CHM 113 End of Semester Quiz - Prelab and Quizzes review
a student started the purification and recrystallization with a crude sample of adipic acid that weighed 20.124 g and obtained a yield of pure adipic acid of 75.3%. How much pure adipic was recovered.
% recovery = weight of pure adipic acid / weight of crude adipic acid x 100% 75.3% = x / 20.124 g x 100% x = 15.2 g pure adipic acid
Given that metal cylinder has following measurements and determine the radius in centimeter. height: 12.34 cm mass: 25.33 g density: 0.912 g/mL
0.912 = 25.33 / x x = 27.77412281 mL v = pi r^2 h 27.77412281 = pi r^2 (12.34) r = 0.846423397 r = 0.846 cm
a rock weighs 143 g in air 82 g in H2O what is mass of H2O displaced? volume H2O displaced? density of the rock?
143 g - 82 g = 61 g H2O displaced 61 g H2O x (1 cm^3 / 1g) x (1 ml / 1 cm^3) = 61 mL H2O displaced 143 g (rock) / 61 mL H2O = 2.344262295 2.3 g/mL
A graduated cylinder weighs 28.102 g. A solution has been created which levitates a piece of PVC. The graduated cylinder containing 6.25 mL of that solution weights 34.200 grams. what is the density of the solution? that of the PVC suspended in it?
34.200 g - 28.102 g = 6.098 g / 6.25 mL = 0.97568 density = 0.976 g/mL -------------------------------------------------------- 0.976 g/mL the piece of PVC has the same density as the density of the solution because if a solution is levitating a piece of PVC, the PVC pipe would have to have the same density as the solution
at what temperature water has maximum density?
4 degrees C
The ratio of O, C, H in the molecular formula of adipic acid is
4:6:10
suppose that for the same 10.0 mL sample above, the mass of the crucible with precipitate was 21.450 g, and the mass of the empty crucible (tare weight) was 21.310 g. Calculate the concentration of the Ba(OH)2 solution from this data.
Ba 2+ (aq) + 2 OH- (aq) + 2 H+ (aq) + SO4 2- (aq) = BaSO4 (s) + 2 H2O (l) 21.450 g - 21.310 g = 0.14 g precipitate 0.14 g BaSO4 x (1 mol BaSO4 / 233.386 g BaSO4) x (1 mol Ba(OH)2 / 1 mol BaSO4) = 0.000599865 mol Ba(OH)2 10.0 mL x (1 L / 1000 mL) = 0.01 L 0.000599865 mol Ba(OH)2 / 0.01 L = 0.0599865 0.0600 M Ba(OH)2
given a 10.0 mL sample of the unknown Ba(OH)2 solution, calculate the concentration of the solution if it took 11.08 mL of a 0.0970 M H2SO4 to reach the equivalence point.
Ba 2+ (aq) + 2 OH- (aq) + 2 H+ (aq) + SO4 2- (aq) = BaSO4 (s) + 2 H2O (l) M = moles/liter 0.0970 M H2SO4 = moles / 0.01108 L moles H2SO4 = 0.00107476 moles H2SO4 0.00107476 moles H2SO4 x (1 mol Ba(OH)2 / 1 mol H2SO4) = 0.00107476 moles Ba(OH)2 10.0 mL x (1 L / 1000 mL) = 0.01 L 0.00107476 moles Ba(OH)2 / 0.01 L = 0.107 M Ba(OH)2
write the balanced equation for the reaction in today's experiment
Ba(OH)2 (aq) + H2SO4 (aq) = BaSO4 (s) + 2 H2O (l)
name the reaction Na2SO4 + Ba(NO3)2 =
Ba(SO4) (s) + 2 Na(NO3) (aq) precipitation
generally soft drinks are acidic due to carbonic acid. which gas is responsible to make carbonic acid in soft drink?
CO2
which would have higher conductivity: H+ or Na+? why?
H+ both have the same charge, but H+ is smaller and therefore has higher conductivity because it can move through solutions faster than Na+ (which is larger) and it has a higher charge to mass ratio
suppose a small amount of lead (II) chloride got into your Ba(OH)2 sample before your titration, contaminating it. How do you think the contamination would affect your calculated concentration for the sample? What about a small amount of FeCl3?
Lead (II) chloride is soluble and Pb 2+ can precipitate with SO4 2-. This will lead to a reduction of the yield of BaSO4 because there will be less SO4 2- to precipitate with Ba, causing the calculated concentration to be higher than the actual value FeCl3 is soluble in water, but does not precipitate with sulfate so there is no loss of sulfate and no change in calculations
the industrial synthesis of adipic acid is carried out by the oxidation of cyclohexanol with nitric acid. Nitrous oxide, a harmful waste product is formed during this process a. what is the molecular formula of nitrous oxide? b. name two environmental hazards related with this waste product c. give two uses of adipic acid
N2O - global warming - acid rain -smog food flavorings synthesis of nylon-6,6
name the reaction HNO3 + NH3 =
NH4NO3 acid base
[OH-] = 1 x 10^-12 find [H3O+], pH and classification
[H3O+] = 1 x 10^-2 pH = 2 acid
classification = neutral find [H3O+], [OH-], and pH
[H3O+] = 1 x 10^-7 [OH-] = 1 x 10^-7 7
pH = 10.50 find [H3O+], [OH-] and classification
[H3O+] = 3.16 x 10^-11 [OH-] = 3.16 x 10^-4 base
[H3O+] = 1 x 10^-5 find [OH]-, pH and classification
[OH-] = 1 x 10^-9 pH = 5 acid
what is a base?
a base is a proton acceptor
endothermic reaction
a chemical reaction in which heat is absorbed (increase in temp)
exothermic reaction
a chemical reaction in which heat is released (decrease in temp)
intensive property
a physical quantity whose value does not depend on the amount of the substance for which it is measured
extensive property
a physical quantity whose value is proportional to the size of the system it describes or to the quantity of matter in the system
which of the following ions would exhibit the greatest conductivity? a. Li+ or Cs+ b. Mg 2+ or Al 3+
a. Li+, because it is the smaller ion of the two b. Al 3+, because it has a higher charge
in this experiment, we will add activated charcoal to the boiling solution of adipic acid before filtration. Give two reasons why activated charcoal is used
absorbs impurities in adipic acid aide in filtration
type of reaction rxn 1 + 2
acid base
type of reaction rxn 8
acid base gas evolution redox
type of reaction rxn 3
acid base precipitation
define acids and bases with one example of each
acids are proton donors, ex. hydrochloric acid bases are proton acceptors, ex. sodium hydroxide
what is an acid?
an acid is a proton donor
what should the drip rate be in order for drops to be counted accurately by the drop counter?
approximately one drop per second
what is the relationship between pH and pOH?
as pH increases, pOH decreases, and vice versa also as the hydrogen ion concentration increases, the hydroxide ion concentration decreases and vice versa pH + pOH = 14
solubility is the intensive property that we are utilizing today for the purification of the sample. how does this property respond to temperature? Show the nature of temperature versus solubility plot define the term solubility
as the temperature increases, the solubility of adipic acid increases - direct linear relationship the ability of a substance to dissolve in solution
when you measured the melting point of the purified adipic acid, you found that melting point was lower than literature value. What information can you get about the purity of your sample?
because the measured melting point was found to be lower than that of literature value, we can infer that our sample contained impurities when a sample contains impurities, its melting point tends to be lower than that of literature value because impurities disrupt the intermolecular forces that hold adipic acid together
what do you think careless curt may have done wrong? See previous question
careless curt may not have used his MelTemp correctly or he may have lost some of his adipic acid while completing the lab (spills on lab counter, etc)
name the reaction A + B = AB
combination
name the reaction Fe + S = FeS
combination
name the reaction C + O2 = CO2 + Heat
combustion
name the reaction CH4 + 2O2 = CO2 + 2 H2O
combustion
what is the conductivity of a solution?
conductivity is the ability of a substance to conduct electricity
Determine which of the following are intensive/extensive properties or neither. Use I for intensive, E for extensive, and N for neither density - mass - volume - melting point - boiling point - length
density - I mass - E volume - E melting point - I boiling point - I length - N
For a piece of wood having: length = 10.35 cm width = 6.42 cm height = 1.90 cm mass = 72.412 g calculate the density
density = mass / volume volume = l x w x h 10.35 x 6.42 x 1.90 = 126.2493 cm^3 density = 72.412 g / 126.2493 mL density = 0.573563576 g/ml density = 0.574 g/mL
a piece of PVC is levitated into a solution of calcium chloride. The volume of the solution is 6.62 mL and its mass is 36.231 g. What are the densities of the solution and PVC?
density = mass/volume 36.231 g / 6.61 mL = 5.472960725 5.47 g/mL -------------------------------------------------------- 5.47 g/mL If something is levitating in a solution, the means it has the same density as the solution the density of the solution is 5.47 g/mL, so that is the density of the PVC
a cylinder has: diameter = 1.28 cm height = 3.85 cm mass = 39.730 g what is its density?
density = mass/volume volume = pi r^2 h volume = pi(0.64)^2 (3.85) volume = 4.954165951 cm^3 density = 39.730 g / 4.954165951 mL density = 8.019513354 density = 8.02 g/mL
Given the information in the manual, predict the solubility curve vs temperature for adipic acid in water
direct linear relationship
name the reaction AB + CD = AC + BD
double displacement
type of reaction rxn 5
double displacement
if a solution is neutral, its pH should be
equal to 7
adipic acid why do we use fluted filter paper (as opposed to flat filter paper)?
fluted filter paper is used instead of flat filter paper because the numerous folds in the fluted filter paper provide a larger surface area for contact with the adipic acid solution, leading to a more rapid rate of filtration, which is important as the adipic acid may begin to crystallize before fully coming into contact with the filter paper (adipic acid must be poured quickly so it is absorbed quickly - fluted filter paper helps with the rate of absorption)
name the reaction CaCO3 + 2H+ = Ca 2+ + H2O + CO2 (gas)
gas evolution
name the reaction CaCO3 = CaO + CO2
gas evolution
type of reaction rxn 4
gas evolution
gravimetric determination
gravimetric determination is a method of quantitative analysis in which the constituent sought is converted into a substance (of known composition) that can be separated from the sample and weighed
if a solution is basic, its pH should be
greater than 7
the melting point of Careless Curt's adipic acid was 15 degrees below the literature value. Was his adipic acid pure or impure?
his adipic acid was impure, as his melting point was significantly lower than the literature temperature
suppose the barium sulfate weighed in the crucible above was not completely dry. How would this affect the concentration calculated for the barium hydroxide solution?
if the barium sulfate is not completely dry, the mass observed will be higher than it should be, and the students will think they have more barium sulfate than they actually do. this will result in a higher calculated concentration of the Ba(OH)2 solution
how do the size and charge of ions affect the conductivity of a solution?
if the ions of a solution are of the same charge, the smaller ion should be a slightly better conductor than the larger ion, due to the smaller ion's higher charge to mass ratio if the ions of a solution are of different charges, the higher charged ion is a better carrier of charge, due to the higher charged ion's ability to carry more charge however, the higher charged ion is not significantly better than the smaller charged ion due to the high polarizing (water dragging) nature of the higher charged ion
if a solution is acidic, its pH should be
less than 7
which state of water has highest density?
liquid water
list three methods for determining pH? among three different methods, what is the most accurate method of determining pH?
litmus test universal indicator pH meter the most accurate method is the pH meter
when impurities are present, the melting point is _________ than in the pure compound adipic acid
lower and broader
given a 10 mL solution of NaOH at known concentration, what would happen to the conductivity of the solution as 20 mL of an equimolar solution of HCl is added drowse?
make a v shaped graph (conductivity on y, drops added on x) because there is less of the NaOH solution compared to the HCl solution, the conductivity of the solution would decrease as the free ions in the solution begin to react with their counter parts however, once the equivalence point is reached, the conductivity of the solution increases due to the presence of free ions that are added to the solution that don't have available counterparts to react with
Sean and Laura started their experiment with 170 mL of unknown concentration of Ba(OH)2. The mass of crucible with precipitate was 15.0578 g. Determine the concentration of Ba(OH)2 using the gravimetric method. The mass of the dry crucible was 12 g.
mass of dry crucible = 12 g molecular weight of BaSO4 = 233 g/mol 15.0578 g - 12.0 g = 3.0578 g BaSO4 3.1 g BaSO4 3.1 g BaSO4 x (1 mol BaSO4 / 233 g BaSO4) x (1 mol Ba(OH)2 / 1 mol BaSO4) = 0.013304721 = 0.013 mol Ba(OH)2 170 mL x (1 L / 1000 mL) = 0.17 L 0.013 mol Ba(OH)2 / 0.17 L = 0.076 M Ba(OH)2
Emily started to purify the 53.205 g of crude adipic acid. After the experiment was completed, she let the purified adipic acid crystal dry for a week on the filter paper. At the next lab session, she found the mass of paper and crystal to be 36.805 g. What was the percentage of recovery if the weight of empty paper was 0.221 g?
mass of paper + crystal = 36.805 g - mass of filter paper = 36.584 g crystal percent recovery = mass of pure / mass of crude x 100% 36.584 / 53.205 x 100% 68.760%
because a rock is irregular object, it is difficult to use a ruler to determine its volume. Using spring balance, you determine that the mass of a rock in air is 0.302 kg. when rock is taken into water, its mass is 0.212 Kg what is the mass of displaced water? what is the volume of water displaced? what is the density of the rock in g/cm^3?
mass of rock in air - mass of rock in water = mass of displaced water 0.302 kg - 0.212 kg = 0.09 kg = 90 g H2O -------------------------------------------------------- 90 g H2O x (1 mL H2O / 1 g H2O) = 90 mL H2O 90 mL H2O = 90 cm^3 H2O -------------------------------------------------------- 0.302 Kg = 302 g 302 g/90 cm^3 = 3.355555556 3.36 g/cm^3
name the reaction Sn 2+ = Sn 3+ + e-
oxidation
name the reaction Sn 2+ = Sn 4+ + 2e-
oxidation
because of impurities, the color of adipic acid is brown. what are the two impurities that cause the sample to be brown?
oxidized compounds fine carbon particles
if the pH of a solution is 3.1, then what is [H+]? find the [OH-] is this solution acidic or basic?
pH = -log 10 (H+) [H+] = 10^-3.1 = 7.9 x 10^-4 -------------------------------------------------------- 14 - 3.1 = 10.9 = pOH [OH-] = 10^-10.9 1.3 x 10^-11 -------------------------------------------------------- acidic
if the pH of a solution is 9.3, what is the [OH-]?
pH = 9.3 pOH = 4.7 [OH-] = 10^-pOH [OH] = 10^-4.7 [OH-] = 2.00 x 10^-5
define pH
pH is the negative log of the hydrogen ion concentration or -log 10 (H+)
name the reaction AgNO3 (aq) + NaCl (aq) = AgCl(s) + NaNO3 (aq)
precipitation
type of reaction rxn 6
precipitation
what is the difference between qualitative and quantitative analysis?
qualitative analysis is the determining of what constituents are present in a substance quantitative analysis is the determination of how much of a constituent is in a substance
qualitative analysis
qualitative analysis is the identification of the constituents, elements or functional groups, present in a substance
quantitative analysis
quantitative analysis is the measurement of the quantities of particular constituents in a substance
list any three requirements for gravimetric analysis
reaction must be complete (99.9% yield or more) crystals produced must be large enough (can't pass through the filter) the reaction must be pure and of known stoichiometry
what is the technique that can be used in the purification of adipic acid?
recrystallization
acids turn litmus paper ____ and bases turn litmus _____
red blue
type of reaction rxn 7
redox
name the reaction Cu 2+ + e- = Cu +
reduction
name the reaction Fe 3+ + e- = Fe 2+
reduction
name the reaction AB + C = AC + B
single displacement
name the reaction Cl2 + 2NaBr = 2NaCl + Br2
single replacement
which chemical compound is used in acid spill?
sodium bicarbonate
adipic acid this lab is based on separation of a pure substance from impurities. what property of adipic acid is used in the separation?
solubility
define the term specific gravity and also list its unit
specific gravity is the ratio of the density of a substance to the density of water specific gravity is unitless
density
the density of a substance is the ratio of its mass to its volume density = mass/volume
define equivalent point
the equivalence point is the volume at which the conductivity value reaches a minimum
what would you expect to happen to the observed temperature in an endothermic reaction? why?
the observed temperature in an endothermic reaction would increase, because heat is absorbed in endothermic reactions
what is "p function" in pH?
the p function in pH is the negative log of a desired value it is similar to pH (-log of hydrogen ion concentration), but deals with values instead of concentrations
specific gravity
the specific gravity of a substance is the ratio of density of the substance to the density of water
cond/grav determination of BaSO4 what shape will the titration curve have?
the titration curve will be shaped like a V x axis = volume (mL) y axis = conductivity in (muu)s
specify the following statements as true or false: one Siemens is equal to the reciprocal of one ohm sodium, magnesium, aluminum cations do not interfere by producing precipitates with sulfate ions
true true
what is universal indicator? what range of pH does it detect?
universal indicator is a mixture of dyes that is sensitive to acids and to bases (the acidity or alkalinity of a solution) universal indicator can detect roughly a range of pH from 4-9
what is the use of methanol in the conductimetric/gravimetric determination of BaSO4?
used to wash precipitate used to help get the barium sulfate out of the beaker into the crucible for accurate analysis
when using litmus paper in the presence of a base what color does it turn? In the presence of an acid?
when using litmus paper in the presence of a base, the litmus paper will turn blue when using litmus paper in the presence of an acid, the litmus paper will turn red
what happens if you boil the cabbage too long while making cabbage juice?
you denature its natural pigments, rendering them useless as universal indicator
why do you need to heat the solution during gravimetric determination?
you need to heat the solution during gravimetric determination to allow the barium sulfate to flocculate, or to cause to aggregate into a mass, for accurate filtering and weighing purposes
