CHM 114 Final Quiz
An empty 10.00 ml volumetric flask weighs 12.02g. Once filled with unknown, the flask weighs 23.45g. What is the density of the unknown?
D=m/v; 1.143g/ml
A tarred beaker has a mass of 26.85g. A liquid with a density of 2.03 g/ml is added to the beaker until it reaches a mass of 49.65g. How much in mL of the unknown was added to the beaker?
D=m/v; 11.23ml
What is back titration?
Excess of acid is added to react completely. Seeing amount consumed will determine concentration.
True or False. The delta H is negative change in endothermic reactions, and positive in heat releasing reactions.
False
True or False. The indicator in your experiment turns from colorless to a dark pink color at the endpoint and goes on to a faint-pink when the endpoint is overshoot.
False
If a reaction rate doubles when the concentration doubles then what is the order of the reaction?
First
If a sample od solid KNO3 is weighed and submitted to cation exchange according to the procedure of the experiment, an aqueous solution of what substance (compound) will emerge from he bottom of the Amberlite resin column?
HNO3
What are the three requirements for a chemical to be considered for use as a primary standard.
High purity, known composition, and reacts with stoichiometry
Would it be harder for the indicator or the ascorbic acid to oxidize?
Indicator
What is the rate constant of a first order action if the half life is 97 seconds?
.0071
A reaction has a rate constant of 4*10^-5 at 8C. What is the rate constant at 25C if the Ea is 140.
.00765
If 0.123 g of KNO3 were submitted to the procedures of this experiment, how many moles of the substance you identifyd would emerge (elute) from the bottom of the column?
0.00122 mol
How many mL of a 0.1002 M NaOH solution would be required to titrate the moles of substance eluded from he column in the previous question.
0.012 L
A 0.128g sample of KHP required 28.54 mL of NaOH solution to reach a phenolphthalein endpoint. Calculate the molarity of the NaOH. (molar mass of KHP = 204.23g)
0.0219 M NaOH
A 20.00 mL sample of HCl was titrated with the NaOH solution from the previous question. To reach the endpoint 23.82 mL of the NaOH. Calculate the molarity of the HCl.
0.0259
Precision
0.05% to 0.2% of desired volume; ex. volumetric flask, the pipet, and buret
A student titrates a 0.4432 g of sample of KHP with a solution of NaOH that is approximately 0.1 M. The titration requires exactly 20.85 mL of the sodium hydroxide solutions to reach the point where the indicator changes color. What is the calculated molarity of the NaOH from the titration?
0.104 M
Calculate the specific heat of an unknown metal that gave the following data: Volume of H20 = 50 mL Initial H20 Temp = 21.2 degrees celsius Initial Metal Temp = 100 degrees celsius Final Temp = 28.4 degrees celsius Mass of Metal = 22.7622
0.22 cal/(g*degrees celsius)
You have analyzed a 25.00mL sample of fruit juice, which you titrate with a 0.01002M iodine solution. Your initial buret reading is 13.28mL and your final buret reading is 18.02mL. What is the concentration of Vitamin C in the fruit juice? How much juice would you have to drink to ingest the RDA of 75mg of Vitamin C?
0.3345 g/L; 224.2mL
A 12.1187 g metal with unknown heat capacity is heated to 100 degrees celsius and then submerged into 100mL of 21.0 degrees celsius water. If the final equilibrium temperature is 26.3 degrees celsius, what is the heat capacity of the metal?
0.593 g/mol
Suppose you were given an unknown that contained 2.150g of ascorbic acid per liter of solution. What volume of a 0.01002M iodine solution would you need to reach the equivalence point if you titrated a 10.00mL sample of the ascorbic acid solution?
12.19 mL iodine
If 325 g of water at 4.2 degrees celsius absorbs 12.28 KJ of heat, what is the final temperature of the water?
13.2 degrees celsius
A student has attempted to perform today's experiment as outline in the lab 0.1198 g of unknown salt of alkali metal, MX, was introduced into the chromatography assembly. It was found that 12.05 mL of 0.9981 M NaOH solution was required to titrate the moles of the substance from the column. What is the molecular mass of this unknown salt?
9.96 g
Beer-Lambert Law
A(absorbance)=EBC (E=molar absorptivity, B= length of pathway, C= concentration)
Acid or Base: CO2 HCO3- SO2 H2SO3 SO32-
BABAB
How do you get rid of excess CO2
Boil off CO2
The phenol/hydroxide reaction is like most reactions in how to reacts to temp. Will it be faster or slower at 5C compared to room temperature?
Slower
Is the ascorbic acid redox reaction spontaneous or non spontaneous?
Spontaneous
What indicator will be used in today's reaction and what color will the solution turn when the endpoints are reacted?
Starch; turns yellow to blue/black
What is the indicator that is being used in this experiment?
phenolphalein
Indicator in soda ash experiment
phenomfythelene
What is the correct method to mix concentrated acid with water?
pour the acid into the water using a stirring rod
The kinetics experiment aims to find the ______ of a reaction
rate constant
What is the standard method to read the volume in a buret?
read from the bottom of the meniscus and remember to start reading from the top down of the buret
enthalpy of formation (delta Hf)
the heat given off when one mole of substance is prepared from its constituent
Rank the following liquids in order of decreasing acidity. Coffee, tomato juice, bleach, and milk
tomato juice > coffee > milk > bleach
After standardizing the NaOH with KHP, you begin to standardize the HCl with the standardized NaOH. While doing so you overshoot the endpoint. Does this result in a erroneous calculation for the concentration of the HCl? If so, is it too high to too low?
too high
While weighing the unknown for the experiment, a student contaminated the same with a few grains of sand, recorded the weight of the contaminated sample, and did the experiment. Would the students molecular weight be too high, too low, or would there be no error?
too high
When using a pipet, a student notices some residual solution remains in the pipet. The student shakes out the pipet to expel this solution into the collection beaker. The volume of the solution in the beaker is now ________________.
too large
True or False. Most solutions form a curved surface when placed in a glass container. This surface is called the meniscus.
true
How many acidic Hydrogen does the KHP have?
ummmm
What property of the solution would you need to know accurately before the same is shared onto the column?
volume
Do you think this molecular mass by chromatography experiment could be used to find the molarity of an aqueous solution of a salt (instead of the MW of a solid unknown as in the procedure given here)?
yes
A student is presented with 0.110 M solution of an unknown weak acid. The pH of the solution is 3.05. What is the Ka and the pKa?
Ka = ([H+] x [A-])/[HA], pKa = -log(Ka); 7.28 & 5.14
What would happen if you left your sample in the open?
O2 would enter the solution so the value would increase
Will a slower chemical reaction give a plot with a shallow or steep slope?
Shallow
What does TC stand for? Give one example of this type of glassware.
"to contain"; volumetric flask
What does TD stand for? Give two examples of this type of glassware.
"to deliver"; volumetric pipet and buret
What is the molecule weight of KHP to four significant figure?
204.2 g/mol
What is the numerical value of the heat evolved in the experiment described in the previous question...how many cal of heat were produced by the reaction in the calorimeter?
-487.5 cal
A student titrates 35.14 mL of HCl that is approximately 0.1 M with an NaOH solution that has been standardized and found to be 0.102 M. It is found that the titration requires a volume of 34.25 mL of the NaOH to reach the indicator color change. What is the molarity of HCl solution?
0.9863 M
Error could be easily introduced into this experiment in a variety ways. Describe two possible sources of errors as outlines in your lab manual and explain how they would affect the calculated molecular mass.
1. you could weigh you unknown incorrectly 2. titrate incorrectly while adding NaOH
Serum levels of 0.002 g of gold per 100mL of serum solution is useful in the treatment of rheumatoid arthritis. What is the molarity of the gold in this solution?
1.02 x 10^-4 M
What is the unit of the rate constant if the chemical reaction is in first order?
1/min
Accurate
2% of desired volume; ex. graduated cylinder
How many mL of a 3.0 M stock solution of NaOH would be required to make up 500 mL of 0.1 M NaOH?
16.67 mL
Calculate the Cole of 3M HCl needed to make 500 mL of 0.1 M solution.
16.67 mL HCL
Calculate the delta Hrxn for the following reaction: 2H2O2 --> 2H2O + O2 H20 (l) = -285.8 kJ/mol and H2O2 (l) = 196.4 kJ/mol
196.4 kJ/mol
How many methods were used in lab 2 to determine the Ka of an acid? Describe each one.
2 methods: 1. find the equivalence point using a weak acid-strong base titration 2. use unknown acid to determine pH(1/2) value
HCl: Na2CO3 ratio
2:1
A 0.4016 g sample of impure sodium carbonate (soda ash) is dissolved in 50 mL of distilled water. Phenolphthalein was added and 11.40 mL of 0.09942 M HCL was required to reach the first end point. Excess volume of HCL was added according to the lab procedure (if x is the amount of acid needed to complete the first titration, you will add a total of 2x + 10mL of acid to ensure excess). After boiling, the excess acid was titrated with 0.1020 M NaOH. It was found that 10.78 mL of the NaOH was required to reach the end point of this titration. Answer the following about this determination: 1. How many total mL of the 0.09942 M HCL will have been added if the lab procedure is followed? 2. Based on your answer to #1 above, how many total moles of HCL were added to the sample? 3. How many moles of NaOH were used in the back titration? 4. How many moles of the HCL in problem #2 were used up in reacting with sodium carbonate in the sample of unknown? 5. What was the % sodium carbonate in the original unknown sample?
32.8;3.26*10^-3;1.1*10^-3;2.16*10^-3;28.5%
A first order reaction is 50% complete in 140 sec. What is the rate constant
4.95*10^-3 sec^-1
The specific heat of ethanol is 2.46 J/g*C. Find the heat energy to raise the temperature of 193g of ethanol from 19 to 35 degrees celsius.
7.80 kJ
how many mL of 3.0 M HCl is required to prepare 250 mL of 1.0 M HCl by dilution?
83 ml
What would happen if you forgot to boil off the CO2 from the solution. Would the value be higher be higher or lower?
CO2 will remain and the percentage will lower
T or F: You reach the first equivalence point when the solution goes from pink to clear
True
T or F: You reach the second equivalence point to occur at an acidic pH
True
True or False. So you should be able to write the equation for your experiment like this: (acid + base ----> salt + water)
True
True or False. Enthalpy, a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.
True (check this answer)
What is the heat capacity of dilute HCl solution you will be using today?
UMMM....
Two methods to determine endpoints of titrations?
Visually and the Highest jump in pH
Common name for ascorbic acid?
Vitamin C
Why do we record two readings of the chilled cuvette?
Water won't increase absorbance by directly absorbing photons
Could a specific heat of an unknown pure metal sample be used to help identify the metal? Why or why not?
Yes, all metals have a unique specific heat property
In the titration of 10.00 ml of an unknown weak acid (HX) with a strong base that has a molarity of 0.1002M, the equivalence point was found to be 19.20 ml. Calculate the concentration of HX. If the initial pH of the solution was recorded as 3.12, what is the Ka and pKa of HX?
a. mol of acid = mol of base, M = mole/liters, pKa = -logKa; M = 0.1849, Ka = 3.13x10^-6 and pKa of HX = 5.50
heat capacity
ability to absorb heat (from calorimeter)
The kinetics experiment measures:
absorbance
Given the specific heat you calculates for the unknown metal in the previous question, is the meal most likely to be aluminum, copper, gold, or iron?
aluminum
Phenol/Sodium Hydroxide reaction
c20H14O4 + 2NaOH-> C20H12O4 2- + NaOH -> C20H13O5 3-
Two neutralization steps of carbonate ions with HCl
co3 2- + H+ <-> HCO3- + H+ <-> H2CO3 <-> H2o+CO2
What is the first law of thermodynamics?
energy is neither lost or gained in any energy transformations
If a chemical reaction is carrier out in a calorimeter containing 125 mL of water solution and the temperature is observed to rise from an initial value of 21.2 to 25.1 degrees celsius , was the reaction endothermic or exothermic?
exothermic
True or False. The amount of liquid that remains in TD glassware when liquid is poured out is not an important quantity?
false
When you titrate a weak acid with a strong base the equivalence point will be more than, less than, or equal to 7?
greater than 7
What reaction occurs at 25 degrees celsius for the symbol [H2SO4 (l)]?
idk
What is a formula of the primary standard used to determine the molarity of NaOH in your today's experiment?
idkkkk
What would a plotted graph with the mass of a sample of an unknown liquid on the y-axis and volume of the sample on the x-axis look like?
increasing with a positive slope (mass on the y-axis and volume x-axis)
What is the type of chromatography that will be performed in this experiment?
ion exchange chromatography
Assume that there is a bubble in the bottom of the buret before you began dispensing. While dispensing, the bubble is pushed out of the buret tip. Have you added more, less, or the same amount as the reading on the buret?
less than
Know the activation energy formula
ln(k1/k2)=Ea/R(1/T2-1/T1)
What is the curved surface of liquid in a buret called?
meniscus
What are the two common characteristics that all chromatographic techniques share?
mobile phase and stationary phase
In the lab we assume the no heat is lost from the calorimeters to the surroundings. If heat is lost to the surroundings, is the effect on the calculated results positive error, negative error, or has not effect?
negative error
Why is the pH at half-titration point equal to the pKa in today's experiment?
pH(1/2)=pKa because half the acid is neutralized and half of it is not, so there will still be 50% left to be neutralized by the strong base
Half Equivalence Point
pH(1/2)=pKa; half the acid is neutralized, so the concentrations of [A-] and [HA] are equal
A popular brand of lemonade has a [H3O+] of 9.90 X 10^-5. What is the oH of the lemonade?
pH=-log[H+]; 4.00
