chem lab procedures etc

Experiment 1: Measurements I: Density of a Liquid Purpose

Practice measuring devices such as balances, graduated cylinders, and volumetric pipette and determine density of a liquid

Exp 1: Density Formula

Density = Mass/ Volume

Exp 1: How many places is a buret read to?

2 decimal places

Exp 1: If your pipet was calibrated incorrectly so that it transferred 5% too much solution, how would it affect the liquid's density?

If the pipet transferred too much solution into a flask, it would add to the mass. Therefore, it would make the numerator (D=M/V) larger and make the density larger.

Exp 1: Which measured best?

Graduated cylidner gave best results,

Experiment 2: Emission of Light from Hydrogen and Metal Atoms Purpose

The purpose of this lab is to examine the emission spectrum of Hydrogen and identify unknown metal ions using a flame test

Exp 2: How does a spectroscope work?

Light is emitted from a discharge tube and refracted into each color. Each line in spectrum is light of a particular wavelength. Scale readings of spectroscope correspond to known wavelengths and a calibration curve is created.

Exp 2: Why is a calibration curve needed?

Scale on spectroscope is not super accurate

Exp 2: How are frequency and wavelength related?

As frequency increases, wavelength decreases and energy increases. Wavelength and Frequency are inversely related while Energy and Frequency are directly related

Exp 2: Rydberg Equation

n1 is lower energy level, n2 is higher

Exp 2: Rydberg constant?

Rh = 1.097 x 10^7 m^-1

Exp 2: Energy equation

E=hv where h is planck constant

Exp 2: Which series returns to n1=1? And which region of spectrum does this correspond to?

Lyman series. Corresponds to ultraviolet Balmer (n1=2) corresponds to visible Paschen (n1=3) corresponds to infrared

Exp 2: Flame Test?

Heating metal atoms excited the electrons and when they come back down they release a photon which corresponds to some wavelength

How is energy of light and frequency related?

E= hv (planck constant times frequency) meaning it is directly related

Of the following lines in the emission spectrum of helium, which corresponds to the highest energy electron transition?

Lowest wavelength means highest energy transition

EXP 3: Density of a Solid Purpose

The purpose of this lab is to determine the density of a solid through indirect means

Exp 3 procedure

Weigh 25 mL Erlenmyer flask with and without water and divide by density to get volume. Get mass of water surrounding metal by subtracting mass of stoppered flask water metal from mass of empty flask and mass of metal. Divide mass of water by density to get volume. Subtract volumes to get volume of metal. Divide by mass to get density.

One of the lines in the hydrogen atom emission spectrum occurs in the UV region at 397 nm. It results from a transition from an upper energy level to n=2. What is the principle quantum number of the upper energy level?

Solve for higher level (n^2 h)

A graduated cylinder is filled with water to the 25.0 mL mark. After 27.5 g of a solid is added, the volume is 31.5 mL. What is the density of the solid to the proper number of sig figs

31.5 - 25.0 = 6.5 mL 27.5/6.5 = 4.2 g/cm^3

Lab 4: Paper Chromatography Purpose

The purpose of this lab is to create a chromatogram of food dye and to determine unknown ions

Exp 4 Procedure

Add drops of food dye to paper, place in beaker with 1M NaCl and allow it to come up

Do the same thing for part B but with metal ions and NH3

Exp 4: Rf formula

Distance component moved/ Distance solvent moved Can never be greater than 1 since its a ratio

Exp 4: Solvent Front

The solvent front is the distance the solvent moves

Exp 4: Mobile Phase?

The component that interacts most strongly with the mobile (liquid) phase will travel up the paper at a faster rate - thus it will travel the greatest distance in the same amount of time

Exp 5: Using Models to Predict Molecular Structure Purpose

The purpose of this lab is to practice constructing molecules

Exp 5: What is electronegativity

The tendency of an atom to attract electrons

Exp 5: What atoms can possess more than an octet

Elements in the third row and below in the periodic table can form compounds in which they have greater than eight valence electrons. P and Cl are both in the third row.

Exp 5: How to count formal charge?

Formal charge is Valence electrons - bonding electrons (Bonding electrons count as one each, so a single bond counts as one electron, a double bond counts as two)

Exp 5: When is a molecule unstable?

When it breaks the octet rule (and is not allowed to)

Exp 6: Water of Hydration: Purpose

The purpose of this lab was to study the properties of hydrates by identifying them, and determining unknown hydrates

Exp 6: Procedure

Part A: Place crystals of compounds in watch glasses and leave them to see if they pick up or lose water
Part B: Clean crucible and heat it and then weigh. Weigh again with the sample, heat for 10 minutes and then weigh one more time.
Part C: Heat CuSO4 and then add water back into it. Look for physical and color changes
Part D: Heat compound in test tube to see if it is a hydrate

Exp 6: Effloresence vs Hygroscopic vs Deliquescence

Efflorescent substances lose water to air

Hygroscopic substances gain water from humid air

Deliquescent substances take up so much water that they dissolve into water

Exp 6: What defines a true hydrate?

Must release water on heating and be soluble in water

True hydrates are also reversible

Exp 6: How are crystals built

Held together by intermolecular forces like Hydrogen bonding or Dipole-Dipole bonding

Exp 6: How to calculate formula of a hydrate?

First, find the mass of the water. This can be found by subtracting the mass of the crucible, cover, and sample from the mass of the crucible, cover, and anhydrous. Divide this by 18.02 to get your mols of water. Next, find the mass of the anhydrous by subtracting the mass of the empty crucible from the anhydrous. Divide this by the molar mass of the salt. Divide the mols of water by the mols of anhydrous to get n

Exp 6: How do organic carbohydrates behave?

Lose water by being heated but the process is not reversible

Exp 7: Spectrophotometry and Beer's Law: Purpose

The purpose of this lab was to practice using a spectrophotometer and find the mass percentage of Cu in a penny

Exp 7: Procedure

A-

Insert a cuvet of red food dye into spectrometer. Get wavelength being absorbed.

B- Prepare penny solution by combining it with NO3. Find absorbance by placing into spectrometer. Find absorbance vs concentration and make calibration curve.

y=mx+b where absorbance is the y and you solve for x (concentration)

Exp 7: Beer's Law?

Absorbance = molar absorptivity (epsilon) times path length times concentration