CHEM 121 LAB FINAL

While setting up a beaker to boil a solution on a hot plate, you notice that the stirring is erratic and unstable. What should you do to stabilize the stirring solution?

- Move the beaker to the center of the hot plate. - Turn down the stirring speed.

What visible signs indicate a precipitation reaction when two solutions are mixed?

- Solid settling out in the test tube - A hazy or cloudy appearance

Identify the potential uses for an iron ring.

- Suspending a funnel - Holding a crucible placed in a clay triangle - Supporting a beaker on a piece of wire mesh

A series of measurements in the lab led to an experimental result of 32.9 mL, with a calculated standard deviation of 0.3 mL. What is the standard way to report this result?

32.9 ± 0.3 mL explanation: When reporting a numeric value associated with a standard deviation, it is a good practice to also include the standard deviation along with the value. This gives the reader an idea of the precision associated with the value.

How many significant figures are in the number 510.9? Give a numerical answer.

4 explanation: All nonzero digits are significant and any zero between nonzero digits is significant. Thus, the number 510.9 has 4 significant figures.

Consider the balanced equation for the reaction of aluminum with hydrochloric acid. 2Al+6HCl⟶2AlCl3+3H2 Fill in the conversion factors required to calculate the mass of HCl needed to react with 5.00 g of Al. 5.00 g Al×( A )26.9815 g Al×( B )( C )×( D )1 mol HCl=20.3 g HCl5.00 g Al×( A )26.9815 g Al×( B )( C )×( D )1 mol HCl=20.3 g HCl

A) 1 mol Al B) 6 mol HCl C) 2 mol Al D) 36.454 g HCl

What characteristics of a molecule determine whether or not it is polar?

- The polarity of the individual bonds in the molecule - The arrangement of bonds around the molecule explanation: A polar molecule has an overall dipole moment with an asymmetrical arrangement of electrons around it. Thus, polarity requires polar bonds arranged in a non-symmetrical way. Both bond polarities and molecular geometry, or bond arrangement, determine the polarity of a molecule.

A polymer is ________ made of _________, known as ___________. Polymers can be natural, such as ________, or synthetic, such as ________.

- a macromolecule - a single chain of ions - monomers - proteins - steel

An indicator is a substance added to a sample that has __________ change, such as a ___________ change, in response to the ____________ of the sample.

- a visible - color - chemical composition

To determine an ionic formula from a compound name, start by ____________ for each element in the compound. Then, use the ______________ to determine the subscripts necessary to ____________.

- finding the expected charge - charge of each ion -create a formula unit with no net charge

When balancing a redox reaction, begin by separating the reaction into ____________. Balance each of these in terms of ______________. Multiply by some factor if necessary so that the number of ________________ appearing in both is the same. Add these together, canceling out any terms that appear on both sides of the final equation.

- half reactions - atoms and charge - electrons

Consider the reaction of copper with nitric acid. Cu(s)+4HNO3(aq)⟶Cu(NO3)2(aq)+2NO2(g)+2H2O(l) The copper is oxidized by the _____________ in nitric acid. The _________ is not capable of the oxidation because ________________.

- nitrate ion - hydrogen ion - it is more reactive than copper on the activity series

A covalent bond is an interaction in which ____________ are __________ between two atoms in a molecule. A covalent bond is indicated in a structural formula with a _____________.

- valence electrons - shared - dash

Identify the common indicators that a chemical reaction has occurred.

-Precipitate being formed -Bubbles being produced -A color change -A change in temperature

Calculate the moles of ammonia present in a 8.181 g sample if the molar mass of ammonia is 17.030 g/mol.

0.4804 explanation: The molar mass of a compound is the mass of one of compound. Therefore, if you divide a mass of the compound by its molar mass, you will find how many moles of the compound are present. moles of substance = mass in g * (1 mol of substance / molar mass)

Identify characteristics of ammonia, NH3: 1. Number of single bonds 2. Number of double bonds 3. Number of triple bonds 4. Electron geometry 5. Molecular geometry

1. 3 2. 0 3. 0 4. tetrahedral 5. trigonal pyramidal

What are the best practices while sharing a lab balance with other students?

1. Brush off any chemical dust around the balance after each use. 2. Alert your TA or instructor about any issues with the balance.

When you are done using most glassware in the lab, what should you do?

1. Clean the glassware with a detergent solution 2. Return the glassware to the appropriate location to dry 3. Dispose of any chemicals in the proper waste container.

When using a properly stabilized balance, how should you ensure that you get the most accurate mass reading possible?

1. Close the side shields on the balance during reading. 2. Measure the mass of the sample at room temperature.

Determine the molecular geometry based on the description of bonding and lone pairs of electrons around the central atom. 1. Three double bonds and no lone pairs of electrons 2. Two single bonds and two lone pairs of electrons 3. Three single bonds and one lone pair of electrons 4. Two double bonds and no lone pairs of electrons 5. Four single bonds and no lone pairs of electrons

1. trigonal planar 2. bent 3. trigonal pyramidal 4. linear 5. tetrahedral

A 24.5 g sample of solution has a density of 0.768 g/mL. What is the sample volume (in mL)?

31.901 mL explanation: Density, d, is equal to mass, m, divided by volume, V. d= m/v Rearrange this equation to solve for volume. v= m/d v= 24.5 g / 0.768 g/mL V=31.9 mL

What is the advantage of fluted filter paper shown compared with cone-shaped filter paper?

Fluted filter paper has more surface area suitable for collecting solid.

Which procedure cannot be performed on a hot plate, requiring a Bunsen burner instead?

Heating a crucible to remove water from a hydrate

What is the best description of precision as applied to a set of measurements or data?

How well data points within a data set agree with each other

What is the best description of accuracy as applied to a set of measurements or data?

How well the average of a data set agrees with a known value

Which reaction is occurring in the test tube?

KCl(aq)+AgNO3(aq)⟶AgCl(s)+KNO3(aq) explanation: The image shows a precipitation, in which a solid product is formed from two reactant solutions. Thus, the reaction equation matching the test tube in the image needs to have aqueous reactants on the left side of the reaction arrow and a solid product on the right side of the reaction arrow.

Which compound name does not correspond to an ionic compound?

Phosphorus pentafluoride

Which formula is not an example of an ionic compound? Select one: CaO K2O SO3 Al2O3

SO3 explanation: An ionic compound is composed of a cation, usually formed from a metal, and an anion, usually formed from a nonmetal. Thus, for compounds containing only two elements, any compound that contains both a metal and a nonmetal is an ionic compound.

When heating liquids in a test tube, it is important that the test tube be positioned _____________, pointed _______________ people and __________

at an angle, away from, half- full

What is the name of the compound with the formula of CS?

carbon monosulfide

What is the name of the compound with the formula of Cr2S3?

chromium(III) sulfide

When working in the fume hood, it is important to make an effort to minimize ____________. Only keep items in the hood if they are being used for ____________. Do not ____________ chemicals in the fume hood unless instructed to do so.

clutter, the current experiment, store

The process of separating a liquid/solid mixture by slowly pouring the liquid component into a new vessel as the solid settles to the bottom of the original vessel is known as

decanting

Predict the relative size of the radius for the lithium cation versus the neutral atom.The radius of Li+ is _________ that for Li.

smaller than explanation: The radius of the lithium ion is predicted to be smaller than the neutral atom.

Suppose that two students perform a titration experiment multiple times, resulting in the average concentrations reported here. Student A = 0.125 ± 0.008 M Student B = 0.12 ± 0.03 M The more precise work was done by __________ because ___________________________ .

student A because that student's data has a smaller standard deviation

To measure out a volume of liquid, start by choosing the appropriate graduated cylinder and moving the bumper to the _______ of the graduated cylinder to protect it from breakage. Then, pour the liquid into the graduated cylinder until the _________ of the meniscus aligns with the desired volume marking when you look at the graduated cylinder from _________

top, bottom, eye level

Identify the components of the ionic formula based on the name strontium phosphide. 1. What is the symbol for the element that forms the positive cation? 2. What is the symbol for the element that forms the negative anion? 3. What is the subscript on the cation in the neutral formula? 4. What is the subscript on the anion in the neutral formula?

1. Sr 2. P 3. 3 4. 2 explanation: In an ionic compound, the cation is named before the anion. Therefore, the cation is formed from strontium. Its symbol is Sr. The name of the anion's element has its ending changed to -ide. The anion is formed from phosphorus. Its symbol is P. Based on the position of each element on the periodic table, the charge of the Sr cation is +2 and the charge of the P anion is -3. To combine these two ions into a neutral formula unit, you can use the magnitude of each ion's charge as the other ion's subscript. This leads to three Sr ions with a total charge of +6 and two P ions with a total charge of -6. The formula for strontium phosphide is Sr3P2.

Determine whether each of the errors listed affects the accuracy of pipets, or can lead to the contamination of pipets. 1. The liquid level in a pipet is read from the top of the curve rather than the meniscus. 2. After the liquid is drained from the pipet, the final drop is pushed through with the pipet bulb. 3. The pipet is not cleaned thoroughly between uses. 4. Air bubbles are present as the liquid is drawn up into the pipet and dispensed. 5. Pipets are washed with detergent and then put to use immediately.

1. accuracy 2. accuracy 3. contamination 4. accuracy 5. contamination

Identify the term that matches each definition. 1. The front vent of a fume hood, which helps maintain proper air circulation ________ 2. The glass panel in front of the fume hood that shields the user from fumes and other hazards _______ 3. A characteristic that describes substances that evaporate readily, producing large amounts of vapors ________ 4. The horizontal, flat area of a fume hood upon which experiments are carried out __________

1. airfoil 2. sash 3. volatile 4. work surface

Match each formula to its name. 1. CaCl2 2. Cu2O 3. CuCl2 4. Cu2O3 5. CaO

1. calcium chloride 2. copper (I) oxide 3. copper (II) chloride 4. copper (III) oxide 5. calcium oxide

Determine whether the stopcock should be completely open, partially open, or completely closed for each activity involved with titration. 1. Conditioning the buret with titrant 2. Filling the buret with titrant 3. At the beginning of a titration 4. Close to the calculated endpoint of a titration

1. completely closed 2. completely closed 3. completely open 4. partially open

Suppose you are given the mass of each element in a compound sample. To calculate the empirical formula, start by ____________________ using __________________. Then, __________________ by _____________________.

1. converting the mass of each element to moles 2. each element's molar mass 3. calculate the ratio between the elements 4. dividing the moles of each element by the smallest number of moles present

Identify the type of each reaction in the copper cycle. 1. Cu(NO3)2(aq)+2NaOH(aq)⟶ Cu(OH)2(s)+2NaNO3(aq) 2. CuSO4(aq)+Zn(s)⟶ ZnSO4(aq)+Cu(s) 3. Cu(OH)2(s)⟶ CuO(s)+H2O(g) 4. CuO(s)+2H2SO4(aq)⟶ CuSO4(aq)+H2O(l)

1. double displacement 2. single displacement 3. decomposition 4. double displacement

When drawing the Lewis structure of a molecule, start by determining the total number of available valence based on each element's _____________. Then, use the total number of electrons needed for each element to be stable, generally based on ___________ to determine the _________ by finding the difference between the number of needed and available electrons divided by two. Next, identify the central atom, which is the element with the _________ other than hydrogen. Finally, arrange the number of bonds around the central atom to fulfill the stable number of electrons for each element.

1. group number 2. the octet rule 3. total number of bonds 4. fewest valence electrons

Determine the molecular geometry based on the description of bonding and lone pairs of electrons around the central atom. Two double bonds and no lone pairs of electrons _______________ Two single bonds and two lone pairs of electrons ______________ Three single bonds and one lone pair of electrons _______________ Four single bonds and no lone pairs of electrons ______________

1. linear 2. bent 3. trigonal pyramidal 4. tetrahedral

Determine the type of each chemical equation describing a precipitation reaction. 1. CaCl2(aq)+Na2CO3(aq)⟶2NaCl(aq)+CaCO3(s) 2. Ca2+(aq)+CO32−(aq)⟶CaCO3(s) 3. Ca2+(aq)+2Cl−(aq)+2Na+(aq)+CO32−(aq)⟶CaX2+(aq)+2ClX−(aq)+2NaX+(aq)+COX3X2−(aq)⟶ 2Na+(aq)+2Cl−(aq)+CaCO3(s)

1. molecular equation 2. net ionic equation 3. complete ionic equation

Identify the best heat source for each situation listed. 1. A test tube must be heated to a very high temperature. 2. A test tube needs to be warmed gently to a constant temperature. 3. A flask or beaker must be heated to a very high temperature.

1. place in a bunsen burner flame 2. clamp in place in a water bath on a hot plate 3. place on a hot plate

Determine whether each described molecule is polar or non-polar. 1. Trigonal pyramidal PF3 2. Trigonal planarBF3 3. LinearCS2 4. Bent H2O 5. Tetrahedral CH4 6. Linear HF

1. polar 2. non-polar 3. non-polar 4. polar 5. non-polar 6. polar

Choose whether or not each type of glassware can be heated. 1. volumetric flasks 2. beakers 3. graduated cylinders 4. Erlenmeyer flasks 5. test tubes

1. should not be heated 2. can be heated 3. should not be heated 4. can be heated 5. can be heated

Determine each type of reaction. 1. 2Fe(s)+6HCl(aq)⟶2FeCl3(aq)+3H2(g) 2. CaCl2(aq)+Na2CO3(aq)⟶2NaCl(aq)+CaCO3(s) 3. 2C2H2(g)+5O2(g)⟶4CO2(g)+2H2O(l) 4. CO(g)+2H2(g)⟶CH3OH(l) 5. NH4NO3(s)⟶N2O(g)+2H2O(l)

1. single replacement 2. double replacement 3. combustion 4. combination 5. decomposition

Identify each category of substance as soluble or insoluble in water. 1. most nitrate salts 2. salts of Group 1 elements 3. most halide (Br-, Cl-,I-) salts 4. most carbonate and phosphate salts 5. most silver salts

1. soluble 2. soluble 3. soluble 4. insoluble 5. insoluble

When heating a solution to boiling on a hot plate, start by ________________________. Then, turn the heat to ______________ to start. If necessary, _________________ after waiting about ten minutes without seeing boiling.

1. starting and stabilizing the stir function 2. a medium heat setting 3. turn up the heat setting

Determine whether each of the properties described applies to volumetric or graduated glassware. 1. Used for applications in which great accuracy is needed ________________ 2. Capable of measuring a range of volumes of liquid ______________ 3. Designed to measure one specific volume of liquid ________________

1. volumetric 2. graduated 3. volumetric explanation: Volumetric glassware is designed to accurately measure and dispense one specific volume of liquid, such as the volumetric pipette pictured here. Graduated glassware may be used to measure and dispense a range of volumes of liquid, but with less accuracy, such as the graduated pipette pictured here.

Suppose you are performing an experiment in which you produce a solid and measure its mass. You run the six trials reported in the table to find the best average mass of the product. 2.00 g 1.54 g 1.28 g 1.19 g 1.14 g 2.63 g What is the average mass, in grams, of the product based on the six trials?

1.63 g explanation: The average is the sum of the values divided by the number of values. There are six trials, so there are six values to be added and the denominator should be 6.

Barium can be analyzed by precipitating it as BaSO4 and determining the mass of the precipitate. When a 0.269-g sample of a barium compound was treated with excess H2SO4, 0.0891 g of BaSO4 formed. What percentage of barium is in the compound?

19.5

Provide the coefficients needed to balance the redox reaction given. _Fe(s) + _Cl2(g)→ _Fe3+(aq) + _Cl-(aq)

2,3,2,6

Copper(II) hydroxide reacts with sulfuric acid to produce copper(II) sulfate. What volume (in mL) of 3.0 M H2SO4 do you need to completely react with 0.61 g Cu(OH)?

2.1 mL (see notes)

Consider the balanced reaction of magnesium and oxygen. 2Mg+O2⟶2MgO What mass, in grams, of MgO can be produced from 1.38 g of Mg and 2.73 g of O2?

2.29 explanation: Start by identifying the limiting reactant. Check the amount of product corresponding to each reactant. Whichever reactant can produce less is the limiting reactant. Complete the calculation by finding the moles of each reactant, the moles of product produced from the moles of reactant, and finally the mass of product. mass of product based on amount of Mg 1.38 g Mg× (1 mol Mg / 24.305 g Mg) × (2 mol MgO / 2 mol Mg) × (40.304 g MgO / 1 mol MgO) mass of product based on amount of O2mass of product based on amount of OX2 2.73 g O2 × (1 mol O2 / 31.998 g O2) × (2 mol MgO / 1 mol O2) × (40.304 g MgO / 1 mol MgO) Because the mass of Mg produces less MgO, it is the limiting reactant. The mass produced by Mg is the amount that can actually be made as it uses up all the Mg.

Calculate the mass percent of a vinegar solution with a total mass of 97.02 g that contains 2.28 g of acetic acid.

2.35 explanation: The definition of percent by mass for a solution is % mass of a solution = (mass of solute / mass of solution)*100

From a 2.767 g sample containing only iron, sand, and salt, 0.900 g of iron and 1.212 g of sand were separated and recovered. What was the percent of salt in the original sample?

23.7 explanation: mass of salt=mass of sample−mass of iron−mass of sand= 2.767 g−0.900 g−1.212 g Then, divide by the total mass and multiple by 100 to find the percentage. % of salt = (mass of salt / mass of sample) * 100

Suppose a student starts with 2.3804 g of a sand mixture and separates the components into 1.3012 g of NaCl, 0.5881 g of SiO2, and 0.4503 g of CaCO3. Based on the amount of recovered, what is the percent of SiO2 in the starting mixture?

24.71 explanation: % of SiO2= (0.5881g / 2.3804 g) * 100

A student performed a density experiment in triplicate and recorded the data shown. Calculate the average density (in g/mL) for this experiment. Density trial 1 4.58 g/ml trial 2 4.92 g/ml trial 3 4.86 g/ml

4.79 g/ml explanation: An equation for calculating the average is, avg = n1+n2+n3 / n

Consider the balanced equation of KI (molar mass=166.0 g/mol) reacting with Pb(NO3)2 to form a precipitate. 2KI(aq)+Pb(NO3)2(aq)⟶PbI2(s)+2KNO3(aq) What mass of PbI2 (molar mass=461.0 g/mol) can be formed by adding 3.67 g of KI to a solution of excess Pb(NO3)2?

5.1 (see notes)

Suppose a 15.7500 g sample of a NaCl and KCl mixture contains 7.5385 g of NaCl. . What is the percent of KCl in the mixture?

52.14 explanation: % of NaCl = (7.5385g / 15.7500 g) * 100 The percent compositions of the two components should add to 100%. Subtract the percent of NaCl from 100. % of KCl= 100% - % of NaCl

A pill that is 91.5% aspirin is found to contain 53.43 mg of aspirin. What is the mass of the pill in milligrams?

58.4 mg explanation: The equation for the percent composition of a mixture component is % composition=(mass of mixture component/ total mass of mixture)×100 Rearrange the equation to solve for the mass of the mixture, which is the pill in this example. total mass of pill=mass of aspirin(% composition / 100) =53.43 mg(91.5% / 100)

The cycle of copper reactions starts with solid copper metal and ends with solid copper metal. Suppose you start with 0.492 g of Cu. After performing all the reactions, you have 0.469 g of Cu. What percentage of the copper did you recover?

95.3 explanation: Percent recovery compares the mass of copper at the end to the mass of copper at the beginning. % recovery = (final mass of copper/ initial mass of copper) * 100

Suppose a student starts with 2.3524 g of a sand mixture and separates the components, recovering 1.3012 g of NaCl, 0.5774 g of SiO2, and 0.4503 g of CaCO3. What is the percent recovery of the mixture?

99.001 explanation: The percent recovery is the amount of all mixture components compared to the starting total. % recovery=(mass of mixture component 1 + mass of mixture component 2 + mass of mixture component 3 / starting mass of mixture)×100 % recovery = (mass of NaCl + mass of SiO2 + mass of CaCO3 / starting mass of mixture) * 100

Which described method is NOT an example of a physical separation?

Adding a solution that reacts with only one component of the mixture to create a precipitate explanation: A physical separation uses differences in physical properties or involves physical changes. Therefore, evaporation, filtration, and manipulating solubility are all examples of physical separation methods. Chemical separation methods use a reaction to separate out the components, such as the given example of adding a solution to cause a reaction with only one component.

Which formula is not an example of an ionic compound?

Al2O3

Which reaction is NOT an example of a decomposition reaction?

CaO+CO2⟶CaCO3 explanation: A decomposition reaction separates a single reactant into two or more products. The products can be either elements or compounds. The key component in recognizing a decomposition reaction is that there is one reactant on the left side of the reaction arrow and multiple products on the right side of the reaction arrow.

How should you prepare a buret for titration before loading it with titrant?

Condition the buret with titrant solution

When using a clamp and ring stand to hold glassware and tools, what is the best position for the clamp?

Directly above the base of the ring stand

Which of the following compounds requires a Roman numeral in its name?

MnO2

After clamping a buret to a ring stand, you notice that the set-up is tippy and unstable. What should you do to stabilize the set-up?

Move the buret clamp to a ring stand with a larger base.

Suppose a student repeats a measurement two times and then calculates the standard deviation. Because the standard deviation is small, the student reports that their experiment was extremely precise. Is the student's conclusion appropriate?

No, because there were not enough measurements to use standard deviation.

Identify the products for the reaction of lead(II) nitrate (Pb(NO3)2(aq)) and potassium iodide (KI(aq)

PbI2 (s) and KNO3 (aq)

What is the purpose of stirring a solution while it is being heated?

To help evenly distribute heat throughout the solution

What is indicated by the term crosslinked polymer?

Two polymer chains that are connected by a molecule

When describing the uncertainty of a measurement, the term __________ refers to the closeness between a measurement and its accepted value, whereas the term _________ refers to the closeness among a set of measurements.

accuracy, precision

After assembling a gravity filtration apparatus, begin the separation of a mixture by _____________ it into the filter paper. Pour the entire contents of the mixture into the filter paper, _________________ the solid in the filter paper if needed to speed up the filtration. After all the liquid has drained through the filter paper, finish by rinsing the solid with _____________

decanting, stirring, solvent explanation: In a gravity filtration, it is important to separate the liquid and solid components of a mixture as thoroughly as possible, and maximize the collected yield of the desired product. The desired product may be the solid, the liquid, or both. Review the procedure for each experiment for instructions on how to handle or discard each component after the filtration.

What is the name of the compound with the formula of N2O3?

dinitrogen trioxide

Which types of hazards can a fume hood help protect the user against?

fires, explosions, fumes

When using a clamp to secure a flask to a ring stand, begin by choosing a ring stand and clamp that are appropriately sized for the _____________. Position the clamp directly ___________ the base of the ring stand. Turn the knobs of the clamp, making sure not to _______________ the clamp around any glassware.

glassware, above, overtighten

Predict the relative size of the radius for the fluorine anion versus the neutral atom.The radius of F- is ___________ that for.

larger than explanation: The radius of the fluoride ion is predicted to be larger than the neutral atom.