Gen Chem Lab Final
How do you determine the relativities of metals?
By systematically observing the displacement reactions among a series of metals and solution of their cations, it is possible to determine the relative oxidation potentials of the metals. The metal with the lower reduction potential will reduce a cation of a metal with a higher reduction potential. Currently, all are listed as reduction potentials.
Why is it necessary to rid the distilled water of CO2?
Carbon dioxide should be removed from the water because it is an acid anhydride and reacts with water to produce carbonic acid according to the reaction CO2 + H2O <--> H2CO3. Its presence would lead to an erroneous determination of the amount of a particular acid or base in solution. It is particularly detrimental to sodium hydroxide solutions as these absorb carbon dioxide to produce sodium carbonate.
How many joules are required to change the temperature of 50.0 g of water from 21.3 degrees C to 43.5 degrees C?
Delta T = 43.5 C = 21.3 C = 22.2 C heat required = (50.0 g)(4.184 J/g-C)(22.2 C) = 4.64 x 10(3) J
What does electron affinity measure?
Electron affinity is the energy involved when an electron is added to a neutral species or strictly speaking an atom in the gas phase and is the inverse of the ionization energy in a physical sense. But the magnitudes are not just equal and of opposite sign because you are considering slightly different processes.
Why is the KMnO4 solution filtered, and why should it not be stored in a rubber-stoppered bottle?
The permanganate is filtered to remove insoluble MnO2. Because rubber reduces MnO4- to MnO2, the solution should not contact rubber or other organic materials.
Why does the solution decolorize upon standing after the equivalence point has been reached?
The solution decolorizes after the equivalence point has been reached because permanganate undergoes photochemical reduction and is slowly reduced by water.
Write molecular, complete ionic, and net ionic equations for the reactions that occur, if any, when solutions of the following substances are mixed: a) nitric acid and potassium carbonate b) sodium bromide and lead nitrate c) acetic acid and calcium hydroxide d) calcium nitrate and sodium sulfate e) ammonium chloride and lithium hydroxide
a) Molecular: 2HNO3 (aq) + K2CO3 (s) -> 2KNO3 (aq) + CO2 (g) + H2O (l) Ionic: 2H+ (aq) + 2NO3- (aq) + K2CO3 (s) -> 2K+ (aq) + 2NO3- (aq) + Co2 (g) + H2O (l) Net Ionic: K2CO3 (s) + 2H+ (aq) -> 2K+(aq) + H2O (l) + CO2 (g) b) Molecular: 2NaBr (aq) + Pb(NO3)2 (aq) -> 2NaNO3 (aq) + PbBr2 (s) Ionic: 2Na+ (aq) + 2Br (aq) + Pb(2+) (aq) + 2NO3- (aq) -> 2Na+ (aq) + 2NO3- (aq) + PbBr2 (s) Net Ionic: Pb(2+) (aq) + 2Br- (aq) -> PbBr2 (s) c) Molecular: 2CH3COOH (aq) + Ca(OH)2 (aq) -> 2H2O (l) + Ca(CH3COO)2 (aq) Ionic: 2CH3COOH (aq) + Ca(2+) (aq) + 2OH- (aq) -> 2H2O (l) + Ca(2+) (aq) + 2CH3COO- (aq) Net Ionic: 2CH3COOH (aq) + 2OH- (aq) -> 2H2O (l) + 2CH3COO- (aq) d) Molecular: Ca(NO3)2 (aq) + Na2SO4 (aq) -> 2NaNO3 (aq) + CaSO4 (s) Ionic: Ca(2+) (aq) + 2NO3- (aq) + 2Na+ (aq) + SO4(2-) -> 2Na+ (aq) + 2NO3- (aq) + CaSO4 (s) Net Ionic: Ca(2+) (aq) + SO4(2-) -> CaSO4 (s) e) Molecular: NH4Cl (aq) + LiOH (aq) -> NH3 (g) + H2O (l) + LiCl (aq) Ionic: NH4+ (aq) + Cl- (aq) + Li+ (aq) + OH- (aq) -> NH3 (g) + H2O (l) + Li+ (aq) + Cl- (aq) Net Ionic: HN4+ (aq) + OH- (aq) -> HN3 (g) + H2O (l)
If 30.50 mL of 0.25 M NaOH exactly neutralizes 32.20 mL of HCl, what is the molarity of the HCl?
m moles NaOH = m moles HCl 30.5 mL x 0.25 M = 36.20 mL x M and M = (30.5 mL x 0.25 M)/(36.20 mL) = 0.21 M
Water-soluble salts
1) Na+, K+, NH4+ = all sodium, potassium, and ammonium salts are soluble. 2) NO3-, ClO3-, CH3COO- = all nitrates, chlorates, and acetates are soluble. 3) Cl- = All chlorides except AgCl, Hg2CL2, and PbCl2. 4) Br- = All bromides are soluble except AgBr, Hg2Br2
What volume of 0.100 M KMnO4 would be required to titrate 0.23 g of K2[Cu(C2O4)2] . 2H2O?
16H+ (aq) + 2MnO4- (aq) + 5C2O4(2-) (aq) -> 10CO2 (g) + 2Mn(2+) (aq) + 8H2O (l). moles MnO4- = (2/5) moles C2O4(2-) = (2/5)[((0.23. g)(2 mol C2O4(2-)/mole K2[Cu(C2O4)2].2H2))/(353.83 g/mole K2 [Cu(C2O4)2] . 2H2O) = 5.2 x 10(-4) mol = (VKMnO4)(MKMnO4) VKMnOr = (5.2 x 10(-4) mol)/0.100 mol/L = 5.2 x 10(-3) L = 5.2 mL
Complete and balance the following: Mg (s) + O2 (g) -> Zn (s) + HCl (aq) -> Zn (s) + Cu(2+) (aq) ->
2Mg (s) + O2 (g) -> 2MgO (s) Zn (s) + 2HCl (aq) -> ZnCl2 (aq) + H2 (g) Zn (s) + Cu(2+) (aq) -> Zn(2+) (aq) + Cu (s)
How many millimoles of NaOH are present in 31.20 mL of 0.125 M NaOH? How many grams of NaOH are present?
31.20 mL x 0.125 mmoles/mL = 3.90 mmol (40.00 g/mol)(1 mol/1000 mmol)(3.90 mmol) = 0.156 g
A 720 mL sample of water was cooled from 50.0 degrees C to 10.0 degrees C. How much heat was lost?
(720 mL)(1.00 g/mL)(50.0 C - 10.0 C)(4.184 J/g-C) = 120,384 J = 120 kJ
What is parallax? Why should you avoid it?
Parallax is the apparent displacement or the difference in apparent direction of an object as seen from two different points not on a straight line with the object. It should be avoided in titrations because it introduces an error in the volume measurements.
Which of the following are strong electrolytes: BaSO4 AgNO3 HBr HNO3 CH3COOH
AgNO3, HBr, and HNO3 are strong electrolytes
Why do you determine a mass by difference?
You determine the mass by difference because this is generally more accurate than determining the mass directly.
Define the following terms: analyze, standard solution, titration, titrant, and standardization.
An analyte is the substance being determined in an analysis; a standard solution is a solution whose concentration is accurately known; titration is a volumetric method of analysis carried out by adding a standard solution (usually called the titrant) to another solution until the chemical reaction between the two solutes is complete; standardization is the process of accurately determining the concentration of a solution.
What are equivalence points and end points? How do they differ?
An equivalence point is the point in a titration at which stoichiometrically equivalent amounts of the two reactants are brought together. An end point is the point in a titration where some indicator (such as a dye or an electrode) undergoes a discernible change and the titration is stopped. Ideally, the hope is that these two points coincide, but in practice, they differ slightly. Of primary importance is to minimize the difference if accuracy is desired. The equivalence point is a theoretical point, whereas the endpoint is physical point in the lab procedure.
Define endothermic and exothermic reactions in terms of the sigh of Delta H.
An exothermic reaction is a reaction that produces heat; its delta H will be less than zero, or negative. An endothermic reaction is a reaction that absorbs heat; its delta H will be greater than zero, or positive.
Why must oxidation be accompanied by a reduction?
An oxidation must be accompanied by a reduction because the species being oxidized must transfer electron(s) to some other species that is reduced. The electron cannot just be given up to free space.
Which of the following are weak electrolytes: HNO3 HF HI NH3 (aq) KOH
Hf and NH3 are weak electrolytes
What does ionization energy measure?
Ionization energy is the energy required to remove an electron from an atom in the gaseous state.
Define the term molarity.
Molaraity is the number of moles of solute in a liter of solution.
What distinguishes a metal from a nonmetal?
Most metals have high thermal and electrical conductivities, high luster, malleability, and ductility, whereas nonmetals usually have low thermal and electrical conductivities, low luster, low malleability, and low ductility. In addition, relative to nonmetals, metals have low ionization potentials and low electron affinities. Most metals are solids while the physical states of nonmetals is variable.
Define standardization and state how you would go about doing it.
Standardization is the process of determining the exact concentration of a solution. It is usually achieved by titrating the solution to be standardized against a known amount of a primary standard substance according to a known reaction and procedure.
Titration of an oxalate sample gave the following percentages: 15.53%, 15.55%, and 15.56%. Calculate the average and the standard deviation.
The average is 15.55% and the standard deviation is 0.02%.
Which of the following are not water-soluble: Ba(NO3)2 FeCl3 CuCO3 CuSO4 ZnS ZnSO4
The following are not water-soluble: CuCO3 and ZnS
Define the term heat capacity.
The heat capacity of a substance is the amount of energy, usually in the form of heat, necessary to raise the temperature of a specified amount of the substance (usually 1 g) by 1 degree C or 1K. If the mass is 1.00 g then this defines the specific heat.
Define the term titration.
Titration is the technique and procedure of accurately measuring the volume of a solution that is required to react with a known amount of another reagent.
If 0.4586 g of sodium oxalate, Na2C2O4, requires 33.67 mL of a KMnO4 solution to reach the end point, what is the molarity of the KMnO4 solution?
You can calculate the molarity after recognizing that moles oxalate = 5/2 moles permanganate. M = 2/5(( g Na2C2O4)/(molar mass Na2C2O4))(1/VKMnO4) = 2(0.4586g)/5(134.0 g/mol)(0.03367 L) = 0.04066 M
