Chem 1212 Lab Midterm

If an error caused the initial temperature to be larger (and the final temperature okay), how does this affect the calculation of the heat of solution (qsolution)?

The larger Tinitial would produce a smaller ΔT, which would result in a smaller q

acidic buffer

a mixture of a weak acid and the salt of its conjugate base

neutral solution

a solution whose pH equals 7

percent yield =

actual yield/theoretical yield x100%

mathematically explain how experimental errors would affect the actual yield and percent yield

if something was left behind in a beaker then the actual yield would be lower than it should be and then would affect the percent yield

(Experiment 4) if filtrate is basic and pink

indicates the ethylenediamine is in excess

(Experiment 8) In this experiment, you will be using and measuring various chemical species by a variety of units. Which units of measure is used for the temperature of water?

kelvin

Sink (large black sink)

located at the back of the lab, on the opposite side from the hood

Emergency exits (doors that leave the lab)

located at the front of the lab and also at the rear of the lab, the connecting door to adjacent labs

(Experiment 4) For the procedural error indicate if the error will affect the actual yield, and if it does does it lower or raise it? - spilling solution while transferring solid to beaker

lowers the actual yield

For the procedural error indicate if the error will affect the actual yield, and if it does does it lower or raise it? - Left some product behind in the beaker, not all in the Büchner funnel

lowers the actual yield

Density=

mass/volume

when two liquids mix completely with each other

miscible

(Experiment 8) In this experiment, you will be using the gas constant, R. Which unit is NOT found in R?

molarity

Eye wash station (in green box)

mounted on the wall by the sink

Fire extinguisher (red canister)

next to the door, by the light switch

Safety shower (drench hose)

next to the white board, on the side closest to the door

(Experiment 7) In the reaction below, classify the chemical species as the type of electrolyte. Ba(OH)2(aq) + H2SO4(aq) → BaSO4(s) + 2 H2O(ℓ) - BaSO4

nonelectrolyte

(Experiment 7) In the reaction below, classify the chemical species as the type of electrolyte. Ba(OH)2(aq) + H2SO4(aq) → BaSO4(s) + 2 H2O(ℓ) - H2O

nonelectrolyte

Fire Blanket (in large red canister)

on the opposite side of the door from the fire extinguisher

(Experiment 5) What color is expected for the product, [Ni(C2H8N2)3]Cl2 (s), if both C2H8N2 and NiCl2·6 H2O are present in the exact mole ratio needed for the reaction (neither is the limiting reagent)?

pink-violet

(Experiment 4) For the procedural error indicate if the error will affect the actual yield, and if it does does it lower or raise it? - weighing crystals while they are still wet

raises the actual yield

percent yield

ratio of the actual yield to the theoretical yield

limiting reagent

reactant which is completely consumed or "used up" during the reaction (in this experiment if it is pink & basic as well)

ability of a solid or gas to dissolve in a liquid

solubility

(Experiment 7) What is the conductivity classification for an unknown G that ionizes completely in water?

strong electrolyte

buffering capacity

the amount of acid or base that can be added before the pH changes by 1 pH unit

overall reaction rate

the rate of the slowest step

layering order from experiment 1

tube 1: 3 layers, C6H14, H20, CH2Cl2 (top to bottom) tube 2: 2 layers H20, C6H14+ CH2Cl2

Two future experiments (Exp. 11 & 12) use a bright yellow K2CrO4 solution. Using the Figure 10-2 Color Star, what color of wavelengths are being absorbed?

violet

Select all the statements that are true concerning pH and buffers.

- as an acidic solution is diluted, the pH increases - The greater the concentrations of the buffer components, the greater its buffering capacity

Select all that apply to an exothermic reaction.

- heat is the product - Removing heat (cold water bath) will cause the equilibrium to shift toward products.

If chemical gets on a large area of skin or on clothing

- notify TA - flood area with water from the safety shower for 15 minutes (you will be given other clothing before you leave the lab)

If chemical gets in your eye and you are wearing contacts

- notify TA - immediately flush the eye wash for a minute, then take out contacts and resume flushing for 15 minutes

If chemical gets on small area of skin

- notify TA - immediately run water for 15 minutes over the affected area

Reduction (gain of electrons)

B+me^- --->B^-m

(Experiment 3) red brown solid

Cu

(Experiment 3) black solid

CuO

Flame over circle

Represents: oxidizer, oxidizing agent Precautions to use: avoid mixing with other chemicals except as directed. Keep chemical away from contact with skin, eyes, or clothing. Always wear appropriate personal protective equipment

General Health Hazard

Represents: respiratory sensitizer, organ toxicity, carcinogen Precautions to use: use care when handling, avoid contact with skin, eyes, or lungs, do not eat or drink anything in the lab, always wear appropriate personal protective equipment

Skull & Crossbones

Represents: severe to fatal toxicity (generally must be ingested to become toxic) Precautions to use: avoid contact with skin and eyes, avoid inhalation, swallowing or skin contact, do not eat or drink anything in the lab, always wear appropriate personal protective equipment

In case of broken glass

-clean up broken glass -notify TA - if broken glass is on lab bench use whisk broom from spill kit to sweep up broken glass, deposit it into the broken box at front of lab - if glass is on the floor, go to stockroom to get broom and dustpan, sweep up the broken glass and deposit it into broken glass box at front of lab -never place broken glass in trash can, broken glass could harm the custodians that empty the trash cans

appropriate clothing in the lab

-long hair must be tied back -shirts must cover the shoulders and all of the torso, no plunging necklines in front or back, no midriffs, and no tears or holes - pants or long skirts must cover your legs to the ankles, pants must be loose fitting, no capris or cut offs, no tears or holes in the pants/jeans, no leggings or very tight skinny jeans - shoes must have closed heel and toe. the shoe should cover the top of the foot, no sandals, flip flops, or shoes that have holes in them (crocs)

If fire is in beaker or container

-notify TA - cover the container with a watch glass or lid to remove the oxygen

If fire is large

-notify TA - either TA or you can use fire extinguisher to put out fire, use steps of PASS (pull, aim, squeeze and sweep)

If chemical gets in your eye

-notify TA - immediately flush they eye with eye wash for 15 minutes, hold your eye open with your fingers so the water reaches your eyeball

If chemical gets on your face (goggles still in place)

-notify TA - immediately wash your face with water for 15 minutes, leaving your goggles on

If persons clothing or hair is on fire

-notify TA - smother the fire by covering the person with the fire blanket, then have the person stop, drop, and roll

In case of chemical spill

-notify TA - spill kit gives instructions on how to dispose of the chemical in the appropriate method based on its hazards -each spill kit contains: chemical absorbent pads, diasorb granules, acid neutralizer, and dustpan with small whisk broom

Personal Protective Equipment (PPE)

-splash proof goggles -chemical resistant apron -gloves when specified

oxidation (loss of electrons)

A --> A^+n + n^e-

Which definition corresponds to aliquot?

A small portion of a chemical species

Oxidation + Reduction

A+B ---> A^+n + B^-m

Combination

A+B --> AB

Decomposition

ABC --> AB+C

Single Displacement

AC+B--> A +BC

Double displacement

AC+BD --> AD+BC

How to determine limiting reagent from calculations

Find theoretical yield of both and the lowest is going to be the limiting reagent

(Experiment 6) Which of the following statements are TRUE if the standardization titration (Part II) was over‑titrated? I. The molarity of DCIP would be lowered since the volume of titrant is in the denominator of the calculation. II. Too much DCIP was added in the titration, causing the Molarity of the ascorbic acid to be lowered. III. With a lower molarity of DCIP, the amount of Vitamin C will also be lower even if the titrations in Part II were done correctly.

I and III are true

(Experiment 6) Which of the following statement(s) is/are TRUE for the citric acid titration? I. Over-titrating means too much analyte was added to the reaction. II. Since the volume of titrant is too large, multiplying by a large number in the calculation of citric acid makes the mass of citric acid too high. III. Over-titrating in this reaction produces a dark pink (or peach) solution.

II and III are true

(Experiment 7) Which statements explain the shape of the titration curve observed in lab? I. Initially, the conductivity is zero since the reaction has not begun. II. During the reaction, the conductivity decreases due to the production of nonelectrolytes. III. During the reaction, the conductivity decreases due increase of ions. IV. After the endpoint, the conductivity increases due to the excess titrant.

II and IV are true

(Experiment 8) Piers & Aida performed this experiment. Aida read the initial volume of hydrogen peroxide as 7.5 mL, but Piers read the volume as 8.5 mL. Which of the following statement(s) are TRUE about Piers' calculations? I. Piers' calculations will give a higher value of moles of O2(g) than Aida. II. Piers' calculations will give a higher partial pressure of O2(g) than Aida. III. Piers' calculations will give a lower molarity of H2O2 than Aida.

III is true

Which statement about the spectrophotometric analysis of Red 40 dye is TRUE?

If there is no Red 40 dye present in the solution, the absorbance will be zero.

For the following error, select the answer that correctly describes how it will affect the value of the final temperature of the water/solution in the calorimeter: As the aluminum rods were added, the calorimeter was knocked over and some of the water was split. The aluminum rods were still covered, but the total volume of water was less.

Increases the value of final Temperature

Fume Hood

Located at the back of the lab, on the opposite side from the sink

rate constant expression

Mathematical expression showing the relationship between the measured rate and the concentration of the reactants

(Experiment 7) Predict the conductivity of C12H22O11, a molecular compound.

Nonelectrolyte

(Experiment 7) What is the conductivity classification for an unknown C that dissolves completely in water and but doesn't dissociate into ions?

Nonelectrolyte

(Experiment 7) What is the conductivity classification for an unknown F that dissolves completely in water and doesn't have any ions present in solution?

Nonelectrolyte

(Experiment 6) Will under-titrating the end point in Part II affect the value of Molarity of DCIP?

Raises the value of Molarity of DCIP

(Experiment 6) For the error, indicate if the error will affect the mg of citric acid present per mL of juice, and if it does, will it raise or lower the value of the mg citiric acid/ mL of juice? - Diluting the NaOH solution before filling the buret

Raises the value of mg citric acid/mL juice

(Experiment 6) For the error, indicate if the error will affect the mg of citric acid present per mL of juice, and if it does, will it raise or lower the value of the mg citiric acid/ mL of juice? - Over-titrating the end point (adding too much titrant)

Raises the value of mg citric acid/mL juice

(Experiment 6) Will overtitrating the end point in Part III affect the value of mg of Vitamin C?

Raises the value of mg of Vitamin C

Environment

Represents: aquatic toxicity, environmental hazard Precautions to use: use care when handling, do not discard down the drain or in the trash. Must discard in appropriate waste container. Always wear appropriate Personal Protective Equipment.

Corrosion

Represents: corrosive to skin (chemical burn), corrosive to metals Precautions: avoid contact with skin, eyes, and clothing. Always wear appropriate Personal Protective Equipment

Flame

Represents: flammable, pyrophorics, emits flammable gases Precautions to use: keep chemical away from heat, sparks, or flames. Keep container closed when not in use. Always wear appropriate personal protective equipment.

Exclamation Mark

Represents: irritant (skin and eye), respiratory tract irritant, acute toxicity (harmful) Precautions to use: Avoid contact with skin and eyes, do not breathe vapors, do not eat or drink anything in the lab, always wear appropriate personal protective equipment

(Experiment 7) Predict the conductivity of NaBr, a soluble, ionic compound.

Strong electrolyte

Irritant

Substance that can cause itching, dryness, or sensitivity on skin or in eyes

Lachrymator

Substance that causes eyes to produce tears

Corrosive

Substance that irreversibly destroys living tissue when in contact with the skin or eyes

Hygroscopic

Substance that is moisture sensitive (can absorb water from the air)

Carcinogen

Substance that is suspected or proven to cause cancer

Toxic

Substance that may cause bodily harm through ingestion, inhalation, or skin absorption

Sully, Fay & Tia worked together on the redox titration of Fe+2 with MnO4- (Part I). Fay & Tia used the equivalence point volume of MnO4- as determined from titration graph. However, Sully used the volume of MnO4- when the solution first turned brown, which was a smaller volume than Fay & Tia's volume. Will Sully's calculations of the molarity of Fe+2 be different than Fay & Tia's calculation? How and why?

Sully's M of Fe+2 will be lower than the other two students.Since the volume of MnO4- is in the numerator for the calculation of M of Fe+2, the lower volume of MnO4- results in lower M of Fe+2

(Experiment 4) Which statement best explains what happens to the percent yield if the crystals (product) were washed with hot water?

The actual yield will decrease since part of the product will dissolve and not be recovered as a solid.Since actual yield is in the numerator, the percent yield will also decrease

Which definition corresponds to theoretical yield?

The amount of product that could be produced using a given amount of reactant.

Which definition corresponds to excess reagent?

The reactant that is present as extra material when the reaction is complete

actual yield (experimental yield)

amount of product recovered in the experiment

theoretical yield

amount of product that could be produced from the limiting reagent if the reaction were 100% efficient. calculated from the limiting reagent or reactant

To carefully pour a liquid into another container.

decant

The liquid that was carefully poured into a new container.

decantate