Chemistry 121 Lab Quizzes
What should you do every time you are about to heat glassware on a hot plate?
Ensure that the glassware is designed for heating. Inspect the hot plate for frayed cords. Check that there are no cracks in the glassware
Which types of hazards can a fume hood help protect the user against?
Explosions, fires, fumes
Which formula is no an example of an ionic compound?
SO3
In a precipitation reaction, what symbol identifies the precipitate product?
(s)
Suppose you are titrating a sulfuric acid solution of unknown concentration with a sodium hydroxide solution according to the equation H2SO4+2NaOH⟶2H2O+Na2SO4 If you require 32.64 mL of 0.778 M NaOH solution to titrate 223.9 mL of H2SO4 solution, what is the concentration of the H2SO4 solution?
0.0567M
Calculate the moles of ammonia present in a 5.586 g sample if the molar mass of ammonia is 17.030 g/mol.
0.328 mole
From a 2.573 g sample containing only iron, sand, and salt, 0.876 g of iron and 1.282 g of sand were separated and recovered. What was the percent of salt in the original sample?
16.13%
Suppose you are titrating vinegar, which is an acetic acid solution of unknown strength, with a sodium hydroxide solution according to the equation HC2H3O2+NaOH⟶H2O+NaC2H3O2 If you require 34.71 mL of 0.1569 M NaOH solution to titrate 10.0 mL of HC2H3O2 solution, what is the molar concentration of acetic acid in the vinegar?
0.545M
Copper(II) hydroxide reacts with sulfuric acid to produce copper(II) sulfate. What volume (in mL) of 3.0 M H2SO43.0 M do you need to completely react with 0.52 g Cu(OH)2?
1.78 mL
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%
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
Suppose a student starts with 2.3524 g of a sand mixture and separates the components into 1.3012 g of NaCl , 0.5774 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?
24.55
Calculate the mass percent of a vinegar solution with a total mass of 96.88 g that contains 3.43 g of acetic acid.
3.54%
A 24.5 g sample of solution has a density of 0.768 g/mL. What is the sample volume (in mL)?
31.9 mL 24.5g/0.768 g/mL=
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
What percentage of sodium is in pure table salt? Include two decimal places in your answer.
39.34%
How many sig figs in the number 5.0002?
5
A pill that is 91.5% aspirin is found to contain 58.41 mg of aspirin. What is the mass of the pill in milligrams?
63.8 mg
Suppose a 16.4467 g sample of a NaCl and KCl mixture contains 3.6985 g of NaCl. What is the percent of KCl in the mixture?
77.51%
Suppose a student starts with 2.4306 g of a sand mixture and separates the components, recovering 1.3012 g of NaCl, 0.5045 g ofSiO2 and 0.4503 g of CaCO3 . What is the percent recovery of the mixture?
92.82%
The cycle of copper reactions starts with solid copper metal and ends with solid copper metal. Suppose you start with 0.486 g of Cu. After performing all the reactions, you have 0.470 g of Cu. What percentage of the copper did you recover?
96.7%
Identify the common indicators that a chemical reaction has occurred.
A change in temp. color change bubbles being produced. precipitate being formed
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
Identify techniques to be used for accurate solution preparation using a volumetric flask.
After the solvent is added, stopper and invert the flask to mix the solution. Read the liquid volume at eye level from the bottom of the meniscus
Molecular, complete ionic, and net ionic equations
As is, break down to charges, what is left when everything is cancelled
When working in a fume hood, what is the best position of the hood sash?
As low as possible, no more than halfway up
Which compounds could be represented by the empirical formula CH2?
C2H4, C3H6, C8H16
What is the correct net ionic equation to describe this precipitation reaction? Co(NO3)2(aq)+2NaOH(aq)⟶2NaNO3(aq)+Co(OH)2(s)
Co2+(aq)+2OH−(aq)⟶Co(OH)2(s)
What should you do if you are using a balance that has persistent fluctuations in mass?
Contact your TA or instructor to adjust the balance
What is the name of the compound with the formula of N2O3?
Dinitrogen trioxide
Identify effective techniques for accurate pipet use.
Do not let liquid enter the pipet bulb or pump. Measure liquid by aligning meniscus with the volume line.
Which procedure cannot be performed on a hot plate, requiring a Bunsen burner instead?
Heating a crucible to remove water from a hydrate
When using a properly stabilized balance, how should you ensure that you get the most accurate mass reading possible?
Measure the mass of the sample at room temp. Close the side shields on the balance during reading.
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), KNO3(aq)
Which compound name does not correspond to an ionic compound?
Phosphorous Pentafluoride
When you are done using most glassware in the lab, what should you do?
Return the glassware to the appropriate location to dry. Clean the glassware with a detergent solution. Dispose of any chemicals in the proper waste container.
Suppose that two students perform a titration experiment multiple times, resulting in the average concentrations reported here. Student A : 0.125+/- 0.008M Student B: 0.12+/- 0.03 M The more precise work was done by_____ because_____
Student A, the students data has a smaller standard deviation
What purpose can funnels serve in the lab?
Support for filter paper during gravity filtration. Assistance of pouring liquids in burets. Help for transferring solid chemicals from weigh boats.
What is an iron ring used for?
Supporting a beaker on a piece of wire mesh. Suspending a funnel. Holding a crucible placed in a clay triangle.
What statements are always true about limiting reactants?
The limiting reactant is completely used up in the reaction. The limiting reactant dictates the amount of product. There will be an excess of other reactants at the end of the reaction.
Why should you always condition a buret before running a titration?
To ensure there is no dilution from water that remains from cleaning
What is indicated by the term crosslinked polymer?
Two polymer chains that are connected by a molecule
What visible signs indicate a precipitation reaction when two solutions are mixed?
hazy or cloudy appearance. Solid settling out in the test tube
A polymer is a _____ made of _____, known as ______. Polymers can be natural such as _____, or synthetic, such as ______
a macromolecule, many repeated subunits, protein, plastics
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
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
Average mass calculations
add all data up and divide by the number of trials
AlCl3
aluminum chloride
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
In order to use a pipet, place a _____ at the top of the pipet. Use this object to fill the pipet such that the ______ of the liquid is even with the volume line. Release the liquid, touching the tip of the pipet to the side of the container if necessary to release the last drop _____ the pipet tip.
blub or pump, meniscus, outside the pipet
CS
carbon monosulfide
An ion is a _____version of an atom that is formed by _______compared to the atom.
charged , losing or gaining electrons
Cr2S3
chromium (III) sulfide
Determine whether the stopcock should be completely open, partially open, or completely closed for each activity involved with titration. Filling the buret with titrant Conditioning the buret with titrant Close to the calculated endpoint of a titration At the beginning of a titration
closed closed partially open open
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
Determine whether the name given is correct: CoI2: cobalt(II) iodide BaCl2: barium dichloride Rb2S: rubidium sulfide SrBr2: strontium(II) bromide Cs2O: cesium oxide
correct incorrect incorrect incorrect correct
Determine whether the given ionic formula for each named compound is correct or incorrect: Titanium(IV) iodide: TiI4 Aluminum selenide: Al3Se2 Ruthenium(IV) oxide: Ru2O4 Barium sulfide: BaS
correct incorrect incorrect correct
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
Suppose you are titrating an acid solution with a base solution of known concentration. To calculate the concentration of the acid solution, use three steps. 1. Use the ___________ base ______ endpoint and the known concentration of the base solution to find the _______ base used. 2. Use the _______ the moles of acid from the moles of base. 3. Divide the moles of acid by the volume of _____ the titration to find the concentration of acid.
delivered volume, to reach, moles , molar ratio, acid solution before
Know the types of reactions
double replacement combustion decomposition combination single replacement
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
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
Which elements do not strictly follow the octet rule when they appear in the Lewis structure of a molecule?
hydrogen, sulfur, chlorine
When preparing for work in the fume hood, be sure to gather all necessary tools, glassware, and chemicals ______ to minimize the number of times the hood sash is raised and lowered. Work as much as possible in the _______ of the work surface to keep the area tidy and promote air flow. If you need to step away from the experiment to obtain another item, _____ the sash during this time.
in advance, middle, lower
Balancing Equations
keep mass of products and reactants the same by adjusting coefficients as necessary
The radius of O2- is _____ that for O
larger than
The radius of Te2- is ____ that for Te
larger than
The radius of Li+ is _____ that for Li
smaller tham
After a mixture has been poured through filter paper, the ________ component remains on top while the ___________ flows through. To collect the solid, spread the filter paper ___________and allow the solvent to ________
solid, liquid, on a watch glass, evaporate
Consider the reaction of copper with nitric acid. Cu(s)+4HNO3(aq)⟶Cu(NO3)2(aq)+2NO2(g)+2H2O(l) what is being oxidized?
the copper is oxidized by the nitrate ion in the nitric acid. The hydrogen ion is not capable of the oxidation because it is more reactive than copper on the activity series.
When filling a buret for a titration, first adjust the buret in the clamp so that __________. Then, ________ to add the titrant into the buret. The titrant should be filled ______
the opening is near eye level, use a funnel, almost to the zero mark
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