Search found 17646 matches

by Chem_Mod
Mon Aug 22, 2011 12:42 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: For a pH of 7.21, what is the acceptable range?
Replies: 1
Views: 262

Re: For a pH of 7.21 acceptable, what is the range?

Answer: The 6-8 answer is a little rough. Stay with the +/- 1 range for a good buffer solution. 6.2 to 8.2 is fine.
by Chem_Mod
Mon Aug 22, 2011 12:42 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: For a pH of 7.21, what is the acceptable range?
Replies: 1
Views: 262

For a pH of 7.21, what is the acceptable range?

Question: Since the pH region is +/-1 pH, is the range of 6-8 for a pH of 7.21 acceptable, or should it be 6.21-8.21? Should this be rounded before finding the pH range?
by Chem_Mod
Mon Aug 22, 2011 12:34 am
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Can we use H-H eq to calc pH after the addition of titrant?
Replies: 1
Views: 209

Re: Can we use H-H eq to calc pH after the addition of titra

Answer: Use the H-H equation for a buffer solution when you know both the initial acid concentration and initial salt concentration.
by Chem_Mod
Mon Aug 22, 2011 12:34 am
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Can we use H-H eq to calc pH after the addition of titrant?
Replies: 1
Views: 209

Can we use H-H eq to calc pH after the addition of titrant?

Question: When do you use the Henderson-Hasselbalch equation? In regards to titrations of a weak acid & strong base (or) weak base and strong acid, can the Henderson-Hasselbach equation be applied to calculate the pH after an addition of a titrant (strong acid or base) instead of using the quad...
by Chem_Mod
Mon Aug 22, 2011 12:29 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Effect of replacing hydrogens of central C in acetic acid
Replies: 1
Views: 211

Re: Effect of replacing hydrogens of central C in acetic aci

They stabilize the anion by withrawing e- density away from the COO- .
by Chem_Mod
Mon Aug 22, 2011 12:29 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Effect of replacing hydrogens of central C in acetic acid
Replies: 1
Views: 211

Effect of replacing hydrogens of central C in acetic acid

How does replacing the hydrogens around the central carbon in acetic acid with halogen atoms facilitates proton donation? Wouldn't the halogens exert a stronger pull on the proton?
by Chem_Mod
Sun Aug 21, 2011 4:26 pm
Forum: Trends in The Periodic Table
Topic: Knowledge of Periodic Table you need to know
Replies: 1
Views: 192

Re: Knowledge of Periodic Table you need to know

Answer: You must know all the s and p-block elements and the 1st transition row (up to zinc) which we discussed in class.
by Chem_Mod
Sun Aug 21, 2011 4:26 pm
Forum: Trends in The Periodic Table
Topic: Knowledge of Periodic Table you need to know
Replies: 1
Views: 192

Knowledge of Periodic Table you need to know

Question: How much of the Aufbau principle and the Periodic Table will we have to know? Do we have to all the exceptions of the transition metals, or just in general?
by Chem_Mod
Sun Aug 21, 2011 4:23 pm
Forum: *Shrodinger Equation
Topic: Meaning and Effectiveness of Shielding
Replies: 1
Views: 332

Re: Meaning and Effectiveness of Shielding

Answer: Shielding means that inner electrons shield the outer electrons from the positive charge of the nucleus. Electrons in S-orbitals are more effective at shielding.
by Chem_Mod
Sun Aug 21, 2011 4:22 pm
Forum: *Shrodinger Equation
Topic: Meaning and Effectiveness of Shielding
Replies: 1
Views: 332

Meaning and Effectiveness of Shielding

Question: What is shielding? What is meant by less effective shielding and more effective shielding?
by Chem_Mod
Sun Aug 21, 2011 4:18 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Predict diamagnetic and paramagnetic
Replies: 1
Views: 338

Re: Predict diamagnetic and paramagnetic

The bond number tells you only the number of bonds. You have to look at the MO energy diagram to determine if there are unpaired e-.
by Chem_Mod
Sun Aug 21, 2011 4:18 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Predict diamagnetic and paramagnetic
Replies: 1
Views: 338

Predict diamagnetic and paramagnetic

Does the bond number obtained predict if a molecule is diamagnetic or paramagnetic? Or is it just predicted by checking if there are unpaired electrons? If the bond number that is obtained has a half (e.g 2.5) does that make it paramagnetic and if the number is a whole (e.g 3) does that make it diam...
by Chem_Mod
Sun Aug 21, 2011 4:16 pm
Forum: Resonance Structures
Topic: In resonance structure, do we need equivalent structures?
Replies: 1
Views: 287

Re: In resonance structure, do we need equivalent structures

Answer: Resonance structures must have the same number of single and double bonds but the double bonds are in different positions. Formal charges will be the same for resonance structures. Different Lewis Structures have different numbers of bonds. Formal charges will NOT be the same for different ...
by Chem_Mod
Sun Aug 21, 2011 4:16 pm
Forum: Resonance Structures
Topic: In resonance structure, do we need equivalent structures?
Replies: 1
Views: 287

In resonance structure, do we need equivalent structures?

Question: When referring to resonance structures, do all the structures have to be equivalent (do they have to have the same number of double bonds, single bonds, etc.)? For example in the SO2 example, one of the resonance structures has two double bonds whereas the others have only single bonds. A...
by Chem_Mod
Sun Aug 21, 2011 4:13 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: HOMO-LUMO e- transition and absorption spectrum
Replies: 1
Views: 367

Re: HOMO-LUMO e- transition and absorption spectrum

In HOMO to LUMO transitions. e- transitions give rise to UV and visible absorption spectrum. e- transition from highest occupied molecular orbital to the lowest unoccupied molecular orbital is a HOMO to LUMO transition.
by Chem_Mod
Sun Aug 21, 2011 4:13 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: HOMO-LUMO e- transition and absorption spectrum
Replies: 1
Views: 367

HOMO-LUMO e- transition and absorption spectrum

What are e- transitions in with respect to molecular orbitals (HOMO-LUMO), and how do they give rise to absorption spectrum?
by Chem_Mod
Sun Aug 21, 2011 4:10 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Bond enthalpy and unpaired electrons relation
Replies: 1
Views: 196

Re: Bond enthalpy and unpaired electrons relation

In F----F both atoms have 3 lone pairs of e- which results in e-/e- repulsion which weakens the bond. No you can't predict magnetism from the LE model.
by Chem_Mod
Sun Aug 21, 2011 4:10 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Bond enthalpy and unpaired electrons relation
Replies: 1
Views: 196

Bond enthalpy and unpaired electrons relation

How is bond enthalpy related to presence of unpaired electrons? Is it possible to predict whether a molecule is paramagnetic or diamagnetic from the Localized Electron model of the molecule?
by Chem_Mod
Sun Aug 21, 2011 4:02 pm
Forum: Sigma & Pi Bonds
Topic: Cylindrically symmetrical meaning
Replies: 1
Views: 519

Re: Cylindrically symmetrical meaning

Answer: The object looks like a water pipe.
by Chem_Mod
Sun Aug 21, 2011 4:02 pm
Forum: Sigma & Pi Bonds
Topic: Cylindrically symmetrical meaning
Replies: 1
Views: 519

Cylindrically symmetrical meaning

Question: What does it mean to be cylindrically symmetrical?
by Chem_Mod
Sun Aug 21, 2011 3:55 pm
Forum: Formal Charge and Oxidation Numbers
Topic: XeO4 single bonds, why not double as formal charge suggest?
Replies: 1
Views: 942

Re: XeO4 single bonds, why not double as formal charge sugge

Answer: Check the number of valence e- for each atom.
by Chem_Mod
Sun Aug 21, 2011 3:54 pm
Forum: Formal Charge and Oxidation Numbers
Topic: XeO4 single bonds, why not double as formal charge suggest?
Replies: 1
Views: 942

XeO4 single bonds, why not double as formal charge suggest?

Question: The XeO4 molecule has an Xe atom has O atoms surrounding with single bonds. According to formal charge, the more stable atom would be with double bonds all around, but the book displays single bonds. Why is this so?
by Chem_Mod
Sun Aug 21, 2011 3:48 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Concentration and rate of the reaction
Replies: 1
Views: 218

Re: Concentration and rate of the reaction

Yes that's true, but the concentration of reactants is decreasing.
by Chem_Mod
Sun Aug 21, 2011 3:48 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Concentration and rate of the reaction
Replies: 1
Views: 218

Concentration and rate of the reaction

Is it true that when a reaction first starts its forward reaction is very fast and as the concentration of the reactants decrease, the rate of the forward reaction rate also decreases. So can we say, as concentration increases, the rate of a reaction increases?
by Chem_Mod
Sun Aug 21, 2011 3:41 pm
Forum: Ideal Gases
Topic: The difference: ideal gas, ideal condition, ideal behavior
Replies: 1
Views: 369

Re: The difference: ideal gas, ideal condition, ideal behavi

An ideal gas is a made up of gas molecules that do not attract or repel each other. Ideal conditions would be low pressure and a temp range were the molecules remain in the gas phase.
by Chem_Mod
Sun Aug 21, 2011 3:41 pm
Forum: Ideal Gases
Topic: The difference: ideal gas, ideal condition, ideal behavior
Replies: 1
Views: 369

The difference: ideal gas, ideal condition, ideal behavior

When we talk about gases and equilibrium, what are the differences between an ideal gas, ideal conditions, and ideal behavior?
by Chem_Mod
Sun Aug 21, 2011 3:36 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: P(total) for products and reactants at constant temperature
Replies: 1
Views: 296

Re: P(total) for products and reactants at constant temperat

Only if the total number of moles remained constant. Since PV = nRT and if T and V is constant then P will remain constant only if n remains constant.
by Chem_Mod
Sun Aug 21, 2011 3:36 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: P(total) for products and reactants at constant temperature
Replies: 1
Views: 296

P(total) for products and reactants at constant temperature

Does P(total) remain constant for products and reactants of a reaction if the temperature remains constant? In other words, if the temperature remained constant, would P(total) in equilibrium be equal to P(total)not in equilibrium (but in the same temperature)??
by Chem_Mod
Sun Aug 21, 2011 3:27 pm
Forum: Ionic & Covalent Bonds
Topic: Anions size, covalent, and solubility issue
Replies: 1
Views: 435

Re: Anions size, covalent, and solubility issue

Answer: Because more e- are pulled into the bonding region between the atoms. The higher the e- density in the bonding region, the more covalent the bond. Ionic species are more soluble in water than covalent molecules.
by Chem_Mod
Sun Aug 21, 2011 3:27 pm
Forum: Ionic & Covalent Bonds
Topic: Anions size, covalent, and solubility issue
Replies: 1
Views: 435

Anions size, covalent, and solubility issue

Question: Why is it that as anions become bigger, they become more covalent and therefore insoluble?
by Chem_Mod
Sun Aug 21, 2011 3:21 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: neutral bromine atom the d orbitals are completely filled
Replies: 1
Views: 318

Re: neutral bromine atom the d orbitlas are completely fille

Answer: The 3d orbitals must be filled before the 4p. However the 4d orbitals in Br are empty.
by Chem_Mod
Sun Aug 21, 2011 3:21 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: neutral bromine atom the d orbitals are completely filled
Replies: 1
Views: 318

neutral bromine atom the d orbitals are completely filled

Question: Can you explain why in the neutral bromine atom the d orbitals are completely filled?
by Chem_Mod
Sun Aug 21, 2011 3:18 pm
Forum: Bond Lengths & Energies
Topic: Double Bond and Single Bond Length
Replies: 1
Views: 246

Re: Double Bond and Single Bond Length

Answer: Consider what a double bond consists of, which is a sigma bond and a pi bond. A single bond merely has a sigma bond. Therefore, in order to break a double bond, one must supply energy equal to both bonds. Therefore, a double bond is a much more stabler bond. It is analogous to why one stick...
by Chem_Mod
Sun Aug 21, 2011 3:18 pm
Forum: Bond Lengths & Energies
Topic: Double Bond and Single Bond Length
Replies: 1
Views: 246

Double Bond and Single Bond Length

Question: Can you explain why double bonds are shorter than single bonds?
by Chem_Mod
Sun Aug 21, 2011 1:28 pm
Forum: *Indicators
Topic: How do we know which indicator to use for an acid/base?
Replies: 1
Views: 604

Re: How do we know which indicator to use for an acid/ base?

Answer: You should know one example each of an indicator for titration with acidic, neutral and basic stoichiometric point. The indicator should change color where you expect the endpoint to be.
by Chem_Mod
Sun Aug 21, 2011 1:27 pm
Forum: *Indicators
Topic: How do we know which indicator to use for an acid/base?
Replies: 1
Views: 604

How do we know which indicator to use for an acid/base?

Question: How do we know which indicator to use for an acid/base?
by Chem_Mod
Sun Aug 21, 2011 1:27 pm
Forum: *Indicators
Topic: Would thymol blue be a valid indicator along with phenolph?
Replies: 1
Views: 586

Re: Wouldn't thymol blue be a valid indicator along with phe

Answer: Yes. Often there is more than one suitable indicator to use in a titration.
by Chem_Mod
Sun Aug 21, 2011 1:27 pm
Forum: *Indicators
Topic: Would thymol blue be a valid indicator along with phenolph?
Replies: 1
Views: 586

Would thymol blue be a valid indicator along with phenolph?

Question: Wouldn't thymol blue be a valid indicator along with phenolphthalein?
by Chem_Mod
Sun Aug 21, 2011 1:26 pm
Forum: *Indicators
Topic: Use "thymol blue" for both basic and acidic indicator?
Replies: 1
Views: 721

Re: can we use"thymol blue" for both a basic and acidic indi

Answer: This is possible, but make sure you know what color changes will occur for whether you are finding an acidic stoichiometric point or a basic stoichiometric point.
by Chem_Mod
Sun Aug 21, 2011 1:26 pm
Forum: *Indicators
Topic: Use "thymol blue" for both basic and acidic indicator?
Replies: 1
Views: 721

Use "thymol blue" for both basic and acidic indicator?

Question: "thymol blue" is listed as both an acidic and basic indicator with ranges (1.2-2.8) and (8.0 - 9.6), is this an error? If it is not, then can we use it for both a basic and acidic indicator?
by Chem_Mod
Sun Aug 21, 2011 1:25 pm
Forum: *Indicators
Topic: Indicator application, (Indicator below 7)
Replies: 1
Views: 516

Re: indicator application, (Indicator below 7)

Answer: Yes. Be careful with interpreting the color changes. Methyl orange, for example, would change from yellow to red.
by Chem_Mod
Sun Aug 21, 2011 1:25 pm
Forum: *Indicators
Topic: Indicator application, (Indicator below 7)
Replies: 1
Views: 516

Indicator application, (Indicator below 7)

Question: For the indicators with a pH range of color change below 7 used for a titration of a weak base with a strong acid?
by Chem_Mod
Sun Aug 21, 2011 1:25 pm
Forum: *Indicators
Topic: Consider the reaction involving indicator if it produce H+?
Replies: 1
Views: 623

Re: consider the reaction involving indicator if it produce

Answer: Yes, even though the indicators do have an effect on the hydronium concentration, indicators are used in minute concentrations so that their effect is negligible. At the same time, their colors are still intense enough to be observed at very low concentration.
by Chem_Mod
Sun Aug 21, 2011 1:24 pm
Forum: *Indicators
Topic: Consider the reaction involving indicator if it produce H+?
Replies: 1
Views: 623

Consider the reaction involving indicator if it produce H+?

Question: Do we consider the reaction involving an indicator, which produces hydronium ions, as insignificant when considering the change in the concentration of hydronium ions?
by Chem_Mod
Sun Aug 21, 2011 1:23 pm
Forum: *Indicators
Topic: Must have pH indicators within +/- 1 of our given PH?
Replies: 1
Views: 585

Re: must have pH indicators within +/- 1 of our given PH?

Answer: No they don't need to be within 1 pH unit. However phenolphthalein is not appropriate for a neutral solution.
by Chem_Mod
Sun Aug 21, 2011 1:22 pm
Forum: *Indicators
Topic: Must have pH indicators within +/- 1 of our given PH?
Replies: 1
Views: 585

Must have pH indicators within +/- 1 of our given PH?

Question: Do the pH's that used to represent acidic, neutral, and basic solutions need to have pH indicators within +/- 1 of our pH values given exactly or they be represented with extremes? For example to represent a neutral solution at a pH=7 can we use phenolphthalein even though its pH value is...
by Chem_Mod
Sun Aug 21, 2011 1:21 pm
Forum: *Titrations & Titration Calculations
Topic: When to use ICE box and when can just use info directly
Replies: 1
Views: 267

Re: when to use ICE box and when can just use infor directly

Answer: Need to use the ice box whenever there is a weak acid or weak base.
by Chem_Mod
Sun Aug 21, 2011 1:20 pm
Forum: *Titrations & Titration Calculations
Topic: When to use ICE box and when can just use info directly
Replies: 1
Views: 267

When to use ICE box and when can just use info directly

Question: I'm working on the titration questions and I'm having trouble determining when I need an ICE box and when I can just use the information given. Which cases call for an ICE box, and which don't?
by Chem_Mod
Sun Aug 21, 2011 1:20 pm
Forum: *Titrations & Titration Calculations
Topic: How to determine how a salt affect pH without know reactant
Replies: 1
Views: 273

Re: How to determine how a salt affect pH without know react

Answer: From the salts obtained you can determine what the original species were (strong/weak acid/base). For each combination of strong/weak acid/base we know the pH at the stoichiometric point. E.G, for the first one the conjugate base is NH3 and the conjugate acid is HBr, meaning that we are tit...
by Chem_Mod
Sun Aug 21, 2011 1:20 pm
Forum: *Titrations & Titration Calculations
Topic: How to determine how a salt affect pH without know reactant
Replies: 1
Views: 273

How to determine how a salt affect pH without know reactant

Question: How do you determine how a salt will affect pH without knowing the reactants?
by Chem_Mod
Sun Aug 21, 2011 1:19 pm
Forum: *Titrations & Titration Calculations
Topic: How is the initial concentration of a base determined?
Replies: 1
Views: 291

Re: How is the initial concentration of a base determined?

Answer: To calculate the Kb, you just need the information given at the beginning of the problem about the initial pH (before any acid is added). If the moles of base and the initial volume is know, the initial molarity of the base can be calculated. The base behaves as the following equilibrium: B...
by Chem_Mod
Sun Aug 21, 2011 1:18 pm
Forum: *Titrations & Titration Calculations
Topic: How is the initial concentration of a base determined?
Replies: 1
Views: 291

How is the initial concentration of a base determined?

Question: How is the initial concentration of a base determined? Does the total volume need to be known?
by Chem_Mod
Sun Aug 21, 2011 1:18 pm
Forum: *Titrations & Titration Calculations
Topic: Do we ignore the hydronium ions that may be generated?
Replies: 1
Views: 224

Re: do we ignore the hydronium ions that may be generated?

Answer: For titrations, this is usually the case. Assume that it is a new problem in that the acid hasn't had time to react with water yet before adding the strong base. This makes the calculation easier, and it doesn't effect the answer too much (especially as the Ka becomes smaller and smaller si...
by Chem_Mod
Sun Aug 21, 2011 1:16 pm
Forum: *Titrations & Titration Calculations
Topic: Do we ignore the hydronium ions that may be generated?
Replies: 1
Views: 224

Do we ignore the hydronium ions that may be generated?

Question: In titrations, do we ignore the hydronium ions that may be generated and solve the equation as if starting a new problem?
by Chem_Mod
Sun Aug 21, 2011 1:16 pm
Forum: *Titrations & Titration Calculations
Topic: Reaction of acetic acid and sodium hydroxide, why use CH3CO2
Replies: 1
Views: 428

Re: reaction of acetic acid and sodium hydroxide, why use CH

Answer: If the concentrations of acetic acid and NaOH are equal, then the titration is at the equivalence (stoichiometric) point. Therefore, NaOH is not used to calculate the pH because it has all been consumed. You must use the Kb equation for acetate to determine the amount of [OH-] generated.
by Chem_Mod
Sun Aug 21, 2011 1:15 pm
Forum: *Titrations & Titration Calculations
Topic: Reaction of acetic acid and sodium hydroxide, why use CH3CO2
Replies: 1
Views: 428

Reaction of acetic acid and sodium hydroxide, why use CH3CO2

Question: In a reaction of acetic acid and sodium hydroxide, why do we use CH3CO2- to find the pH of the titration rather than NaOH?
by Chem_Mod
Sun Aug 21, 2011 1:15 pm
Forum: *Titrations & Titration Calculations
Topic: Volume of solution double at the stoichiometric point?
Replies: 1
Views: 401

Re: volume of solution double at the stoichiometric point?

Answer: This is a special case when the acid and base have the same molarity. At the stoichiometric point, moles of acid are equal to the moles of base. If the acid and base have the same molarity, they must also have the same volumes in order to have the same moles (M1V1 = M2V2 so if M1 = M2, then...
by Chem_Mod
Sun Aug 21, 2011 1:14 pm
Forum: *Titrations & Titration Calculations
Topic: Volume of solution double at the stoichiometric point?
Replies: 1
Views: 401

Volume of solution double at the stoichiometric point?

Question: Does the volume of solution double at the stoichiometric point?
by Chem_Mod
Sun Aug 21, 2011 1:14 pm
Forum: *Titrations & Titration Calculations
Topic: How to determine mol of acid without knowing volume at stoic
Replies: 1
Views: 268

Re: How to determine mol of acid without knowing volume at s

Answer: The stoichiometric point is a special point in a titration where the moles of acid added equals the moles of base. If the moles of base are known (from the concentration and volume), then it is also equal to the moles of acid. If we know the moles of acid and the concentration of acid then ...
by Chem_Mod
Sun Aug 21, 2011 1:13 pm
Forum: *Titrations & Titration Calculations
Topic: How to determine mol of acid without knowing volume at stoic
Replies: 1
Views: 268

How to determine mol of acid without knowing volume at stoic

Question: How do we determine the amount in mols of an acid without knowing the volume at stoichiometric point?
by Chem_Mod
Sun Aug 21, 2011 1:13 pm
Forum: *Titrations & Titration Calculations
Topic: How can you find the pH at halfway titration?
Replies: 1
Views: 185

Re: How can you find the pH at halfway titration?

Answer: Halfway point just means that the moles of added acid = half of the moles of base (moles acid = (1/2)moles base). For weak bases, pOH=pKb (and pH=pKa for weak acids). However, for the titration of a weak base by a strong acid just calculate how much acid and base you start with, and how muc...
by Chem_Mod
Sun Aug 21, 2011 1:13 pm
Forum: *Titrations & Titration Calculations
Topic: How can you find the pH at halfway titration?
Replies: 1
Views: 185

How can you find the pH at halfway titration?

Question: How can you find the pH at halfway titration?
by Chem_Mod
Sun Aug 21, 2011 1:12 pm
Forum: *Titrations & Titration Calculations
Topic: How is concentration at the halfway point calculated?
Replies: 1
Views: 276

Re: How is concentration at the halfway point calculated?

Answer: First figure out the volume of the equivalence point, which was 10mL of HCl. Thus halfway there is 5 mL, adding this to the 5 mL of NaOH we started with gives a total volume of 10 mL. Then, just use the number of moles to find concentration.
by Chem_Mod
Sun Aug 21, 2011 1:11 pm
Forum: *Titrations & Titration Calculations
Topic: How is concentration at the halfway point calculated?
Replies: 1
Views: 276

How is concentration at the halfway point calculated?

Question: How is concentration at the halfway point calculated? For example, use the equivalence point of 10mL of HCl and 5mL NaOH.
by Chem_Mod
Sun Aug 21, 2011 1:11 pm
Forum: *Titrations & Titration Calculations
Topic: How is # of mols of titrant calculated at the stoic. pt?
Replies: 1
Views: 197

Re: How is #of moles of titrant calculated at the stoichiome

Answer: Calculate the moles initially present of the species being titrated and know that this is equal to the moles of titrant at the stoichiometric point.
by Chem_Mod
Sun Aug 21, 2011 1:10 pm
Forum: *Titrations & Titration Calculations
Topic: How is # of mols of titrant calculated at the stoic. pt?
Replies: 1
Views: 197

How is # of mols of titrant calculated at the stoic. pt?

Question: How is the number of moles of titrant calculated at the stoichiometric point?
by Chem_Mod
Sun Aug 21, 2011 1:10 pm
Forum: *Titrations & Titration Calculations
Topic: When should we assume equilibrium has been reached
Replies: 1
Views: 199

Re: When should we assume equilibrium has been reached

Answer: It's an approximation not to consider the slight change in the reactants due to equlibrium of weak acids and bases. Every time we do a titration calculation, we act like we are starting over again, with pure reactants. We assume that the small amount of conjugate acid/base that we made will...
by Chem_Mod
Sun Aug 21, 2011 1:10 pm
Forum: *Titrations & Titration Calculations
Topic: When should we assume equilibrium has been reached
Replies: 1
Views: 199

When should we assume equilibrium has been reached

Question: When should we assume equilibrium has been reached before the titrant is added and when do we not make this assumption?
by Chem_Mod
Sun Aug 21, 2011 1:09 pm
Forum: *Titrations & Titration Calculations
Topic: How do you write out an equation where HCl is added to NaOH?
Replies: 1
Views: 324

Re: How do you write out an equation where HCl is added to N

Answer: Remember acid + base = salt + water. The acid and base will dissociate: H+ + Cl- + Na+ + OH- ----> Na+ + Cl- + H2O. Ans2: If its a titration then again write salt + water. Also strong base and weak acid gives alkaline soln. At stoichiometric pt soln is basic (salt + water), then look to see...
by Chem_Mod
Sun Aug 21, 2011 1:09 pm
Forum: *Titrations & Titration Calculations
Topic: How do you write out an equation where HCl is added to NaOH?
Replies: 1
Views: 324

How do you write out an equation where HCl is added to NaOH?

Question: How do you write out an equation for the strong acid-strong base titration where HCl is added to NaOH? My other question is it says NaOH is added to HCOOH; what does this equation look like for this strong base-weak acid titration? The book has HCOO- + H2O ---> HCOOH + OH-. Why is it not ...
by Chem_Mod
Sun Aug 21, 2011 1:09 pm
Forum: *Titrations & Titration Calculations
Topic: Calculating molarity in an equilibrium rxn
Replies: 1
Views: 200

Re: CH3COOH + OH- <--> CH3COO- + H2O, molarity of CH3COO- ?

Answer: At the equivalence point, the moles of acid = moles of base (i.e. moles CH_{3}COOH = moles of OH^{-} ). When these two react, they produce water and CH_{3}COO^{-} , so from this reaction, you can figure out the moles of CH_{3}COO^{-} produced. To find the molarity of the CH_{3}COO^{-} , you...
by Chem_Mod
Sun Aug 21, 2011 1:08 pm
Forum: *Titrations & Titration Calculations
Topic: Calculating molarity in an equilibrium rxn
Replies: 1
Views: 200

Calculating molarity in an equilibrium rxn

Question: How to you calculate the molarity of
in the equilibrium reaction: ?
by Chem_Mod
Sun Aug 21, 2011 1:08 pm
Forum: *Titrations & Titration Calculations
Topic: At HALF stoichiometric point, why does pH = pKa
Replies: 1
Views: 1098

Re: At HALF stoichiometric point, why does pH = pKa

Answer: At half stoichiometric point, the moles of the titrant (say NaOH) = half the moles of analyte (say CH3COOH). Knowing this and that CH3COOH reacts with NaOH to give CH3COO- and H2O, you find that at the halfway stoichiometric point, you have equal amounts of CH3COOH and CH3COO-. Plugging the...
by Chem_Mod
Sun Aug 21, 2011 12:58 pm
Forum: *Titrations & Titration Calculations
Topic: At HALF stoichiometric point, why does pH = pKa
Replies: 1
Views: 1098

At HALF stoichiometric point, why does pH = pKa

Question: At HALF stoichiometric point, why does pH = pKa (or pOH = pKb)?
by Chem_Mod
Sun Aug 21, 2011 12:58 pm
Forum: *Titrations & Titration Calculations
Topic: How is the pH at the stoichiometric point calculated?
Replies: 1
Views: 503

Re: How is the pH at the stoichiometric point calculated?

Answer: At the stoichiometric point, the moles of acid = moles of base. This means that the added NaOH reacts with all of the CH3COOH. This reaction produces CH3COO- and H2O. So now all that remains is CH3COO- and H2O. Finding the pH of this solution is found with an ice box, find the concentration...
by Chem_Mod
Sun Aug 21, 2011 12:57 pm
Forum: *Titrations & Titration Calculations
Topic: How is the pH at the stoichiometric point calculated?
Replies: 1
Views: 503

How is the pH at the stoichiometric point calculated?

Question: How is the pH at the stoichiometric point calculated?
by Chem_Mod
Sun Aug 21, 2011 12:57 pm
Forum: *Titrations & Titration Calculations
Topic: Amount of acid/base not equal to original amount, why?
Replies: 1
Views: 216

Re: amount of acid/base not equal to original amount, why ?

Answer: When we do titration calculations, we assume that we are restarting the titration with every calculation, so at each step the reactions between species will be different, leading to a difference in left over product. It depends on how much of the reactant dissociates.
by Chem_Mod
Sun Aug 21, 2011 12:55 pm
Forum: *Titrations & Titration Calculations
Topic: Amount of acid/base not equal to original amount, why?
Replies: 1
Views: 216

Amount of acid/base not equal to original amount, why?

Question: When solving titrations, the amount of acid/base sometimes doesn't add up to the original amount of acid/base before the neutralization, why is this so?
by Chem_Mod
Sun Aug 21, 2011 12:54 pm
Forum: *Titrations & Titration Calculations
Topic: Tiration of weak acid with strong base
Replies: 1
Views: 485

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 ...
by Chem_Mod
Sun Aug 21, 2011 12:53 pm
Forum: *Titrations & Titration Calculations
Topic: Tiration of weak acid with strong base
Replies: 1
Views: 485

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...
by Chem_Mod
Sun Aug 21, 2011 12:53 pm
Forum: *Titrations & Titration Calculations
Topic: Titration calculations for strong/weak acid/base
Replies: 1
Views: 279

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+].
by Chem_Mod
Sun Aug 21, 2011 12:52 pm
Forum: *Titrations & Titration Calculations
Topic: Titration calculations for strong/weak acid/base
Replies: 1
Views: 279

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...
by Chem_Mod
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: 240

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.
by Chem_Mod
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: 240

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?
by Chem_Mod
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: 205

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.
by Chem_Mod
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: 205

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?
by Chem_Mod
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: 339

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.
by Chem_Mod
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: 339

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.
by Chem_Mod
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: 447

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...
by Chem_Mod
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: 447

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...
by Chem_Mod
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: 255

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...
by Chem_Mod
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: 255

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...
by Chem_Mod
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: 455

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.
by Chem_Mod
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: 455

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?
by Chem_Mod
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: 3261

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) ...
by Chem_Mod
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: 3261

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?
by Chem_Mod
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: 7491

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...
by Chem_Mod
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: 7491

(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?
by Chem_Mod
Sun Aug 21, 2011 12:36 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Why are buffers used?
Replies: 1
Views: 418

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...
by Chem_Mod
Sun Aug 21, 2011 12:35 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Why are buffers used?
Replies: 1
Views: 418

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?

Go to advanced search