Chem Lab

What do I need to know from Lab 9: Molarity?

Make sure to study the introductory material. You will be asked to calculate the number of grams (mass) needed to make a specific volume of solution at a specified Molarity. You will also be asked how many moles of solute are in a specific volume of a specified Molarity (moles = Volume (in L) * Molarity).

Lab manual

· Solution – another way of saying homogenous mixture. In a solution the solvent dissolves the solute, which results in a mixture of completely uniform composition.

o Water dissolves the salt and makes saltwater

· Solvent - a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid.

· Soluble – if somethings dissolves in a particular solvent its soluble, if it doesn’t its insoluble

· Unsaturated solution – can hold more solute than what it already contains

· Saturated solution – holds as much solute as it can contain at that temperature

· Super saturated solution contains more solute than it should be able to hold at a given temperature

o Generally made by heating a solvent and adding solute, then cooling the solution

· Aqueous solutions – solvent is water and polar compounds and ionic compounds tend to dissolved much better than nonpolar compounds because of the structure of the water molecule.

So far I know that in a solution the solvent (water) dissolves the solute (salt) and creates a homogenous mixture in that is completely uniform in the process. Unsaturated solutions can hold more solute than what it already contains. And saturated solution can hold more solute as it can contain at that temperature

· The math in the lab handout can help

· Molarity (m) – the molality of a solution is the number of moles of a solute that has been added to one kilogram of solvent

o The molarity of a solution is calculated by dividing the moles of solute by the volume of the solution. Molarity (M) = moles of solute (mol)/liters of solution (V)

· Percent by mass – percent of the weight of the solution that’s due to the mass of the solute

o Percent by mass = mass of solute/mass of solution x 100%

· Percent by volume – percent of the volume of the solution that’s due to the volume of the solute

o If you have 15.0 mL of alcohol that has had water added to it until the total volume is 100.0 mL, the percent by volume will be 15.0 mL/100.0 mL – 15.0%

Pre Lab Questions:

If you were to calculate the molarity of a solution form solid NaCl and water, what are some values and/or measurements that you would need in order to perform the calculation?

· The percent mass, percent by value and molarity

Using solution vocabulary, explain why McDonald’s sweet tea might taste different from sweet tea you make at home

· Sugar solute

· Tea solvent

How would you make a saturated solution unsaturated

· You dilute it by increasing the solutions volumes

Math:

· Molarity – mol solute/volume of solution

· Multiply the concentration (0.5 mols/Liters) by the volume of solution you want (0.5 Liters) to find the moles of NaCl you need. 2. Multiply the moles of NaCl by its molar mass (58.44 g/mol) to find the grams of solute needed.

What do I need to know from Lab 10: Determination of Acetic Acid in Vinegar?

Make sure to study the introductory material. You will be asked to use the formula and calculate % acetic acid (the formula will be provided). You will also be asked what the result of the experiment would be if some of the values in the experiment were changed (drops of vinegar, molarity of NaOH).k

Lab Manual:

· Active ingredient in vinegar is acetic acid, %%-*% acetic acid by weight. The formula for it is CH3COOH

· The molar mass of acetic acid is 60.06 g/mol

· The most concentrated form of acetic acid is referred to as glacial acetic acid and can form ice crystals below room temperature. Glacial acetic acid is 99.5% acetic acid and is considered 17.4 M

· Titration - process of determining the concentration of a dissolved substance in terms of the smallest amount of reagent of known concentration required to bring about a given effect in reaction with a known volume of the test solution.

· Indicator – phenolphthalein is a clear and colorless in acidic solutions like vinegar, when excess base like sodium hydroxide is added to acetic acid the phenolphthalein will turn pink

Pre-Lab questions:

How would the safety protocol for this lab change if you were using glacial acid as opposed to using vinegar

· You would need to avoid shock and friction when handling and avoiding contact with skin, eyes, and inhaling it

What would happen if you forgot to add phenolphthalein to your reaction mixture

· It would not change color

Find formular and calculate % acetic acid and other math

What do I need to know from Lab 11: Line Spectra?

Study the introductory material in your lab manual including the definitions you turned in for the pre-lab. Make sure you have a rough idea of what your line spectra looked like in the procedure section. (You will not have to identify the elements. J)

Introductory material:

· Bohr generated his atomic model based off of the spectral lines generated by hydrogen gas. In order to see the spectral lines, Bohr added energy to the hydrogen sample to excite the atoms electrons. When the atoms returned to their ground state a specific wavelength color was detected

· Atom that possesses excess energy is in an excited state – when it returns to the ground state it emits excess energy as photons of electromagnetic radiation including visible light. The internal energy states of an atom are discrete

· Each element has different characteristics discrete energy states which are different from the energy states of all other elements

Pre-Lab Questions

The wavelength of electromagnetic radiation

· The distance between waves

The frequency of electromagnetic radiation

· Speed/rate of a wave

The speed of electromagnetic radiation (speed of light)

· Light travels at the same speed as wave lengths

The around state of an atom - Electrons of the lowest energy level

Why only certain wavelengths of light are emitted by excited atoms of a given element

· Because of different # of protons and arrangement of electrons

What it means to say that energy levels of an atom are quantized

· Atoms can only exist at certain discrete energy levels electrons only have certain energy levels