Gravimetric Analysis, Solutions, and Titration Flashcards

Vocabulary flashcards for quick review.

Gravimetric Analysis

A method to determine the mass of precipitate formed when combining two aqueous solutions.

Steps of Gravimetric Analysis

Weigh sample, dissolve in water, add chemical to form precipitate, filter, rinse precipitate, heat to remove water, repeat until mass is constant.

Stoichiometry

Used in gravimetric analysis for mole ratios between reactants and products, and mass to mole conversions.

Common Error in Gravimetric Analysis

Precipitate is not dry when final mass is taken, leading to a higher percent yield.

Solubility Rules Reminder

All sodium, nitrate, ammonium, and potassium compounds are soluble; these ions are excluded from net ionic equations.

Purpose of Repeated Drying

Ensures all water is driven off, leading to a constant mass of precipitate.

Making Solutions

Process of dissolving a mass of solute in a volume of solvent to achieve a specific concentration (molarity).

Steps to Making Solutions

Measure solute mass, add to volumetric flask, fill halfway with solvent, swirl to dissolve, add solvent dropwise to fill line.

Molarity Formula

Molarity = moles / liters

Common Error in Making Solutions

Overfilling volumetric flask which results in a dilute solution.

Proper Glassware for Solutions

Volumetric flask provides best precision in concentration.

Formula Mass

Used to convert mass to moles.

Dilution

Creating a solution with a smaller molarity from a solution with a larger molarity.

Steps to Dilution

Use volumetric pipette to obtain stock solution, add to volumetric flask, fill halfway with water, swirl, add water dropwise to fill line.

Dilution Formula

M1V1 = M2V2

Error in Dilution

Adding water to acid instead of acid to water which could cause splattering.

Titration

Determining the concentration of a solution with an unknown molarity by reacting it with a solution of known molarity.

Titration Steps

Dispense analyte with volumetric pipette, add indicator, add titrant from burette dropwise until color change occurs.

Equivalence Point

Moles of analyte equals moles of titrant.

Analyte

Substance in flask w/ unknown molarity.

Titrant

Substance in buret w/ known molarity.

Standard Solution

Solution of known concentration, usually goes into the buret.

Endpoint

Point in titration where flask solution changes color.

Equivalence Point

Point in the titration where the moles of acid are equal to the moles of base or moles of titrant is equal to moles of analyte

Titration Error

Overshooting the titration leading to concentration of the unknown being inaccurate.

Spectroscopy (Beer’s Law)

Creating absorbance vs concentration graphs to determine the concentration of an unknown solution or kinetics of a reaction.

Spectrophotometer

Device used to measure the absorbance of light by a sample.

Spectroscopy Step 1

Pick the wavelength for the solution where absorbance is highest (for solute).

Beer's Law equation A = εbc

Absorbance = (molar absorptivity)(cuvette pathway length)(concentration)

Spectroscopy Applications

Determining concentration of unknown using solutions of known concentration, kinetics reactions.

Spectroscopy Calibration

Calibrate the spectrophotometer with a blank of just solvent to account for absorbance due to the solvent and cuvette.

Calibration Curve

Graph absorbance vs concentration.

Spectroscopy Error: Lower Absorbance

Cuvette cleaned with distilled water and immediately filled, creating a more dilute solution.

Spectroscopy Error: Higher Absorbance

Cuvette is dirty with fingerprints/dust.

Chromatography

Separation of mixtures using differences in intermolecular forces of attraction.

Retention Factor (Rf value)

distance component traveled / distance solvent front traveled

Chromatography Substances

Substance that travels further up the paper is more attracted to the solvent.

Polar Substances

Tend to lack symmetry, have polar bonds, and have lone pairs on the central atom.

Chromatography Error

Solvent reaches the top of the paper strip which causes Rf values to be invalid.

Calorimetry

Determining the amount of heat transferred.

Calorimetry Equation

q = mCΔT where q=heat, m=mass, C=specific heat capacity, ΔT=change in temperature

Endothermic

Processes that absorb heat cause the temperature of the water in the calorimeter to decrease.

Exothermic

Processes that release heat cause the temperature of the water in the calorimeter to increase.

Calorimetry Errors

Not stirring the solution which would cause temperature variation.

Collecting Gas Over Water Goal

Determine the amount of gas produced by a reaction.

Collecting Gas Over Water Formula

PV = nRT and Total pressure = sum of the partial pressures

Gas Over Water Temp

Take the temperature of the bath to get the temperature of the gas.

Collecting Gas Over Water Source of Error

If the gas produced by the reaction is polar it will be attracted to the water.

Percent Composition of a Hydrate

Calculate the mole ratio between water and anhydrate.

Hydrated Salt

Before heating

Anhydrous Salt

After heating

Percent Composition of a Hydrate

Moles of anhydrous salt: moles of water = ratio for hydrate.

Overheating Hydrate

Anhydrous salt could decompose in the heat.

Distillation

Separation of mixtures of liquids based on boiling points

Distillate

Substance collected in the flask at the end - substance with lower boiling point

Distillation Rule

The substance with the lower boiling point has a greater vapor pressure and weaker intermolecular forces → will separate first.