dat booster gen chem test 1
What is the maximum number of electrons that the d-subshell can hold?
10 (s, p, d, and f-subshells can hold 2, 6, 10, 14 respectively)
What is the bond angle that exists within a molecule of SO3?
120 DAT Pro Tip: Below are some common shapes and bond angles to know for the DAT. Linear - In a linear model, atoms are connected in a straight line. The bond angles are set at 180°. For example, CO2. Trigonal planar - Molecules with the trigonal planar shape are somewhat triangular and in one plane. The bond angles are set at 120°. For example, BF3. Tetrahedral - This shape is found when there are four bonds all on one central atom, with no extra unshared electron pairs. The bond angles between the electron bonds are 109.5°. For example, CH4. Bent or V-shaped - Has a non-linear shape with an angle of about 105°. For example, H2O.
For the reaction below, which of the following sets of coefficients would balance the reaction? __HNO3 + __S → __H2SO4 + __NO2 + __H2O
6, 1, 1, 6, 2 (To solve this question, we must first determine which element to start balancing first. There are four elements involved in balancing this reaction: H, N, O, and S. Out of these four elements, it's best to start balancing hydrogen as it's the only element that can be definitely balanced on both sides without possibly encountering any issues in the future)
A NaOH solution has a molarity of 2.00 M and is titrated with 75.0 mL of 0.500 M H2SO4. What volume of NaOH is needed to reach the second equivalence point?
0.03750 L DAT Pro-Tip: One way to solve this calculation easier is by keeping in mind that anything multiplied by 0.5 is like dividing by 2. Therefore, (0.0750L)(0.500 mol/L) is the same as (0.0750L)/(2).)
According to the following reaction, how many grams of hydrogen gas is formed when 15g of aluminum reacts with excess acid? 2Al + 6HCl → 2AlCl3 + 3H2
(15)(3) ------- (27) STEP 1: To determine the answer to this question, we need to first find out the limiting reagent. Since HCl is in excess, Al will be the limiting reagent. Remember, the limiting reagent is what determines the extent to which the reaction would proceed. STEP 2: Now we can calculate the number of moles of Al below. moles of Al = (mass) / (molar mass) moles of Al = (15g) / (27g/mol) STEP 3: Next, we can determine how many moles of hydrogen is present relative to the number of aluminum moles. Keep in mind, there are 3 moles of hydrogen for every 2 moles of aluminum. moles of hydrogen = moles of Al x (mole ratio of H to Al) moles of hydrogen = (15/27) x (3 mol H2/2 mol Al) = (15)(3) / (27)(2) STEP 4: Lastly, we can calculate the grams of hydrogen below. grams of hydrogen = moles of hydrogen x molar mass grams of hydrogen = [(15)(3) / (27)(2)] x 2 = (15)(3) / (27) We can also solve this using an alternative method involving ratios, called dimensional analysis. The ratios should be arranged such that the unit present in the numerator of the first ratio is cancelled with the unit present in the denominator of the next ratio. Conversions continue until all units are cancelled out and only the desired unit remains.
How many moles of oxygen are in a 13g solution of NaNO3 solution? (molar mass of NaNO3 = 85g/mol)
(3)(13) ------- (85) STEP 1: To solve this question, we must first find the number of moles in a 13g solution of NaNO3 (molar mass = 85g/mol): # moles of NaNO3 = mass / molar mass # moles of NaNO3 = (13g) / (85g/mol) STEP 2: The ratios of the compound are 3 moles of oxygen, 1 mole of sodium, and 1 mole of nitrogen. As such, for every 1 mole of NaNO3, there are 3 moles of oxygen, and the answer is: # moles of oxygen = (3) x (13/85) We can also solve this using an alternative method involving ratios, called dimensional analysis. The ratios should be arranged such that the unit present in the numerator of the first ratio is cancelled with the unit present in the denominator of the next ratio. Conversions continue until all units are cancelled out and only the desired unit remains.
A 200g sample of mercury at 25°C was heated to 75°C with the addition of 3kJ of energy. Calculate the specific heat of mercury in J/g°C.
(3000) -------- (200) (50) STEP 1: To determine the answer to this question, we need to utilize the following equation: q = mcΔT q = heat gained (positive value) or lost (negative value)c = specific heat capacity of an object at a given state (changes depending on whether it's liquid, solid or vapor phase)ΔT = final temperature - initial temperature Note: When using this equation, it is important to make sure that the units are identical in order for them to cancel out. Also, be sure to convert 3KJ to 3000 Joules OR change the units for specific heat to KJ/g°C. STEP 2: To solve, simply plug in the values into the equation in order to derive the answer: q = mcΔT → c = q/mΔT c = (3000J) / (200g * (75°C - 25°C)) c = (3000) / (200*50)
A container holds 4.0L of gas at 3.5 atmospheres and a temperature of 27oC. If the pressure is reduced to 0.8 atmospheres without a change in temperature, what would be the volume of the gas?
18.0 L To solve this question, we must use the following equation: P1 = initial pressure, P2 = final pressureV1 = initial volume, V2 = final volumen1 = initial moles of gas, n2 = final moles of gasT1 = initial temperature in kelvin (Celsius + 273), T2 = final temperature in kelvin (Celsius + 273) Since the question does not specify that there is a change in gas molecules, we can assume n1 = n2. Furthermore, since temperature is also said to be constant, we can simplify the equation and substitute numbers to determine the answer: P1 V1 = P2 V2 (4)(3.5) = (0.8)(V2) V2 = (14)/(0.8) = 17.5 = ~18L DAT Pro Tip: On the real DAT, you will not have a calculator to solve any chemistry questions. One way to estimate this calculation is by breaking 3.5 into 3 and 0.5. This way (4)(3) = 12, (4)(0.5) = 2 which adds up to 14. Dividing this by 0.8 is like multiplying by 1.25 (1/0.8 = 1.25).
Which of the following best represents "X" in the decay process shown below? 230 Th →0 β+X 90 -1
230 Pa 91 Radioactive decay is a process that occurs in unstable atomic nuclei. There are many different types radioactive decay that may occur depending on the size of the nuclei and whether the instability is due to an abundance of protons or neutrons. The various types of radioactive decay are summarized in the table below. In this question, we can see that Thorium (Th) undergoes Beta decay. In this process, a neutron is converted into a proton and a negative charge is expelled. As a result, the atomic number of the element increases by 1. Since the atomic number (or the number of protons) changes, so does the element. This leads to the formation of the element with an atomic number of 91, which is called Protactinium (Pa) - Option A.
How many equivalent resonance structures can be drawn for the carbonate ion, CO32- ?
3 o determine the equivalent resonance structures, we must first determine the number of valence electrons. By looking at the periodic table, we can see that carbon belongs to Group 4, while oxygen belongs to Group 6A. Since the group number represents the number of outermost electrons, we know that carbon has 4 valence electrons while oxygen has 6 valence electrons. Now that we know the number of valence electrons per element, we need to compute the total number of valence electrons: 4 + (3 x 6) = 22 electrons Note: Since the whole molecule has a -2 charge, we need to keep this into consideration as well. Therefore, the total number of valence electrons is: 22 + 2 = 24 electrons Now that we have the total valence electrons, we can draw out all the possible resonance structures of CO32- without violating the octet rule. By doing this, we determine that there are THREE possible resonance structures can be drawn for carbonate ions, CO32- as shown below:
Which of the following interactions is the strongest?
Ionic Bonds (Ionic compounds also generally have a high melting point and also tend to be soluble in water)
If a mixture of oxygen and nitrogen contains 1 mol of N2(g) and 2 mol of O2(g), and the total pressure is 180kPa. What is the partial pressure of N2(g)?
60kPa To tackle this question, we need to know that the total pressure in a system is the sum of all individual gas molecule partial pressures. To find the partial pressure, we multiply the total pressure by the mole fraction of the given gas using the following steps. STEP 1: To obtain the mole fraction, we divide the moles of a gas by the total mole in a system. So in this case, the total # of moles in the system = 3 (1 mole of nitrogen + 2 moles of oxygen). Next, we can calculate the mole fraction of nitrogen: Mole fraction of nitrogen = # moles of nitrogen / total # moles = 1/3 Thus, the mole fraction of nitrogen gas is ⅓. STEP 2: Next we multiply the mole fraction of nitrogen by the total pressure (in this case, 180 kPa): (1/3) x (180kPa) = 60 kPa
How many electrons are involved in the following basic redox reaction? 4Zn + NO3- + 7OH- + 6H2O → 4Zn(OH)42- + NH
8 STEP 1: Since this is a redox reaction, we must break the reaction down into oxidation and reduction half reactions as follows: Oxidation reaction: Zn → Zn(OH)42− Reduction reaction: NO3- → NH3 STEP 2: Next, we must balance the individual half-reactions. We do this by first balancing all non-hydrogen and oxygen elements. Then we must add as many water molecules as needed to balance out the oxygen molecules. This is followed by adding protons (H+) in order to balance out the number of hydrogens on each side: Zn → Zn(OH)42− Zn + 4H2O → Zn(OH)42− Zn + 4H2O → Zn(OH)42− + 4H+ NO3- → NH3 NO3- → NH3 + 3H2O NO3- + 9H+ → NH3 + 3H2O Note: Unlike an acidic solution, we add the same number of hydroxide groups on both sides as the number of protons in the equation. The protons and hydroxide groups that reside on one side of the equation combine to form water. STEP 3: Next, we add in the appropriate number of electrons to balance out the charges in the reaction: Zn + 4H2O + 4OH- → Zn(OH)42− + 4H+ + 4OH- Zn + 4H2O + 4OH- → Zn(OH)42− + 4H2O (the waters cancel out on the next step) Zn + 4OH- → Zn(OH)42− Zn + 4OH- → Zn(OH)42− + 2e- NO3- + 9H+ + 9OH- → NH3 + 3H2O + 9OH- NO3- + 9H2O → NH3 + 3H2O + 9OH- (the waters cancel out on the next step) NO3- + 8e- + 6H2O → NH3 + 9OH- STEP 4: Next, we make sure that the electron coefficients for the two reactions are identical and we add them up to make an overall reaction like so: 4Zn + 16OH- → 4Zn(OH)42−+ 8e- NO3- + 8e- + 6H2O → NH3 + 9OH- --------------------------------------------------------------------------------------------------------------- 4Zn + NO3- + 6H2O + 7OH- → 4Zn(OH)42− + NH3 Therefore, the number of electrons involved in balancing out this reaction in a basic solution is 8.
How many electrons, protons, and neutrons respectively does mercury have?
80, 80, 120 Based on the periodic table, mercury has an atomic number of 80 and a mass of 200, as shown in the image below. Since atomic number is defined as the number of protons and the mass number is the sum of protons and neutrons, we can find the number of neutrons by subtracting the atomic number from the mass number. Furthermore, since the question never stated that we are dealing with mercury ions, we assume that it's a neutral element (i.e it will have equal numbers of protons and electrons). Thus, we can conclude that mercury has 80 protons, 80 electrons and 120 (200-80) neutrons.
Each of the following are examples of non-colligative properties of a liquid EXCEPT one. Which one is the EXCEPTION?
Boiling point Colligative properties are properties of solutions that depend on the ratio of the number of solute particles to the number of solvent molecules in a solution, and not on the nature of the chemical species present. Colligative properties include vapor pressure, boiling point, freezing point and osmolarity. They are properties that relate to the number of solutes within a given solvent and do not depend on the solvent within solution.
If a chemist wants to measure 800μL of a solution for an experiment, which laboratory equipment would be the BEST to use?
Micropipette Micropipettes are pipettes used in most standardized biology laboratories. They are specifically used to measure volumes in the microliter range, such as 800μL. Therefore, Option A. Micropipette is the best answer.
Which of the following is NOT an intermolecular force?
Covalent bonds Intermolecular forces are interactive or repulsive forces that exist between molecules. Intermolecular forces are much weaker than the intramolecular forces of attraction but are important because they determine the physical properties of molecules like their boiling point, melting point, density, and enthalpies of fusion and vaporization. These forces include: Hydrogen bonding - Is a partially electrostatic attraction between a hydrogen (H) atom which is bound to a more electronegative atom or group, such as nitrogen (N), oxygen (O), or fluorine (F). Ion-Dipole - Occurs when polar molecules interact with ions. Dipole-Dipole - Occurs when polar molecules interact with one another. Dipole-induced Dipole - occurs when polar bonds interact and cause a transient dipole moment within non-polar molecules. London Dispersion/Van der Waal forces - Is a brief dipole moment elicited by non-uniform distribution of charges.
A point where the maximum temperature and pressure that allows gas to remain at equilibrium between gaseous and liquid phase is known as the ________________.
Critical point A phase diagram summarizes the effect of temperature and pressure on a substance in a closed container. Every point in this diagram represents a possible combination of temperature and pressure for the system. The diagram is divided into three areas: solid, liquid, and gaseous states of the substance, which can be seen in the image below. There are two points of equilibrium on a phase diagram that should be given special attention for the DAT: Critical point - A point at which high pressures and temperatures cannot be distinguished between liquid and vapor. The critical point can be seen in the image below (black dot towards the top-right). Triple point - A point at a given temperature and pressure in which the chemical is present in both the solid, liquid and gaseous phase
An aqueous mixture contains CuF2 and BaF2 (Ksp = 3.0×10−6). What should be added to the solution in order to precipitate CuF2?
Cu(NO3) To determine the answer to this question, we must understand the common ion effect. If a solution contains two salts that have a common ion, the common ion supplied by one salt introduces a common ion effect that disturbs the solubility equilibrium of the other salt. This causes its equilibrium to shift left toward the reactants. The common ion effect is essentially a specific scenario involving Le Châtelier's principle, which states that if an equilibrium is disrupted, the equilibrium will shift to minimize the change and establish a new equilibrium. In order to precipitate CuF2 from a solution mixture of CuF2 and BaF2, Cu2+ ions need to be introduced into the solution. The increase in Cu2+ concentration disturbs the product side of the solubility equilibrium and causes it to shift toward the reactants. Therefore, adding Cu(NO3)2 as a source of Cu2+ ions will selectively cause the CuF2 in the mixture to precipitate.
All of the following are properties of an enzyme EXCEPT one. Which one is the EXCEPTION?
Decreases the rate constant of a reaction Enzymes are biological catalysts which accelerate chemical reactions by providing an alternative route for the reaction with a lower activation energy. The molecules upon which enzymes act are called substrates and the enzyme converts the substrates into different molecules known as products. A catalyst is specific for a specific reaction (lock-and-key mechanism) and is neither a product or reactant as it does not change in the reaction. These are important properties of enzymes/catalysts that you must know for the DAT. Firstly, catalysts change the rate constant of a reaction. Recall, the rate constant of a reaction is increased by the presence of an enzyme, not decreased. This can be inferred from the Arrhenius equation, where the rate is dependent on the activation energy. Since the activation energy is lowered by the enzyme, then the rate constant is subsequently increased.
Vaporization is which of the following types of processes?
Endothermic Vaporization is a phase change in which a liquid becomes a gas. All phase changes are physical changes, not chemical changes! During vaporization, bonds are being broken as the molecules enter the less organized and higher entropy state. In order for bonds to be broken, energy is required. Therefore, all reactions that break bonds are endothermic. As a result, when we go from solid to liquid (melting/fusion), solid to gas (sublimation) or liquid to gas (vaporization), we are breaking bonds and thus require the input of heat (endothermic) to derive the reaction forward. DAT Pro Tip: It is useful to know that entropy is also increasing for these reactions as well. The opposite is held true for the reverse reactions of the aforementioned processes, where the reaction is exothermic and entropy decreases.
Which one of the following properties applies to alkaline earth metals?
Form 2+ cations The Alkaline Earth Metals are six elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), as show in the image below. These elements have the following properties: Appear shiny, silvery-white Are somewhat reactive metals Have high melting and boiling points Form 2+ cations since they have a valance of 2 electrons in their outer shell
Which one of the following molecules is polar?
H2S To determine the most polar molecule, we must draw out the VESPR diagrams for each option choice. Note: Keep in mind, just because a bond is polar does NOT mean that the entire molecule as a whole is polar as well. Remember, dipoles can cancel each other out.
Calcium chromate (CaCrO4) is a yellow solid with a Ksp of 7.1 x 10-4. Determine the ion product constant and whether a precipitate would form when an aqueous solution contains 26 mM of Ca2+ and 29 mM of CrO42-.
IP = 7.54 x 10-4; yes, precipitation will occur. (To determine whether a precipitate will form, we have to compare ion product constant to the given Ksp value. Since IP > Ksp, the reaction is considered saturated and will shift to the left. Therefore, a precipitate will form)
Which of the following changes to the system would result in an equilibrium shift towards the reactants? MgO(s) + CO2(g) ↔ MgCO3(s) ∆H = +118 kJ•mol-1
Increasing the volume of the system Le Chatelier's principle states that if a system that is in equilibrium is disturbed by changes in temperature, pressure, and concentration of components, the system will tend to shift its equilibrium position so as to counteract the effect of the disturbance. MgO(s) + CO2(g) ↔ MgCO3(s) ∆H = +118 kJ•mol-1 In this case, increasing the volume of the system would result in an equilibrium shift towards the reactants because this system involves gas molecules, and therefore an increase in the volume is accompanied by a decrease in pressure and concentration. To understand this concept, imagine the gas molecules are allowed to expand further and are less confined. According to Le Chatelier's principle, the system will try to counteract this change by shifting the equilibrium to increase the number of gas molecules. This would mean that the shift would be aim towards the side of the reaction with more gas molecules. Therefore, the equilibrium will shift towards the reactant side in the reaction above, and this makes Option D. Increasing the volume of the system is the correct answer.
Which of the following elements exists as a diatomic gas in its standard state and contains a double covalent bond?
Oxygen Diatomic molecules are molecules composed of only TWO atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear. If a diatomic molecule consists of two different atoms, such as carbon monoxide (CO), the molecule is said to be heteronuclear. Seven elements exist as diatomic molecules in their standard elemental state in the periodic table, as shown in the image below. These seven elements are: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine. Atoms of these elements form covalently bonded pairs by sharing valence electrons and occur naturally as H2, N2, O2, F2, Cl2, Br2, and I2, respectively. Due to differences in orbitals and the number of valence electrons, H2, F2, Cl2, Br2, and I2 can achieve a full valence shell by forming a pair with only a single covalent bond, but O2 must form a double bond and N2 must form a triple bond. An easy way to remember the 7 elements is through the following mnemonic: H2, N2, F2, O2, I2, Cl2, Br2. "Have No Fear Of Ice Cold Beer"
Which of the following BEST describes a Bronsted-Lowry base?
Proton acceptor Arrhenius bases dissociate to form hydroxide (OH-) ions. Arrhenius acids dissociate in water, forming proton (H+) ions. Lewis bases are electron pair donors. Lewis acids are electron pair acceptors. Bronsted-Lowry base is a chemical species that accepts a proton. Bronsted-Lowry acid is a chemical species that donates a proton. Acids that can donate more than one proton are called "polyprotic acids" and produce more than one ionic species.
Given the data shown below, what is the rate law for the following chemical reaction?
Rate = k[A]2[B]2 For this question, we will be using the equation: Rate = k[A]x[B]y Where, k is the rate constant, and x and y are the order of reaction with respect to A and B STEP 1: First, we can compare 2 rates with a common factor. Rate 2 and 1 share the same concentration of [B], and therefore we can use them to find the exponents as follows: When we simplify, we get 16 = 4x, and since 16 is 4 squared, we get x = 2. Thus, the reaction order of reagent A is 2. STEP 2: Next, we do the same for reagent B by comparing rates 3 and 1: When we simplify, we get 4 = 2y, and since 4 is 2 squared, we get y = 2. Thus, the reaction order of reagent B is 2. STEP 3: Lastly, we can plug these values into the formula. As a result, the rate law of the reaction is: Rate = k[A]2[B]2
Which of the following is TRUE for a reaction occurring at 25°C that has a positive ΔH value?
The reaction will be spontaneous if ΔH < ΔS A spontaneous process occurs naturally under certain conditions, in which it releases free energy and moves to a lower, more thermodynamically stable energy state. A non-spontaneous process, on the other hand, will not take place unless it is "driven" by the continual input of energy from an external source. Note: The spontaneity of a process is not correlated to the speed of the process. Some might be really slow but still considered as a spontaneous process. For a reaction to be spontaneous, ΔG (Gibbs free energy) needs to be a negative number. Based on the equation ΔG = ΔH -TΔS, we can see that in order for a reaction to be spontaneous (negative ΔG), then ΔH (enthalpy) needs to be exothermic (negative) and ΔS (entropy/disorder) needs to be increasing. However, a reaction can have a negative ΔG value even with an endothermic reaction (positive ΔH) as long as the -TΔS value is larger (i.e. more negative) than the positive ΔH, and vice-versa for a negative ΔH value. Here is a quick summary of ΔG and what its value means for the DAT: Negative: the process is spontaneous and may proceed in the forward direction as written. Positive: the process is non-spontaneous as written, but it may proceed spontaneously in the reverse direction. Zero: the process is at equilibrium, with no net change taking place over time.
Which of the following pairs are typically found in alkaline buffer solutions?
Weak base and its conjugate acid Buffers are solutions that resist changes in pH when small amounts of acid or base are added. They consist of a mixture of either a weak acid and a salt of its conjugate base, or a weak base and a salt of its conjugate acid. The acidic component of a buffer can neutralize an added base while the basic component of a buffer can neutralize an added acid. This means that large changes in pH will be repressed. For example, CH3COOH is a weak acid, and its conjugate base is CH3COO−. As such, a buffer could be made by mixing equal concentrations of each into solution. Typically, weak bases and their conjugate are found in alkaline (pH > 7) solutions, while weak acids and their conjugates are found in acidic (pH < 7) solutions. This is because to be efficient buffers, they need to have pK values which is equal to or can be +/- 1 value different than the pH.
