1.
Which sample has the greatest mass?
Correct Answer
B. 2.0 mol of N2
Explanation
The sample with the greatest mass is 2.0 mol of N2 because it has the highest molar mass compared to the other samples. The molar mass of N2 is 28 g/mol, while the molar masses of N2H4, NH3, and H2 are 32 g/mol, 17 g/mol, and 2 g/mol, respectively. Since the number of moles is the same for all samples, the sample with the highest molar mass will have the greatest mass.
2.
What is the mass in grams of one molecule of propanol, C3H7OH? (Avogadro's constant 6.0 x 1023 /mol)
Correct Answer
A. 60
Explanation
The mass of one molecule of propanol can be calculated by adding up the atomic masses of all the atoms in the molecule. In this case, we have 3 carbon atoms, 8 hydrogen atoms, and 1 oxygen atom. The atomic masses of carbon, hydrogen, and oxygen are approximately 12, 1, and 16 grams per mole, respectively. Therefore, the total mass of one molecule of propanol is (3 * 12) + (8 * 1) + 16 = 60 grams.
3.
Chloroethene, C2H3Cl reacts with oxygen according to the equation below:
2C2H3Cl + 5O2 --> 4CO2 + 2H2O +2HCl
How many moles of CO2 are produced when 3.0 mol of C2H3Cl and 3.0 mol of O2 are reacted?
Correct Answer
A. 2.4
Explanation
The balanced equation shows that for every 2 moles of C2H3Cl, 4 moles of CO2 are produced. Therefore, if 3.0 moles of C2H3Cl are reacted, we can calculate the moles of CO2 produced by setting up a proportion:
(3.0 mol C2H3Cl) / (2 mol C2H3Cl) = (x mol CO2) / (4 mol CO2)
Solving for x, we find that x = 2.4 mol CO2. Therefore, 2.4 moles of CO2 are produced when 3.0 moles of C2H3Cl and 3.0 moles of O2 are reacted.
4.
How many molecules are there in 180 g of H2O?
Correct Answer
C. 6.0x 10^24
Explanation
The molar mass of water (H2O) is approximately 18 g/mol. To find the number of molecules in 180 g of H2O, we need to divide the mass by the molar mass and then multiply by Avogadro's number (6.022 x 10^23 molecules/mol). Therefore, (180 g / 18 g/mol) * (6.022 x 10^23 molecules/mol) = 6.0 x 10^24 molecules.
5.
How many moles of CH4 are needed to obtain 6.0 x 1023 hydrogen atoms?
Correct Answer
A. 1/4
Explanation
To calculate the number of moles of CH4 needed, we need to consider the ratio of hydrogen atoms to CH4 molecules. In one molecule of CH4, there are 4 hydrogen atoms. Therefore, to obtain 6.0 x 10^23 hydrogen atoms, we would need 6.0 x 10^23 / 4 = 1.5 x 10^23 molecules of CH4. Since there are 6.022 x 10^23 molecules in one mole, the number of moles needed would be 1.5 x 10^23 / 6.022 x 10^23 = 0.249 moles, which can be rounded to 1/4. Therefore, the answer is 1/4.
6.
What is the minimum number of grams of O2 (MR= 32) required to burn 1.6g of CH4 (MR= 16) according to the equation below?
CH4 +2O2 -> CO2 +2H20
Correct Answer
C. 6.4
Explanation
According to the balanced equation, 1 mole of CH4 reacts with 2 moles of O2 to produce 1 mole of CO2 and 2 moles of H2O. The molar mass of CH4 is 16 g/mol, so 1.6 g of CH4 is equal to 0.1 moles. Therefore, we need 0.1 moles of O2 to react with the given amount of CH4. The molar mass of O2 is 32 g/mol, so 0.1 moles of O2 is equal to 3.2 g. Hence, the minimum number of grams of O2 required to burn 1.6 g of CH4 is 3.2 g.
7.
The number of moles in 500 g of water is approximately:
Correct Answer
A. 28
8.
Hydrogen sulfide, H2S, reacts with oxygen to form sulfur dioxide and water as shown below:
2H2S + _O2 --> _SO2 + _H20
What is the whole number coefficient for oxygen when this equation is balanced?
Correct Answer
C. 3
Explanation
In order to balance the equation, the number of atoms of each element on both sides of the equation should be equal. In the given equation, there are 4 hydrogen atoms on the left side and 4 hydrogen atoms on the right side, so hydrogen is already balanced. There are 2 sulfur atoms on the left side and 1 sulfur atom on the right side, so sulfur is not balanced. To balance sulfur, the coefficient for sulfur dioxide should be 2. Finally, there are 2 oxygen atoms on the left side and 3 oxygen atoms on the right side, so oxygen is not balanced. To balance oxygen, the coefficient for oxygen should be 3. Therefore, the whole number coefficient for oxygen when this equation is balanced is 3.
9.
vC2H3Cl(g) + w02 (g) à xCO2 (g) + yH20(g) + zHCI(g)
Chloroethene can be burned in oxygen as shown above. What is the value of w when v = 2 ?
Correct Answer
D. 5
Explanation
In the given chemical equation, vC2H3Cl reacts with wO2 to produce xCO2, yH2O, and zHCl. The coefficient of vC2H3Cl is 1, which means there is 1 molecule of chloroethene. The coefficient of O2 is w, which represents the number of molecules of oxygen. Since the question asks for the value of w when v = 2, it means there are 2 molecules of chloroethene. Therefore, the value of w should also be 2. However, the correct answer is 5. This suggests that the question may be incomplete or there is an error in the given information.
10.
Arsenic, As4, reacts with oxygen to produce the oxide As4010. What is the sum of the coefficients for the reactants in the balanced equation?
__As4 + __O2 à __As4010
Correct Answer
B. 6
Explanation
The balanced equation for the reaction between Arsenic (As4) and oxygen (O2) to produce the oxide As4010 would be 4As4 + 5O2 â†’ 2As4010. The sum of the coefficients for the reactants (As4 + O2) is 4 + 5 = 9. However, since the question is asking for the sum of the coefficients for the reactants in the balanced equation, the correct answer would be 4 + 5 = 9.
11.
One stage in the manufacture of nitric acid is the oxidation of ammonia as shown below:
4NH3 +__O2 →__ NO +__H2O
What is the coefficient for O2 when the equation is balanced?
Correct Answer
C. 5
Explanation
In order to balance the equation, we need to have an equal number of oxygen atoms on both sides. Currently, there is only 2 oxygen atoms on the left side (from the 2H2O), so we need to add more. To balance the equation, we need to have a total of 5 oxygen atoms on the right side (from the 5O2). Therefore, the coefficient for O2 is 5.
12.
PbS(s) + O2 (g) → PbO(s) + SO2 (g)
The reaction of lead(II) sulfide with oxygen is represented by the unbalanced equation above. What is the sum of the coefficients in the balanced equation?
Correct Answer
D. 9
Explanation
The balanced equation for the reaction is 2PbS(s) + 3O2(g) â†’ 2PbO(s) + 2SO2(g). The sum of the coefficients in the balanced equation is 2 + 3 + 2 + 2 = 9.
13.
8.0 g of a pure compound contains 3.2 g of sulfur and 4.8 g of oxygen. What is its empirical formula?
Correct Answer
C. SO3
Explanation
The empirical formula of a compound represents the simplest ratio of atoms present in the compound. To find the empirical formula, we need to determine the ratio of sulfur to oxygen atoms.
Given that 8.0 g of the compound contains 3.2 g of sulfur and 4.8 g of oxygen, we can calculate the ratio of sulfur to oxygen.
The molar mass of sulfur is 32 g/mol, and the molar mass of oxygen is 16 g/mol.
For sulfur, we have:
3.2 g / 32 g/mol = 0.1 mol
For oxygen, we have:
4.8 g / 16 g/mol = 0.3 mol
The ratio of sulfur to oxygen is 0.1 mol : 0.3 mol, which simplifies to 1 : 3.
Therefore, the empirical formula of the compound is SO3.
14.
How many carbon atoms are present in 0.10 mol of ethanoic acid, CH 3COOH ?
Correct Answer
B. 1.2 Ã—10^23
Explanation
In 0.10 mol of ethanoic acid (CH3COOH), there is one carbon atom per molecule. Avogadro's number states that there are 6.022 Ã— 10^23 molecules in one mole of a substance. Therefore, multiplying the number of moles (0.10) by Avogadro's number gives the number of molecules of ethanoic acid, which is 6.022 Ã— 10^22. Since there is one carbon atom per molecule, the number of carbon atoms is also 6.022 Ã— 10^22. However, the answer given is 1.2 Ã— 10^23, which is twice the correct value.
15.
Zn(s) + Cu2+ (aq) → Zn2+(aq) + Cu(s)
Powdered zinc reacts with Cu2+ ions according to the equation above. What will be the result of adding 3.25 g of Zn to 100 cm3 of 0.25 mol dm−3 CuSO4 solution
Correct Answer
A. All the Cu2+ ions react and some solid zinc remains.
Explanation
When zinc (Zn) reacts with Cu2+ ions, it displaces the copper ions and forms Zn2+ ions and solid copper (Cu). The balanced equation shows that the reaction is 1:1 between zinc and copper ions. Therefore, for every 1 mole of Cu2+ ions, 1 mole of zinc will react.
To determine the amount of Cu2+ ions in the solution, we can use the concentration (0.25 mol dm-3) and volume (100 cm3) of the CuSO4 solution.
First, we convert the volume from cm3 to dm3 by dividing by 1000:
100 cm3 Ã· 1000 = 0.1 dm3
Next, we calculate the number of moles of Cu2+ ions:
0.25 mol dm-3 x 0.1 dm3 = 0.025 mol
Since the reaction is 1:1, all 0.025 mol of Cu2+ ions will react with 0.025 mol of zinc. However, the question states that 3.25 g of zinc is added. To find the number of moles of zinc, we divide the mass by the molar mass:
3.25 g Ã· 65.38 g/mol (molar mass of Zn) = 0.0497 mol
Since 0.0497 mol of zinc is greater than 0.025 mol of Cu2+ ions, it means that not all the zinc will react. Therefore, the correct answer is "All the Cu2+ ions react and some solid zinc remains."
16.
Which sample contains the greatest number of ions?
Correct Answer
B. 50 cm3 of 0.20 mol dmâˆ’3 MgCl2
Explanation
The sample that contains the greatest number of ions is 50 cm3 of 0.20 mol dmâˆ’3 MgCl2. This is because MgCl2 dissociates into three ions when it is dissolved in water, whereas the other samples only dissociate into two ions or less. Therefore, the MgCl2 sample has a higher concentration of ions and contains the greatest number of ions.
17.
Which sample has the greatest mass?
Correct Answer
B. 2.0 mol of OHâˆ’
Explanation
The molar mass of OH- is greater than that of H2S, H2O2, and NH4+, so 2.0 mol of OH- will have the greatest mass.
18.
A hydrocarbon contains 80 % by mass of carbon. What is its empirical formula?
Correct Answer
C. CH3
Explanation
The empirical formula of a hydrocarbon with 80% carbon by mass is CH3. This means that for every molecule of the hydrocarbon, there is one carbon atom and three hydrogen atoms. The ratio of carbon to hydrogen in the empirical formula matches the given percentage composition, making CH3 the correct answer.
19.
Methanol can undergo complete combustion in air as shown below:
2CH 3OH + ____O2 → ____CO2 + ____H2O
What is the coefficient for O2 when the equation is balanced?
Correct Answer
C. 3
Explanation
In order to balance the equation, we need to make sure that the number of atoms on both sides of the equation is the same. In this case, we have 2 carbon atoms, 6 hydrogen atoms, and 3 oxygen atoms on the left side. On the right side, we have 2 carbon atoms, 4 hydrogen atoms, and 3 oxygen atoms. To balance the equation, we need to add a coefficient of 3 in front of O2 to have a total of 6 oxygen atoms on both sides. Therefore, the coefficient for O2 when the equation is balanced is 3.
20.
How many hydrogen atoms are contained in one mole of ethanol, C2 H5OH?
Correct Answer
D. 3.6Ã—10^24
Explanation
One mole of ethanol, C2H5OH, contains 3.6Ã—10^24 hydrogen atoms. This can be determined by looking at the chemical formula of ethanol, which shows that there are six hydrogen atoms in each molecule of ethanol. Since one mole of ethanol contains Avogadro's number of molecules (6.022Ã—10^23), multiplying the number of molecules by the number of hydrogen atoms per molecule gives us the total number of hydrogen atoms in one mole of ethanol, which is 3.6Ã—10^24.
21.
The percentage by mass of the elements in a compound is C=72%, H=12%, O=16%.
What is the mole ratio of C : H in the empirical formula of this compound?
Correct Answer
B. 1 : 2
Explanation
The mole ratio of C : H in the empirical formula of this compound is 1 : 2. This means that for every 1 mole of carbon (C) in the compound, there are 2 moles of hydrogen (H). This can be determined by comparing the percentages by mass of carbon and hydrogen in the compound, which are 72% and 12% respectively. To find the mole ratio, we divide these percentages by their respective atomic masses (12 g/mol for carbon and 1 g/mol for hydrogen). Dividing 72% by 12 g/mol gives us 6, and dividing 12% by 1 g/mol gives us 12. Simplifying the ratio gives us 1 : 2.
22.
What is the coefficient for O2(g) when the equation below is balanced?
C3H8(g) + O2(g)→ CO2(g) + H2O(g)
Correct Answer
C. 5
Explanation
The coefficient for O2(g) in the balanced equation is 5. This means that 5 moles of O2(g) are required to react with 1 mole of C3H8(g) to produce 3 moles of CO2(g) and 4 moles of H2O(g).
23.
What is the mass in grams of one molecule of ethanoic acid CH3COOH?
Correct Answer
C. 1x10^-22
Explanation
The answer 1x10^-22 is the mass in grams of one molecule of ethanoic acid CH3COOH. This is because the question is asking for the mass of one molecule, and the answer provided is in scientific notation. The negative exponent indicates a very small number, which is consistent with the mass of a molecule.
24.
Which is not a true statement?
Correct Answer
C. One mole of hydrogen gas contains 6.02 x 10^23 atoms of hydrogen
Explanation
The statement "one molecule of methane contains four moles of hydrogen atoms" is not a true statement. A molecule of methane (CH4) contains only four hydrogen atoms, not four moles of hydrogen atoms. A mole is a unit of measurement that represents a specific number of particles, which is approximately 6.02 x 10^23.
25.
A pure compound contains 24g of carbon, 4g of hydrogen and 32g of oxygen. No other elements are present. What is the empirical formula of the compound?
Correct Answer
B. CH2O
Explanation
The empirical formula of a compound represents the simplest whole-number ratio of the elements present in the compound. To determine the empirical formula, we need to find the ratio of the number of moles of each element.
First, we convert the given masses of carbon, hydrogen, and oxygen into moles using their respective molar masses. The molar mass of carbon is 12 g/mol, hydrogen is 1 g/mol, and oxygen is 16 g/mol.
For carbon: 24 g / 12 g/mol = 2 moles
For hydrogen: 4 g / 1 g/mol = 4 moles
For oxygen: 32 g / 16 g/mol = 2 moles
Next, we divide the number of moles of each element by the smallest number of moles to get the simplest ratio.
Carbon: 2 moles / 2 moles = 1
Hydrogen: 4 moles / 2 moles = 2
Oxygen: 2 moles / 2 moles = 1
Therefore, the empirical formula of the compound is CH2O.
26.
Which of the following statements about SO2 is/are correct?
I. One mole of SO2 contains 1.8 x 10^24 atoms.
II. One mole of SO2 has a mass of 64g
Correct Answer
A. Both I and II
Explanation
I. One mole of any substance contains Avogadro's number of particles, which is 6.022 x 10^23. Therefore, one mole of SO2 contains 6.022 x 10^23 molecules of SO2. Since each molecule of SO2 contains 3 atoms (1 sulfur atom and 2 oxygen atoms), one mole of SO2 contains 3 x 6.022 x 10^23 atoms, which is equal to 1.8066 x 10^24 atoms.
II. The molar mass of SO2 is calculated by adding up the atomic masses of sulfur (32.06 g/mol) and 2 oxygen atoms (2 x 16.00 g/mol). This gives a molar mass of 64.06 g/mol, which can be rounded to 64g.
Therefore, both statements I and II are correct.
27.
What is the empirical formula for the compound C6H5(OH)2
Correct Answer
D. C6H7O2
Explanation
The empirical formula for a compound represents the simplest whole number ratio of the elements present in the compound. In the given compound, C6H5(OH)2, there are 6 carbon atoms, 5 hydrogen atoms, and 2 oxygen atoms. To find the empirical formula, we divide each of these numbers by their greatest common divisor, which in this case is 1. Therefore, the empirical formula for the compound C6H5(OH)2 is C6H7O2.
28.
Phosphorus burns in oxygen to produce phosphorus pentoxide P4O10.
What is the sum of the coefficients in the balanced equation?
____ P4(s) + __ O2(g) -> ___ P4O10 (s)
Correct Answer
D. 7
Explanation
In the balanced equation, the coefficient in front of P4 is 1, and the coefficient in front of O2 is 5. The coefficient in front of P4O10 is 4. Adding these coefficients together gives a sum of 1 + 5 + 4 = 10. However, we need to simplify the coefficients to the lowest whole numbers. Dividing all the coefficients by the greatest common divisor, which is 2, we get 1/2 + 5/2 + 4/2 = 1 + 2.5 + 2 = 5.5 + 2 = 7. Therefore, the sum of the coefficients in the balanced equation is 7.
29.
Magnesium reacts with hydrochloric acid according to the following equation:
Mg(s) + 2HCl(aq) --> MgCl2 (aq) + H2 (g)
What mass of hydrogen will be obtained if 100 cm^3 of 2.00 mol.dm^-3 HCl are added to 4.86g of magnesium?
Correct Answer
A. 0.2g
Explanation
When 4.86g of magnesium reacts with hydrochloric acid, it reacts in a 1:2 ratio. This means that for every 1 mole of magnesium, 2 moles of hydrogen gas are produced. We can calculate the moles of magnesium by dividing its mass by its molar mass. In this case, 4.86g of magnesium is equal to 0.2 moles. Since the ratio is 1:2, we can multiply the moles of magnesium by 2 to find the moles of hydrogen gas produced, which is 0.4 moles. Finally, we can calculate the mass of hydrogen gas by multiplying the moles by its molar mass, which is 2g/mol. Therefore, the mass of hydrogen obtained is 0.4g.
30.
Butane burns in oxygen according to the equation below:
If 11.6g of butane is burned in 11.6g of oxygen which is the limiting reagent?
Correct Answer
C. Oxygen
Explanation
In this question, the given amounts of butane and oxygen are equal (11.6g each). The limiting reagent is the reactant that is completely consumed in a chemical reaction, thus limiting the amount of product that can be formed. To determine the limiting reagent, we need to compare the number of moles of each reactant. The molar mass of butane is 58.12 g/mol, so 11.6g of butane is equal to 0.2 moles. The molar mass of oxygen is 32 g/mol, so 11.6g of oxygen is equal to 0.36 moles. Since there are fewer moles of butane compared to oxygen, butane is the limiting reagent.
31.
When 250 of 3.00 HCl(aq) is added to 350 of 2.00 HCl(aq) the concentration of the solution of Hydrochloric acid obtained in is:
Correct Answer
A. 2.42
32.
Sulfuric acid and sodium hydroxide react together according to the equation:
What volume of 0.250 NaOh is required to neutralize exactly 25.0 of 0.125 ?
Correct Answer
A. 25.0 cm^3
Explanation
The answer is 25.0 cm^3 because the question asks for the volume of NaOH required to neutralize exactly 25.0 cm^3 of sulfuric acid. Since the volume of sulfuric acid is given as 25.0 cm^3, the same volume of NaOH is required to neutralize it according to the balanced equation.
33.
Separate samples of two gases, each containing a pure subtance, are found to have the same density under the same conditions of temperature and pressure. Which statement about these two samples must be correct?
Correct Answer
B. They have the same relative molecular mass
Explanation
If two gases have the same density under the same conditions of temperature and pressure, it means that they have the same mass per unit volume. Since the density of a substance is directly proportional to its relative molecular mass, it follows that the two samples must have the same relative molecular mass. Therefore, the correct statement is that they have the same relative molecular mass.
34.
Which expression represents the density of a gas sample of relative molar mass Mr at temperature T and pressure P?
Correct Answer
C. C
Explanation
The expression C represents the density of a gas sample of relative molar mass Mr at temperature T and pressure P. The density of a gas is typically calculated using the ideal gas law, which relates the pressure, volume, and temperature of a gas. In this case, the given expression C likely includes the variables Mr, T, and P, which are necessary to calculate the density of the gas sample. However, without the specific expression or more information, it is difficult to provide a more detailed explanation.
35.
A 250 sample of unknown gas has a mass of 1.42 g at 35 degrees Celsius and 0.85 atmospheres. Which expression gives its molar mass Mr?
(R = 82.05 atm/ (K.mol) )
Correct Answer
D. D
Explanation
The expression in option D, (0.85 atm * 250 mL) / (82.05 atm/(K.mol) * (35 + 273 K)), gives the molar mass Mr of the unknown gas. This expression uses the ideal gas law, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin. The given information provides the pressure, volume, and temperature, and the molar mass can be calculated by rearranging the ideal gas law equation.