chem lab final
HEXP 6: find qcalorimeter
(-qhot - qcold) -(-qhot - qcold) = + - + becomes the difference between the 2 round to 4 sig figs to help w more accurate calculation unit J
HEXP 6: find deltaHrxn; average deltaHrxn
(qrxn/molesMgSO4) until J/mol convert to kJ/mol average: kJ.mol; 4 sig figs usually
HEXP 4: H oxidation state in reactants and in products
+2, +1
DEXP 4: DEXP 4: A sample of 7.88 g of Mg(OH)2 is added to 26.0 mL of 0.225 M HNO3. How many moles of HNO3 are present after the reaction is complete?
0 mol Since HNO3 is the limiting reactant in the neutralization reaction, none of it remains after the reaction is complete.
DEXP 2: experimental errors resulting in this percent recovery?
1. errors when calculating measurements 2. loss of sample throughout experiment, such as spilling out of the evaporating dish
DEXP 1: You are weighing out a powder on an analytical balance. What should you report in your laboratory notebook if the screen reads: 1.5400?
1.5400 g
DEXP 8: Calculate the density of NO2 gas at 0.960 atmatm and 38 ∘C
1.73 g/L The density of NO2 gas can be calculated using the ideal-gas law, PV=nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature. First, the relationship n=m/M where m is mass and M is molar mass is substituted for n. Since density (d) is the mass per unit volume, d=m/V is used to solve for density. In this case, it can be assumed that V=1 L; therefore, d=m. The temperature is given in degrees Celsius, so it must be converted to kelvins using K=∘C+273. Rearranging the equation to solve for d yields d=M×P/RT = 46.0 g/1 mol× (1 mol⋅K/0.08206 L⋅atm) × (0.960 atm/311 K) =1.73 g/L
DEXP 3: Write the overall reaction between aqueous HCl and solid Na2CO3 to form sodium chloride, water, and carbon dioxide.
2HCl(aq) + Na2CO3(s) → 2NaCl(aq) + H2O(l) + CO2(g)
help 4: Hydrogen peroxide as an oxidizing agent
2I-(aq) + H2O2(aq) + 2 H+(aq) -> I2(aq) + 2H2O(l)
DEXP 3: Write the overall reaction for the reaction of concentrated sulfuric acid and solid sodium chloride
2NaCl(s) + H2SO4(l) → Na2SO4(s) + 2HCl(g)
DEXP 3: Addition of a solution containing ____ to a solution containing NaCl forms a white precipitate of AgCl .
Ag+
DEXP 3: Write the net ionic reaction for the reaction of a silver ion with a chloride ion under aqueous conditions
Ag+(aq) + Cl-(aq) → AgCl(s) Silver ion precipitates with chlorides to form AgCl(s), which is a white crystalline solid.
DEXP 4: Enter the net ionic equation for the reaction of aqueous sodium chloride with aqueous silver nitrate.
Ag+(aq) + Cl−(aq) → AgCl(s)
DEXP 2: background
All matter can be classified as either a mixture or a pure substance. Mixtures can be further classified as heterogeneous or homogeneous. Pure substances can be further classified as elements or compounds.
DEXP 11: The experimental procedure has you wash your thermometer and dry it after you measure the temperature of the NaOH solution and before you measure the temperature of the HCl solution. Why?
Any NaOH adhering to the thermometer would neutralize the HCl, changing its concentration and thus resulting in an error.
HEXP 3: what was it ab
Applications of Metathesis Reactions: Testing for the carbonate ion in food household fooditems by acid-base and precipitation reactions
DEXP 7: If 3.28 gg Cu(NO3)2 are obtained from allowing 2.17 g of Cu to react with excess HNO3: What is the percent yield for this reaction under the given conditions?
51.2%
DEXP 7: If 3.28 gg Cu(NO3)2 are obtained from allowing 2.17 g of Cu to react with excess HNO3: What is the theoretical yield in grams for this reaction under the given conditions?
6.40 g The theoretical yield is the amount you would get if the reaction went to completion giving a yield of 100%. In practice, 100% yield is difficult to achieve because the experimental techniques used to isolated the product are not completely efficient.
DEXP 11: Consider this combination reaction: 2Mg(s)+O2(g)→2MgO(s) ΔH=−1204 kJ What is the enthalpy for the decomposition of 1 mole of MgO(s) into Mg(s) and O2(g)?
602 kJ/mol
HEXP 6: find calorimeter constant
C = qcal/deltaTcold unit J/C 3 sig figs
DEXP 2: How could you separate Chemical 1 from Chemical 2? NH4Cl and CaSO4
Heat the mixture with a bunsen burner. Chemical 1 will sublime forming a gas, whereas chemical 2 is stable upon heating and can be isolated after chemical 1 is removed
DEXP 3: Solutions of ____ salts will react with Cl2 to liberate I2 which will appear brown in H2O and purple in mineral oil.
I-
DEXP 9: At present, automobile batteries are sealed. When lead storage batteries discharge, they produce hydrogen. Suppose the void volume in the battery is 100 mL at 1 atm of pressure and 25°C. What would be the pressure increase if 6×10−2 g H2 were produced by the discharge of the battery?
7 atm Does this present a problem? Do you know why sealed lead storage batteries were not used in the past? Clearly this does present a problem, as gas is extremely explosive. Because lead-storage batteries produce H2 , sealing them would be dangerous.
DEXP 4: Imagine that A and B are cations and X, Y, and Z are anions, and that the following reactions occur: AX(aq) + BY(aq) → no precipitate AX(aq) + BZ(aq) → precipitate Which of the following choices is insoluble?
AZ
DEXP 2: How could you separate zinc chloride from SiO2?
Add water to the mixture, dissolve the zinc chloride, and then filter to separate the zinc chloride from the SiO2.
DEXP 4: What salt is produced in each of the following neutralization reactions? HCl(aq) + KOH(aq) → H2O(l) + ?
KCl
DEXP 4: What salt is produced in each of the following neutralization reactions? HNO3(aq) + KOH(aq) → H2O(l) + ?
KNO3
DEXP 5: what is it ab
Metathesis Reactions & Net Ionic Eqns
HEXP 3: Sodium Carbonate(aq) + Magnesium Sulfate Heptahydrate(aq) containing anion + vinegar reaction
MgCO3(s) + 2HC2H3O2(aq) -> CO2(g) + Mg(C2H3O2)2(aq) + H2O(l)
DEXP 4: According to your friend's logic, which of these chemical reactions could occur, thus helping you identify the solution in the bottle?
More than one, but not all, of the reactions described above could occur. -Barium sulfate could precipitate. -Lead sulfate could precipitate -Lead chloride could precipitate.
HEXP 5: limiting reagent
NaHCO3
DEXP 2: Why should one never weigh a hot object? Select all of the answers that are correct.
The hot object may cause damage to the delicate balance. Hot objects can result in air movement within the balance that can decrease the accuracy of your measurement.
DEXP 4: Suppose that aqueous solutions of barium nitrate and potassium carbonate are mixed. What is the name of the compound or compounds that precipitate?
barium carbonate
HEXP 2: percent difference and percent deviation
blank
DEXP 11: When HCl(aq) and NaOH(aq) are mixed in a beaker, the beaker feels warm to the touch. What is known about the enthalpy of this reaction?
The reaction is exothermic.
HEXP 4: stock solutions of the reagents
all colorless, no precipitates KI, starch, ascorbic acid, hydrogen peroxide
HEXP 6: what's it ab
applications of calorimetry to measure the insulating efficiency ofcontainers and to measure the heat of a reaction
DEXP 9: Which factor is the major cause for deviation from ideal behavior, the volume of the molecules or the attractive forces between them?
attractive forces between them The first term in the equation above (1.003) corrects for the molecular volume. The second term (-0.013) corrects for intermolecular attraction and is the major reason for deviation from ideal behavior since its magnitude is larger.
DEXP 10: reporting your value and uncertainty ; reported percent chloride
average +/- standard deviation (as a %) average + 2(standard deviation); average - 2(standard deviation) = range
DEXP 3: look at data sheet report for
household ammonia, baking soda, table salt, Epsom salts, bleach, and unknown effects
DEXP 7: what is the gas
hydrogen gas bc excess zinc can react w H+, no more H+ reacting when colorless and no bubbles
DEXP 8: If an insufficient amount of liquid unknown had been used, how would this have affected the value of the experimental molar mass?
lower The molar mass would have been too low because the flask would not have been filled with vapor.
DEXP 1: You are given a sample resembling zinc. Which of the following properties could be used to help determine whether the sample is really zinc?
the melting point of the sample the density of the sample *A sample of any substance in the universe could have any given volume. This extensive property does not narrow down the identity of the unknown sample in any way. However, very few substances have a density of 7.13 g/mL, are bluish gray in color, and melt at 419.58 ∘C. For this reason, intensive properties are most useful for identifying unknown substances.
DEXP 10: absolute value of the deviation
| average - data point | or vice versa; easier to do absolute value of data point - average
DEXP 10: standard deviation
sq rt (sum of deviations^2/ number of points - 1) 2 decimal places
DEXP 10: relative standard deviation (%)
standard deviation/average x 100 should have 2 decimal places
DEXP 2: The process in which a solid is directly converted to the gaseous state is called
sublimation
DEXP 10; average deviation
sum of all deviations/number of points
DEXP 1: What are important things to do before you take a measurement with an analytical balance?
-Remove any dust or powder from the balance pan -Press the tare button to make sure that the balance reads 0.0000 before you begin measuring -Make sure that the balance doors are closed
DEXP 7: When Cu(OH)2(s) is heated, copper(II) oxide and water are formed. Write a balanced equation for the reaction.
Cu(OH)2(s)→CuO(s)+H2O(l)
DEXP 7: When sulfuric acid and copper(II) oxide are allowed to react, copper(II) sulfate and water are formed. Write a balanced equation for this reaction.
CuO(s)+H2SO4(aq)→CuSO4(aq)+H2O(l)
DEXP 9: Why do you equalize the water levels in the bottle and the beaker?
Equalizing the water levels equalizes the pressures and ensures that the total pressure in the bottle is atmospheric and does not contain a contribution from the pressure due to the height of the water column.
HEXP 4: Describe what happens when the peroxide is added to the KI solution. Was iodide oxidizedto molecular iodine?
Once adding the peroxide to the KI solution, the color immediately changedfrom clear to a deep blue. The solution was also bubbling and fizzling. The iodide was oxidized tomolecular iodine. In the presence of starch, iodine forms a complex with a deep blue color that is extremely easy to detect by eye (which I observed)
DEXP 4: Pb(NO3)2(aq)+2KCl(aq)->
PbCl2(s)+2KNO3(aq) Precipitation of Pb2+ by aqeous chloride salts results in the formation of solid lead chloride, which is a white crystalline material.
DEXP 1: What is the most efficient way to add a powder to beaker or flask and obtain and accurate weight?
Place the beaker on the analytical balance and use the tare function to zero the balance. Then add the powder until you reach the desired mass of powder.
DEXP 9: gas law constant, R, from ideal gas law
R = PV/nT **make sure V in L not mL **convert gO2 to molO2 gO2 x (32g/molO2/1gO2) **convert C to K +273.15 units: L.atm/mol.K
HEXP 4: what's it ab
Reduction oxidation reactions: Studying the antioxidant power of Vitamin C with a commonhousehold oxidizing agent, hydrogen peroxide
DEXP 3: Solutions of salts containing SO42- will precipitate BaSO4 when treated with aqueous BaCl2
SO42-
DEXP 2: Why is the NaCl extracted with water three times as opposed to only once?
To ensure all of the NaCl is dissolved.
DEXP 1: An experiment requires 11.0 g of cyclohexane, which has a density of 0.7781 g/mL at 25∘C. What volume of cyclohexane should be used?
V = 14.1 mL Since the units divide and multiply along with the values (in a dimensional analysis), you can confirm the accuracy of the calculation by evaluating the final units. In this case, the correct calculation yields a value with the units of mLmL, which confirms that the calculation was set up correctly because you needed to solve for volume. To convert from volume to mass, simply invert the conversion factor (density) such that units of volume cancel.
DEXP 1: volume of a cylinder equation
V = pi^2h r = radius h = height unit^3
HEXP 4: Describe your observations including any color changes when the ascorbic acid is added to the solution
When the ascorbic acid was added to the solution, there was no noticeable color change, only a bit of flakes floating around
DEXP 8: if asks about dry gas
daltons law of partial pressures
HEXP 1: equations
density
HEXP 4: half reactions
oxidation: 2I-(aq) -> I2(aq) + 2e- reduction: 2H+(aq) + H2o2(aq) + 2e- -> 2H2O(l) total number of electrons transferred in reaction: 2
DEXP 2: percent gained/lost
percent recovered - 100% answer is a percentage
DEXP 11: heat gained by solution
qsoln = (msoln x 4.184 J/gC x (Teq - Ti))
DEXP 3: what is it ab
qualitative analysis of household chemicals
HEXP 2: what was it ab
quantitative analysis and separation of mixtures
HEXP 6: qwater equation
qwater = mcdeltaT
HEXP 4: I oxidation state in reactants and in products
reactants: -1, products: 0
DEXP 4: look at data sheet to see
reaction between elements; oxidation-reduction reactions;
DEXP 7: what's it ab
reactions of copper
DEXP 7: percent yield
recovered mass of Cu/initial mass of Cu x 100
DEXP 7: color of copper sample
red/copper brown
DEXP 1: average mass dispensed from syringe and average volume dispensed by syringe at 1.00 mL indicated volume
same number ex. average mass = sum of masses of water dispensed from syringed at 1.00 mL indicated volume = 1.0093 g; average volume dispensed by syringe at 1.00 mL indicated volumes: 1.009 mL
DEXP 2: what was it ab
separation of mixtures
DEXP 11: How should the two heats of reaction for the neutralization of NaOH and the two acids compare?
similar, except they will differ by the heat of ionization for acetic acid
DEXP 5: Predict whether each of the following compounds is soluble in water. SrBr2, K3PO4, Zn(CH3COO)2, AgI, Sn(OH)2
soluble in water: SrBr2, K3PO4, Zn(CH3COO)2 insoluble in water: AgI, Sn(OH)2 Unfortunately, there are no rules based on simple physical properties such as ionic charge to guide us in predicting whether a particular ionic compound will be soluble. Experimental observations, however, have led to guidelines for predicting solubility for ionic compounds. All compounds containing acetate and nitrate are soluble. All phosphates and carbonates are insoluble, except for compounds of NH4+ and the alkali metal cations. All sulfates are soluble except compounds of Sr2+, Ba2+, Hg22+, and Pb2+. All chlorides, iodides, and bromides are soluble except for compounds of Ag+, Hg22+, and Pb2+. All hydroxides and sulfides are insoluble except for compounds of NH4+, the alkali metal cations, Ca2+, Sr2+, and Ba2+.
DEXP 4: Classify each substance as a strong acid, strong base, weak acid, or weak base.
strong acids: HCl, HBr, HI, H2SO4, HClO4, HNO3 weak acids: HF, HCN, HNO2, CH3COOH, HCOOH strong bases: LiOH, NaOH, KOH, Ca(OH)2, Ba(OH)2, CsOH weak bases: NH3, CH3NH2, (CH3)2NH
DEXP 5: Which of the following is soluble in water at 25∘C?
Ni(NO3)2
HEXP 4: Describe your observations when you add hydrogen peroxide to the solution containing KI, starch, and ascorbic acid; after 30-60 seconds?
No color change; The solution changed from colorless to a dark blue; fizzling.
HEXP 4: tarnished penny after polishing
No longer has luster, parts of gray and black faded away, looks shinier and more copper. Yes, my observations suggest that the surface was contaminated with copper oxide.
DEXP 3: Concentrated sulfuric acid, H2SO4(l), can be used to distinguish solid barium chloride from solid barium sulfate. What would your observations be if you added H2SO4(l) to these solids.
No observable reaction occurs with the barium sulfate. Barium chloride will liberate a pungent gas that turns blue litmus red
DEXP 3: Assume you had a mixture of solid Na2CO3(s) and NaCl(s). Could you use only concentrated H2SO4(l) to determine whether or not Na2CO3(s) was present?
No, reaction of H2SO4(l) with Na2CO3(s)or NaCl(s) both form a gas, so it can't be determined which sodium salt is present. Adding concentrated sulfuric acid results in the formation of CO2(g) gas from the Na2CO3(s) and HCl(g) gas from the NaCl(s). Since both evolve a gas, other tests would be necessary to determine if both ions were present.
DEXP 9: uncertainty in R; max/min value
P = +/- 0.1 mmHg T = +/- 0.1 C V = +/- 0.0001 L m = +/- 0.0001 g max value = add uncertainties/subtract uncertainties min value = subtract uncertainties/add uncertainties maximum R = (Pmin x Vmin)/ (nmin x Tmin) minimum R = (Pmax x Vmax)/ (nmax x Tmax) min = -1 max = +1 m = nmin and nmax once convert to moles from g R = Rmin + Rmax/2 +/- Rmax - Rmin/2 Rmax +/- R found above
DEXP 8: gas law
PV =nRT n = PV/RT Given the number of moles of a gas and its molar mass, you can calculate the mass of the gas. Since density is equal to the ratio of the mass and volume, you can then divide by the volume to find density. Alternatively, you can use the ratio n/V from the ideal gas equation where n is the number of moles and V is the volume, and convert from moles per unit volume to grams per unit volume using molar mass
DEXP 4: Which substances are always produced in an acid-base neutralization reaction?
a salt Acid-base neutralization reactions always produce a salt. Water is always produced in neutralization reactions that involve a strong base, and sometimes produced in those with weak bases. Weak nitrogen-based bases often produce only a salt. If the carbonate or sulfite ion is involved, the reaction will produce a gas, i.e. carbon dioxide gas, and water in addition to the salt. 2HCl(aq) + Na2CO3(aq) → 2NaCl + H2O + CO2 Other groups of bases containing the ions sulfides, hydrogen sulfides, hydrogen sulfites, and hydrogen carbonates undergo similar reactions that produce gas and water in addition to a salt.
HEXP 5: Theoretical yield of CO2 (moles) based on vinegar
average mass percent of acetic acid x mass of vinegar = _____ ____ x (1molHC2H302/60.05gHC2H3O2) x (1molCO2/1molHC2H3O2) = molCO2 Reminder: Vinegar contains acetic acid, HC2H3O2
HEXP 2: percent difference - determining percent composition of sand in known sample
average percent composition of sand in the mixture - percent composition of sand in the mixture/ percent composition of sand in the mixture x 100
HEXP 6: qcalorimeter equation
qcalorimeter = CdeltaT and qcalorimeter = -qhot - qcold
DEXP 11: heat gained by cold water
qcold = cold x 4.184 J/gC x (Teq - Tcold)
DEXP 11: heat lost by water
qhot = hot x .184 J/gc x (Teq - Thot)
HEXP 6: find qrxn
-(qwater + qcalorimeter) difference between the 2 4 sig figs unit J
HEXP 4: O oxidation state in reactants and in products
-1, -2
DEXP 11: The enthalpy for the formation of 1 mole of NH3(aq) is -80.29 kJ/mol. What is the enthapy for the formation of 3 moles of NH3(aq)?
-240.87 kJ
DEXP 9: R from the van Der Waals equation
(P + n^2a/V^2)(V -nb) = nRT a and b given units: L.atm/mol.K
DEXP 11: A 50.0-mL sample of a 1.00 M solution of is mixed with 50.0 mL of 2.00 M KOH in a calorimeter. The temperature of both solutions was 20.2 ∘C before mixing and 26.2 ∘C after mixing. The heat capacity of the calorimeter is 12.1 J/K. From these data calculate ΔH (in kJ/mol) for the process: CuSO4(1M)+2KOH(2M)→Cu(OH)2(s)+K2SO4(0.5M) Assume the specific heat and density of the solution after mixing are the same as those of pure water.
-52 kJ/mol The reaction is for the formation of 0.050 mol Cu(OH)2. The reaction is exothermic and has a negative sign for ΔH.
HEXP 6: -qhot equation
-qhot = qcold + qcalorimeter -mhotcdeltaThot = mcoldcdeltaTcold + CdeltaTcold
HEXP 6: -qrxn equation
-qrxn = qwater + qcalorimeter or -qrxn = mcdeltaT + CdeltaT SO qrxn = -(mcdeltaT + CdeltaT)
DEXP 4: A sample of 7.88 g of Mg(OH)2 is added to 26.0 mL of 0.225 M HNO3. How many moles of Mg(OH)2 are present after the reaction is complete?
0.132 mol The amount of Mg(OH)2 present after the reaction is complete can be calculated by considering the reaction stoichiometry, as well as the fact that HNO3 is the limiting reactant. The number of moles of Mg(OH)2 was calculated in Part B. Subtract the number of moles required to react with HNO3 to find the excess number of moles of Mg(OH)2: moles Mg(OH)2 remaining = (moles Mg(OH)2 initially)−(moles Mg(OH)2 that react) =0.135 mol Mg(OH)2 − (1 mol Mg(NO3)2/2mol HNO3)(5.85×10−3mol HNO3) =0.132 mol Mg(OH)2
DEXP 3: How could you distinguish sodium chloride (table salt) from sodium iodide (a poison)?
1. Use AgNO3(aq) solution: forming AgCl(s) (white), turns purple in light; or forming Agl(s) (yellow). 2.Use concentrated H2SO4(l) on solid: chloride ion forms HCl(g), a pungent gas; iodide ion forms dark solid and purple vapors appear.
DEXP 1: Say you glued two samples together; a 5.92 g sample of acrylic with a density of 1.20 g/mL and a 1.63 g sample of Teflon (d = 2.22 g/mL). What is the density of the combined sample? Be careful here and remember the difference between intensive and extensive properties.
1.33 g/mL Density = mass/volume; combining the two objects together means that you must use their combined mass and their combined volume to calculate the density of the two peices glued together.
DEXP 4: A sample of 7.88 g of Mg(OH)2 is added to 26.0 mL of 0.225 M HNO3. How many moles of Mg(NO3)2 are present after the reaction is complete?
2.93 x 10^-3 mol The amount of Mg(NO3)2present after the reaction is complete can be calculated by considering the reaction stoichiometry as determined in Part A, as well as the fact that HNO3 is the limiting reactant: moles Mg(NO3)2=(5.85×10−3mol HNO3)(1 mol Mg(NO3)2/2mol HNO3) =2.93×10−3 mol Mg(NO3)2
DEXP 2: A mixture was found to contain 1.03 g SiO2, 0.690 g of cellulose, and 2.22 g of calcium carbonate. What is the percentage of SiO2 in the mixture?
26.1%
DEXP 4: K2CO3(aq)+Ba(NO3)2(aq)→
2KNO3(aq)+BaCO3(s) The carbonate anion forms insoluble salts with many cations including Ba2+,Ca2+,Cu2+,andAg+. All of these solids have a white color except for CuCO3 which takes on the blue color of the copper (II) ion.
DEXP 7: Calcium oxide reacts with water in a combination reaction to produce calcium hydroxide:CaO (s) + H2O (l) →→ Ca(OH)2 (s). In a particular experiment, a 3.00-g sample of CaO is reacted with excess water and 3.46 g of Ca(OH)2 is recovered. What is the percent yield in this experiment?
87.4
HEXP 3: Baking powder is mixture of baking soda and a solid weak acid such as tartaric acid. Explainin one or two sentences why adding water to baking soda produced no significant reaction but a reaction was observed when water was added to baking powder.
Adding water to baking soda produced no significant reaction but a reaction was observed whenwater was added to baking powder due to the fact that water causes a solid weak acid in baking powderto dissociate into H+ ions, which react with carbonate ions in order to create the fizzling/bubbling observedin the test tubes. This also represents the release of CO2 gas. Baking soda does not contain the weakacid for a reaction to occur, thus this process does not take place, and there is no significant reaction.
DEXP 3: Write the net ionic reaction for the reaction of a barium ion with a sulfate ion under aqueous conditions.
Ba2+(aq) + SO42-(aq) → BaSO4(s)
DEXP 5: What is the correct net ionic equation, including all coefficients, charges, and phases, for the following set of reactants? Assume that the contribution of protons from H2SO4 is near 100%. Ba(OH)2(aq)+H2SO4(aq)→
Ba2+(aq)+2OH−(aq)+2H+(aq)+SO42−(aq)→BaSO4(s)+2H2O(l) Although most hydroxides are insoluble, Ba(OH)2 is an exception and is soluble. It readily dissociated into Ba2+ and OH− ions. Sulfuric acid, H2SO4, readily dissociates into H+ and SO42− ions. Both H2O(l) and BaSO4(s) form as products of the acid-base reaction. Since BaSO4 is insoluble, it is included in the net ionic equation. A soluble salt would not be included in the net ionic equation.
DEXP 4: Ba(NO3)2(aq) + Na2SO4(aq)→
BaSO4(s)+2NaNO3(aq) Barium ions can be precipitated in the presence of aqueous sulfate salts forming a white precipitate of BaSO4
DEXP 4: Which element is oxidized in this reaction? 2CuO + C → 2Cu + CO2
C is oxidized Carbon gets oxidized in the process of reducing copper. Copper gets reduced in the process of oxidizing carbon.
DEXP 4: Which substance is the reducing agent in this reaction? 16H+ + 2Cr2O72− + C2H5OH → 4Cr3+ + 11H2O + 2CO2
C2H5OH is the reducing agent. The reducing agent acts to reduce another species and therefore must itself be oxidized
DEXP 9: In general, which of the following gases would you expect to behave the least ideally under extreme conditions?
CO
DEXP 3: Addition of an acid to a solution containing _____ will release gaseous CO2 which will react with aqueous BA(OH)2 to precipitate solid BaCO3.
CO32-
DEXP 4: What salt is produced in each of the following neutralization reactions? HNO3(aq) + Ca(OH)2(aq) → H2O(l) + ?
Ca(NO3)2
DEXP 4: What salt is produced in each of the following neutralization reactions? HCl(aq) + Ca(OH)2(aq) → H2O(l) + ?
CaCl2
DEXP 2: How could you separate Chemical 1 from Chemical 2? CaCl2 and BaSO4
Chemical1 is more soluble in water than Chemical2 is. Extract the Chemical1 with water and separate the insoluble Chemical2 by filtration.
DEXP 3: Solid salts containing ____ will release gaseous HCl when heated with concentrated H2SO4. The presence of _____ can be confirmed by adding AgNO3 solution, which will result in the formation of a white precipitate of AgCl.
Cl-
DEXP 4: Which element is reduced in this reaction? 16H+ + 2Cr2O72− + C2H5OH → 4Cr3+ + 11H2O + 2CO2
Cr is reduced Carbon gets oxidized in the process of reducing chromium. Chromium gets reduced in the process of oxidizing carbon.
DEXP 4: Which substance is the oxidizing agent in this reaction? 2CuO + C → 2Cu + CO2
CuO is the oxidizing agent Notice that the oxidizing agent is itself reduced. The species oxidized is not the oxidizing agent, but the reducing agent. Think of the oxidizing agent as the species the acts upon another species causing oxidation.
DEXP 11: enthalpy of reaction
DeltaHrxn = qrxn/moles of HCl convert J to kJ then divide by moles 2 sig figs
HEXP 1: what was it ab
Exploring Density and Buoyancy: Determining the density of an egg by neutral buoyancy
HEXP 5: what's it ab
Gas Laws, Stoichiometry, and Antacids ± Predicting the volume of CO2 produced from thereaction of bicarbonate and vinegar
DEXP 9: In general, which of the following gases would you expect to behave the most ideally even under extreme conditions?
H2
HEXP 3: Sodium Carbonate(aq) + Magnesium Sulfate Heptahydrate(aq) reaction
Na2CO3(aq) + MgSO4.7H2O(aq) -> Na2SO4(aq) + 7H2O(l) + MgCO3(s)
DEXP 4: 2HCl(aq) + BaCO3(s)→
H2O(l) + CO2(g) + BaCl2(aq) Reactions of carbonate salts with acids are an example of gas forming reactions, which produce carbon dioxide gas. The carbon dioxide gas can be detected by suspending a drop of Ba(OH)2(aq) over the reaction which will form a cloudy precipitate of BaCO3.
DEXP 4: 2HI(aq)+K2SO3(s)→
H2O(l)+2KI(aq)+SO2(g) The reaction of sulfite salts with acids is a second example of a gas forming reaction and the gaseous product is SO2 gas.
DEXP 3: Write the overall reaction between aqueous HCl and solid NaHCO3 to form sodium chloride, water, and carbon dioxide.
HCl(aq) + NaHCO3(s) → NaCl(aq) + H2O(l) + CO2(g)
DEXP 4: A sample of 7.88 g of Mg(OH)2 is added to 26.0 mL of 0.225 M HNO3. Which is the limiting reactant in the reaction?
HNO3 To determine the limiting reactant, calculate the number of moles of Mg(OH)2 from its mass using the molar mass as a conversion factor: moles Mg(OH)2 = (7.88g Mg(OH)2)* (1 mol Mg(OH)/258.3g) =0.135 mol Find the number of moles of HNO3by multiplying the volume of the nitric acid solution in liters by its molarity: moles HNO3=(26.0mL soln)(1L soln/1000mL soln)(0.225 mol HNO3/1L soln) =5.85×10−3 mol The coefficients in the balanced equation indicate that the reaction requires 2 mol of HNO3for every 1 molof Mg(OH)2. Therefore, for all Mg(OH)2 to react completely, 2×0.135 mol=0.270 mol HNO3 would be needed. Since there are only 5.85×10−3 mol of HNO3HNO3, not all of the Mg(OH)2 can react, so it is the excess reactant, and HNO3 is the limiting reactant.
DEXP 4: HCl(aq)+AgNO3(aq)→
HNO3(aq) + AgCl(s) The silver ion forms insoluble salts with many anions. Silver nitrate is one of the few soluble forms of silver ion.
DEXP 5: precipitates
In the first step: Silver ion is precipitated by the chloride forming solid silver chloride. All of the other chloride compounds are soluble. In the second step: Barium ion is precipitated by the sulfate ion forming barium sulfate. All of the other sulfates are soluble. Remember, all of the silver was removed in the first step. In the third step: Since no precipitate is formed when adding hydroxide ions, there CANNOT be any copper or manganese ions present since these would form precipitates.
DEXP 4: Insoluble sulfide compounds are generally black in color. Which of the following combinations could yield a black precipitate?
Li2S(aq) + Pb(NO3)2(aq) K2S(aq) + Sn(NO3)4(aq)
DEXP 9: Under what conditions of temperature and pressure would you expect gases to obey the ideal-gas equation?
Low pressure, high temperature
DEXP 8: Calculate the molar mass of a gas if 2.60 g occupies 0.870 L at 690 torr and 38∘C.
M = 84.0 g/mol The molar mass of the unknown gas of known mass (mm) is calculated using the ideal-gas law, PV=nRT. Since we are solving for molar mass, the relationship n=m/M is substituted for n. The pressure must be converted to atm using 1 atm=760 torr, and the temperature must be converted to KK using K= ∘C+273. Rearranging the equation to solve for MM yields: M=mRT/PV = 2.60 g/0.870 L×(0.08206 L⋅atm/mol⋅K)×(311 K/690 torr)×(760 torr/1 atm) =84.0 g/mol
DEXP 8: how to find molar mass of vapor
M = mRT/PV
DEXP 4: A sample of 7.88 g of Mg(OH)2 is added to 26.0 mL of 0.225 M HNO3. Enter the chemical equation for the reaction that occurs.
Mg(OH)2(s) + 2HNO3(aq) → Mg(NO3)2(aq) + 2H2O(l) When an acid and a base are mixed, a neutralization reaction occurs. The product of this reaction is a salt (Mg(NO3)2) and water. The base Mg(OH)2 is insoluble in water. Most compounds formed with the hydroxide anion are insoluble with exceptions including comPounds of the alkali metal cations, Ca2+, Sr2+, and Ba2+. However, most nitrates are soluble with no notable exceptions. Thus, Mg(NO3)2 is soluble. The chemical equation for the reaction between Mg(OH)2 and HNO3 is as follows: Mg(OH)2(s) + 2HNO3(aq) → Mg(NO3)2(aq) + 2H2O(l)
DEXP 8: To identify a diatomic gas (X2), a researcher carried out the following experiment: She weighed an empty 3.4-L bulb, then filled it with the gas at 1.30 atm and 25.0 ∘C and weighed it again. The difference in mass was 5.1 g . Identify the gas
N2
DEXP 3: Addition of a strong base to a solution containing ______ will release a gas which will cause a piece of moist, red litmus held above the reaction solution to turn blue.
NH4+
DEXP 9: Suggest a reason why real gases might deviate from the ideal-gas law on the molecular level.
The ideal-gas law assumes that the gas particles have no volume. At high pressures their volume may become appreciable relative to the volume of the container.
DEXP 7: If your percent yield of copper were greater than 100%, what are two plausible errors you may have made?
The sample was contaminated with an impurity. The product was not sufficiently dried. The factor which is most important is likely that the product was not sufficiently dried and contained water, making the percent yield larger than 100%.
DEXP 2: A student found that her mixture was 15% NH4Cl, 18% NaCl, and 78% SiO2. Assuming her calculations are correct, what did she most likely do incorrectly in her experiment?
The sand and salt were not sufficiently dried. Submit
DEXP 9: Why does the vapor pressure of water contribute to the total pressure in the bottle?
The vapor pressure of water is reasonably high at ambient temperature, it makes a significant contribution to the total pressure.
DEXP 8: The metabolic oxidation of glucose, C6H12O6, in our bodies produces CO2, which is expelled from our lungs as a gas: C6H12O6(aq)+6O2(g)→6CO2(g)+6H2O(l). Calculate the volume of oxygen you would need, at 1.00 atmatm and 298 KK, to completely oxidize 55 gg of glucose. Calculate the volume of dry CO2 produced at body temperature (37 ∘C) and 0.960 atm when 25.5 g of glucose is consumed in this reaction.
V = 22.5 L First, grams of glucose are converted to mol CO2 using the molar ratio from the balanced equation, 1 mol C6H12O6:6 mol CO2, and the molar mass of glucose, 180.1 g/mol. nCO2=25.5 g glucose× (1 mol glucose/180.1 g) ×(6 mol CO2/1 mol glucose) =0.84953 molCO2 Next, the volume of CO2 gas produced is calculated using the ideal-gas law, PV=nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature. The temperature is given in ∘Cand is converted to K using K= ∘C+273. Rearranging the equation to solve for V yields V=nRTP =0.84953 mol×(0.08206 L⋅atm/mol⋅K) ×(310 K/0.960 atm) =22.5 L CO2
DEXP 8: The metabolic oxidation of glucose, C6H12O6, in our bodies produces CO2, which is expelled from our lungs as a gas: C6H12O6(aq)+6O2(g)→6CO2(g)+6H2O(l). Calculate the volume of oxygen you would need, at 1.00 atmatm and 298 KK, to completely oxidize 55 gg of glucose.
V = 44.8 L First, grams of glucose are converted to mol O2 using the molar ratio from the balanced equation, 1 mol C6H12O6:6 mol O2, and the molar mass of glucose, 180.1 g/mol. nO2=55 g glucose×(1 mol glucose/180.1 g)×(6 mol O2/1 mol glucose) =1.8323 mol O2 Next, the volume of O2 gas produced is calculated using the ideal-gas law, PV=nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is temperature. Rearranging the equation to solve for V yields V=nRTP= 1.8323 mol×(0.08206 L⋅atm/mol⋅K)×(298 K/1 atm) =44.8 L O2
DEXP 1: After the label fell off a bottle containing a clear liquid believed to be benzene, a chemist measured the density of the liquid to verify its identity. A 25.0-mL portion of the liquid had a mass of 21.95 g. A chemistry handbook lists the density of benzene at 15∘C as 0.878 g/mL. Is the calculated density in agreement with the tabulated value?
Yes Additionally, you could confirm the density value by using it to convert between mass (mm) and volume (VV). The fraction representing density should be set up such that the appropriate units cancel. For example, if you convert mass to volume, the mass value and unit for density should be in the denominator: V = 21.95 g×1 mL/0.878 g = 25.0 mL
HEXP 4: Based on your observations, does hydrogen peroxide act as an oxidizing agent?
Yes, the hydrogen peroxide acted as an oxidizing agent, since it was the substance that oxidized iodide. Hydrogen peroxide carries the ability of gainingor losing electrons, as its oxygen atoms are in the -1 oxidation state. When a substance acts as an oxidizing agent, is gains electrons (removing themfrom the oxidized species). When hydrogen peroxide (H2O2) serves as an oxidizing agent, the oxygen is reduced to H2O, which is seen in the testtube, since the addition of the hydrogen peroxide immediately affected the solution by the noticeable color change and bubbles/fizzling that were givenoff and produced as wel
DEXP 3: Assume you had a mixture of salts containing the I− and SO42− ions. How could you show the presence of both iodide and sulfate in this mixture? Select the correct tests.
You can detect the presence of SO42− by adding BaCl2(aq), which will result in the formation of a white precipitate. The addition of H2SO4(l) results in the formation of violet vapors of I2, which confirms the presence of I−
DEPX 11: moles of HCl or NaOH
calculated from solution's molarity and volume 2 sig figs
DEXP 10: key concepts
calculating average mass. average deviation, standard deviation, relative percent deviation
DEXP 4: what was it ab
chemical reactions
DEXP 2: How could you separate Chemical 1 from Chemical 2? benzophenone and α−naphthol
chemical1 is soluble in cyclohexane whereas chemical2 is not. Add cyclohexane to the mixture and filter off the chemical2.
DEXP 8 concept
converting between atm, mmHg, etc; converting between K and degrees C
DEXP 7: what copper compound is present in the beaker
copper oxide
DEXP 7: what is present in the solution
copper solid and hydrogen gas; excess SO42- and H+
DEXP 1: density equation
d = mass/volume unit^3
DEXP 9: How does the solubility of oxygen in water affect the value of R you determined?
decrease It lowers the value of R somewhat because the pressure is lowered due to there being less gaseous oxygen.
DEXP 8: Calculate the density of oxygen, O2, under each of the following conditions: STP and 1.00 atm and 10.0 ∘C
density at STP, density at 1 atm and 10.0 ∘C = 1.43, 1.38 g/L When temperature increases, a gas expands and its density decreases.
DEXP 1: what was it ab
density of acrylic
DEXP 7: look at data sheet
describing reactions w copper
HEXP 3: look at data sheet for
examination of acid-bae properties of sodium carbonate; detecting carbonate in house-hold food items from its chemical properties
DEXP 7: what are you removing by washing
excess sodium nitrate
DEXP 7: what are you removing by washing now?
excess zinc and sulfate, then water, then acetone
DEXP 9: what's it ab
experimental determination of the value of "r" in PV = nRT
DEXP 10: key concept %
finding percentage of element in compound ex. % if sodium in pure table salt
DEXP 5: look at dats sheet
for metathesis reactions; observations and reactions
DEXP 8: what's it ab
gas laws and molecular mass of a gas
DEXP 10: what's it ab
gravimetric analysis of a chloride salt
DEXP 11: whats it ab
heat of neutralization
DEXP 2: Classify the following mixtures as homogeneous or heterogeneous: steel, white wine, salt water, potato salad, compost
homogeneous mixture: steel, white wine, salt water heterogeneous mixture: potato salad, compost A solution is another name for a homogeneous mixture. For example, white wine is a solution of alcohol and water. If something has a percentage value (such as 40% alcohol by volume), this is a good indication that you are dealing with a solution and not a pure substance.
DEXP 2: experiment errors resulting in percent recovery greater than 100?
if the sand was not completely dried, it would have additional mass, resulting in a greater percent recovery
DEXP 1: intensive vs extensive properties of zinc
intensive: -begins to melt at 419.58 degrees C -has a density of 7.13 g/mL -bluish gray in color extensive: -has a mass of 63.74 g -has a volume of 8.94 mL *two extensive properties such as mass and volume can combine to give an intensive property such as density.
HEXP 6: find qhot AND qcold
qhot: mass x 4.184 J/gC x deltaThot qcold: mass x 4.184 J/gC x deltaTcold round to 4 sig figs to help w more accurate calculation unit J
DEXP 11: heat of the reaction
qrxn = -(qsoln + qcal) difference between 2
DEXP 4: What is the identity of the unknown white solid?
lead nitrate Salts containing the carbonate anion are generally insoluble, except for compounds of NH4+ and the alkali metal cations. Thus, SrCO3does not dissolve in water to give a clear solution and it can be eliminated as a possible identify for the salt. Of the remaining possibilities, Pb2+ has a sulfate precipitate, but Mg2+ does not. The compound is indeed lead nitrate.
DEXP 1: A spherical ball of lead has a diameter of 5.5 cm. What is the mass of the sphere if lead has a density of 11.34 g/cm3? (The volume of a sphere is 4/3πr3 where r is the radius.)
m = 990 g Theoretical volume is based on a perfect sphere, but volume is more accurately determined by displacement of a liquid in a graduated beaker or cylinder. Density can change with temperature because volume can change with temperature, but the mass remains constant for a material that does not react. Therefore, it is usually more useful to establish the mass under controlled conditions and reference that mass rather than volume when describing how much of the material is present.
DEXP 10: converting mass of AgCl(s) to mass of Cl- in unknown original sample
mass AgCl x (1molAgCl/143.32gAgCl) x (1molCl-/1molAgCl) x (35.45g/1molCl-) = massCl- gravimetric factor = 0.2473 OR can do: mass AgCl x 0.2473 = mass Cl-
DEXP 10: % Chloride in original sample
mass Cl-/mass of unknown x 100
HEXP 5: mass of acetic acid reacted (show work below, use mass of CO2 and stoichiometry)
mass of CO2 lost to atmosphere x (1molCO2/44.01gCO2) x (60.05gHC2H3O2/1molHC2H3O2) = gHC2H3O2
HEXP 6: find moles of magnesium sulfate
mass of MgSO4 x (1molMgSO4/246.47 g/mol)
HEXP 5: mass percent of acetic acid in vinegar
mass of acetic acid reacted/mass of vinegar x 100
HEXP 5: Theoretical yield of CO2 (moles) based on baking soda, NaHCO3
mass of baking soda x (1molNaHCO3.84.0gNaHCO3) x (1molCO2/1molNaHCO3) = gHC2H3O2
HEXP 2: percent composition of sand in mixture
mass of sand recovered/mass of known sand/salt mixture x 100
HEXP 6: find qwater
mass x 4.184 J/gC x delta T 4 sig figs unit J
DEXP 2: percent of NH4Cl (or SiO2)
massNH4Cl/original mass x 100
DEXP 1: percent difference
measured value - accepted value/ accepted value x 100
DEXP 5: Label each of the following substances as a metathesis or NOT: Na2CO3 + CuSO4 -> Na2SO4 + CuCO3, BaCO3 + 2HCl -> BaCl2 + H2O + CO2, Cu(NO3)2 + Zn -> Cu + Zn(NO3)2, 2KClO3 -> 2KCl + 3O2
metathesis reaction: Na2CO3 + CuSO4 -> Na2SO4 + CuCO3, BaCO3 + 2HCl -> BaCl2 + H2O + CO2 not: Cu(NO3)2 + Zn -> Cu + Zn(NO3)2, 2KClO3 -> 2KCl + 3O2
DEXP 1: Part complete Convert your densities to kg/L and compare these values with those in g/mL
no effect
DEXP 5: Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water. CH3CH2OH, H2SO3, NH3, NaBr, KClO2
nonelectrolyte: CH3CH2OH weak electrolyte: H2SO3, NH3 strong electrolyte: NaBr, KClO2 To determine whether a substance is a nonelectrolyte, weak electrolyte, or strong electrolyte in water, first identify whether a substance is ionic or molecular. Most ionic compounds are composed of a metal and a nonmetal. Generally, ionic compounds are considered to completely dissociate in solution and are strong electrolytes, such as KClO2. Molecular compounds may be strong electrolytes, weak electrolytes, or nonelectrolytes. Strong acids and bases completely ionize in solution and would be considered strong electrolytes. Weak acids and bases, however, only partially ionize. Some molecules remain in solution. Thus, they are weak electrolytes. Any molecular substance that is not an acid or a base is most likely a nonelectrolyte.
HEXP 2: percent deviation - determining percent composition of sand in known sample
percent composition of sand in mixture - average percent composition of sand in mixture/ average percent composition of sand in mixture x 100
HEXP 3: is carbonate present/not in baking soda, baking powder, and salt?
present in baking soda and in baking powder; not present in salt
DEXP 9: 14.0 moles of gas are in a 3.00 L tank at 22.7 ∘C . Calculate the difference in pressure between methane and an ideal gas under these conditions. The van der Waals constants for methane are a=2.300L2⋅atm/mol2 and b=0.0430 L/mol.
pressure difference = 21.6 atm The answer to this question represents the error incurred by using the ideal gas law for real gases. This error is very tiny at low pressure and high temperature, but becomes quite significant for compressed gases (high pressure).
DEXP 11: heat gained by the calorimeter
qcal = C x (Teq - Ti)
DEXP 1: We recorded the temperature of the thiosulfate solution before carrying out the density matching experiment but did not use this information in our calculations. However, the density of thiosulfate solutions does exhibit a strong temperature dependence with density decreasing with increasing temperature. If you repeated the experiment at a temperature of 10.0°C higher than you did today, how would your density measurements change? In general, temperature changes effect the density of liquids more significantly than solids. Assume in this case that the temperature change of 10.0°C has a significant (measureable) effect on the density of the thiosulfate solution but has an insignifcant (not-measureable) on the density of the acrylic slug.
there would be no effect on the measured density value The answer to this question is that the outcome (density you measure) will be the same regardless of the temperature. Regardlesss of the starting conditions, the experiment concludes with you achieving neutral buoyancy (density of solution = density of acrylic). It is true that the density of the sodium thiosulfate solution will be slightly lower because of the elevated temperature. The consequence of this would be that you would add slightly less water (2 syringes rather than 3) to achieve neutral buoyancy but in the end the density of the warmer solution (more concentrated) solution would be the same as the cooler (less concentrated solution)
DEXP 2: percent recovered
total mass of recovered components/initial mass of mixture x 100
DEXP 1: For the density matching experiment, imagine that you spilled a bit of one thiosulfate solution sample during the measurement. As a result, your average mass of the thiosulfate solution was actually 27.5 mg too low. Apply an appropriate correction to your mass measurement and recalculate your observed density. In this case, the experimental error underestimates the mass of thiosulfate solution. Does this error result in an over or underestimate of your observed density?
underestimate Density = mass/volume; The small amount of liquid that was lost during the measurement would give you a smaller mass than the actual mass for the solution. Since the volume is assumed to be the same, the calculated density of the thiosulfate solution will be lower than the actual value. At neutral bouyancy, we assume that the density of the solution is equal to that of the acrylic slug and so the error will give an underestimate of the acrylic's density.
DEXP 9: key concept
van der Waals equation
DEXP 9: pressure O2 gas
vapor pressure of water (mmHg) x (1 atm/760 mmHg) = ____ barometric pressure (in atm) - ____ = pressure of O2 gas (in atm)
DEXP 7: possible error
when decanting, one lost some sample by pouring it out assuming one had excess, yet removed the excess by washing approximate/incorrect volumes of acids/bases were added
HEXP 3: Sodium Carbonate(aq) + Magnesium Sulfate Heptahydrate(aq) observations
white precipitate is formed, surrounded by initially clear solution, turns a bit yellow
HEXP 3: Sodium Carbonate(aq) + Magnesium Sulfate Heptahydrate(aq) containing anion + vinegar observations
white solid at bottom, CO2 bubbles released; some fizzling
DEXP 7: concept
write balanced chemical equations for a reaction; limiting reactant; grams of each present after reaction
DEXP 5 concept
writing balanced net ionic equations ___ + ___ -> _____
DEXP 1: A 32.75 g sample of a solid is placed in a flask. Toluene, in which the solid is insoluble, is added to the flask so that the total volume of solid and liquid together is 49.00 mL. The solid and toluene together weigh 58.28 g. The density of toluene at the temperature of the experiment is 0.864 g/mL. What is the density of the solid?
ρ = 1.68 g/mL Since density is defined as the amount of mass in a unit volume of a substance, the volume of 32.75 g of the solid placed in the flask should be found. To do this, first, calculate the mass of toluene added to the flask as the difference between the mass of the flask with the solid and toluene and the mass of the solid, and then convert it to the volume of toluene, using density as a conversion factor: Vtoluene=(58.28g−32.75g)×1mL/0.864g =29.5mL Use this value to find the volume of the solid sample as the difference between the total volume within the flask and the volume of toluene. Finally, calculate the density of the solid as the ratio of its mass to its volume: ρ=32.75g/(49.00mL−29.5mL) =1.68g/mL