53 pm
Forum: *Titrations & Titration Calculations
Topic: Titration calculations for strong/weak acid/base
Replies: 1
Views: 271

Re: Titration calculations for strong/weak acid/base

Answer: The 1st example is correct, provided [H3O+] > [OH-]. If not then subtract [H3O+] from [OH-] and take the -log to get pOH. Then use pH + pOH = 14 obtain pH.
For a titration involving a weak acid or base one has to set up an equilibrium table (ICE) to obtain [OH-] or [H3O+].
Sun Aug 21, 2011 12:52 pm
Forum: *Titrations & Titration Calculations
Topic: Titration calculations for strong/weak acid/base
Replies: 1
Views: 271

Titration calculations for strong/weak acid/base

Question: In titrating a strong acid and a strong base, we use the pure concentrations and subtract OH concentration from H30 concentration and take the -log of the H30 concentration to get the pH. Conversely, when titrating weak acids and weak bases, we do the same steps, however we follow those c...
Sun Aug 21, 2011 12:51 pm
Forum: *Titrations & Titration Calculations
Topic: How do we find the initial and final pH for a titration?
Replies: 1
Views: 234

Re: How do we find the initial and final pH for a titration?

Answer: Calculating the initial pH is the same as calculating the pH of a strong base before titrant is added. As acid is continually added in the titration the pH of the solution will approach the pH of the titrant and thus have a final pH of the titration.
Sun Aug 21, 2011 12:50 pm
Forum: *Titrations & Titration Calculations
Topic: How do we find the initial and final pH for a titration?
Replies: 1
Views: 234

How do we find the initial and final pH for a titration?

Question: How do we find the initial and final pH for a titration?
Sun Aug 21, 2011 12:50 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: What the ratio of the "concentrations of two species" are?
Replies: 1
Views: 201

Re: what the ratio of the "concentrations of two species' a

Answer: It doesn't matter if you put the acid/base or the base/acid. The same answer should be obtained and based on the question the value can be inversed to find the right ratio.
Sun Aug 21, 2011 12:50 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: What the ratio of the "concentrations of two species" are?
Replies: 1
Views: 201

What the ratio of the "concentrations of two species" are?

Question: How do we know what the ratio of the "concentrations of the two species" are? How do we know which concentration is the numerator and which one is the denominator?
Sun Aug 21, 2011 12:48 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: pH = 3 would lactic acid or trichloroacetic acid be used?
Replies: 1
Views: 330

Re: Ph=3would lactic acid or trichloroacetic acid be used?

Answer: Lactic acid has a pKa of 3.86 while trichloroacetic acid has a pKa 2.85. Several weak acids have suitable buffers for a pH~3, not just trichloroacetic acid.
Sun Aug 21, 2011 12:45 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: pH = 3 would lactic acid or trichloroacetic acid be used?
Replies: 1
Views: 330

pH = 3 would lactic acid or trichloroacetic acid be used?

Question: For a pH of 3, would lactic acid or trichloroacetic acid be used? It seems like lactic acid is a better answer because the pKa is 3.08 which is closer to 3 than 2.85.
Sun Aug 21, 2011 12:45 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Acidic buffer solution, strong base added, concept
Replies: 1
Views: 442

Re: Acidic buffer solution, strong base added, concept

Answer: The amount of H3O+ changes for this reason: You add a strong base, so you are right, the only direct change from that is the change in concentration of acetic acid and acetate. This essentially means you are no longer at K, you are at Q now (changing the concentrations does that to you), wh...
Sun Aug 21, 2011 12:45 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Acidic buffer solution, strong base added, concept
Replies: 1
Views: 442

Acidic buffer solution, strong base added, concept

Question: To calculate the pH of an acidic buffer solution to which some strong base has been added, how is the concentration of hydronium ions expected to change (resulting in a change in pH) when it seems the only concentrations that are changing are the acid (used up by the hydroxide ions) and c...
Sun Aug 21, 2011 12:44 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Adding very low concentrations of acid, must use ICE?
Replies: 1
Views: 248

Re: add very low concentration of acid, must use ICE?

Answer: For this question it seems as if that would be okay since the change in x is so small that the H3O+ concentration doesn't change significantly. But you should always set up the ice box for this type of problem because you will not necessarily know if x will be so small that you can disregar...
Sun Aug 21, 2011 12:43 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Adding very low concentrations of acid, must use ICE?
Replies: 1
Views: 248

Adding very low concentrations of acid, must use ICE?

Question: It asks for us to calculate the change in pH that occurs with the addition of .65 x 10^-6 mol H3O+ to sample. Instead of creating another ICE diagram, can we calculate the new moles of H3O+ in the reaction, find its molarity using the new number of moles, and then take the negative log of...
Sun Aug 21, 2011 12:42 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: K < 10^-5, ok to neglect x even if equation is not cubic?
Replies: 1
Views: 449

Re: k<10^-5, ok to neglect x even equation is not cubic?

Answer: It depends on the expression K. If K = x^2/(1-x), x can be ignored in the (1-x) in order to simplify the calculation if K < 10^-5. In this case, we can neglect the x in 1-x and left with K = x^2.
Sun Aug 21, 2011 12:40 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: K < 10^-5, ok to neglect x even if equation is not cubic?
Replies: 1
Views: 449

K < 10^-5, ok to neglect x even if equation is not cubic?

Question: If K is less than 10^-5, can we neglect x even if the equation to be solved is quadratic and not cubic?
Sun Aug 21, 2011 12:39 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: When can we neglect [x], Ka Kb value less than 10^-5?
Replies: 1
Views: 3199

Re: when can we neglect [x], ka kb value less than 10^-5?

Answer: The whole Ka or Kb being 10^-5 or less is just a very general rule of thumb that tells you if you should even bother to assume the 5% rule (because if you do, and your x is NOT less than 5% of the initial concentration, you have to use the quadratic). The approximation (a.k.a. the 5% rule) ...
Sun Aug 21, 2011 12:38 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: When can we neglect [x], Ka Kb value less than 10^-5?
Replies: 1
Views: 3199

When can we neglect [x], Ka Kb value less than 10^-5?

Question: When is it okay to approximate when finding the equilibrium concentrations of acids and bases by assuming that [x] is negligible? Is it when Ka or Kb is 10^-5 or less?
Sun Aug 21, 2011 12:37 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: (mole base)/(mole acid) in HH equation, same using molarity?
Replies: 1
Views: 7059

Re: (mole base)/(mole acid) in HH equation, same using molar

Answer: In the Henderson-Hasselbach equation, you SHOULD put in the molarity, but since the total volume is the same for both the base and the acid (they are sitting in the same solution, so they have the same total volume of solution), the volumes will cancel. For example say the total volume is 1...
Sun Aug 21, 2011 12:36 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: (mole base)/(mole acid) in HH equation, same using molarity?
Replies: 1
Views: 7059

(mole base)/(mole acid) in HH equation, same using molarity?

Question: Even though we technically CAN use (moles base)/(moles acid) in the Henderson-Hasselbalch equation, is it the same as using molarity?
Sun Aug 21, 2011 12:36 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Why are buffers used?
Replies: 1
Views: 412

Re: Why are buffers used?

Answer: A buffer can resist pH change even with the addition of small amounts of strong acid or base (i.e. acids/bases that are not part of your buffer system). a buffer can effectively "absorb" added acid with little change in pH when [A-]/[HA] is at least 0.10. This is yet another way t...
Sun Aug 21, 2011 12:35 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Why are buffers used?
Replies: 1
Views: 412

Why are buffers used?

Question: Why are buffers used? Isn't the addition of small amounts of acids or bases contradict the purpose of resisting a change of pH?
Sun Aug 21, 2011 12:33 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: # of deprotonation steps in solution make buffer stronger?
Replies: 1
Views: 249

Re: # of deprotonation steps in solution make buffer stronge

Answer: No, extra deprotonation steps just give the buffer more ranges in which to be used. Nonpolar solvents like hexane and toluene are not effective as proton donors/acceptors, but there are plenty of other polar (protic and aprotic) solvents that have acid/base reactivity
Sun Aug 21, 2011 12:33 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: # of deprotonation steps in solution make buffer stronger?
Replies: 1
Views: 249

# of deprotonation steps in solution make buffer stronger?

Question: Does the number of deprotonation steps in solution make a given buffer inherently stronger, i.e. a H3PO4 & Na3PO4 buffer or H2CO3 & Na2CO3? Also, do these steps always require water, or can other solvents be used to achieve the same effect?
Sun Aug 21, 2011 12:32 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Can the HH equation be written for pOH instead of PH?
Replies: 1
Views: 217

Re: Can the HH equation be written for pOH instead of PH?

Answer: Yes, it would take the form of pOH = pKb + log ([acid] / [base]).
Sun Aug 21, 2011 12:31 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Can the HH equation be written for pOH instead of PH?
Replies: 1
Views: 217

Can the HH equation be written for pOH instead of PH?

Question: Can the Hendeson-Hasselbach equation be written for pOH instead of pH?
Sun Aug 21, 2011 12:31 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: How do salts play a role in a buffer?
Replies: 1
Views: 200

Re: How do salts play a role in a buffer?

Answer: Salts work well to buffer the pH of solution because you pick a specific salt wisely. In the generic equation HA --> H+ + A-, you pick your salt to contain the cation A-. Thus, in a solution of this salt and HA, due to the high relative concentrations of HA and A-, the solution is rather ro...
Sun Aug 21, 2011 12:31 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: How do salts play a role in a buffer?
Replies: 1
Views: 200

How do salts play a role in a buffer?

Question: How do salts play a role in a buffer?
Sun Aug 21, 2011 12:29 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: H3PO4 has only one H atom?
Replies: 1
Views: 228

Re: H3PO4 has only one H atom?

Answer: At pH 12 the solution is alkaline and the H3PO4 has already lost 2 or 3 H+ to form Na2HPO4 and Na3PO4. These are the species in solution at pH 12.
Sun Aug 21, 2011 12:29 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: H3PO4 has only one H atom?
Replies: 1
Views: 228

H3PO4 has only one H atom?

Question: When determining the pH values of a buffer, how come the pH value listed for the compound H3PO4 is 12, but the species NaHPO4 added with Na3PO4 also have a pH of 12. Why do these species only have one H atom, instead of 3 in H3PO4.
Sun Aug 21, 2011 12:28 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: How to find volume of solution added using HH equation
Replies: 1
Views: 533

Re: how to find volume of solution added using HH equation

Answer: Using the Henderson-Hasselbalch equation you can determine the ratio of acid to base. This is equal to the ratio of moles of acid and base. Given the known moles of the acid you can then determine the moles of base necessary and calculate the volume necessary to deliver that many moles of b...
Sun Aug 21, 2011 12:27 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: How to find volume of solution added using HH equation
Replies: 1
Views: 533

How to find volume of solution added using HH equation

Question: How can we find the volume of a solution added using the Henderson-Hasselbalch equation?
Sun Aug 21, 2011 12:24 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: What conditions can we use the HH equation?
Replies: 1
Views: 380

Re: what conditions can we use the Henderson equation

Answer: The Henderson-Hasselbalch equation is used under the condition of weak acid and a salt or a weak base and a salt. Both of these are buffer solutions.
Sun Aug 21, 2011 12:23 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: What conditions can we use the HH equation?
Replies: 1
Views: 380

What conditions can we use the HH equation?

Question: Under what conditions can we use the Henderson equation to calculate the pH if we're not told in the question that there is a buffer involved? How do we know if a solution contains a buffer or not?
Sun Aug 21, 2011 12:20 pm
Forum: Identifying Acidic & Basic Salts
Topic: KBr is neutral, but why KF is basic?
Replies: 1
Views: 7830

Re: KBr is neutral, but why KF is basic?

F- is an exception in that it is the only halogen that affects the pH of a solution. If one thinks about the series H-F, H--Cl, H---Br, H----I and recalls that H-F is the weakest acid (strongest bond) then it makes sense that F- will pick up H+ from water to form H-F and OH- and hence raise the solu...
Sun Aug 21, 2011 12:20 pm
Forum: Identifying Acidic & Basic Salts
Topic: KBr is neutral, but why KF is basic?
Replies: 1
Views: 7830

KBr is neutral, but why KF is basic?

K+ is not an acid and Br- is not a base, so the solution is neutral. But KF is basic, why is it not also neutral since they both have K+ and Br and F are in the same group? Also for compounds such as AlCl3 and Cu(NO3)2, how do I determine that it is Al(H2O)6 or Cu(H2O)6 when I am writing out the che...
Sun Aug 21, 2011 12:20 pm
Forum: Identifying Acidic & Basic Salts
Topic: How do you write the reaction for NaOH + CH3HOOH?
Replies: 1
Views: 303

Re: How do you write the reaction for NaOH + CH3HOOH?

base + acid ---> salt + water NaOH + CH3COOH -----> CH3COO-Na+ + H2O
Sun Aug 21, 2011 12:19 pm
Forum: Identifying Acidic & Basic Salts
Topic: How do you write the reaction for NaOH + CH3HOOH?
Replies: 1
Views: 303

How do you write the reaction for NaOH + CH3HOOH?

How do you write the reaction for NaOH + CH3HOOH?
Sun Aug 21, 2011 12:18 pm
Forum: Polyprotic Acids & Bases
Topic: H2SO3 and NaOH, how many moles of NaOH are needed to neutral
Replies: 1
Views: 1544

Re: H2SO3 and NaOH, how many moles of NaOH are needed to neu

Because H2SO3 has two protons, 2 hydroxides are required to neutralize it, yielding the 2:1 ratio of NaOH:H2SO3 needed.
Sun Aug 21, 2011 12:18 pm
Forum: Polyprotic Acids & Bases
Topic: H2SO3 and NaOH, how many moles of NaOH are needed to neutral
Replies: 1
Views: 1544

H2SO3 and NaOH, how many moles of NaOH are needed to neutral

For a reaction of H2SO3 and NaOH, how many moles of NaOH are needed to neutralize it?
Sun Aug 21, 2011 12:18 pm
Forum: Polyprotic Acids & Bases
Topic: why use the pKa for H2PO3- not HPO3(2-)?
Replies: 1
Views: 1693

Re: why use the pKa for H2PO3- not HPO3(2-)?

Use the Henderson-Hasselbach equation, pH = pKa + log([base]/[acid]). In the case of these species, H2PO3- + H2O -> HPO3(2-) + H30+, thus the dihydrogen species is the acid, and the monohydrogen specie is the base. Given that, in the Henderson-Hasselbach equation the pKa of dihydrogen phosphate must...
Sun Aug 21, 2011 12:18 pm
Forum: Polyprotic Acids & Bases
Topic: why use the pKa for H2PO3- not HPO3(2-)?
Replies: 1
Views: 1693

why use the pKa for H2PO3- not HPO3(2-)?

How do we differentiate to use the pKa for potassium dihydrogen phosphate and not the pKa for potassium hydrogen phosphate?
Sun Aug 21, 2011 12:16 pm
Forum: Polyprotic Acids & Bases
Topic: How do you find the value for pKa3 for phosphoric acid?
Replies: 1
Views: 1179

Re: How do you find the value for pKa3 for phosphoric acid?

Remember that phosphoric acid is a triprotic acid (H3PO4). Ka1 refers to the reaction that removes the first hydrogen: H3PO4 + H2O <-> H2PO4- + H3O+. Ka2 refers to the reaction that removes the second hydrogen: H2PO4- + H2O <-> HPO4-2 + H3O+. Ka3 refers to removing the last hydrogen: HPO4-2 + H2O <-...
Sun Aug 21, 2011 12:16 pm
Forum: Polyprotic Acids & Bases
Topic: How do you find the value for pKa3 for phosphoric acid?
Replies: 1
Views: 1179

How do you find the value for pKa3 for phosphoric acid?

How do you find the value for pKa3 for phosphoric acid?
Sun Aug 21, 2011 12:15 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: What is the relationship between pKa to the pH or pOH?
Replies: 1
Views: 288

Re: What is the relationship between pKa to the pH or pOH?

Answer: The relationship between pKa and pH is given by the Henderson-Hasselbach equation. Acid strength increases with decreasing pKa. A strong acid is not represented with an equilibrium constant because it is assumed to dissociate completely (Ka is "infinite," if you want). Weak acid d...
Sun Aug 21, 2011 12:15 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: What is the relationship between pKa to the pH or pOH?
Replies: 1
Views: 288

What is the relationship between pKa to the pH or pOH?

Question: Is there any relation between pKa and the pH or pOH? The smaller the pKa, the stronger the acid. The lower the pH, the stronger the acid. But why are certain acids with very small pKa (ex trichloroacetic) still considered weak acids?
Sun Aug 21, 2011 12:15 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Use KaKb=Kw for strong acid/base, ICE box for weak?
Replies: 1
Views: 676

Re: Use KaKb=Kw for strong acid/base, ICE box for weak?

Answer: When you have strong acids and bases that dissociate completely, you can directly calculate the pH (pOH) without having to do an ICE box. You wouldn't use Ka or Kb for strong acids and bases, respectively, because dissociation is assumed to be 100%.
Sun Aug 21, 2011 12:14 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Use KaKb=Kw for strong acid/base, ICE box for weak?
Replies: 1
Views: 676

Use KaKb=Kw for strong acid/base, ICE box for weak?

Question: When we calculate the the H3O+ and OH- concentrations for strong acids and bases, can we use KaKb = Kw, because these acids/bases dissociate completely? As opposed to weak acids and bases when we have to use the ICE box?
Sun Aug 21, 2011 12:13 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: How can a solution be neutral if [H3O+] is less than 10-7?
Replies: 1
Views: 344

Re: How can solution be neutral if [H3O+] is less than 10-7?

Answer: Neutral water has 10-7 M H3O+. If one calculates that a compound when added to neutral water produces H3O+ (equivalent to a concentration of 10-10 M H3O+) then the compound is hardly increasing the H3O+concentration above 10-7 M. In other words, add 10-10 M H3O+ + 10-7 M H3O+ and then take ...
Sun Aug 21, 2011 12:13 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: How can a solution be neutral if [H3O+] is less than 10-7?
Replies: 1
Views: 344

How can a solution be neutral if [H3O+] is less than 10-7?

Question: I was confused about the last statement you made at the end of class: "If [H3O+] < 10-7, then the solution is considered neutral because we know that as a result of autoprotolysis they are 10-7 M H3O+." I am have trouble understanding how a solution would be neutral if [H3O+] is...
Sun Aug 21, 2011 12:13 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: What do one arrow and double arrows stand for?
Replies: 1
Views: 7799

Re: what do one arrow and double arrows stand for?

Answer: Correct! Although, all chemical reactions are reversible, so a double arrow is never incorrect.
Sun Aug 21, 2011 12:12 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: What do one arrow and double arrows stand for?
Replies: 1
Views: 7799

What do one arrow and double arrows stand for?

Question: For a strong acid and strong base reaction, there is only one arrow representing that all of the reactants are converted to products, right? So, for weak acids and bases that do not dissociate completely, the double arrows are used, right?
Sun Aug 21, 2011 12:11 pm
Forum: Conjugate Acids & Bases
Topic: Ka and Kb able to tell acid/base weak or strong?
Replies: 1
Views: 3355

Re: Ka and Kb able to tell acid/base weak or strong?

Really strong acid/base has a Ka/Kb larger than 1. Although I would consider a strong acid/base with a Ka/Kb larger than 10^-3.
Sun Aug 21, 2011 12:10 pm
Forum: Conjugate Acids & Bases
Topic: Ka and Kb able to tell acid/base weak or strong?
Replies: 1
Views: 3355

Ka and Kb able to tell acid/base weak or strong?

For the section on weak acids and bases, if only Ka or Kb are given, is there a way to tell whether the acid/base will be weak or strong?
Sun Aug 21, 2011 12:09 pm
Forum: Conjugate Acids & Bases
Topic: Clarification for Ka and Kb
Replies: 1
Views: 280

Re: Clarification for Ka and Kb

All your statements are correct.
Sun Aug 21, 2011 12:09 pm
Forum: Conjugate Acids & Bases
Topic: Clarification for Ka and Kb
Replies: 1
Views: 280

Clarification for Ka and Kb

I wanted to clarify the concept of Ka (aciditiy constant) and Kb (basicity constant). We know that when Ka is a large number, such as 10-1, then it is a stronger acid because it has greater [H3O+]. So if Kb is also a large number such as 10-1, then it should also be a stronger base compared to a Kb ...
Sun Aug 21, 2011 12:09 pm
Forum: Conjugate Acids & Bases
Topic: Are all carbonic acids generally considered to be weak?
Replies: 1
Views: 340

Re: Are all carbonic acids generally considered to be weak?

Since carbonic acid, H2CO3 has Ka1 = 4.3 x 10^-7, it is a weak acid.
Sun Aug 21, 2011 12:08 pm
Forum: Conjugate Acids & Bases
Topic: Are all carbonic acids generally considered to be weak?
Replies: 1
Views: 340

Are all carbonic acids generally considered to be weak?

Are all carbonic acids generally considered to be weak?
Sun Aug 21, 2011 12:08 pm
Forum: Conjugate Acids & Bases
Topic: Does Kw = [H3O+][OH-] = 1.0 x 10-14 only apply pure water?
Replies: 1
Views: 968

Re: Does Kw = [H3O+][OH-] = 1.0 x 10-14 only apply pure wat

No, it is applicable to situations in which water is the solvent. Kw is always constant for a given temperature, and that is why we can calculate pH upon addition of acid or base in the first place.
Sun Aug 21, 2011 12:08 pm
Forum: Conjugate Acids & Bases
Topic: Does Kw = [H3O+][OH-] = 1.0 x 10-14 only apply pure water?
Replies: 1
Views: 968

Does Kw = [H3O+][OH-] = 1.0 x 10-14 only apply pure water?

Does the equation Kw = [H3O+][OH-] = 1.0 x 10-14 only apply to pure water?
Sun Aug 21, 2011 12:07 pm
Forum: Conjugate Acids & Bases
Topic: HClO has pKa =7.53. How is it acid if its pH is >7
Replies: 1
Views: 1401

Re: HClO has pKa =7.53. How is it acid if its pH is >7

You are confused between pH and pKa which are very different. pKa tells the degree of dissociation of an acid. pKa= -logKa and Ka = [H3O+]*[A-]/[HA]. The smaller the the pKa, the larger the Ka meaning the acid is strongly dissociated into H3O+. So indeed HClO is a strong acid compare to HBrO (pKa = ...
Sun Aug 21, 2011 12:07 pm
Forum: Conjugate Acids & Bases
Topic: HClO has pKa =7.53. How is it acid if its pH is >7
Replies: 1
Views: 1401

HClO has pKa =7.53. How is it acid if its pH is >7

HClO which has a pKa of 7.53. How is it an acid if its pH is greater than 7? Is it dependent on whether is a proton donor rather than the pH?
Sun Aug 21, 2011 12:05 pm
Forum: Conjugate Acids & Bases
Topic: Why need autoprotolysis if the PH is greater than 6 ?
Replies: 1
Views: 363

Re: Why need autoprotolysis if the PH is greater than 6 ?

In the pH range of ~6-8, the hydronium ion concentration provided by the weak acid is comparable to that of the autoprolysis of water. Because of this, the latter cannot be ignored because neither one of the hydronium ion sources is dominant enough to ignore the other. To take into account the autop...
Sun Aug 21, 2011 12:05 pm
Forum: Conjugate Acids & Bases
Topic: Why need autoprotolysis if the PH is greater than 6 ?
Replies: 1
Views: 363

Why need autoprotolysis if the PH is greater than 6 ?

Why must autoprotolysis need to be taken into account if the pH is greater than 6?
Sun Aug 21, 2011 12:05 pm
Forum: Conjugate Acids & Bases
Topic: How do I know whether I am supposed to use the Ka or the Kb?
Replies: 1
Views: 11593

Re: How do I know whether I am supposed to use the Ka or the

If you have a weak base in soln then use Kb. If a weak acid then use Ka. Remember you can always convert Ka to Kb and Kb to Ka. Ka x Kb = 10^-14
Sun Aug 21, 2011 12:04 pm
Forum: Conjugate Acids & Bases
Topic: How do I know whether I am supposed to use the Ka or the Kb?
Replies: 1
Views: 11593

How do I know whether I am supposed to use the Ka or the Kb?

How do I know whether I am supposed to use the Ka or the Kb?
Sun Aug 21, 2011 12:04 pm
Forum: Conjugate Acids & Bases
Topic: How do you tell when to use Ka and Kb when solving problems?
Replies: 1
Views: 776

Re: How do you tell when to use Ka and Kb when solving probl

Usually Kb is used if the initial species are bases and Ka when your initial species are acids.
Sun Aug 21, 2011 12:04 pm
Forum: Conjugate Acids & Bases
Topic: How do you tell when to use Ka and Kb when solving problems?
Replies: 1
Views: 776

How do you tell when to use Ka and Kb when solving problems?

How do you tell when to use Ka and Kb when solving problems?
Sun Aug 21, 2011 12:03 pm
Forum: Conjugate Acids & Bases
Topic: HCO3- can act acid and base, how do you tell which it is
Replies: 1
Views: 22650

Re: HCO3- can act acid and base, how do you tell which it i

HCO3- (known as bicarbonate) is the conjugate base of H2CO3, a weak acid, and the conjugate acid of the carbonate ion. HCO3- acts as a base when mixed with a compound that is more acidic than itself (larger Ka) and as an acid when mixed with a compound that is more basic than itself (smaller Ka). Ac...
Sun Aug 21, 2011 12:03 pm
Forum: Conjugate Acids & Bases
Topic: HCO3- can act acid and base, how do you tell which it is
Replies: 1
Views: 22650

HCO3- can act acid and base, how do you tell which it is

It seems as if HCO3- can act as both a base and an acid. How do you tell which it is?
Sun Aug 21, 2011 12:02 pm
Forum: Conjugate Acids & Bases
Topic: KF has PH higher than 7 why KBr is neutral?
Replies: 1
Views: 776

Re: KF has PH higher than 7 why KBr is neutral?

HF is a weak acid, so F- from KF will pick up a proton from water to produce OH-.
Sun Aug 21, 2011 12:02 pm
Forum: Conjugate Acids & Bases
Topic: KF has PH higher than 7 why KBr is neutral?
Replies: 1
Views: 776

KF has PH higher than 7 why KBr is neutral?

The pH for the KF solution is above 7, but the pH for KBr is neutral. I don't understand why they're so different.
Sun Aug 21, 2011 12:01 pm
Forum: Conjugate Acids & Bases
Topic: How does HF, a weak acid, have F- as a weak base?
Replies: 1
Views: 878

Re: How does HF, a weak acid, have F- as a weak base?

It is a sliding scale for the strength of acids and the strength of the conjugate base. The equation Kw=Ka*Kb tells us what the books says that "the stronger the acid the weaker the conjugate base", and vice versa. However, this doesn't exclude the fact that weak acids will have weak conju...
Sun Aug 21, 2011 12:01 pm
Forum: Conjugate Acids & Bases
Topic: How does HF, a weak acid, have F- as a weak base?
Replies: 1
Views: 878

How does HF, a weak acid, have F- as a weak base?

How does HF, a weak acid, have F- as a weak base?
Sun Aug 21, 2011 12:01 pm
Forum: Conjugate Acids & Bases
Topic: why does KF have a pH greater than 7 and not a pH equal to 7
Replies: 1
Views: 4183

Re: why does KF have a pH greater than 7 and not a pH equal

Because F- is the anion of a weak acid (remember that HF is NOT a strong acid like the rest of the hydrohalic acids). The conjugate base of a weak acid is in fact basic in solution, raising the pH above 7. Both HBr and KOH are strong acids and bases, respectively. Conversely, Br- and K+ must be very...
Sun Aug 21, 2011 12:00 pm
Forum: Conjugate Acids & Bases
Topic: why does KF have a pH greater than 7 and not a pH equal to 7
Replies: 1
Views: 4183

why does KF have a pH greater than 7 and not a pH equal to 7

Anions of strong acids are such weak bases that they have no significant effect on the pH of a solution and are considered basic in water, why does KF have a pH greater than 7 and not a pH equal to 7? Why is the pH 7 and not above 7 for KBr?
Sun Aug 21, 2011 12:00 pm
Forum: Conjugate Acids & Bases
Topic: How do highly electronegative atoms diffuse net charge?
Replies: 1
Views: 328

Re: How do highly electronegative atoms diffuse net charge?

If you draw the Lewis structure for the conjugate base of HClO4 which is ClO4-. You will soon see that the anion is greatly stabilized by many resonance structures. Second, remember that O is more electronegative then Cl, so all O=Cl bonds would pull the electron densities away from the "-"...
Sun Aug 21, 2011 11:59 am
Forum: Conjugate Acids & Bases
Topic: How do highly electronegative atoms diffuse net charge?
Replies: 1
Views: 328

How do highly electronegative atoms diffuse net charge?

How do highly electronegative atoms in a polyatomic conjugate base (like trichloroacetate) create a "chain effect" that diffuses the net charge and makes it more stable? Is this why a higher oxidation number for the central atom of an oxoacid (e.g. HClO4) makes it a stronger acid when depr...
Sun Aug 21, 2011 11:59 am
Forum: Conjugate Acids & Bases
Topic: Strong acid-> strong or conjugate base?
Replies: 3
Views: 428

Re: Strong acid-> strong or conjugate base?

No. If you have a strong acid, that means that it is totally deprotonated in solution. A strong base would be completely protonated in solution-- so the conjugate of either would have to be weak or else, by definition, the conjugate acid or base would completely ionize again to form the original aci...
Sun Aug 21, 2011 11:58 am
Forum: Conjugate Acids & Bases
Topic: Strong acid-> strong or conjugate base?
Replies: 3
Views: 428

Strong acid-> strong or conjugate base?

If there is a strong acid, then does that mean it has a strong or weak conjugate base? And how about for the strong base ?
Sun Aug 21, 2011 11:57 am
Forum: Lewis Acids & Bases
Topic: Why is SbF5 considered a lewis acid?
Replies: 1
Views: 1501

Re: Why is SbF5 considered a lewis acid?

The Sb has an empty d-orbital that can accept an electron pair.
Sun Aug 21, 2011 11:57 am
Forum: Lewis Acids & Bases
Topic: Why is SbF5 considered a lewis acid?
Replies: 1
Views: 1501

Why is SbF5 considered a lewis acid?

Why is SbF5 considered a lewis acid?
Sun Aug 21, 2011 11:56 am
Forum: Lewis Acids & Bases
Topic: SbF5, lone pairs on F? it act as base?
Replies: 1
Views: 660

Re: SbF5, lone pairs on F? it act as base?

The Sb has an empty d-orbital while the F lone pairs are tightly held.
Sun Aug 21, 2011 11:56 am
Forum: Lewis Acids & Bases
Topic: SbF5, lone pairs on F? it act as base?
Replies: 1
Views: 660

SbF5, lone pairs on F? it act as base?

I have a question about SbF5 as a lewis acid/base. What about all the lone pairs on the F atoms? Couldn't these be donated so that SbF(5) would act as a base? Or is it because of the electronegativity of F that that won't happen?
Sun Aug 21, 2011 11:56 am
Forum: Lewis Acids & Bases
Topic: Compare H2O and H2S
Replies: 1
Views: 2801

Re: Compare H2O and H2S

Your reasoning is correct but there are more factors that determine e- pair availability and it turns out that H20 is more basic. Clearly their is a balance between the larger negative charge and the availability of the lone pairs. In the case of H20 versus H2S, the larger negative charge favors H20...
Sun Aug 21, 2011 11:55 am
Forum: Lewis Acids & Bases
Topic: Compare H2O and H2S
Replies: 1
Views: 2801

Compare H2O and H2S

According to the solution manual H20 is more basic or is a stronger Lewis base than H2S because oxygen is more electronegative than S and has a higher partial negative charge. But if O is more electronegative than S, wouldn't that mean that O has a greater pulling force of electrons than S? And if t...
Sun Aug 21, 2011 11:55 am
Forum: Lewis Acids & Bases
Topic: how to distinguish a Lewis Acid from a lewis base
Replies: 1
Views: 248

Re: how to distinguish a Lewis Acid from a lewis base

A Lewis base must have a lone pair of electrons avialable to pick up a proton. A Lewis acid must be able to accept a pair of electrons. Since boron in BF3 has 6 valence electrons it can accept 2 more giving it an octet. In many cases it is helpful to know the Lewis structure or the electron configur...
Sun Aug 21, 2011 11:54 am
Forum: Lewis Acids & Bases
Topic: how to distinguish a Lewis Acid from a lewis base
Replies: 1
Views: 248

how to distinguish a Lewis Acid from a lewis base

I am unsure how to distinguish a Lewis Acid from a lewis base. For example, how do we know that BF3 is a Lewis acid?
Sun Aug 21, 2011 11:54 am
Forum: Lewis Acids & Bases
Topic: Why did AlCl3 get substituted by Al(H2O)6?
Replies: 1
Views: 339

Re: Why did AlCl3 get substituted by Al(H2O)6?

Al3+ forms a complex with water as ligands and Al3+ is a Lewis acid; therefore, AlCl3 gets substituted by Al(H2O)6.
Sun Aug 21, 2011 11:53 am
Forum: Lewis Acids & Bases
Topic: Why did AlCl3 get substituted by Al(H2O)6?
Replies: 1
Views: 339

Why did AlCl3 get substituted by Al(H2O)6?

Why did AlCl3 get substituted by Al(H2O)6?
Sun Aug 21, 2011 11:53 am
Forum: Lewis Acids & Bases
Topic: How is AlCl3 acidic?
Replies: 1
Views: 861

Re: How is AlCl3 acidic?

Small, highly charged cations (Fe3+, Al3+, etc.,) form weekly acidic solutions by interacting with water and the water releasing a proton. When Al3+ is disolved in water, it becomes hydrated, and the hydrated form acts as a Bronsted-Lowry acid.
Sun Aug 21, 2011 11:53 am
Forum: Lewis Acids & Bases
Topic: How is AlCl3 acidic?
Replies: 1
Views: 861

How is AlCl3 acidic?

How is AlCl3 acidic?
Sun Aug 21, 2011 11:52 am
Forum: Lewis Acids & Bases
Topic: Why are pyridine, H+, and AlCl3 considered Lewis Acids?
Replies: 1
Views: 452

Re: Why are pyridine, H+, and AlCl3 considered Lewis Acids?

Pyridine is a base, it is basic because of the nitrogen on it that can donate its electron pair. H+ and AlCl3 are acidic because H+ and Al(3+) are electron deficient.
Sun Aug 21, 2011 11:52 am
Forum: Lewis Acids & Bases
Topic: Why are pyridine, H+, and AlCl3 considered Lewis Acids?
Replies: 1
Views: 452

Why are pyridine, H+, and AlCl3 considered Lewis Acids?

Why are pyridine, H+, and AlCl3 considered Lewis Acids?
Sun Aug 21, 2011 11:51 am
Forum: Lewis Acids & Bases
Topic: How to determine acidic or basic if no H+ and OH-
Replies: 1
Views: 299

Re: How to determine acidic or basic if no H+ and OH-

Electronegativity can be useful, as the more electronegative a substance is, the stronger the acid it is. Another useful tool is by considering either its lewis structure or its electron configuration and determining if it is likely to gain or lose electrons.
Sun Aug 21, 2011 11:50 am
Forum: Lewis Acids & Bases
Topic: How to determine acidic or basic if no H+ and OH-
Replies: 1
Views: 299

How to determine acidic or basic if no H+ and OH-

How do you identify whether species are acidic or basic if presented with a molecule that doesn't have the common H- for acids and OH- for bases?
Sun Aug 21, 2011 11:49 am
Forum: Amphoteric Compounds
Topic: Should Bi2O2 be basic or amphoteric?
Replies: 1
Views: 233

Re: Should Bi2O2 be basic or amphoteric?

It is amphoteric.
Sun Aug 21, 2011 11:48 am
Forum: Amphoteric Compounds
Topic: Should Bi2O2 be basic or amphoteric?
Replies: 1
Views: 233

Should Bi2O2 be basic or amphoteric?

Should Bi2O2 be basic or amphoteric?
Sun Aug 21, 2011 11:48 am
Forum: Amphoteric Compounds
Topic: In water, should we assume HSO4- acts as an acid or a base.
Replies: 1
Views: 1815

Re: In water, should we assume HSO4- acts as an acid or a ba

These compounds are amphiprotic, meaning that in water they can behave as both a proton donor or a proton acceptor (acid or a base). In general it is difficult to determine the pH of an amphiprotic compound (how to do that is discussed more in Section 10.15, which is not part of your assigned readin...
Sun Aug 21, 2011 11:48 am
Forum: Amphoteric Compounds
Topic: In water, should we assume HSO4- acts as an acid or a base.
Replies: 1
Views: 1815

In water, should we assume HSO4- acts as an acid or a base.

In water, should we assume HSO4- acts as an acid or a base. Also for HCO3-?

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