Chemistry 1027A/B Lecture Notes - Lecture 8: Molar Mass, Stoichiometry, Reagent

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15 Mar 2015

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Given solubilities in gl-1: divide by molar mass to get x. Given ksp: write equation out and find ksp formula, solve for x. Given ksp & concentration of one product: solve for ksp equation and plug in values. Given ksp & concentration of one product & volume of solution: solve for other concentration, use concentration & volume to find moles, use moles, stoichiometry & molar mass to find mass. Given two molarities & two volumes: find concentrations after mixing volumes, solve for ksp. Given two molarities, two volumes & ksp asked to find if precipitates: solve for concentrations after mixing, solve for q equation, compare q to ksp. Given ph: solve for concentration of oh, oh = x or 2x solve for x, use volume to find moles from concentration, find mass with stoichiometry & molar mass. How many grams precipitated: find limiting reagent, find final concentration of one product in solution.

Related Questions

You are to make 90.0 mL of a 0.27 M buffer at ph 7.20 using the acid form of the Good buffer EPPS (MW = 252.332 g / mol, pKa = 8.00)

Questions:

1. Using the molarity, volume, and molecular weight, calculate how many grams of solid EPPS you need to weigh out?

2. Using the Henderson-Hasselbalch equation and the information given, calculate the value of [A-] / [HA]

3. Using the value of [A-] / [HA] calculated in question 2 and the concentration given at the beginning (Conc.), solve for x in this equation:

[A-] / [HA] = x / (Conc. -x)

4. The unknown x is in units of Molar. Given the volume from the beginning, how many moles of NaOH would this be?

5. Calculate how many mL of a 1 M NaOH solution you would need for the number of moles calculated in the previous question.

When making a buffer using two solutions - one of the conjugate acid, one of the conjugate base - the calculations are very similar.

You are to make 100.0 mL of a 0.50 M acetate buffer ( pKa = 4.72) at ph 5.00 using 0.50 M stocks of acetic acid and sodium acetate

6. Using Henderson-Hasselbalch and the information given, calculate the value of [A-] / [HA]

7. Reuse the equation from questions 3, but in place of Conc. use the final volume (100 mL) of the solution. The unknown (x) is now the volume of base form we need to add. Using [A-] / [HA] calculated in questions 6 and the equation shown, solve for x.

8. If the final volume is the total of the acid and base solutions, how many mL of the acid form do you need to combine with the base form in the previous question?

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Chemistry 1027A/B Lecture Notes - Lecture 8: Molar Mass, Stoichiometry, Reagent

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