AP Chem EC Test
It does not conduct electricity because its ions cannot move freely within the solid.
Which of the following correctly indicates whether the solid represented by the particulate model shown above conducts electricity and explains why or why not?
NH3
Which of the following is the conjugate acid of NH2- ?
F−(aq)+H+(aq)→HF(aq)
Which of the following is the net ionic equation for the reaction between aqueous sodium fluoride and hydrochloric acid?
(2.0g/(20.18g/mol))(6.0x10^23 particles/mol)
Which of the following numerical expressions gives the number of particles in 2.0g of Ne?
Zn(s)+Ni^2+(aq) --> Zn^2+(aq)+Ni(s)
An experiment was performed to investigate the reaction between metal and at different concentrations. Because the ion is green, the extent of the reaction was determined using spectrophotometric analysis. Four standard solutions of were prepared by dissolving (molar mass ) in water. The absorbance of each solution was measured; the results are shown both in the table below and in the following plot of the absorbance data. Which of the following equations best represents the reacting species in the reaction between metal and ?
12
. . . C10H12O4S(s) + . . . O2(g) → . . . CO2(g) + . . . SO2(g) + . . . H2O(g) When the equation above is balanced and all coefficients are reduced to their lowest whole-number terms, the coefficient for O2(g) is
5
...C3H8(g) + ...O2(g) → ...H2O(g) + ...CO2(g) When the equation for the reaction represented above is balanced and all coefficients are reduced to the lowest whole-number terms, the coefficient for O2(g) is
Oxygen, which changes from -1 to 0
5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g) In a titration experiment, H2O2(aq) reacts with aqueous MnO4-(aq) as represented by the equation above. The dark purple KMnO4 solution is added from a buret to a colorless, acidified solution of H2O2(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.) Which element is being oxidized during the titration, and what is the element's change in oxidation number?
pH> 7, because CH3OO-(aq) is a weak base.
A 0.08 M solution of CH3COOH (pKa=4.74) is titrated with 0.10 M NaOH (aq). What is the pH at the equivalence point of the titration and why?
HC2H3O2(aq) + OH-(aq) → C2H3O2-(aq) + H2O(l)
A 20. mL sample of 0.50 M HC2H3O2(aq) is titrated with 0.50 M NaOH(aq). Which of the following best represents the species that react and the species produced in the reaction?
.28 M
A 40.0 mL sample of 0.25 M KOH is added to 60.0 mL of 0.15 M Ba(OH)2. What is the molar concentration of OH-(aq) in the resulting solution? (Assume that the volumes are additive.)
SF6
A sample of a compound contains 3.21 g of sulfur and 11.4 g of fluorine. Which of the following represents the empirical formula of the compound?
3,4,6,7
A sample of carbonate rock is a mixture of and . The rock is analyzed in a laboratory, and the results are recorded in the table above. Which columns in the table provide all the information necessary to determine the mole ratio of to in the rock?
Which sample has the higher purity?
A student has two samples of , each one from a different source. Assume that the only potential contaminant in each sample is . The student runs an experiment to determine the percent by mass of chlorine in each sample. From the results of this experiment alone, which of the following questions is most likely to be answered?
The mass of in each mixture
A student is given two samples, each a mixture of only and but in different proportions. Which of the following pieces of information could be used to determine which mixture has the higher proportion of ?
After the water has evaporated, the white crystals in the beaker have a mass of 20.0g
A student mixes 20.0g of white crystals with distilled water in a beaker. After the mixture was stirred, no crystals are visible and the solution is clear. After several days, all of the water evaporates and white crystals are found in the beaker. Which of following pieces of experimental evidence would best help the student to confirm that a new compound had not been made and that only a physical change occurred?
The mass of the sample increased, so a chemical change occurred when bonds formed between the metal and another substance.
A student places a sample of a pure metal in a crucible and heats it strongly in air. Data from the experiment are given in the table above. The final mass was determined after the sample was cooled to room temperature. Which of the following statements related to the experiment is correct?
MgO
According to the information in the table above, a 1.00 g sample of which of the following contains the greatest mass of oxygen?
The mass spectrum of Cu has a peak at 63 amu and another peak at 65 amu
According to the information in the table above, a 1.00 g sample of which of the following contains the greatest mass of oxygen?
What is the formula unit of each compound?
According to the information in the table above, a 1.00 g sample of which of the following contains the greatest mass of oxygen?
.080 M
An experiment was performed to investigate the reaction between metal and at different concentrations. Because the ion is green, the extent of the reaction was determined using spectrophotometric analysis. Four standard solutions of were prepared by dissolving (molar mass ) in water. The absorbance of each solution was measured; the results are shown both in the table below and in the following plot of the absorbance data. The concentration of ions in solution was
C4H8
Complete combustion of a sample of a hydrocarbon in excess oxygen produces equimolar quantities of carbon dioxide and water. Which of the following could be the molecular formula of the compound?
It is a redox reaction, because Cu(s) is oxidized and the nitrogen atom in NO3−(aq) is reduced.
Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H2O(l) Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 M HNO3(aq) into their beakers. The reaction between the copper in the mixture and the HNO3(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu2+(aq). The solutions were then diluted with distilled water to known volumes. Which of the following is true about the reaction?
Pb2+(aq)+2Br-(aq)-->PbBr2(s)
Equal volumes of .2 M solutions of lead(II) nitrate and potassium bromide are combined to form lead(II) bromide as a yellow precipitate. Which of the following is the correct net ionic equation for the reaction?
20 g
H2 + F2 → 2 HF In the reaction represented above, what mass of HF is produced by the reaction of 3.0 x 1023 molecules of H2 with excess F2 ? (Assume the reaction goes to completion.)
The oxidation number of Se changes from -2 to +6.
H2Se(g) + 4 O2F2(g) → SeF6(g) + 2 HF(g) + 4 O2(g) Which of the following is true regarding the reaction represented above?
H2O(l) and Cl-(aq)
HCl(aq)+H2O(l)-->H3O+(aq)+Cl-(aq) For the dissolution of in water represented above, which of the following pairs includes the Brønsted-Lowry bases?
1.2 x 10^23
How many carbon atoms are contained in 2.8 g of C2H4 ?
Graph that is exact same as graph shown
In pure water, some of the molecules ionize according to the equation . The extent of the ionization increases with temperature. The graph above shows the of pure water at different temperatures. Which of the following represents the variations in the of pure water under the same conditions?
25%
Li3N(s) + 2 H2(g) ⇄ LiNH2(s) + 2 LiH(s) ΔH° = -192 kJ/molrxn Because pure H2 is a hazardous substance, safer and more cost effective techniques to store it as a solid for shipping purposes have been developed. One such method is the reaction represented above, which occurs at 200°C. When 70. g of Li3N(s) (molar mass 35 g/mol) reacts with excess H2(g), 8.0 g of LiH(s) is produced. The percent yield is closest to
NH3(aq) and Cl-(aq)
NH3(aq) + HCl(aq) ⇄ NH4+(aq) + Cl-(aq) The Brønsted-Lowry bases in the reaction represented above are
0.1 M KI (aq) because KI completely dissociates in water to produce ions.
Of the three solutions listed in the table above, which one, if any, has the greatest electrical conductivity and why?
higher than the actual value, since water is included in the apparent mass of KHP
Potassium hydrogen phthalate, KHP, is used as a primary standard for determining the concentration of a solution of NaOH by titration. If the KHP has not been dried before weighing, the calculated molarity of the NaOH would be
The oxidation number of oxygen changes from -1 to 0.
The following balanced equation represents the decomposition of hydrogen peroxide, 2H2O2(aq)-->2H2O(l) + O2(g) The student claims that the reaction is an oxidation-reduction reaction. Which of the following statements correctly describes a change in oxidation number as the decomposition reaction proceeds?
Ca2+(aq) + SO42-(aq) → CaSO4(s)
The following questions refer to the reactions represented below. (A) H2SeO4(aq) + 2 Cl-(aq) + 2 H+(aq) → H2SeO3(aq) + Cl2(g) + H2O(l) (B) S8(s) + 8 O2(g) → 8 SO2(g) (C) 3 Br2(aq) + 6 OH-(aq) → 5 Br-(aq) + BrO3-(aq) + 3 H2O(l) (D) Ca2+(aq) + SO42-(aq) → CaSO4(s) (E) PtCl4(s) + 2 Cl-(aq) → PtCl62-(aq) A precipitation reaction
Zr
The mass spectrum of an average sample of a pure element is shown in the figure above. Which of the following is the identity of the element?
Ga
The mass spectrum of an element is represented above. Which of the following is most likely the identity of the element?
11
The pH of a solution prepared by the addition of 10. mL of 0.002 M KOH(aq) to 10. mL of distilled water is closest to
The initial amount of in the container must have been 0.10 mol. C6H12O6 + 6O2 --> 6CO2 + 6H2O
The reaction between C6H12O6 and O2 is represented by the balanced equation above. In an experiment, .30mol of CO2 was produced from the reaction of 0.05 mol of C6H12O6 with excess O2. The reaction was repeated at the same temperature and in the same container, but this time 0.60 mol of CO2 was produced. Which of the following must be true?
Sr2+(aq)+SO42−(aq)→SrSO4(s)
The reaction between aqueous strontium chloride (srCl2) and aqueous potassium sulfate (K2SO4) forms a precipitate of strontium sulfate (SrSO4). Which of the following represents the net ionic equation for the reaction?
Reheat the sample until its mass is constant.
To determine the percentage of water in a hydrated salt, a student heated a 1.2346 g sample of the salt for 30 minutes; when cooled to room temperature, the sample weighed 1.1857 g. After the sample was heated for an additional 10 minutes and again cooled to room temperature, the sample weighed 1.1632 g. Which of the following should the student do next?
It contains ionic bonds
Two pure elements react to form a compound. One element is an alkali metal, , and the other element is a halogen, . Which of the following is the most valid scientific claim that can be made about the compound?
CrO3
What is the empirical formula of an oxide of chromium that is 48 percent oxygen by mass?
PH=14.00 - (-log(0.0015)) and pOH= -log(0.0015)
Which of the following pairs of mathematical expressions can be used to correctly calculate the pH and pOH of a 0.0015M KOH(aq) solution at 25 C?
pH=2.00, because [H+] =1.0x10^-2 M
Which of the following statements about the pH of 0.010 M HClO4 is correct?
The dehydrated sample absorbed moisture after heating
After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38 percent. The correct value for the percentage of water in the hydrate is 51 percent. Which of the following is the most likely explanation for this difference?
Mo
Which of the following elements has the mass spectrum represented above?
0.20 M
What is the molarity of I-(aq) in a solution that contains 34 g of SrI2 (molar mass 341 g) in 1.0 L of the solution?
[PO43−] < [NO3−] < [Na+]
When 100 mL of 1.0 M Na3PO4 is mixed with 100 mL of 1.0 M AgNO3, a yellow precipitate forms and [Ag+] becomes negligibly small. Which of the following is a correct listing of the ions remaining in solution in order of increasing concentration?
4.5 M
When 70. milliliter of 3.0-molar Na2CO3 is added to 30. milliliters of 1.0-molar NaHCO3 the resulting concentration of Na+ is
10
When a 3.22 g sample of an unknown hydrate of sodium sulfate, Na2SO4 ⋅ H2O(s), is heated, H2O (molar mass 18 g) is driven off. The mass of the anhydrous Na2SO4(s) (molar mass 142 g) that remains is 1.42 g. The value of x in the hydrate is
The acid is HNO2 (aq) and the conjugate base is NO2-(aq).
Which of the following correctly identifies a Brønsted-Lowry conjugate acid-base pair in a solution prepared by mixing together HNO2(aq) and NH3(aq)?
