CHEM 144 Lab Final (Experiments 1 - 5)

How would your experimental formula (CuxCly⋅⋅zH2O) have been affected if the final products were not dried completely before weighing it?

"x" would have been larger than it should be incomplete drying is calculated as increased amount of copper or Cu in the formula.

accuracy limit of a balance

0.001

accuracy limit of a volumetric flask

0.03

accuracy limit of graduated cylinder

1%

what is weighing by difference?

1. obtain mass of clean and dry flask 2. obtain mass of flask and solution 3. subtract mass of flask and solution by mass of flask by itself

how do you qualitatively transfer something?

1. transfer as much of the substance to a beaker as possible 2.rinse out crucible with deionized water 3-4 times 3. pour into beaker each time

If a 10 mL volumetric flask is used to measure its maximum volume, what is the measurement recorded to the correct number of significant figures?

10.00 mL (2 decimal places)

If hydrochloric acid (HCl) is sold as a 28% solution, this means that the reagent contains 28 grams of HCl per 100 grams of the solution. What is the mass of the solvent in grams?

100 - 28 = 72

Place the instructions for Experiment #2 in order: 1.Measure the mass of the popped corn. 2.Measure the mass of several unpopped popcorn kernels. 3.Pop the corn by allowing the water inside to turn to steam and expand the kernel.

2 3 1

To determine the density of a substance, it's mass and volume must be measured. Which piece of glassware will be used to measure the volume of the solution in Part II (Measurement of Solution Density)?

25 mL volumetric flask

In the acid-base reaction of aqueous citric acid with aqueous sodium hydroxide, how many moles of base are needed to react with (neutralize) one mole of citric acid?

3 moles of base to 1 mole of acid

Including both rapid and accurate titrations, how many trials are conducted in Part I (Traditional Titration Using an Indicator Dye)?

4

In Part I (Preparation of Standard Solutions), students will be preparing solutions that each have a different w/w% of sugar (range 0%-20%). How many solutions will be prepared?

5

accuracy limit of a beaker

5%

accuracy limit of an erlenmeyer flask

5%

a normal distribution occurs when ____ of data falls within plus or minus one standard deviation of the mean (xm ± 1sx);

68.3%

how many kernel samples are there?

8

For the acid-base reaction of citric acid and sodium hydroxide, the equivalence point occurs at a pH of:

8.5

In Experiment #4, you will perform the following reaction as part of the experimental procedure to determine the empirical formula of an unknown copper chloride hydrate. 3Cu2+ (aq) + 2Al (s) → 3Cu (s) + 2Al3+ (aq) What is the reducing agent in this reaction?

Aluminum is the reducing agent (oxidixed)

The purpose of this lab is to introduce you to statistical analysis and the tools necessary to analyze the data you will collect in this and other experiments this semester. In __________ you will see the topics and tools that you will need for this and other lab reports this semester (ex. definitions and equations of different items such as mean and standard deviation, rules for significant figures and rounding, etc.). Appendix II provides a tutorial in the use of _______ (this program is not required, but is very useful for repetitive calculations).

Appendix I Excel

Why must a colorless soda be used for the traditional titration method?

Because colorless sodas allow you to see a color change to faint pink.

Why are all of the answers for moles (NaOH and citric acid) reported to three significant figures?

Because the concentration of NaOH is reported to three significant figures. Because the volumes from the graduated cylinder are reported to three significant figures.

Goggles and gloves must be worn at all times for Experiment #4. Which substance, used in the experiment, is highly toxic by ingestion or inhalation and corrosive to the skin and eyes?

Hydrochloric acid

what is the titrant in this lab?

NaOH

Why was it important that the solution be colorless after the aluminum foil was added to the beaker

The lack of color indicates that the reduction of Cu2+ (aq) is complete

The purpose of adding aluminum to the copper chloride solution is to

To reduce Cu 2+ to Cu

After you've lit the Bunsen burner and transferred an unpopped kernel to the evaporating dish, it's important to heat the dish gently and keep the kernel in constant motion.

True

The popcorn kernels used in this experiment have been stored in the first floor laboratory preparation area. Therefore, they are to be regarded as laboratory chemicals (and are not to be consumed!).

True

Why should the total volume not be used in the calculations for Part 2 (titration with the pH electrode)?

Vtotal is beyond the equivalence point since the titration doesn't stop until after pH 10 If Vtotal was used, the molarity would be larger than it should be. Vtotal represents the total amount of NaOH added not the volume where the moles of acid equal the moles of base

what indicates the end point has been reached in a traditional titration?

a persistent slight pink color

polyprotic acid

an acid that has multiple acidic protons that can react with a base

monoprotic acid

an acid that has only one proton to react with a base

what color is the solution after the qualitative transfer?

blue

what color is the copper chloride originally?

blue-green

When the unknown copper chloride hydrate is heated, its color changes to _________.

brown

Which device is used to deliver and measure the volume of sodium hydroxide to the citric acid solution for both parts of the Experiment?

buret

Figure 4-1 of the lab manual shows the apparatus for popping popcorn. The distance from the flame to the bottom of the evaporating dish should be about 8-10 inches so as to prevent ___________ of the kernels.

burning

Experiment 3 introduces the concept of density, specifically, you'll be finding the density of a liquid. Students will be making a ________ curve of known _______ concentration. This curve will help to determine the sugar content of an "unknown" commercial beverage.

calibration sugar

a ______ can be used to determine the concentration of an ________ sample of a compound

calibration curve unknown

what is the analyte in this lab?

citric acid

Carbonated sodas (like Sprite® or 7-Up®) contain carbonic acid in addition to citric acid. How is it possible that the reported results are only for the molarity of citric acid and do not include other acids that are present in sodas?

citric acid is present in much higher concentrations than other acids. carbonic acid is removed when sodas are flattened.

When the redox reaction between Al (s) and Cu2+ (aq) is complete , the solution will be __________.

colorless

after the reaction between the aluminum and the copper chloride, what color is the solution

colorless

What is the name of the vessel in which you will place your unknown copper chloride hydrate sample for heating?

crucible

the density of a given beverage is _______ primarily on the _______ content

density sucrose

to convert mass to moles

divide by molar mass

all graphs made this semester should have _______ dots, connect the dots turned _____, a title, and should be ________

filled off autoscaled

precision is

how close a measured value is to repeated measurements of the same sample.

accuracy is

how close the measured value is to the actual value

One of the objectives of Experiment #4 is to use reaction stoichiometry to determine the number of moles of each of the components of a ________ binary salt.

hydrated

A substance can be characterized by physical properties such as mass, volume, color, and density. Density is an example of an intensive property meaning; it is __________ of the amount of substance present. An extensive property like volume is ____________ on the amount of substance present.

independent dependent

When graphing two variables to find their relationship, the _________ variable (the one you typically have control over the in the experiment) is plotted on the ______ axis.

independent variable x axis

There are two parts to this experiment: In the first part, you will find the linear relationship of two different data sets and you will determine the equation of the form y = mx^n. In the second part, the data set is already expressed as a linear relationship and a "y" value is provided. The purpose here is to __________ the corresponding "x" value by using the slope and intercept from the linear fit.

interpolate

why does the copper chloride solution turn brown

it was dehydrated by heating

Which soda(s) cannot be titrated using the traditional (phenolphthalein) method (Part I)?

jones green apple (green) orange crush (orange)

what is a titrant?

known concentration

The mass of the popped corn will be ____ than the mass of the unpopped corn because ______ has escaped.

less water

Linear regression (also called linear least-squares regression) is a method used to calculate the ___________ that describes the mathematical relationship between two experimental variables that have a linear relationship

line of best fit

Experiment 1 is an introduction to Graphical Analysis. Before coming to lab, you will need to download the software. What is the name of the software program?

loggerpro

Graphs will display a box with the results of the linear regression (see Figure 3-1 of the lab manual). The program displays: the slope of the graph, represented by _____ the y-intercept of the data, represented by ______ the correlation of the data (>0.99 is a great linear fit)

m b

density

mass / volume

how is the mass of chlorine calculated?

mass of dehydrated sample - mass copper

how do you calculate the mass of water evolved?

mass of hydrated - mass of dehydrated

On the y-axis, the dependent variable is plotted. This is typically the variable that is ___________ during the experiment (example: temperature or pH measurement).

measured

Any titration requires that the reaction be monitored to determine when the equivalence point has been reached. For the experiment you will conduct (Part II), the most common methods rely on:

measuring the pH

What are the units of molarity?

mol/L

how many observable end points will citric acid have?

one because all three protons have similar strengths

Classify the following experimental objectives as pertaining to "Part 1", "Part 2" or "both": to learn how to perform an acid-base titration _____________ to detect the end point of a titration based on a visual observation ________ to calculate the molarity of citric acid _________ to learn how to use pH to monitor a titration __________ to learn about acid-base indicators _________

part 1 and 2 part 1 part 1 and part 2 part 2 part 1

what is the indicator dye used?

phenolphthalein

Your group needs 8 kernels that are all popped to about the same size (you can then extinguish the Bunsen burner). Next, to determine the mass of water, subtract the mass of ________ corn from the mass of ___________ corn. The percent water is determined by dividing the mass of water by the mass of unpopped corn and multiplying by 100.

popped unpopped

Why is it important to sand the aluminum foil before it was added to the 150-mL beaker in step #10 of the procedure?

sanding exposes a reactive surface sanding removes the coating on the foil sanding increases the surface area

what is an analyte

solution of unknown concentration

what are the standard solutions?

solutions where the concentration of solute is known

Because aluminum is a more active metal than copper, this means it is a

stronger reducing agent

the mass of the solution can be found by

subtract the mass of the flask + solution by the mass of the empty flask

in experiment 3, the solute is the ______ and the solvent is the _____

sugar water

the molecular formula is

the actual number of moles of each element

Why was a crucible the more suitable vessel for this experimental procedure (rather than a beaker or an Erlenmeyer flask)?

the crucible is heat resistant because of its material

Which of the following explain the difference between the equivalence point and the end point of a titration? Select all that apply.

the equivalence point is the point of stoichiometric equivalence of moles of acid and base the end point is the point at which a titration is stopped the end point is an estimate (or overestimate) of the equivalence point the end point is the point at which the color change happened

what is the end point?

the estimate of the equivalence point the point where the indicator dye changes color

In both the traditional titration (Part 1) and the titration using the pH electrode (Part 2), you reached an estimated equivalence point. Which method gives results that align more closely to the true equivalence point and why?

the pH electrode titration because it doesn't rely on humans determining where light pink is the pH electrode titration because it shows the region of the most rapid pH change

in a modern titration, the estimate of the equivalence point (end point) is indicated by

the point of most rapid pH change

what is the equivalence point?

the point where the number of moles of base added is stoichiometrically equal to the number of moles of acid originally present in the analyte

The analytical method for this experiment is the acid-base titration. Which of the following are true regarding the acid-base titration you performed for this experiment? Select all that apply.

the reaction is monitored and goes until completion (or neutralization) one solution of known concentration is used to determine the concentration of another solution the buret contains the sodium hydroxide the stoichiometry of the reaction must be known

all weighing should be carried out on

the same balance

the empirical formula is

the simplest whole number mole ratio

In Experiment #5, students will determine the concentration of citric acid in carbonated beverages, using a solution of sodium hydroxide (NaOH) of known concentration. Using a solution of known concentration to determine the concentration of another solution through a monitored reaction of known stoichiometry that goes to completion is called a(n) ________________.

titration

What is the purpose of calculating and showing the first derivative along with your titration curve

to identify the estimated equivalence point of the titration

the 8 popped kernels should be relatively the same size

true

how do you calculate moles of NaOH

use molarity and volume to find moles

how do you find moles of citric acid?

use stoichiometry (3 base: 1 acid) divide moles NaOh by 3

how do you find molarity of citric acid

use volume and moles to find molarity

What is the purpose of the Buchner funnel?

vacuum filtration

Students will be measuring the density of aqueous solutions. "Aqueous" means that the solvent that makes up the solution is __________.

water

Unlike a solid, a liquid cannot be weighed on a balance unless it's contained. The standard method for obtaining the mass of a liquid is described in the manual and is called:

weighing by difference

When does the equivalence point occur in an acid-base titration?

when the number of moles of acid is stoichiometrically equal to the number of moles of base added.

the absorbance of the unknown sample should be _______ the range of the measurements of the known samples

within