Chemistry
To solve this equation the molarity equation is needed. M = Moles of solute / Liters of solution Plugging in the values given in the question gives: 7.89 = Moles of solute / 2 So, the moles of the solute would be equal to: (7.89)(2). The question asks for the molar mass which is defined as g/mol. Dividing the grams given in the question by the moles just calculated would give the unknown compound's molar mass: MM = 10g / (7.89)(2)
10g of an unknown compound are added to water to form a 7.89 molar solution. If 2 liters of solution are present, what is the molar mass of the unknown compound?
H2SO4 has two moles of H+ ions (n1=2), while OH only has one mole of OH-(n1=1). Therefore, we must remember to use the normality of the acid in this dilution reaction. (n1)(M1)(V1) = (n2)(M2)(V2) (2)(0.5)(V1) = (1)(0.5)(250) V1 = 125 mL
11. What volume of 0.5M H2SO4 is needed to neutralize 250mL of 0.5M KOH?
Endothermic Thermodynamics consist of a system and its surroundings. In this case, the solution is the system, and the surroundings is the flask. If the flask becomes cold, it means that energy is being drawn away from it. The reaction is pulling energy into it, meaning that the reaction is endothermic. If the flask became warmer, then the reaction is giving off energy to its surroundings, and would be exothermic
17. A chemist mixes two solutions in a flask and notices the flask becomes cold. It can be concluded that the reaction:
Platinum Soduim Germanium Selenium Iodine The compound described matches that of an alkali metal, the first group in the periodic table. The alkali metals display metallic properties due to their low first ionization energies, but they have low melting points due to their weak inter-atomic bonding. Platinum is a metal, but it also has a high melting point. Germanium is a metalloid and has a high melting point as well, and is only conductive under special circumstances (a semi-conductor). Selenium is used in Head and Shoulders shampoo, and is a nonmetal, so it doesn't have a high conductivity. Lastly, iodine does not conduct electricity.
27. An extracted pure compound appears silvery white, exhibits high conductivity to heat and electricity, yet has a very low melting point. Which of the following elements is a possible match for this compound?
Looking at our problem, we can determine the solution's volume by considering density. The mass of cyclohexanol is, Mass = moles * molar mass Mass = molality * kg of solvent * molar mass Mass = (5.0 mol/kg) * 1kg * 100 g/mol Mass = 5.0 moles * 100 g/mol = 500 grams And we know we have 1 kilogram (1000 grams) of water for every 5 mols of cyclohexanol. Therefore, Total mass of solution = 500 grams cyclohexanol + 1000 grams of water Total mass of solution = 1500 grams We know, Density = mass / volume 15 g/mL = 1500 g / volume Volume = 1500 g / 15 g/mL Volume = 100 mL = 0.1 L We are told that we have a 5.0 molal solution (5 mol cyclohexanol / kg solvent), and 1 kg of solvent would contain 5.0 moles of cyclohexanol. Knowing that our solution has a volume of 0.1L, molarity is calculated as: M = mol / L solution M = 5 mol / 0.1 L M = 50 mol / L
A 5.0m saturated solution of cyclohexanol (MM = 100 g/mol) dissolved in water has a density of 15 g/mL. What is the molarity of this solution?
use partial pressure gas formula P1=x1Pt use mole fraction and then times it with total pressure
A mixture of gas is composed of 0.5 mol Ar, 1.5 mol He, and 2.0 mol of N2. What is the partial pressure of N2 in the mixture if the total pressure is 0.95 atm?
Cu2+ forms a complex ion with NH3 The question states a small amount of NH3 was added to a solution of Cu. Initially, the copper will react with the water since it is more abundant compared to the NH3. This produces Cu(OH)2, an insoluble hydroxide precipitate. The crux of this question is understanding the concept of complex ions. As more NH3 is added, a complex ion will form with the copper instead. Complex ions are those such as Cu(NH3)42+. The water molecules that normally surround a cation are replaced with some other electron pair donor (NH3 in this case). With excess ammonia, it is possible to form a complex ion with the copper. Complex ions tend to be very colorful, Cu(NH3)42+ is a deep blue, for example. Reaction with dilute NH3: Cu2+ + 2 NH3 + 2 H2O → Cu(OH)2 + 2 NH4+ Reaction with excess NH3: Cu2+ + 4 NH3 → Cu(NH3)42+
A small amount of aqueous NH3 is added to a solution of Cu2+ and a precipitate forms. However, when excess aqueous NH3 is added, the former precipitate dissolves. Which statement best explains why the precipitate dissolves with excess aqueous NH3?
inaccurate and precise
A student finds that the average number of cells over 10 samples is 2130, with a standard deviation of ±6. However, the professor determines the true average number of cells is 2850. The student's measurement was:
Sharp, well defined melting temperature There are two categories of solids: crystalline and amorphous. Crystalline solids have long range order. This means there is a consistent, crystal lattice network of atoms that is well defined, and repeated throughout the structure. Because of this, crystalline solids have sharp, well defined, characteristic melting temperatures, and break with a cleavage along a very straight plane. Conversely, amorphous solids have only short range order. This means there is no consistent structure of atoms throughout the solid. This leads to a broad range of melting temperatures for any given amorphous solid, and they have irregular breakage patterns.
A student is examining a crystalline solid. Which of the following findings would be most expected during analysis of this substance?
CCl4 is a covalent substance, while NaCl melts is an ionic substance. Because there is less of an electronegativity difference between the atoms involved in a covalent bond, covalent substances have weaker intramolecular and intermolecular bonds than ionic substances. When a substance melts, it undergoes a phase change from solid to liquid. In ionic substances, solid NaCl has a network structure of Na+ and Cl- intramolecular and intermolecular attachments. Lattice energy is a measurement of ionic attraction. Lattice energy is the energy needed to break 1 mole of a solid ionic compound into gaseous ions. During melting of an ionic substance, the energy supplied overcomes these forces, and the cations and anions are liberated. The rigid, tightly held crystal lattice of ionic solids contributes to the high melting points associated with them. Covalent substances lack a rigid, repeating lattice structure. In a covalent substance, melting involves the breakage of the intermolecular bonds, but not the intramolecular bonds (melting is one molecule of CCl4 being able to move more freely from other molecules of CCl4, but not the breakage of the carbon-to-chloride bond)
A student planning an experiment reads that CCl4 melts at -22.9 °C, while NaCl melts at 801 °C. All of the following contribute to this observation EXCEPT one. Which one is the EXCEPTION?
(2)(160)/(380-185)
A volumetric flask weighs 185g when empty and 380g when filled with "liquid A" (density of 2 g•mL-1). If the flask is filled with 160g of "liquid B", what is the density of "liquid B" in g•mL-1?
Increase due to the common ion effect Once you understand the terminology and step back, this is an easy problem. Sodium oxalate is a base, and adding a base to anything will cause an increase in pH. This increase in pH will be due to the common ion effect in this case, because oxalic acid and oxalate share a common ion. Adding reactant does not shift the Ka.
Adding sodium oxalate to a solution of oxalic acid causes the pH to:
4 2 reduce mass
Alpha decay
N2(g) + 3H2(g) → 2NH3(g) From the question stem, we are told we have 21 grams of nitrogen and 18 grams of hydrogen. We need to figure out which will act as the limiting reagent. First, we need to calculate how many moles we have of each. Molar mass of N2 = 28 g/mol Molar mass of H2 = 2 g/mol Moles N2 = 21 g / 28 g/mol = ¾ mol = 0.75 mol Moles H2 = 18 g / 2 g/mol = 9 mol Looking at our balanced chemical equation, the stoichiometric coefficients tell us that 1 N2 is consumed for every 3 H2. Therefore, consuming 0.75 moles of N2 would require 2.25 moles of H2 (1:3 ratio). And since we have 9 moles of H2, H2 is in excess and N2 is the limiting reagent. If 2.25 moles of H2 are consumed, and H2 has a molar mass of 2 g/mol, 4.5 grams of hydrogen will be consumed in this reaction.
Ammonia is formed according to the reaction below. A chemist mixes 21 grams of nitrogen gas and 18 grams of hydrogen gas in a 2.0 L vessel. How many grams of hydrogen gas will be consumed? N2(g) + 3H2(g) → 2NH3(g
to reach equillbrium, the concentration of A will increase while the concentration of B will decrease
An equilibrium mixture for the reaction A⇌B has a Kc = 0.40 at 350K. Which of the following statements is true regarding a A⇌B mixture with a Qc = 20 at 350K?
Ar 1.79 g/L * 22.4 L/1 mol ~40g /mol getting molar mass (g/mol) Ar
An unknown gas has a density of 1.79 g•L-1 at 273K and 1 atm. Identify the gas.
-The volume of the gas molecules is negligibly small compared to the volume of the entire gas. - Gas molecules are in constant, random motion. - Gas molecules collisions are perfectly elastic. - There are no intermolecular forces occurring between gas molecules. Hence, they are assumed to be nonpolar (i.e. no attraction/repulsion between molecules). - The average kinetic energy of the gas molecules depends only on the temperature of the system (not the number of gas molecules!).
Assumption for ideal gases
this solution with a poh of 7 is acidic A neutral solution is one where [H+] = [OH-]. Thus, if the pH of a neutral solution is 6.1, then its pOH is also 6.1, and pH + pOH = 12.2. Therefore, [A] and [D] are incorrect. An acidic solution is one where [H+] > [OH-], i.e. the pH is less than neutral pH. Since at 100 oC, the neutral pH is 6.1, then a solution with pH 6.5 is basic. Therefore, [B] is incorrect. The pH of neutral solution is no longer equal to 7 at 100 oC. This is because Kw, like all equilibrium constants, is temperature dependent. Kw equals 1 x 10-14 at 25 oC, but the value changes with temperature. We would not expect the pH of this neutral solution to still be 6.1 when the temperature changes from 100 oC to 50 oC. Therefore, [E] is incorrect. This solution with pOH = 7 has a pH = 12.2 - 7 = 5.2 and therefore is acidic, since its pH is less than that of a neutral solution.Therefore, [C] is correct.
At 100 oC, the pH of a neutral solution is 6.1. Which of the following statements is true for this solution at this temperature?
The temperature at which the vapor pressure of the liquid equals the surrounding pressure The boiling point of a liquid is reached when the vapor pressure of the liquid equals the surrounding environment's pressure. This is why liquids will boil faster at higher altitudes. There is less pressure, so the vapor pressure of the liquid has to be raised to a lesser amount to equal the surrounding pressure! Since it takes less energy, boiling points at higher altitudes are less than 100°C, which is why it also takes longer for food to cook.
Boiling point definition
According to Boyle's law, the pressure and the volume are inversely related, therefore if pressure is increased, the volume is decreased. The only example that illustrates this is answer option [C]. Pushing on the balloon would decrease volume, but increase the pressure inside of the balloon. Heating a marshmallow or mercury expanding when heated would be dealing with Charles' law that involves temperature and volume. Cooling a hot metal rod is not related to the gas laws. Carbonation in a soda can deal with temperature and pressure, but not pressure and volume.
Boyles law
Increase in electron shielding The effective nuclear charge is the net positive charge felt by the valence electrons. In a given group in the periodic table, the effective nuclear charge stays relatively constant due to the constant number of valence electrons; the increasing number of protons is balanced with an increasing number of core electrons. Going across the periodic table, however, more protons are being added, and the electrons experience a stronger effective nuclear charge. The increasing effective nuclear charge is responsible for the decrease in atomic size across the periodic table from left to right. The electron shielding effect reduces the effect of a full nuclear charge. As more core electrons are added, they begin to "shield" the valence electrons from the increasingly positive nucleus. This allows the outer electrons to move farther away from the nucleus, hence increasing atomic size. The increasing electron shielding effect is responsible for the increase in atomic size moving down groups.
Calcium has a larger atomic radius than magnesium because of the:
w= -P*change in volume When the system does work on the surroundings, we have negative work of the system, and energy will be lost. Alternatively, if the surroundings do work on the system, work is positive and the energy of the system increases.
Calculate the work done by an ideal gas on its surroundings when the gas is heated at constant pressure of 1 atm from volume 50L to 100L at 298K.
Average kinetic energy of gaseous molecules depends on absolute temperature. Since the two gases are at the same temperature, their average kinetic energies are the same. Statement [A] is incorrect since pressure is directly proportional to the amount of the gas sample. There are more moles of Ar gas. Statement [C] is incorrect since the average speed of gases is dependent on both the temperature and the molar mass. Statement [D] is incorrect as there are more moles of Ar gas, and therefore it has a higher entropy. Statement [E] is incorrect as there is 1 mol of He gas and 2 mol of Ar gas (and each mole represents 6.02 x 1023 particles).
Consider two balloons of equal volume at the same temperature; one containing 1 mol of He and the other containing 2 mol of Ar. Which of the following statements is true? A. the two gases have the same temperature b. the two gases have the same average kinetic energy c. the two gases have the same average speed d. the two gases have the same entropy e. the two gases have the same number of particles
For a nucleus to be stable, the nuclear binding energy must be large. The larger the nuclear binding energy, the more stable the nucleus. Binding energy is the energy needed to split the nucleus into the individual components, i.e. protons and neutrons (or nucleons). The higher the binding energy, the harder it is to decompose the nucleus. The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It explains the atomic radii trend across periods. The electron shielding effect dictates the atomic radii trend down a group. Bond dissociation energy deals with compounds, not nuclei.
Element X has a nucleus that is stable against decomposition. Which of the following must be true of Element X?
Use Moles to get answer 1.5 mol C 1 mol H times it by 2 because we can't have decimals
Empirical formula 1. Combustion analysis of a sample compound containing only C and H determines there was 18 g of C and 1 g of H in the sample. What is the empirical formula of this compound?
the equivalence point will be a weak base. so 7.5-9
For the titration of a weak acid with a strong base, what is the equivalence point? number wise
Diffusion of a gas is the process of particles moving from an area of high concentration to an area of low concentration. Effusion of a gas is the movement of a gas through a small opening, from one compartment into another. The relative rate of effusion can be calculated via Graham's law. ...that the rate of effusion of gas 1 relative to gas 2 is equal to the square root of the molar mass of gas 2 over the molar mass of gas 1. as we would expect gas A (4 g/mol) to effuse faster than gas B (36 g/mol).
Gas A has a molar mass of 4 g/mol and gas B has a molar mass of 36 g/mol. If the gases are at the same temperature, what will be the rate of effusion of gas B relative to gas A?
Amount remaining = original amount x (1/2)t, where t represents the number of half-lives. For this problem, the half-life of Uranium-235 is 704 million years. If it has been 2.2 billion years which is equivalent to 2,200 million years, then the number of half lives would be: 2,200 / 704. Substituting the original amount of 100 into the half-life equation results in the answer of: 100(1/2)(2200/704).
Half life formula
Henry's law tells us that the solubility of a gas in liquid is directly proportional to the partial pressure of the gas above the solution. C = kP where C = concentration of gas in solution, k is a proportionality constant, and P is the partial pressure of the gas above the solution. As we can see from the equation, the solubility of a gas is directly proportional to its partial pressure. If we increase the partial pressure of the gas, we are going to have more interactions between the gas and the solution. If the partial pressure is tripled, the solubility will triple. Think about a bottle of soda. First off, you'll notice that the bottle of carbonated soda isn't full all the way up to the lid - there is a space on top of the liquid where gas exists. If you leave the lid on, the partial pressure of the gas above the liquid is high, and the solubility of gas within the soda will be higher. That leads to the soda being carbonated. If you leave the lid off, the partial pressure of the gas above the soda is equivalent to room pressure - much lower. The solubility of the gas in the soda decreases, and your soda becomes 'flat' (or, uncarbonated).
Henry Law
80 g combustion reaction, write how balance formula and solve
How many grams of oxygen are needed to completely react with 0.50 moles of C3H8 (58 g/mol)?
A spontaneously reacting electrochemical cell is known as a voltaic or galvanic cell. A non-spontaneous reacting electrochemical cell is known as an electrolytic cell, and requires the input of energy. We can eliminate option III, as we are told this is a spontaneous reaction. Using the mnemonic AN OX - RED CAT, we can remember that OXidation occurs at the ANode, and REDuction occurs at the CAThode in an electrochemical cell. Therefore, option I is correct. Because we know this is a spontaneous reaction, the reduction potential of the cathode (reduction half cell) must be greater than the reduction potential of the anode (oxidation half cell). We are told that metal A forms the cathode, metal B the anode, and that the reduction potential of metal A is greater than the reduction potential of metal B. Therefore, option II is correct.
In a given electrochemical cell, a spontaneous reaction occurs where metal A forms the cathode and metal B forms the anode. Based on the information provided, which of the following statements is/are correct? I. Oxidation occurs at the anode II. The reduction potential of metal A > the reduction potential of metal B III. This reaction represents an electrolytic cell
B-11is the most abundant isotope Isotopes of an element are atoms with different number of neutrons and thus different mass number. The atomic mass of an element is the weighted average of the masses of all the isotopes of that element. Boron has two isotopes, B-10 with a mass of 10.013 u and B-11 with a mass of 11.093. Of the two isotopes, B-11 is the most abundant, since the atomic weight (average of the mass of the two isotopes) of boron is closest to the mass of B-11.
Naturally occurring boron (10.8 u) exists in two isotope forms: B-10 (10.013 u) and B-11 (11.093 u). Which of the following statements is true?
Mercury is a nonpolar substance and glass is a polar substance (glass is silicon dioxide, or SiO2). "Like attracts like", but mercury and glass are not alike, therefore they will not attract and try to stay as far apart from each other as possible
Polar or nonpolar for Mercury? What polarity is glass ( silicon dioxide or SiO2)
The melting point of a substance is due to the strength of intermolecular forces between the molecules. Pure elemental gases are covalently bonding and are non-polar. As a result, they have very minimal intermolecular forces acting on the molecules. This results in a weak bonding structure in the solid, and thus a low melting point.
Pure elemental gases, such as O2 and N2, have very low melting points, at around -220°C. What is one reason that this is the case?
a>c>b We can see that in oxygen, one of the 2p orbitals contains two electrons. Electonrs are negatively charged, and therefore exhibit a repulsion force on each other. It will be easier to remove one of the electrons from the paired electron orbital in oxygen, since this would relieve the repulsion forces, compared to removing an electron from nitrogen which does not have any paired electrons in orbitals. And if the removal of an electron is easier, the ionization energy is lower. Therefore, oxygen will have a lower ionization energy compared to nitrogen.
Rank the following in order of decreasing first ionization energy (highest first ionization energy to lowest first ionization energy) a. N b. Li c. O
a<c<b
Rank the following in order of increasing neutron/proton ratio. a. 24Mg b. 207Pb c. 65Zn
Mg(OH)2 ⇌ Mg2+ + 2OH- The solution is saturated, meaning all the Mg(OH)2 that can dissolve has dissolved, and there are still 100g of it left as a solid. If we add a strong acid, or essentially H+, it will combine with the OH- to form H2O. Since some of the OH- has been removed, then according to Le Chatelier's principle, the reaction will shift to the right to restore equilibrium. As a result, more Mg(OH)2 will be dissolved, and more Mg2+ will be released
The addition of a strong acid to a saturated solution of Mg(OH)2 that has 100g of solid remaining would cause which of the following?
Na2SO2 use boiling point elevation formula m=molality Kb= molal boiling point constant
The boiling point of a 1.0m aqueous solution is 101.5°C. The molal boiling point constant for water is 0.512°C•m-1. Which of the following substances is most likely dissolved in the water?
The law of conservation of mass states that atoms cannot be created nor destroyed. During a chemical reaction, the mass of the reactants is the same as the mass of the products (no creation of atoms, no destruction of atoms). That is why chemical formulas must be balanced, as no mass is lost during a reaction.
The combustion of hydrogen gas occurs according to the equation below. This observation is supported by which of the following? O2(g) + 2H2(g) → 2H2O(g)
magnesium The ionization energy of an element increases dramatically upon removal of its inner-shell electrons. From the given information, we see that there is a dramatic increase from second to third ionization energy, indicating that the element has two valence electrons. Thus, the most likely element is magnesium.
The first, second, and third ionization energy of an atom of a period 3 element is 738 kJ/mol, 1451 kJ/mol, and 7733 kJ/mol, respectively. The element is most likely sodium magnesiumm aluminum sulfur phosphours
NH4+<HCN<HF An acid-base reaction involving a stronger acid and base on the reactant side is a product-favored reaction and has K > 1. We are given three acid-base reaction with K > 1. We can deduce the relative strength of the acids from these reactions, where the stronger acid is always on the reactant side, which is why K > 1. From reaction I, HF is stronger than HCN; from reaction II, HF is stronger than NH4+; and from reaction III, HCN is stronger than NH4+.
The following acid-base reactions have K > 1. Which of the following choices correctly rank the acids in increasing strength? HF + CN- → HCN + F- NH3 + HF → NH4+ + F- HCN + NH3 → NH4+ + CN-
t1/2 = 0.693/k
The half-life for a first order reaction is:
Colligative properties are properties of a solution that are determined by only the concentration of a solute in a solvent, and do not depend on the identity of the actual solute. That means it doesn't matter if you have NaCl or KBr, it only matters how many particles of the solute is in the solvent. Technically, you could use any colligative property (freezing point, boiling point) to measure the molecular weight of a compound. But the reason osmotic pressure is preferred for polymers (5,000+ g/mol) is because polymers are usually very insoluble. Your solution may only be 1×10-6 M, when trying to dissolve a polymer that weighs thousands of g/mol. So what is easier, measuring the change in freezing point depression in a solution that is 1×10-6 M, or measuring the change in osmotic pressure in a U tube, or osmometer (device that measures osmotic pressure). Your freezing point depression could be less than 0.01°C, which is very difficult to accurately measure. It's a lot easier to accurately measure osmotic pressure; and the Berkeley-Hartley method is known for using osmotic pressure to measure the weights of polymers. Osmotic pressure is the pressure that must be exerted on one side of a U tube to prevent the osmosis of water across a semi-permeable membrane. Small differences in the height of the solution within the U tube can be easily discerned. If osmotic pressure changes slightly, the height of the solution column will raise or lower (depending on the change). And this height change can be easily observed. Therefore, answer choice [A] is correct. Small changes are easier to detect in osmotic pressure than in other colligative properties.
The preferred colligative property for measuring the molecular weight of polymers is osmotic pressure. Which of the following best explains why osmotic pressure is preferred to measure the molecular weight of polymers?
360K
The pressure of a gas is increased from 100 mmHg to 120 mmHg. If the initial temperature of the gas was 300K, which of the following could be the final temperature of the gas?
change in S surrounding + change in S system > 0 Every spontaneous change is accompanied by an increase in the entropy of the universe (system and surroundings). It's important to note the distinction "increase in the entropy of the Universe", as this refers to the Universe as a whole. Locally, a system (or surroundings) can decrease in entropy, but as long as the net entropy of the Universe increases, there is not a violation of this law. For a simple example, if an ice cube is melting in a cup of soup, the entropy (disorder) of the soup in the cup may decrease slightly, as the soup is cooling down. However, there will still be a net increase in entropy in this spontaneous reaction as the increase in entropy of the melting ice cube is greater in magnitude than the decrease in entropy of the soup.
The second law of thermodynamics deals with the spontaneity of the change of matter in terms of entropy (S). A change is spontaneous if
-200 kJ We are provided with the value of the standard heat of formation for liquid methanol. What is happening during this reaction? A reaction occurs, and the bond breakage and formation has a net release of energy, which is why ΔHf is negative. How does liquid methanol compare to gaseous methanol? To go from a liquid to a gas requires an input of energy (endothermic, ΔH = +ve). Therefore, we would expect a gas to have a more positive (less negative) ΔH than a liquid, as more energy is involved (ie. less energy is released). This makes [D] our answer choice, as it is the only answer choice where ΔHf for the gas is more positive than the ΔH f we were provided for the liquid.
The standard enthalpy of formation of liquid methanol is provided below, C(graphite) + 2H2(g) + 1⁄2O(g)2--> CH3(l)OH ΔHf = -239 kJ Which of the following would most likely be the value of the standard enthalpy of formation of gaseous methanol?
Allotropes are different structural forms of the same element. Carbon is capable of forming many allotropes, for example: diamond, graphite, soot, and fullerene.
Which of the following correctly describes an allotrope?
1. Changing the temperature of the reaction. 2. Changing the reaction itself - either by reversing the reaction or by adding coefficients to every substance in the reaction. These changes to the reaction will alter Keq in consistent ways that are useful to memorize.
There are two ways of changing the value of Keq. These are
condenser Homogeneous mixtures are often separated using distillation. In distillation, the different boiling points of the substances are used to separate the mixture. The mixture is boiled, until one of the compounds evaporates. The evaporated compound is then immediately cooled through the condenser and collected on the other end in a flask. The only piece of laboratory equipment given in the answer options that coincides with this process is [C]. A pipet is used for transferring substances of small volumes, a buret is used during titration experiments to determine concentrations, and a filter would be used to separate a heterogeneous mixture. A separatory funnel is useful for separating heterogeneous mixtures, like an organic solvent and aqueous solvent.
To separate a homogeneous mixture of salt water, which of the following pieces of laboratory equipment is necessary?
32 The fourth energy level has four orbitals, s, p, d, and f. S orbitals can hold a maximum of 2 electrons, p orbitals can hold a maximum of 6 electrons, d orbitals can hold a maximum of 10 electrons, and f orbitals can hold a maximum of 14 electrons. Therefore the 4th energy level can hold at most 2 + 6 + 10 + 14 = 32 electrons. Notice that the first energy level can only hold 2 electrons. This is why helium is considered a noble gas even though it only has 2 electrons; it has a full energy level already!
What is the maximum number of electrons that can be held in the 4th energy level?
1 mol in 22.4 L @ 273K & 1 atm
What is the numbers for STP?
12 NaOH is a strong base and fully dissociates into Na+ and OH-. To find the new concentration of NaOH after we dilute it with water, we use: M1V1 = M2V2 (0.02)(0.02) = M2(0.04) 0.01 = M2 Notice that we use 0.04 L for the second volume, NOT 0.02 L. This is because we are adding 0.02 L of NaOH(aq) to 0.02 L of water for a total of 0.04 L. Next, since NaOH is a strong base, we can conclude [OH-] = 0.01 M. pOH = -log([OH-]) pOH = -log(0.01) pOH = 2 pH + pOH = 14 pH = 14 - pOH pH = 14 - 2 = 12
What is the pH of a solution prepared by adding 20 mL of 0.02 M NaOH(aq) to 20 mL of water?
9. React with Hydrocarbon:CxHx with O2 to get CO2 and H2O 1 C2H6O + 3 O2 → 2 CO2 + 3 H2O
What is the sum of the coefficients of the complete balanced equation from combusting C2H6O? what do you need for combustion
Volatility is the ability of a liquid to evaporate. Liquids that readily evaporate have weak intermolecular attractions and can turn into gas at low temperatures. London dispersion forces (Van der Waals forces) are weak intermolecular forces that arise from instantaneous dipoles in molecules without dipoles. London dispersion forces increase with molecular weight. Hydrogen and ionic bonds would not give rise to liquids that can easily evaporate as these are stronger forces. Likewise, something that has a high viscosity has strong bonds and is not going to evaporate at low temperatures. Viscous liquids include substances like honey and molasses, neither of which are able to evaporate easily. A liquid metal would not readily evaporate either. The only answer option that correctly explains a liquid's high volatility is answer choice [E].
What is volatility?
The solubility of an aqueous solute increases with increasing temperature. This is due to an increase in kinetic energy with higher temperature, which allows the solid to dissolve more readily. The presence of a common ion, such as F- (from NaF), will decrease the solubility of BaF2, because the equilibrium shifts to the left. The anion of BaF2, F-, is basic. Adding HCl will increase the solubility of BaF2, because the HCl will react with F-, thereby decreasing the concentration of F- and shifting the equilibrium to the right.
What will be the effect on the solubility of BaF2 if the following changes are made: increasing temperature; adding NaF; adding HCl?
The colligative properties of a solution will depend on the solution's concentration of solute, but not the identity of the solute. As more solute is added to a solution, all of the following properties increase in value: • Molarity = mol solute / L solution • Osmotic pressure = iMRT, where i is the van't Hoff factor, M is the molarity (mol/L), R is the ideal gas constant (0.0821 L atm / mol K) and T is the absolute temperature (K). • Molality = mol solute / kg solvent • Boiling temperature elevation = iKbm, where i is the van't Hoff factor, Kb is the boiling point elevation constant, and m is the molality As we add more solute to a solution, vapor pressure decreases. The reason for this is that as we add solute to to a solution, the solute competes with the solvent at the surface of the solution, and replaces some of the solvent at the surface. With less solvent molecules at the surface, less solvent can escape the liquid and become a gas, and vapor pressure decreases.
When NaCl is added to distilled water, each of the following properties would increase EXCEPT one. Which one is the EXCEPTION?
o correctly balance this equation follow these steps: 1. Balance chromium on both sides by adding a coefficient of 2 in front of the CrO42-. 2CrO42- → Cr2O72- 2. Balance the number of oxygens by adding 1H2O to the right side. Note: By adding the coefficient of 2 in the first step, there are 8 oxygens on the left and only 7 oxygens on the right, which is why only 1 H2O is added on the right. 2CrO42- → Cr2O72- + H2O 3. Balance the hydrogens by adding 2H+ to the left side. Since this is in acidic solution, the H+ will be in the final half-reaction equation. 2H+ + 2CrO42- → Cr2O72- + H2O 4. Add electrons to balance the charges on both sides, as needed. In this case no electrons are needed. 2H+ + 2CrO42- → Cr2O72- + H2O 2h
When the following reaction is balanced in acidic solution using whole number coefficients, what is the coefficient of H+? CrO42- → Cr2O72-
The equivalence point during a titration is the point in an acid-base reaction where equivalent quantities of acid and base have been reacted; it is the point where equal moles of acid react with equal moles of base.
When titrating the monoprotic acid HCl with NaOH of a known concentration, which of the following must be equal at the equivalence point?
Cl- IO3- F2 Zn2+ Cl2 In this case, the reducing agent we're looking for must have an element that will likely give up electrons (or become oxidized). Cl- is a great candidate to act as a reducing agent since it will change oxidation states from -1 to 0. IO3- looks like a possibility, but the oxidation state on iodine is +5, and it isn't likely to give up more electrons. F2 isn't likely to give up more electrons, and neither is Zn2+ or Cl2.
Which of the following acts as a reducing agent?
amphoteric
Which of the following best describes a compound that reacts as both an acid and a base?
Increase pressure of the gas and decrease temperature of the solution In a system where gas exists above a liquid, the solubility of the gas is affected by both pressure of the gas and the temperature of the solution. First, let's look at how the pressure of the gas affects gas solubility: The pressure dependence of gas solubility is expressed by Henry's law: S = kP, where S is the solubility of the gas in the solvent, k is Henry's law constant, and P is the partial pressure of the gas above the surface of the solution. As partial pressure goes up, solubility goes up: ↑ pressure of the gas = ↑ gas solubility ↓ pressure of the gas = ↓ gas solubility Next, let's look at how the temperature of the solution affects gas solubility: ↑ temperature of the solution = ↓ gas solubility ↓ temperature of the solution = ↑ gas solubility Here's an easy way to remember that gas solubility increases as temperature decreases. Ever had a warm soda, or a warm beer? It likely was quite flat (non-carbonated), compared to the cold, fizzy (carbonated) alternative. That's a real life example of colder temperatures allowing higher gas solubility. And have you ever noticed the loud "pop" noise a soda can makes when you crack it open, as the pressure within the can decreases, equalizing with the pressure outside? The reason that sodas are kept under this high pressure is to increase the solubility of the carbon gas within the liquid. For this reason, when you crack the can open, gas escapes, causing a loud "pop" noise, and if you leave an open soda can out for too long, it will become flat. This is a real-life example of high pressure increasing solubility of a gas (carbonation) in a liquid (soda). So, which of the following changes will result in the greatest increase in solubility of O2 gas in water? ↑ pressure of the gas, ↓ temperature of the solution = ↑ gas solubility
Which of the following changes will result in the greatest increase in solubility of O2 gas in water?
Nitrogen and phosphorus are two nonmetallic elements belonging to Group VA of the periodic table. Nitrogen is more electronegative than phosphorus since it is closer to the upper right corner of the periodic table (electronegativity increases from left to right and from bottom to the top of the periodic table). Nitrogen, being on top of phosphorus, and containing fewer electrons has a smaller atomic radius than phosphorus. Because of its smaller size, nitrogen can bond to fewer atoms than phosphorus. Eg. Nitrogen bonds to three chlorine atoms in NCl3 whereas phosphorus can bond to five chlorine atoms forming PCl5. In addition, because of the smaller size of nitrogen, it can approach another nitrogen atom more closely. As a result, formation of π bonds is more effective in nitrogen than in phosphorus.
Which of the following descriptions is correct regarding nitrogen and phosphorus?
All the group 1 elements, the alkali metals, are known to react very vigorously with water to produce hydrogen gas. This is why the alkali metals are usually kept in a jar of oil in the chemistry closet, to minimize the amount of water vapor it comes into contact with. It is also why professors don't allow undergrads to use it in their chemistry laboratory classes. Alkaline earth metals, or group 2 elements, also react with water. However, they do not react as vigorously as the alkali metals.
Which of the following elements reacts explosively with water?
There are two different types of polarity that have to be understood to answer this question. They are bond polarity and molecular polarity. For bond polarity, if there is a large difference in the electronegativities of the elements that make up a bond, then the elements are most likely sharing the electrons in the bond unequally, resulting in a polar bond. However, molecular polarity deals with the shape of the molecule, looking for symmetry. Symmetry leads to a non-polar molecule. The only molecules in the answer options that have a symmetrical shape are CF4 and N2. However, N2 would have non-polar bonds as the N-N bond would have the same electronegativity and would be sharing the electrons equally. Therefore, CF4 must be the answer as the electronegativities vary with the C and the F making the C-F bonds polar.
Which of the following is an example of a compound that has polar bonds but a non-polar shape? SO2 H2O N2 CF4 NH3
The half-reaction for nickel has a negative E° indicating that the reaction prefers to go in the reverse direction. Therefore, the nickel reduction half-reaction must be flipped to yield an oxidation reaction, with an E° of 0.28. The half-reaction of the chlorine is positive, indicating that chlorine prefers the forward reaction and wants to be reduced. E° cell can be calculated by adding the E° cell reduction (Chlorine = 1.36) to the E° cell of the oxidation (Nickel = 0.28).
Which of the following is the Eº cell for the reduction of chlorine?
Know for the DAT that 1A alkali metals and 2A alkaline earth metals react in the presence of pure oxygen. Sodium and the group 1A metals will react violently with pure oxygen. The reactions are normally combustions. Group 2A metals also react with oxygen, but not to the extent of the 1A elements. Germanium, sulfur, and boron react with oxygen to make oxides.
Which of these elements will have a vigorous reaction in the presence of pure oxygen?
endothermic will go on reactant side exothermic will go on product The easiest way to think about the ΔHo of a reaction is to add it into the chemical equation. A negative ΔHo means the reaction is exothermic, so energy is given off, or it is part of the products. The reverse is true for endothermic reactions, the energy would be part of the reactants. The chemical reaction can be rewritten as:
Which side will endothermic or exothermic will go on chemical reaction in equilibrium rxn?
London dispersion intermolecular forces increase as molar mass increases. As molecules get heavier, they exhibit a greater amount of London dispersion forces (nonpolar forces), and these forces become so powerful that iodine actually turns into a solid.
Which statement best explains why bromine is a liquid and iodine is a solid at STP?
The strength of an acid is usually determined by how much the acid dissociates. Thus, the weaker the bond holding the proton to the molecule, the stronger the acid is. The bond strength is largely determined by the difference in electronegativity. Fluorine is one of the most electronegative elements, and thus is not as strong of an acid as HCl or HI, which have weaker bonds, and thus a more readily available proton.
Which statement explains why HI is a stronger acid than HBr, which is a stronger acid than HCl?
An adiabatic process is one in which heat energy remains constant (∆q = 0). In an adiabatic process, because, Δq = 0, ΔU = q - W ΔU = 0 - W, ΔU = -W.
adiabatic
0 -1 n->p on product side
beta decay
A reaction intermediate is a short lived (transient) molecule that forms in a multistep reaction. It is a different, separate existing molecule that is unique from the reactants and the products. This is different than a transition state. A transition state is literally a state of transition from one molecule to another molecule. This is when bonds are being broken and bonds are being formed (partial bonds). This is why [E] is incorrect. Although all reactions involve bonds being broken and formed (transition states), not all reactions have reaction intermediates forming and being consumed (multistep reactions).
difference between reaction intermediates and transition states
These two cells are very similar, the major difference that you can see from the diagram shown below is that in an electrolytic cell the anode is positive and cathode is negative, while in a galvanic cell the anode is negative and the cathode is positive. In both, the flow of the electrons is the same, going from anode to cathode. Because the anode is positive and cathode is negative in electrolytic cells, the reaction will be non-spontaneous. A power source is required to make this reaction occur. In a galvanic cell, the anode is negative and cathode is positive and the reaction is spontaneous. A galvanic cell can act as a power source (a battery).
differences between galvanic and electrolytic cells
0 -1 p->n on reactant side
electron capture
pi=iMRT pi= osmotic pressure i=van't Hoff factor M= molarity R is a constant, T is temperature in Kelvin
formula for osmotic pressure
An isenthalpic process is one in which enthalpy remains constant (∆H = 0).
isenthalpic process
An isentropic process is one in which entropy remains constant (∆S = 0).
isentropic
An isobaric process is one in which pressure remains constant (∆P = 0).
isobaric process
An isothermal process is one in which temperature remains constant (∆T = 0).
isothermal
protons and neutrons
nucleons
0 +1 p->n on reactant side
positron emission
0.082, which is used for atm 8.314 is used for kPa
r for ideal gas
cathode= reduction anode = oxidation Steel tanks can be protected from corrosion by making them the cathode in an electrochemical cell. This way, electrons will be oxidized from the zinc and the zinc will corrode instead of the steel tank. This is called cathodic protection.
reduction or oxidize cathode or anode
Generally, salts with ammonium will dissolve, and salts with chloride, bromide, or iodide will also dissolve. Another important rule is salts with nitrate ions (NO3-) are soluble too. However, iron sulfide (the product) is NOT soluble and will precipitate as a solid.
solubility rule
A state function is a property whose value does not depend on how that state was achieved. An analogy is a trip from New York to California. The destination is a state function. It doesn't matter whether you drove through Canada, or flew direct, all that matters with the destination is that you arrive in California. Destination is a state function. Enthalpy, volume, mass and Gibbs free energy are all state functions. Alternatively, a path function (non-state function) is one in which the process matters. Path functions depend on the transition or change of the state. Think about the trip from New York to California. The amount of work that trip takes certainly depends on the route taken. If you decide to fly from New York to Canada, before heading to California, you're going to require a lot more work than if you fly direct. Heat and work are examples of path (non-state) functions.
state function vs non state function
The main strong acids you should know: HCl - hydrochloric acid HNO3 - nitric acid H2SO4 - sulfuric acid HBr - hydrobromic acid HI - hydroiodic acid HClO3 - chloric acid HClO4 - perchloric acid The main strong bases you should know: LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide Ca(OH)2 - calcium hydroxide RbOH - rubidium hydroxide Sr(OH)2 - strontium hydroxide CsOH - cesium hydroxide Ba(OH)2 - barium hydroxide
strong acid/base
M·s-1 = zero-order s-1 = first-order M-1·s-1 = second-order M-2·s-1 = third-order
units for all rate orders 0 1st 2nd 3rd
A buffer solution consists of a weak acid and its conjugate base or a weak base and its conjugate acid.
what consist in a buffer solution
oxidizing agent is reduced in a chemical rxn
what is a oxidizing agent
reducing agent is oxidized in a chemical rxn
what is a reducing agent
having the same number of electrons F- S2- K+ AR CA2+ All have same amount of electron except F-
what is isoelectronic
The titrant is the stock or known solution
what is titrant?
