Final Exam Review
what is the oxidation number of copper in malachite?
+2
if 0.24 g of a solid acid C₂H₂O₄ were used to titrate, how many moles of the acid were used?
.0027 mol
what is the molarity of Ca²⁺ if 11.66 mL of .079 M EDTA is used to titrate the 25.00 mL water sample? What is the hardness in ppm of CaCO₃?
.037 M 3.7E3 ppm
what is the theoretical yield of copper in a 0.25 g sample of malachite? what is the percentage of copper in the sample?
0.14 g Cu 57.5%
a real malachite bead Cu₂CO₃(OH)₂ with a mass of 0.54 g was refined by the experiment 12 procedure to give 0.26 g of relatively pure copper. what is the theoretical yield of copper? what is the percent yield?
0.31 g 84. %
How many ionizable hydrogens are there in ethanol?
1
If 0.52 g of KHP (C₈H₅O₄K) is dissolved in 100.0 mL of water, what is the 1) number of moles of KHP dissolved 2) molarity of the KHP solution 3) moles of H⁺ available to react with NaOH during titration If the KHP is titrated using 15.68 mL of NaOH solution, what is the concentration of the NaOH solution? If 25.00 mL acetic acid (HC₂H₃O₂) is titrated with 44.44 mL of the NaOH solution, what is the concentration of the acetic acid solution?
1) .0025 mol KHP 2) .025 M KHP 3).0025 mol H⁺ 0.16 M NaOH 0.28 M acetic acid
How many ionizable hydrogens are there in salicylic acid?
2
a student titrates 25.00 mL of tap water using 4.32 mL of .02 M EDTA. Calculate the hardness of the water in terms of ppm CaCO₃
346. ppm
how many bonds can EDTA form with a metal ion? how many ionizable hydrogens does it have
4-6 4
if the actual yield of copper was 0.20 g when the original mass of malachite was 0.52 g, what was the percent yield?
67.%
what is a fuzzy endpoint?
A fuzzy endpoint is one that will not be a sudden change like the titration of acid-base reactions. The endpoint will be hard to accurately determine because the color change is a slow change from pink/purple to a blue with a purple tinge.
aluminum hydroxide
Al(OH)₃
errors present in lab 12
As displayed in table 3, the percent yield for this experiment was 67.%. Although the large majority of the bead maintained intact after heating it twice, trace amounts of copper were inseparable from the charcoal and thus were not accounted in the final weighing of the bead. This is a likely reason as to why our percent yield was less than 100%. As with any experiment, several errors could have affected the results. As previously mentioned, part of the bead could have shattered as it was heated, making it difficult to separate the metal from the charcoal. This would have reduced the actual yield obtained in the experiment as thus reduced the percent yield. Again, this was an error that affected our results. Furthermore, microscopic cracks could have formed in the bead as gaseous carbon monoxide and water escaped the crucible as the bead was heated. This would have lowered the actual yield of copper and thus reduced the percent yield obtained in this experiment. This was also a likely source of error that affected our results.
cations commonly associated with hard water
Ca²⁺, Mg²⁺, Fe³⁺
what is charcoal?
Charcoal is an amorphous form of carbon obtained as residue when organic matter is heated in the air. Carbon is known to adsorb many materials, including dyestuff.
what did charcoal do in experiment 12 - isolation of copper metal from malachite beads?
Charcoal was then added to the copper(II) oxide and reheated. This reduced the copper(II) oxide to solid copper and gaseous carbon dioxide. This can be represented by the following reaction: 2CuO(s) + C(s) ⇌ 2Cu(s) + CO₂(g)
chelating agents are important for many biochemical processes. list and describe three such processes.
Chelating agents, or substances whose molecules can form several bonds to a single metal ion, are used in several biochemical processes. They serve as catalysts and promoters in several reactions, including oxidative phosphorylation (the formation of ATP via electron transport), respiration (process in which cells obtain energy by combining oxygen and glucose, resulting in the release of CO2, H2O, and ATP), and photosynthesis (the use of sunlight to synthesize foods from carbon dioxide and water).
chelating ligands form more stable complexes than ligands that do not chelate. why?
Chelating ligands form more stable complexes than ligands that do not chelate because they are able to form multiple bonds to a single metal ion. Because chelating ligands have more points of attachment, they are able to form a stronger overall attachment and thus more stable complexes than nonchelating ligands.
thioacetoamide
C₂H₅NS
write out the balanced equation of thioacetoamide in water
C₂H₅NS (aq) + H₂O (l) → C₂H₅NO (aq) + H₂S (aq)
dimethylglyoxime
C₄H₈N₂O₂
what is the difference between a pigment and a dye?
Dyes are coloring materials applied as solutions that cling to whatever they're applied. Pigments are insoluble materials that must be mixed with binders or vehicles in order to attach to a substrate. Pigments are often better than dyes at retaining color for many centuries as well as withstanding high heat, intense light, and exposure to weather or chemical agents.
what does EDTA do to the hard water cations to "hide them away"?
EDTA is a multidentate ligand that binds the ions and forms a stable complex with them. this "hides" the effect of the ions without actually removing them from the solution.
what are EDTA and Erio-T used for in experiment 5?
EDTA is used to determine water hardness by binding to metal ions and forming a very stable complex with them. Additionally, Erio-T indicates this color change by turning the solution from pink to blue.
iron(III) hydroxide
Fe(OH)3
iron(II) sulfide
FeS
procedure for lab 5 - determination of water hardness
In this experiment, we determined the "total" permanent hardness in a water sample by titrating it with EDTA. We used Erio-T as the indicator for this experiment, which turned from pink (corresponding to a Ca-calcon complex) to blue (corresponding to uncomplexed indicator - meaning that all of the Ca2+ ions are bound to EDTA).
write out the balanced reduction reaction between malachite and carbon to yield copper metal.
The balanced reduction reaction between malachite and carbon to yield copper metal is represented as follows: Reaction 1: Cu₂CO₃(OH)₂(s) → 2CuO(s) + CO₂(g) + H₂O(g) Reaction 2: 2CuO(s) + C(s) → 2Cu(s) + CO₂(g) Balanced reduction reaction: 2Cu₂CO₃(OH)₂(s) + C(s) → 2Cu(s) + 2CO₂(g) + H₂O(g)
why should we be concerned about water hardness?
The determination of water hardness is a useful test that reflects the quality of a water sample. Water containing Ca2+, Mg2+, Fe3+, SO42-, and HCO3- does not pose any obvious health hazards. However, these ions form insoluble compounds with soap, leading to interference with cleaning action and "soap scum" as a result. Water hardness is also important in many industries because when hard water is heated, it precipitates CaCO3. This clogs boilers and pipes, which can lead to equipment malfunction or damage and expensive cleaning.
goal of lab 7 - bonding and acidity
The goal of this lab was to experimentally determine the number of ionizable H+ in an unknown solid acid and to form hypotheses regarding the relations between bonding and acidity. This was achieved by titrating two weak acids, C₂H₂O₄ and C₇H₆O₂, with a strong base, sodium hydroxide (NaOH).
factors that affect the strength of an acid
The stronger the H—A bond, the weaker the acid. Additionally, the higher the degree of polarity, the stronger the acid.
ways to soften hard water
Two ways to soften hard water are to use boiling and its heat to cause the release of CO2 and to add CaOH which is lime softening.
calculating mole fraction
Xsolute = moles of solute / moles of solution
dentate
a ligand with multiple bonds is able to "bite" the central ion
quantitative analysis
a process of determining the quantity of a substance in a given sample
ligand
a substance that binds with metal ions to form a complex ion
chelating agent
a substance whose molecules can form several bonds to a single metal ion
A student titrates 0.50 g of a compound with a molecular formula of C₇H₆O₂ with 16.4 mL of 0.250 M NaOH solution. Determine the: a) moles of C₇H₆O₂ used b) moles of NaOH used c) moles of H⁺ titrated d) ratio of H⁺:C₇H₆O₂ e) Lewis structure of C₇H₆O₂
a) .0041 mol b) .0041 mol c) .0041 mol d) 1:1 e) see word doc
when 0.24 g of C₂H₂O₄ is titrated with 42.99 mL 0.124 M NaOH... a) How many moles of NaOH were used to neutralize the hydrogen ions? How many hydrogen ions were neutralized? b) How many hydrogen ions were formed from each C₂H₂O₄ molecule? c) What is the term for such an atom?
a) .00533 mol H⁺ b) 2 H⁺ ions c) diprotic acid
there is a theoretical titration of 25.0 mL of 0.1037 M formic acid (HCOOH, pKa = 3.75) solution (diluted to 100 mL volume with DI water) by 0.0964 M solution of KOH a) determine the volume of KOH needed to reach the equivalence point b) calculate pH of the starting solution c) calculate pH at equivalence point d) calculate pH at 150% of volume of equivalence point
a) .0269 L KOH b) 2.69 c )8.06
the vinegar sold in the grocery stores is described as 5.0% (V/V) acetic acid. What is the: a) molarity of the solution (density of 100% AA is 1.05 g/mL) b) mass % of AA in this solution (density of vinegar is 1.01 g/mL) c) mole fraction of AA in the solution d) molality of the solution
a) 0.874 M b) 5.20% c) .0163 d) .920 mol/kg
Out of these, which have 2 ionizable hydrogens per molecule? a) fumaric acid b) oxalic acid c) maleic acid d) benzoic acid e) citric acid f) salicylic acid g) acetic acid h) lactic acid i) ethanol
a, b, c, and f
weak acid
acid that does not completely dissociate in water but instead reaches equilibrium by partially donating its protons to the solution
strong acid
acid that ionizes completely in an aqueous solution by losing one proton, according to the equation HA(aq) → H⁺(aq) + A⁻(aq)
titration
adding a solution of a reactant with a known concentration until all of the analyzed substance in the sample reacts
analyte
an acid of unknown identity and/or concentration
what 2 gases were driven off when the malachite bead was heated in an empty crucible?
carbon dioxide and water vapor
end point
color change
chelate
comes from the greek word for claw
what was the material produced in the first heating of lab 12?
copper(II) oxide, or CuO
Out of these, which have 1 ionizable hydrogen per molecule? a) fumaric acid b) oxalic acid c) maleic acid d) benzoic acid e) citric acid f) salicylic acid g) acetic acid h) lactic acid i) ethanol
d, g, h, and i
Out of these, which is capable of losing 3 ionizable hydrogens per molecule? a) fumaric acid b) oxalic acid c) maleic acid d) benzoic acid e) citric acid f) salicylic acid g) acetic acid h) lactic acid i) ethanol
e
what reactant is formed when thioacetamide is heated with the original sample solution?
hydrogen sulfide or sulfide ion
what determines whether a salt precipitates
if the lattice energy (the energy required to separate a mole of an ionic solid into its constituent ions) is more negative than the sum of the solvation energy (the amount of energy associated with dissolving a solute in a solvent) and entropy (the randomness molecules based on the number of microstates in a reaction), then the salt precipitates
list 2 problems that hard water causes
it causes pipes to become clogged. when soap is used in hard water, it results in soap scum.
multidentate ligands
many clawed ligands, holding onto the metal ion to form a very stable complex
calculating molality
moles of solute / kg of solvent
chelating agents are
multidentate ligands
a compound that has no ions when dissolved in water is defined as a(n)
non-electrolyte
what element is removed from the remains of the malachite bead when the bead was heated strongly with carbon/charcoal?
oxygen
show by calculation and explain why mg CaCO₃/L of water is parts per million (ppm)
ppm means 1 g of solution present in 10⁶ g of water. Since 1 g = 1000 mg, 1 mg = 10⁻³ g. Thus, 1000 mg / 10⁶ g = 1 mg / 1 L (since the density of water is 1 g/mL).
what color is a positive test for iron(III) ion
prussian blue
if a sample of C₂H₂O₄ weighs 0.10 g and you titrate it with 15.9 mL of .0986 M NaOH, determine the ratio of hydrogen ions to moles of acid. this result will also give you...
ratio = 1.4 this also gives you the number of ionizable hydrogens in each acid molecule
what color is a positive test for nickel(II) ion
red
how is EDTA used in foods?
removes metal ions from enzymes to prevent food spoilage, promotes color and flavor retention, inhibits rancidity
solvation energy
results when a molecule is surrounded by and interacts with solvent molecules
Lewis structures for: a) fumaric acid b) oxalic acid c) maleic acid d) benzoic acid e) citric acid f) salicylic acid g) acetic acid h) lactic acid i) ethanol
see word doc
draw a lewis dot diagram consistent with the formulas H₂C₂O₄ and HC₇H₅O₂
see word doc
entropy always favors a
solution
titrant
solution added to the sample
an acid or electrolyte in general that exists as a 100% ionized form when dissolved in water is defined as a(n)
strong acid
water hardness
the amount of dissolved minerals, especially Ca²⁺, Mg²⁺, Fe³⁺, SO₄²⁻, and HCO₃⁻, in a sample of water
lattice energy
the energy required to separate a mole of a solid ionic compound into its constituent ions
the greater the value of Ka
the more the formation of H⁺ is favored and the lower the pH of the solution
what did the results of lab 6 reveal?
the pH values obtained in this experiment reveal that the equivalence and end points of a titration are close to one another but are not necessarily identical
qualitative analysis
the process of identifying unknown substances in a sample. Such analyses yield a yes or no result - either the sample is present, or it isn't.
permanent hardness
water hardness due to Ca²⁺, Mg²⁺, Fe³⁺, and SO₄²⁻
temporary hardness
water hardness due to HCO₃⁻
equivalence point
when the moles of a standard solution (titrant) equal the moles of a solution of unknown concentration (analyte) should be close to the end point
in order to achieve an accurate titration...
you must know the concentration of the titrant (solution added to the sample) and the volume of titrant corresponding to the equivalence point as accurately as possible
equation and acid-dissociation constant representing a weak acid
HA(aq)⇌H⁺(aq)+A⁻(aq) Ka = [A⁻][H⁺] / [HA]
hydrochloric acid
HCl
nitric acid
HNO₃
explain the difference between temporary and permanent hardness.
Hardness arising due to the presence of Ca2+, Mg2+, Fe3+, and SO42- is referred to as permanent hardness, whereas hardness due to HCO3- is referred to as temporary hardness. Whereas temporary hardness can be eliminated by boiling to expel CO2, permanent hardness cannot be eliminated in this way.
rewrite the molecular formulas for C₂H₂O₄ and C₇H₆O₂ to reflect the number of ionizable hydrogens per molecule
H₂C₂O₄ HC₇H₅O₂
hydrogen peroxide
H₂O₂
in lab 6, why is phenolphthalein used as an indicator in both titrations?
In both titrations, a weak acid (potassium hydrogen phthalate, KHP, and acetic acid) is being titrated with a strong base (sodium hydroxide, NaOH). At the equivalence point, this yields a salt of a weak acid and a strong base, producing a mildly basic solution. Thus, the indicator used must have a pKa in the basic range, which phenolphthalein does.
overview of lab 12 - isolation of copper metal from malachite beads
In this experiment, a malachite bead was heated in order to reduce copper and thus determine its percent yield in the reaction. The initial heating of malachite yielded solid copper(II) oxide and gaseous carbon dioxide and water.
develop a hypothesis to account for your experimental results in lab 7
In this experiment, more NaOH was required to neutralize oxalic acid than benzoic acid. Furthermore, based on the molecular structure of these compounds, oxalic acid is more polar and has weaker bonds than benzoic acid. As such, oxalic acid was found to be a stronger acid than benzoic acid. The results of this experiment confirmed things we already knew regarding the relative strength of acids: The stronger the H—A bond, the weaker the acid. Additionally, the higher the degree of polarity, the stronger the acid. Thus, a hypothesis can be proposed for further study that would account for the experimental results of this experiment: as the number of ionizable hydrogens in a weak acid increases, the amount of a strong base needed to neutralize the solution increases.
summary for Lab 6: Quantitative Analysis - How Accurate Can a Titration Get?
In this experiment, two weak, monoprotic acids, potassium hydrogen phthalate (KHP) and acetic acid, were titrated using a strong base - sodium hydroxide. Three titrations were performed for each sample, one of which involved using a pH meter (the other two used only phenolphthalein). After titrating these solutions, titration curves were calculated for both KHP and acetic acid using data from the titration with a pH meter. The equivalence point and molarity of NaOH obtained from the KHP graph and the equivalence point and concentration of vinegar obtained from the acetic acid graph were compared to their experimental values.
overview of experiment 11 - what metal ions are in this solution?
In this experiment, we used qualitative testing to determine the metal ions present in an unknown solution. Qualitative tests tell you a minimum amount of material present; in this lab, the tests depended upon the Ksp value of the metal result resulting from the reaction between the anion and metal cation. To determine which metal ions were in the unknown solution, we first analyzed a substance containing all four metal ions that could possibly be present in the unknown. The four metal ions present in the known sample were nickel(II), iron(III), manganese(II), and aluminum. We performed different reactions that indicated the presence of each ion. Nickel(II) was indicated by a red precipitate; iron(III) was indicated by a blue precipitate; manganese(II) was indicated by a precipitate suspended in purple solution; and aluminum was indicated by a white, translucent precipitate. Using the same procedure, we then analyzed an unknown substance (which contained at least one metal ion) and used the results from the known sample to determine which ions were present in our unknown.
potassium hexacyanoferrate(II)
K₄[Fe(CN)₆]
why is malachite called basic copper carbonate?
Malachite has the same chemical formula as basic copper carbonate, which is Cu₂CO₃(OH)₂. The presence of hydroxide ions is why is it called basic copper carbonate.
manganese(II) sulfide
MnS
ammonia
NH₃
ammonium chloride
NH₄Cl
sodium bismuthate
NaBiO₃
sodium hydroxide
NaOH
nickel(II) sulfide
NiS
