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