CH 102 Final Exam Prep
What are the best practices for using burets?
- Always make sure the buret is clean before and after use - Always condition the buret with the titrant prior to filling - Fill the buret past the zero calibration mark - Avoid air bubbles in the pipet tip; these can be removed using the stopcock - Always condition and fill a buret above the sink - Burets are read to the nearest 0.01 mL
What are the best practices for using centrifuges?
- Always place tubes of equal volume opposite each other to balance the rotor - Never put stoppers or other items in the centrifuge - Always close the lid and wait until the rotor slows down to open it - Never slow the rotor with your hand; wait for it to stop completely before removing test tubes - Ideal centrifugation is 30 seconds
What are the best practices for using pH probes?
- Be very careful when using pH probles - When not in use, place the probes in a pH 7 buffer solution - Clean pH probes with deionized water and blot them dry between liquids
What are the best practices for titration?
- Condition and fill a buret with the titrant, making sure to get rid of air bubbles in the pipet tip using the stopcock - Condition a graduated cylinder with the analyte, and then pour it into the receiving beaker - Indicators can be used to find the endpoint - Add the titrant in small increments using the stopcock, until a color change is apparent for at least 30 seconds (this is the endpoint)
What are the best practices for using graduated cylinders?
- Make sure it is clean (no water drops) - Measure using the bottom of the meniscus
What are the best practices for using Bunsen burners?
- Review Bunsen burner precautions - To extinguish a Bunsen burner, turn off gas at the bench valve - Regulate gas flow with the gas regulator knob - Use the rotating sleeve to adjust the airflow and control the flame
Give examples of proper lab attire.
- Shirt must cover the shoulders - Shirt and pants must overlap ~6" in the middle to cover the torso - Pants must extend to the ankles - Close-toed shoes must be worn - Safety goggles must be worn
What are the best practices for using an analytical balance?
- The balance must be level - Do not lean on the bench while operating the balance - Close the draft shield doors and make sure the display indicates 0.0000 g - Never weigh solid or liquid reagents directly on the pan; use weighing paper or a container - Tare any containers before weighing the solid/liquid - Don't dispense chemicals into a container while it is on the balance pan/don't place wet glassware on the pan - If you overshoot target mass, put it in the waste container or retain it in the experiment - Let hot objects cool before weighing - Read to the nearest 0.001 g
List the recommended precautions for using Bunsen burners.
- The burner must never be left unattended - Flammable liquids should never be heated with a Bunsen burner - The area above a burner must be clear before it is lit - Substances being heated should never be pointed at people - If the flame blows out, the gas must be turned off to prevent explosions - The area near the burner must be clear of flammables
https://imgur.com/a/azcg39c Match the images below the graph to the different labeled sections of the graph.
1) B 2) A 3) D 4) C 5) E
How do you write net precipitation reactions? How do you identify the spectator ions?
1) Break up each compound into the cation and anion component. 2) Cross out any ions that are always soluble per the solubility rules. These are the spectator ions. 3) Match the combinations that are left (cation to anion) 4) Write the cation(aq) and anion(aq) on the reactant side 5) Write the precipitate (s) on the product side. Balance the products and reactants for a neutral precipitate, using the lowest common multiple. You can do this by criss-crossing the charges. 6) Balance the reaction by putting coefficients in from of the reactants to match the subscripts of the precipitate.
List the steps for drawing a lewis structure.
1) Find the ER (electrons required). For all elements but Hydrogen, this can be calculated as: 8 * (# of atoms of that element) For Hydrogen: 2 * (# of Hydrogen atoms) Add together. 2) Find the VE (# of valence electrons). 3) Find the SP (shared pairs) by subtracting ER - VE and then dividing the difference by two. 4) Find the LP (lone pairs) by: LP = 1/2(VE - (2 * SP)) 5) Draw the Lewis structure.
How do you determine the number of atoms per unit cell and the chemical formula given a picture of an ionic solid?
1) Focus on one of the ions first. Count how many are corner atoms, edge atoms and full atoms (atoms inside the unit cell). Unit cells have 1/8 of a corner atom, 1/4 of an edge atom and 100% of whole atoms, so multiply these by the numbers of corner, edge and full atoms of the ions present. (1/8 * x) + (1/4 * y) * (z) 2) Do the same thing for the other ion. 3) Add these two quantities together to find the number of atoms per unit cell. 4) To find the chemical formula, set up a ratio of the number of atoms of one ion vs. the number of atoms of the other. Simplify.
How do you write a net Bronsted acid-base reaction given a substance and the pH of the aqueous solution?
1) Identify the pH and whether it indicates that the substance is acidic or basic. If the pH < 7, the substance is acidic and the reaction will involve hydronium ions in the product. If the pH > 7, the substance is basic and the reaction will involve hydroxide ions in the product. 2) Write the reaction, making sure to not include any spectator ions (e.g. Ca, Li) and by making sure charges are correct on both sides. For acid substances: A + H_2O --> Conjugate Base + H_3O^+ For basic substances: B + H_2O --> Conjugate acid + OH^-
Given a reaction with an initial and final temperature, how do you: 1) Find the temperature change? 2) Identify the reaction as exothermic or endothermic? 3) Indicate what's know about the reaction's entropy?
1) deltaT = Tfinal - Tinitial 2) Pay attention to what the system is and what the surroundings are. For example, if you want to dissolve a compound in water, the compound is the system and water is the surroundings. You can find the temperature of water before and after the dissolution to see if it (water) lost or gained heat. If it (the surroundings) lost heat, this means the compound (the system) gained heat and the reaction is ENDOTHERMIC. If the surroundings gained heat, this means that the system lost heat and the reaction is EXOTHERMIC. 3) Entropy is defined as the number of ways energy can be distributed in a system. It increases when the reaction is endothermic and spontaneous, since the system now has more ways to distribute more energy. Entropy usually cannot be determined for exothermic reactions.
What is a supernatant?
A supernatant is the liquid remaining above the precipitate after centrifugation.
What is the AX_mE_n terminology?
AX_mE_n A = central atom X = surrounding atoms; m is the number of atoms E = lone pair on central atom A; n is the number of lps
What is the effect of adding a reactant/product to a system at equilibrium? Of removing a reactant/product?
Adding material shifts the equilibrium towards the opposite side of the equilibrium to consume the extra material. Removing material shifts the equilibrium towards the same side of the equilibrium to replace the removed material.
https://imgur.com/PsmYTeJ What is the object shown in the image? What is it used for?
Analytical balance Analytical balances are used for very accurate measurements of mass to the nearest 0.001 g.
How do you find atomic volume and volume ratios for different atoms if you're given atomic radii?
Atomic volume = (4/3) * pi * r^3 where r is the atomic radii. To find volume ratios, divide the volume of one atom by the volume of another.
https://imgur.com/DBAZ491 Name the image above.
Body-centered cubic
https://imgur.com/249Xlqn What is the object shown in the image? What is it used for?
Bunsen burner Bunsen burners are used as a heating source in the laboratory.
https://imgur.com/iVK8IbS What is the object shown in the image? What is it used for?
Buret Burets are used for accurately dispensing variable volumes of liquids or solutions.
https://imgur.com/n8o9oIm What is the object shown in the image? What is it used for?
Centrifuge Centrifuges are used to rapidly settle precipitates in solution.
How do you determine hybridization?
Count the number of bonding regions (s for one region, p for the next, p^2, p^3, etc.)
How can you find the density of an object given the mass and volume?
D = m/v
What is decantation?
Decantation is the pouring of the supernatant into another test tube after centrifugation, without disturbing the solid.
Describe the changes that molecules undergo when heat is applied during a phase change.
During a phase change, heat energy is used to move molecules further apart, as well as overcome the intermolecular forces between molecules.
How do you determine standard cell potential?
Ecell = Ecathode- Eanode
How do you find the formal charge of an atom?
FC = VE - (NB + B)
https://imgur.com/ZvxXOrd Name the image above.
Face-centered cubic
How do you determine which ions precipitate and which ions remain in the supernatant?
Given a reagent, you can use the solubility rules to determine which ions form a precipitate with the ions of the reagent. Those that do not are the ones that remain in the supernatant.
https://imgur.com/LbqLQlJ What is the object shown in the image? What is it used for?
Graduated cylinder Graduated cylinders are used to measure and dispense known volumes of liquids.
What is the general response to chemical exposure?
If you spill chemicals on yourself, you should: 1. Flush the affected area with plenty of water. 2. Have your lab partner notify the instructor. If you inhale vapors enough to cause issues, you should: 1. Move outside to fresh air. 2. Have your lab partner notify the instructor.
Describe the changes molecules undergo when heat is applied to a single phase.
In a single phase, heat energy causes an increase in the bond vibrations within the molecule, as well as an increase in the kinetic energy of the molecules and therefore raising the temperature.
What is the effect of raising the temperature of a system at equilibrium?
It shifts the equilibrium towards the higher energy side of the equilibrium.
How do you write an equilibrium expression?
K = [Products]^a / [Reactants]^b MUST BE AQ or GAS (cannot be pure solid or liquid)
List the geometry, shape and bond angle for an AX_2 compound.
Linear, 180
How do you determine the molarity of an analyte in a sample?
M = mol/L moles of solute in a liter of solution
How do you determine the mass percent of an analyte in a sample?
Mass % = [mass of acid in sample]/[mass of solution titrated] * 100
List the geometry, shape and bond angle for an AX_6 compound.
Octahedral, 90
List the geometry, shape and bond angle for an AX_3E_3 compound.
Octahedral, T-shaped, 90
List the geometry, shape and bond angle for an AX_2E_4 compound.
Octahedral, linear, 90
List the geometry, shape and bond angle for an AX_4E_2 compound.
Octahedral, square planar, 90
List the geometry, shape and bond angle for an AX_5E compound.
Octahedral, square pyramidal, 90
https://imgur.com/8UTiE3V What is the object shown in the image? What is it used for?
Pipet Pipets are used to deliver a known volume of a liquid.
How do you write dissolution reactions?
Reactant (s) --> Product (aq) + Product (aq) - Make sure the products and reactants are balanced in their stoichiometric ratio. Example: Na2CO3(s) --> 2Na^+(aq) + CO_3^2-(aq)
https://imgur.com/gD2AhC2 Name the image above.
Simple cubic
What is the difference between a strong acid and a weak acid?
Strong acids dissociate completely and have a K value that is much greater than 1 (extensive). This means that the product hydronium concentration is high. Weak acids don't dissociate as much and have a K value that is much less than 1. This means that not much hydronium is produced (reactant-favored).
TRUE or FALSE: Safety glasses must be worn at all times in the laboratory.
TRUE
List the geometry, shape and bond angle for an AX_4 compound.
Tetrahedral, 109.5
List the geometry, shape and bond angle for an AX_2E_2 compound.
Tetrahedral, bent, 109.5
List the geometry, shape and bond angle for an AX_3E compound.
Tetrahedral, trigonal pyramidal, 109.5
In a battery, which half reaction occurs in the compartment leading up to the anode (-)?
The oxidation half reaction.
In a battery, which half reaction occurs in the compartment leading up to the cathode (+)?
The reduction half reaction.
Acids and oxidants present what hazards?
They are corrosive and produce irritating vapors.
How do you determine the mmol of a titrant or analyte?
Titrant: mmoles_base = [M_base * V_base] x 1000 M_base = M (mol/L) V_base = Liters The mmol of titrant is equal to the mmol of analyte.
List the geometry, shape and bond angle for an AX_5 compound.
Trigonal bipyramidal, 90 (lateral) / 120 (horizontal)
List the geometry, shape and bond angle for an AX_3E_2 compound.
Trigonal bipyramidal, T-shaped, 90 (lateral) / 120 (horizontal)
List the geometry, shape and bond angle for an AX_2E_3 compound.
Trigonal bipyramidal, linear, 90 (lateral) / 120 (horizontal)
List the geometry, shape and bond angle for an AX_4E compound.
Trigonal bipyramidal, seesaw, 90 (lateral) / 120 (horizontal)
List the geometry, shape and bond angle for an AX_3 compound.
Trigonal planar, 120
List the geometry, shape and bond angle for an AX_2E compound.
Trigonal planar, bent, 120
Know how to convert b.w units (review units)
Use dimensional analysis
How are volume and pressure related with regards to the ideal gas law? What is the equation for this relationship?
Volume and pressure are inversely proportional given a constant temperature. If volume increases, pressure decreases and vice versa. This is Boyle's Law, and the equation is: P1V1 = P2V2
https://imgur.com/IpPtxrR What is the object shown in the image? What is it used for?
Volumetric flask Volumetric flasks are used to make solutions with very accurately known concentrations.
What are the different ways wastes can be discarded?
Wastes can be: - Flushed down the sink with plenty of water - Placed into a waste container on the side shelf - Placed into a labeled beaker in the work area, which can then be emptied into a waste container
How do you determine the hydronium ion concentration given a pH value?
[H3O^+] = 10^-pH
Given two reactants, a table with the reduction reactions and the standard state reduction potential, how do you: a) Write the net redox reaction that occurs b) Calculate the standard cell potential c) Identify the strong and weak reducing and oxidizing agents
a) Determine which reactant is the oxidant and which is the reductant using the table with reduction reactions. The oxidant will be the one closest to the bottom left corner of the table, and the reductant will be the one closest to the top right. Write the half reactions. Write the net redox reactions as a combination of the half reactions, ensuring that the electrons completely cancel out. b) Ecell = Ecathode (reductant) - Eanode (oxidant) c) See letter a.
How do you determine the mass of an analyte in a sample?
g_acid = MW_acid * moles_acid MW_acid = molar mass of acid