Free General Chemistry Exam
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Question 1 of 10
1. Question
The following reaction was performed in water:
\( HCl+NaHCO_3 \rightarrow NaCl + H_2CO_3 \)
How many moles of NaCl are produced from 30 Ml of 0.5M NaHCO3 and 15 mL of 0.5M HCl?
Correct
First, we need to find the limiting reagent.
We have 0.03 L * 0.5M = 0.015 mol NaHCO3 and 0.015 * 0.5M = 0.0075 mol of HCl.
1 mol NaHCO3 is consumed for each mole of HCl.
0.015 mol/ 1mol HCl = 0.015 mol
0.005 mol / 1 HCl = 0.005
Because there are fewer moles of HCl, it is our limiting reagent.
Looking at the balanced reaction, we can see there is 1 mol of HCl for every mol of NaCl, therefore the moles of NaCl produced are
0.005 mol HCl * 1 mol NaCl/1 mol HCl = 0.005 mol NaCl
Incorrect
First, we need to find the limiting reagent.
We have 0.03 L * 0.5M = 0.015 mol NaHCO3 and 0.015 * 0.5M = 0.0075 mol of HCl.
1 mol NaHCO3 is consumed for each mole of HCl.
0.015 mol/ 1mol HCl = 0.015 mol
0.005 mol / 1 HCl = 0.005
Because there are fewer moles of HCl, it is our limiting reagent.
Looking at the balanced reaction, we can see there is 1 mol of HCl for every mol of NaCl, therefore the moles of NaCl produced are
0.005 mol HCl * 1 mol NaCl/1 mol HCl = 0.005 mol NaCl
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Question 2 of 10
2. Question
Which of the following statements is NOT true about the first law of thermodynamics?
Correct
To understand the relationship between work and heat, we need to understand a third, linking factor: the change in internal energy. Energy cannot be created nor destroyed, but it can be converted or transferred. Internal energy refers to all the energy within a given system, including the kinetic energy of molecules and the energy stored in all of the chemical bonds between molecules. With the interactions of heat, work and internal energy, there are energy transfers and conversions every time a change is made upon a system. However, no net energy is created or lost during these transfers.
Incorrect
To understand the relationship between work and heat, we need to understand a third, linking factor: the change in internal energy. Energy cannot be created nor destroyed, but it can be converted or transferred. Internal energy refers to all the energy within a given system, including the kinetic energy of molecules and the energy stored in all of the chemical bonds between molecules. With the interactions of heat, work and internal energy, there are energy transfers and conversions every time a change is made upon a system. However, no net energy is created or lost during these transfers.
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Question 3 of 10
3. Question
A particular reaction has a rate constant of 5.5 × 106 M-4s-1. What is the overall order of this reaction?
Correct
The unit of the rate constant of a reaction with an overall order n is
Unit of rate constant = M1-n s-1
Thus, if the unit of the rate constant of a reaction is M-1 S-1, It follows that n=2 or the reaction is second-order overall.
Incorrect
The unit of the rate constant of a reaction with an overall order n is
Unit of rate constant = M1-n s-1
Thus, if the unit of the rate constant of a reaction is M-1 S-1, It follows that n=2 or the reaction is second-order overall.
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Question 4 of 10
4. Question
The phase diagram of a substance is given below. Estimate the normal boiling point and normal freezing point of the substance.
Correct
The normal freezing point is the freezing point (solid-liquid) at 1 atm, similarly, the normal boiling point is the boiling point (liquid-gas) at 1atm. We can establish these values from the graph by drawing a horizontal line at 1 atm and estimating the temperature at the point where it crosses the solid-liquid line (freezing-point) and liquid gas line boiling point as shown below. The normal boiling point. The normal boiling point is approximately 320 oC and the normal freezing point is approximately being 200 oC.
Incorrect
The normal freezing point is the freezing point (solid-liquid) at 1 atm, similarly, the normal boiling point is the boiling point (liquid-gas) at 1atm. We can establish these values from the graph by drawing a horizontal line at 1 atm and estimating the temperature at the point where it crosses the solid-liquid line (freezing-point) and liquid gas line boiling point as shown below. The normal boiling point. The normal boiling point is approximately 320 oC and the normal freezing point is approximately being 200 oC.
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Question 5 of 10
5. Question
Which of the following statements is correct about ionic solids?
Correct
Incorrect A: some Ionic solids are dissolved in in polar solvents
Incorrect B: Ionic solids are usually insulators because electrons are held tightly to the ions. They are hard and have high melting points because ionic bonds are strong. However, they are brittle because when the crystal gets knocked so that the wrong ions are touching, then it will shatter.
Incorrect C: The energy of their crystal lattice increases when the size and electric charge of the ions decreases.
Incorrect E: Ionic solids are made of lattices of alternating ions. They cannot be close-packed structures, because then like ions would have to touch.Incorrect
Incorrect A: some Ionic solids are dissolved in in polar solvents
Incorrect B: Ionic solids are usually insulators because electrons are held tightly to the ions. They are hard and have high melting points because ionic bonds are strong. However, they are brittle because when the crystal gets knocked so that the wrong ions are touching, then it will shatter.
Incorrect C: The energy of their crystal lattice increases when the size and electric charge of the ions decreases.
Incorrect E: Ionic solids are made of lattices of alternating ions. They cannot be close-packed structures, because then like ions would have to touch.
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Question 6 of 10
6. Question
When the following half-reaction is balanced in acidic medium, how many electrons are added to the left-hand side of the half-reaction after balancing?
\( Cr_2O_7 \rightarrow 2Cr^{+3} \)
Correct
The steps for balancing redox reactions in acidic medium is as follows
1. Balance the elements other than H and O\[ Cr_2O_7 \rightarrow 2Cr^{+3} \]
2. Balance O by adding H2O
\[ Cr_2O_7 \rightarrow 2Cr^{+3}+7H_2O \]
3. Balance H by adding H+
\[ 8e^-+14H^++Cr_2O_7 \rightarrow 2Cr^{+3}+7H_2O \]
4. Balance charge by adding e–
The overall charge on the left side is +14 while on the right side is +6. Thus we need to add 8e– on the left side to balance the charge.
Incorrect
The steps for balancing redox reactions in acidic medium is as follows
1. Balance the elements other than H and O\[ Cr_2O_7 \rightarrow 2Cr^{+3} \]
2. Balance O by adding H2O
\[ Cr_2O_7 \rightarrow 2Cr^{+3}+7H_2O \]
3. Balance H by adding H+
\[ 8e^-+14H^++Cr_2O_7 \rightarrow 2Cr^{+3}+7H_2O \]
4. Balance charge by adding e–
The overall charge on the left side is +14 while on the right side is +6. Thus we need to add 8e– on the left side to balance the charge.
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Question 7 of 10
7. Question
Arrange the following compound from the lowest to highest boiling point.
a. KCl
b. Ne
c. Ar
d. H2SCorrect
Electrostatic interactions are strongest for an ionic compound, so we expect KCl to have the highest boiling point. To predict the relative boiling points of the other compounds, we must consider their polarity (for dipole-dipole interactions), their ability to form hydrogen bonds, and their molar mass (for London dispersion forces). Neon is nonpolar and by far the lightest, so it should have the lowest boiling point. H2S is polar while Ar is not. Consequently, N2O should have a higher boiling point.
Incorrect
Electrostatic interactions are strongest for an ionic compound, so we expect KCl to have the highest boiling point. To predict the relative boiling points of the other compounds, we must consider their polarity (for dipole-dipole interactions), their ability to form hydrogen bonds, and their molar mass (for London dispersion forces). Neon is nonpolar and by far the lightest, so it should have the lowest boiling point. H2S is polar while Ar is not. Consequently, N2O should have a higher boiling point.
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Question 8 of 10
8. Question
Which of the following is the strongest acid?
Correct
Oxoacids are acids that contain oxygen
- Trihydrogenhypodiphosphat-ion
- Dihydrogenhypodiphosphat-ion
- Hydrogenhypodiphosphat-ion
- Dihydrophosphat-ion
When comparing oxoacids that contain the same central atom, the strength of the acid increases as the number of oxygens increases. Therefore, H3P2O6– is the strongest acid of the option given.
Incorrect
Oxoacids are acids that contain oxygen
- Trihydrogenhypodiphosphat-ion
- Dihydrogenhypodiphosphat-ion
- Hydrogenhypodiphosphat-ion
- Dihydrophosphat-ion
When comparing oxoacids that contain the same central atom, the strength of the acid increases as the number of oxygens increases. Therefore, H3P2O6– is the strongest acid of the option given.
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Question 9 of 10
9. Question
Given the nuclear equation below, identify element X.
\( ^{212}_{84}Po \text{ } \rightarrow \text{ } ^Z_AX+^4_2He \)
Correct
In nuclear reactions, the mass number and the atomic number must be balanced. The mass number on the reactant side is 212, therefore X must have a mass number of 212-4=208. The atomic number on the left side is 84 which means that X must have an atomic number of 84-2=82, corresponding to a Pb atom (element number 82).
Incorrect
In nuclear reactions, the mass number and the atomic number must be balanced. The mass number on the reactant side is 212, therefore X must have a mass number of 212-4=208. The atomic number on the left side is 84 which means that X must have an atomic number of 84-2=82, corresponding to a Pb atom (element number 82).
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Question 10 of 10
10. Question
The apparatus shown below is used for
Correct
A buret is a glass tube that is open at the top and comes to a narrow pointed opening at the bottom. Right above the bottom opening is a stopcock that can be turned to control the amount of liquid being released. There are markings along the length of the tube that indicate the volume of liquid present.
A buret is used for extremely accurate addition of liquid. By adjusting the stopcock, the amount of liquid that is released can be slowed to a drop every few seconds. Burets are one of the most accurate tools in the lab.
Incorrect
A buret is a glass tube that is open at the top and comes to a narrow pointed opening at the bottom. Right above the bottom opening is a stopcock that can be turned to control the amount of liquid being released. There are markings along the length of the tube that indicate the volume of liquid present.
A buret is used for extremely accurate addition of liquid. By adjusting the stopcock, the amount of liquid that is released can be slowed to a drop every few seconds. Burets are one of the most accurate tools in the lab.