Chemistry Lab Final Review
What were the three temperatures in C using in the gas law experiment?
0, 25, 100
A hydrated sample of copper (II) sulfate (molecular weight 159.61 grams/mol) weighs 2.56 grams. The water is removed from the sample by heating, and the sample is reweighed. The weight of the anhydrous sample is 3.24 grams. How many moles of water were present in the hydrated sample?
0.018 moles of water
Calculate the Rf value if the sample travels 0.5 cm and the solvent travels 2.0 cm
0.25
A hydrated sample of copper (II) sulfate (molecular weight 159.61 g/mole) weighs 3.56 grams. The water is removed from the sample by heating, and the sample is reweighed. The weight of the anhydrous sample is 3.24 grams. How many grams of water were present in the hydrated sample?
0.32 g of water
Convert 655 mm Hg to atm
0.862 atm
Three separate determinations of the mass of water delivered by a volumetric pipet yielded the following data: 25.094 g, 24.955 g, and 24.982 g (density of water=0.9980 g/mL): calculate the average volume of the pipet in mL and calculate the percent relative average deviation about the average volume
1) 25.144 mL, 25.005 mL, 25.032 mL 2) 25.060 mL
Give examples of hydrates, write their chemical names, formulas, and compute their molar masses
1) CoCl2 x 6H2O: cobalt (II) chloride hexahydrate; 237.95 g/mol 2) CuSO4 x 5H2O: Copper (II) sulfate pentahydrate; 249.72 g/mol 3) NiSO4 x 7H2O: Nickel (II) sulfate heptahydrate; 280.9 g/mol
What is the penalty for a student who does not wear safety goggles at all times?
10 points off of the lab
How much concentrated nitric acid is needed to prepare 450 mL of 0.6 M HNO3? (72%)
12.25 g HNO₃
What volume of 1.050 M potassium hydroxide is required to react with 22.2 mL of 0.755 M nitrous acid?
16.0 mL
Define density and calculate the density for a metal bar with a mass of 5.05 g and a volume of 2.1 mL.
2.4 g/mL
What is the vapor pressure of H2O at room temeperature
21.1 mmHg
Which of the following numbers contains five significant figures: 25.9400, 25.9410, 25.940, 25.94001, 25.94
25.940
Calculate the average density if three trials yield 4.56 g/mL, 4.55 g/mL and 6.45 g/mL. Was this experiment precise?
5.19 g/mL; no
Calculate the mass of an object with a density of 2.5 g/mL. The volume is 2.2 L
5500 g
What is the volume of a metal bar that is dropped in water if the initial level of water is 50.0 mL and the final level of the water is 57.2 mL?
7.2 mL
How many total oxygens are in this compound? Ba3(PO4)2
8 oxygens
Describe how a neutral chemical compound is written including anions, cations, and electrical charges
A neutral ionic compound is written with a cation, which has a positive charge, and an anion, which has a negative charge. The cation is on the left and the anion is on the right
What is Beer's law and how is it applied?
Beer's law states that the concentration of a chemical is directly proportional to the absorbance of a solution. The equation is A=EbC. This equation can be used to determine an unknown concentration or absorbance. E=molar absorptivity; b=path length of the sample (cm); C=concentration (molarity)
Write the balanced chemical equation for the reaction of calcium carbonate with hydrochloric acid
CaCO₃ + 2 HCl -> CaCl₂ + H₂CO₃
Describe the relationship known as Avagadro's Law. BE sure to include an equation
Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules: V1/n1=V2/n2
An anion is a positive ion (T/F)
False
Density is an extensive property (T/F)
False
Food and drinks may be brought into the lab (T/F)
False
In the pressure versus temperature experiment, pressure and temperature were inversely related (T/F)
False
In the spectrophotometry experiment absorbance and concentration are inversely related
False
The Rf value can exceed one (T/F)
False
The titrant used in the neutralization experiment with HCl (T/F)
False
Write the balanced equation for the titration performed in the neutralization reaction lab. Also, write the net ionic equation for the titration performed in today's experiment
HCl(aq) + NaOH(aq) -> H₂O(l) + NaCl(aq) H⁺(aq) + OH⁻(aq) -> H₂O (l)
Write a balanced chemical equation for the reaction of acetic acid and sodium hydroxide
HC₂H₃O₂ + NaOH -> NaC₂H₃O₂ + H₂O
Write the reaction of magnesium with hydrochloric acid to produce hydrogen gas
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
Why should you be careful when inserting the metal bar into the graduated cylinder in Part A of this experiment?
One should be careful when inserting the metal bar in order to avoid splashing water out of the cylinder. If water splashes out of the cylinder, it will lead to an inaccurate volume measurement.
Describe Boyles Law using an equation
P1V1=P2V2
What safety measure was taken to ensure the hydrates didn't reabsorb water after heating?
The crucibles were placed in the desiccator until the crucible was cool to prevent the anhydrous salt from absorbing water
What is the effective ingredients in over-the-counter antacids tablets? How does this ingredient provide relief of excess stomach acid?
The effective ingredient in over-the-counter antacid tablets is calcium carbonate. The calcium carbonate reacts with the HCl acid and produces CO₂ and water, which are inoffensive substances that provide relief/
If any type of accident occurs in Chem 2415 lab whom should you notify immediately?
The instructor should be notified
A spectrophotometer is used to determine the intensity of the color (T/F)
True
If the hydrate is colored, a color change may occur upon heating (T/F)
True
If your change the solvent in paper chromatography, this will result in better separation of components (T/F)
True
The end point of the reaction is achieved when the color of your solution changes (T/F)
True
When a proton acid reacts with a hydroxide base the product is salt and water (T/F)
True
What does VSEPR stand for?
Valence Shell Electron Pair Repulsion theory
What action should be taken if you get chemicals in your eyes?
Your eyes should be rinsed in the eye wash station for 15 minutes and the instructor should be notified
What is a hydrate?
a crystalline compound formed from the combing of an anhydrous salt and water
What does a spectrophotometer do?
a machine employed to measure the amount of light that a sample absorbs. The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector
What is a titration?
a process by which a solution of known concentration is brought into reaction with a chemically equivalent substance.
define precipitate
a solid formed in a solution
what is a neutralization reaction?
acid + base → salt + water
Describe the difference between an endothermic and exothermic reaction
an endothermic reaction absorbs heat from the surroundings while an exothermic reaction yields heat to the surroundings
Define soluble
capable of dissolving, specifically in water
Why does the solvent move up the paper?
capillary action
Define precision
closeness of measurements to each other
What does the term anhydrous mean?
describes a compound without water
Define insoluble
incapable of being dissolved
Define solvent front
leading edge of the mobile phase as it moves through the stationary phase
What is the electron geometry for molecules with one or two domains?
linear
List five geometrical shapes possible for the electron distribution of a molecule
linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral
Calculate the mean and the percent error for the following: 4.73 g, 5.45 g, 5.38 g (true value=5.15 g)
mean: 5.19 g; percent error: 0.77%
Give an example of an endothermic reaction
melting ice or the evaporation of water
Define retention factor
movement of the component/movement of the solvent front
Give an example of an exothermic reaction
neutralization reactions or respiration
Can an Rf value ever exceed one? Why or why not?
no; the component cannot move farther than the solvent front
What is the electron geometry for molecules with six domains?
octahedral
Write the equation used to calculate the quantity of heat transferred into or out of a system as it undergoes a chemical or physical change at constant pressure
q=MC∆T
Calculate the standard deviation and relative standard deviation for the following data: 4.73 g, 5.45 g, 5.38 g (true valve=5.15 g)
sd: 0.397; rsd: 7.65%
What properties determine the physical behavior of a gas?
temperature (K), pressure (atm), volume of a gas (L), amount of gas (moles)
What is the electron geometry for molecules with four domains?
tetrahedral
During the boyle's law experiment, what were you measuring the volume and pressure of?
the air
define heat capacity
the amount of energy used to raise the temperature of anything by one degree of Celsius or Kelvin.
define specific heat
the amount of heat required to raise the temperature of one gram of any substance one degree
What is the octet rule?
the atom of the elements in a compound lose, gain, or share valence electrons in order to obtain a noble gas configuaration
Define accuracy
the closeness of the measurement to its true value
define origin
the line or spot where the mixture material is placed before the mobile phase is introduced
Define equivalence point
the point at which chemically equivalent quantities of bases and acids have been mixed
Define endpoint
the point in a titration at which the indicator changes color; the reaction between the titrant and the titrated substance is complete
What information is obtained from the calibration curve?
the slope, intercept and concentration of unknown
Define mobile phase
the solvent liquid or gas that sweeps the mixture through the stationary phase; the mixture that is being separated
What is spectrophotometry?
the study of the interactions of electromagnetic radiation with matter
Define Dalton's Law of Partial pressure
the total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone
Using each positive and negative ion only once, write the formula for three chemical compounds: Fe2+, Na+, Ba2+, PO4-3, NO3-, SO4-2
there are lots of options but these are some examples: FeSO4; Na3PO4; Ba(NO3)2
Why are antacids taken by humans?
to neutralize the HCl in the stomach by turning it into Co2 and water
What is the electron geometry for molecules with five domains?
trigonal bipyramid
What is the electron geometry for molecules with three domains?
trigonal planar
What is the x and y axis in a spectrogram?
x: concentration of green dye y: absorbance
List the five steps associated with VSEPR theory
1. draw the lewis structure of the molecule 2. count the number of regions of electron density on the central atom 3. determine the VSPER AXE notation 4. Determine the geometric shape from the number of areas of electron density 5. Determine molecular shape based on the AXE notation