LabFlow Pre-Lab Quizzes 1-6
Match each lab incident to the item of PPE that will protect you from it. Each item of PPE will only be used once.
While checking on a stirring solution, the solution splashes up towards your face.- Goggles While picking up a buret, an unknown solution left by a previous solution drips onto your hand.- Gloves While transferring a solution from a flask to a beaker, the solution accidentally spills down the front of the lab bench.- Lab coat While pulling an empty beaker off the shelf at the beginning of lab, it slips out of your hand onto the floor. -Closed-toe shoes
Calculate the moles of ammonia present in a 3.785 g sample if the molar mass of ammonia is 17.030 g/mol.
0.2223 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 substancemolar massmoles of substance=mass in g×1 mol of substancemolar mass
Predict the products of hydrochloric acid reacting with zinc metal.
ZnCl2 and H2
Which is NOT a good source of information about the hazards that affect waste disposal in a chemistry lab?
Your lab partner Waste disposal is an important component of working with chemicals. Thus, you should get your waste disposal information from the most direct sources possible. You should personally ensure that you know what to do to safely handle and dispose of the chemicals you use.
Fill in the words to complete each step in liquid spill cleanup.
1. Surround the area with absorbent material, then cover the spill. 2. Scoop up the material and place in a plastic bag. 3. Place the bagged waste in a solid waste container. 4. Wipe down the area with detergent and water. When a liquid is spilled, it is important to quickly remove the spill while taking steps to prevent skin contact and waste leakage. Follow the steps as listed to ensure safe and thorough cleanup of the spilled liquid.
A concentrated salt solution has a mass of 5.22 g for a 5.00 mL sample. What is the specific gravity of this solution?
1.04 Specific gravity is equal to the density of the substance divided by the density of water. The density of water is known (1.00 g/mL), but the density of the substance must be calculated using the density equation.
Knowing that one day is 24 hours, how many days is 64.9 hours?
2.7 The conversion factor should be made from the equivalence between the two units involved. The conversion factor should be set up so that the units of the starting measurement are on the bottom to cancel and give the new units on top. Then, perform the calculation by multiplying the starting value by the number on top of the conversion factor and dividing by the number on the bottom. 64.9 hours×1 day/24 hours Note that because 24 hours is the definition of a unit, the number is considered infinitely significant and does not affect significant figures.
A student performed a density experiment in triplicate and recorded the data shown. Calculate the average density (in g/mL) for this experiment. DensityTrial 1 2.99 g/mL Trial 2 2.82g/mL Trial 3 2.85g/mL
2.89 Three density values are given. To calculate the average density (in g/mL), sum the values and divide the sum by the number of values. An equation for calculating the average is, avg=n1+n2+n3/n where n is the number of trials, n1 is density for trial 1, n2 is the density for trial 2, and n3 is the density for trial 3.
Perform the calculation, rounding your answer to the proper number of significant figures. 0.841 x 7.34 x 5.1 =
31 The mathematical operation in the question is multiplication so follow the significant figure rules for multiplication/division, which look at the number of significant figures in each number. The number 5.1 has the fewest significant figures, so the answer can have only two significant figures. When performing the calculation, the answer appears as 31.481994 but you should round it to 31.
Calculate the volume, in cubic centimeters, of a box which is 125 cm long, 37 cm wide, and 68 cm high. Report your answer with correct significant figures in cubic centimeters.
310000 To calculate the volume of the box, find the product of the length, the width, and the height of the box. volume of the box=length×width×height volume of the box=125 cm×37 cm×68 cm=310000 cm3volume of the box=125 cm×37 cm×68 cm=310000 cm3 Your answer should be reported with two significant figures because both the width and the height were measured to only two significant figures.
What is the correct reading for the graduated cylinder in the close-up?
40.5 mL Determine the volume in the graduated cylinder based on the bottom of the meniscus. Note that volume markings increase going up the graduated cylinder. Therefore, with the meniscus above the 40 mL line, the correct volume is slightly greater than 40 mL. The bottom of the meniscus falls right in the middle of the space between the tick mark for 40 mL and 41 mL. Therefore, a good estimate of the volume is 40.5 mL. You should always report the reading with one estimated digit past the smallest marking by noticing where the bottom of the meniscus falls between the tick marks.
What are the best practices for safely handling waste in the lab?
Always wear appropriate Personal Protective Equipment. Check labels or instructions before any disposal. While handling waste in lab, you should always keep your Personal Protective Equipment (PPE) on. The goggles, labcoat, and gloves protect you from chemical exposure while you are cleaning up an experiment. Do not remove your gloves to manipulate the waste containers. Waste containers are more often messier than reagent bottles or lab equipment, so do not let your guard down while dealing with waste.
Identify the types of information that are necessary to communicate with emergency responders.
Any chemicals involved in an incident How the incident happened Any other hazards present in the lab. Individuals with first-hand knowledge of a lab incident should be prepared to provide information to emergency responders. In order for the responders to be able to react appropriately, they should be made aware of how an incident occurred, what chemicals are involved, and any other hazards present in the lab. Any information that is not relevant for the immediate response to the emergency is not likely to be useful to the responders.
What parts are present in every chemical equation?
At least one reactant At least one product An arrow
Three double bonds and no lone pairs of electrons- Trigonal planar Two double bonds and no lone pairs of electrons- Linear Four single bonds and no lone pairs of electrons Tetrahedral Two single bonds and two lone pairs of electrons -Bent Six single bonds and no lone pairs of electrons d-Octahedral Three single bonds and one lone pair of electrons -Trigonal pyramidal Five single bonds and no lone pairs of electrons -Trigonal bipyramidal
Determine the total steric number of bonding and non-bonding domains to find the electron geometry. Then, use the number of lone pairs to identify the molecular geometry. Single bonds and double bonds each count as one bonding domain.
In the reaction of magnesium metal with hydrochloric acid, how do you determine when the magnesium metal has reacted completely?
Gas bubbles are no longer produced. The magnesium metal is gone. The magnesium metal and the hydrochloric acid react to produce hydrogen gas. The magnesium is completely reacted when no more bubbles are formed and the magnesium metal is gone.
Identify the step that is not recommended when responding to an emergency.
Gather your belongings. When an emergency arises in lab, it is important to respond quickly and with the safety of all individuals in mind. When practical, steps to minimize safety risks should be taken. Lab participants should not be concerned with their belongings, however, especially when quick response to an emergency is needed.
Aluminum selenide: Al3Se2- Incorrect formula Ruthenium(IV) oxide: Ru2O4- Incorrect formula Barium sulfide: BaS- Correct formula Titanium(IV) iodide: TiI4- Correct formula
In an ionic compound, the cation is named before the anion. Use the Roman numeral or the position of the element on the periodic table to determine their charges. The subscripts are the number of each ion necessary to combine into a neutral formula unit.
What action is NOT necessary before lighting a Bunsen burner?
Leave the gas cock open for a few minutes before lighting to clear the line. When lit, the Bunsen burner provides an open flame that you must adjust to your experiment. The area around the burner should be clear of flammable materials before lighting. You should also check that the hose does not leak additional gas to possibly catch on fire. Check that the Bunsen burner can be adjusted before it is lit. You want to be able to easily change the properties of the flame for the experiment. Do not leave the gas cock open before lighting because it allows gas to build up around the burner. The spark involved with lighting the burner could catch all of that released gas on fire.
Identify the precautions to take with exits in the lab
Locate the exits prior to the start of lab. Do not block a door with an EXIT sign. In addition to allowing access in and out of the lab during the lab session, exit doors provide the quickest way to evacuate in case of emergency. Before the start of lab, students should familiarize themselves with the easiest pathway to the exit from their lab stations, and be sure to keep backpacks and other belongings out of the way.
Magnesium reacts with oxygen in the air when lit with a Bunsen burner. Unlike other reactions, you should not look directly at this reaction.
Magnesium burns in air when lit with a Bunsen burner. The reaction produces a lot of light energy so you should not look directly at it. Instead, watch it briefly out of the corner of your eye.
Determine whether the given compound name or formula contains a polyatomic ion.
Magnesium sulfate- Contains a polyatomic ion SO3- Does not contain a polyatomic ion KCN- Contains a polyatomic ion NH4Cl- Contains a polyatomic ion Sodium phosphide- Does not contain a polyatomic ion Calcium hydroxide-Contains a polyatomic ion
What is generally the best approach when liquid from a large reagent bottle is needed in an experiment?
Pour some of the reagent from the bottle into a beaker, then use as needed in the procedure. When liquid from a large container, such as a reagent bottle, is needed in an experiment, it is generally best to begin by pouring a smaller amount of the liquid into a more manageable container, such as a beaker. The smaller container can then be used to dispense liquid as needed in the procedure. This step minimizes the number of times the heavier container must be lifted, and also makes the liquid easier to work with. Glassware and lab tools should never be inserted into a reagent bottle, as this could contaminate the entire bottle.
Identify the common indicators that a chemical reaction has occurred.
Precipitate being formed Bubbles being produced A color change A change in temperature A chemical reaction involves the creation of at least one new substance whereas physical changes are alterations to the starting substance. The formation of bubbles or a precipitate clearly indicates that a new substance has been created and a chemical reaction has occurred. An inherent color change or change in temperature indicates changes to the chemical makeup of the substance, even if the new substances are not visible. Note that external changes to color, such as applying paint, or to temperature, such as heating on a hot plate, are physical changes. These external changes are alterations to the starting substance. A phase change, such as melting or boiling, or a solid being dissolved are signs of physical changes, not chemical reactions. In both cases, the original substance is still present, just in a different form.
What should you do every time before you leave the lab?
Remove your gloves. Wash your hands. Remove your labcoat, if you are wearing one.
Refer to the periodic table to find the correct molar mass for each element and compound.
S-32.059 g/mol O2-31.998 g/mol Cl-35.446 g/mol O-15.999 g/mol C2H6-30.067 g/mol CH4-16.042 g/mol The molar mass of an element is the mass on the periodic table, in g/mol. For a compound, add the molar mass of each element, multiplied by its subscript in the formula. Report the molar mass with as many significant figures as possible to make sure that you use the most accurate and precise molar mass in future calculations.
Which steps are necessary for cleaning a spill involving broken glass?
Stop the spread of the spill. Soak up any spilled liquid with absorbent material. Pick up large pieces of glass with gloved hands. When cleaning a spill involving broken glass, it is necessary to contain the hazard from the spilled material as well as that from the glass pieces. Large pieces of glass can be picked up with gloved hands, and liquid can be soaked up with absorbent material. The floor should be wiped afterward to ensure that cleanup is complete. Broken glass should not be handled any more than absolutely necessary. Laboratory glassware is likely to contain chemical residue, and will have sharp edges if broken.
Δ→ Heat is applied. + There are two separate substances on either the products side or the reactants side. ⟶ Substances on the reactants side are converted to the substances on the products side. (l) The substance is a liquid.
These symbols may include (s),(l),(g), and (aq) for solid, liquid, gas, and aqueous substances, respectively. Chemical equations also commonly include the + symbol to separate reactants or products, and always a reaction arrow to indicate the conversion of reactants to products.
Determine the safest option in the lab if you need your vision to be corrected.
Wear corrective glasses or lenses under your safety goggles for the whole experiment, but always check with your TA or Instructor for your school's policy
Determine when you should remove your goggles in the lab room.
When everyone in the room is done handling any chemicals or glassware
What is the last step of any spill cleanup procedure?
Wipe down the affected area with detergent and water. When chemicals are spilled, students must follow proper protocol in cleaning up liquids with absorbent material and sweeping up any broken glass that may be part of the spill. After the bulk of the spill has been cleaned up, it is necessary to finish cleanup by wiping down the affected area with detergent and water. This step helps remove any remaining liquid and particles.
What is the name of the compound with the formula of Ca3(PO4)2
calcium phosphate The general process to name an ionic compound is to name the cation. Then, name the anion.
Determine the best way to deal with each of the following items that may dangle into the way during lab work.
long necklaces-Remove flowy sleeves-Tie back or secure long earrings-Remove loose bracelets-Remove long hair-Tie back or secure
Determine when to put on disposable gloves for work in the lab.
Before handling any glassware or chemicals for the experiment
Which compounds could be represented by the empirical formula CH2?
C3H6 C2H4 C8H16 An empirical formula is the most reduced ratio of the elements in a compound.
Identify the equipment best suited for extinguishing each type of fire.
large fire on floor-fire extinguisher small benchtop fire-overturned beaker clothing fire-fire blanket When a fire occurs in the lab, it is important to be able to react quickly. For many types of fires, cutting off the supply of oxygen is a quick and effective way to control the flames. This can be done in several ways depending upon the size and location of the fire. For a small benchtop fire, an overturned beaker placed on top will quickly extinguish the flames. For a larger fire on clothing or laboratory surfaces, a fire blanket can be used to smother the flames. Larger fires require the use of a fire extinguisher, which can be used to spray an extinguishing agent over a large surface.
When performing a multiplication or division calculation, significant figures in the calculated result are dictated by the significant figures of the measured numbers. The calculated result should have the same number of significant figures as the measured number in the calculation with the fewest significant figures.
significant figures the same number of significant figures as significant figures.
Determine where to dispose of each type of waste.
titrant solution-Nalgene bottle with cap broken flask-Box lined with puncture resistant bag syringe tips-Sharps container unused solid reagent-Solid waste container Chemical waste needs to be disposed of properly to maintain safety and not harm the environment. Therefore, chemical waste should not be put into the trash can. The trash will not be handled as if it contains hazardous material. Anything removed from its bottle needs to be disposed of as waste, whether it was used or not. Do not return unused reagent to its bottle. The manipulated chemicals could contaminate the other materials in the bottle.
Perform the calculation, rounding your answer to the proper number of significant figures. 0.35200 ÷ 2.740 =
0.1285 The mathematical operation in the question is division so follow the significant figure rules for multiplication/division, which look at the number of significant figures in each number. The number 2.740 has the fewest significant figures, so the answer can have four significant figures. When performing the calculation, the answer appears as 0.12846715 but you should round it to 0.1285.
A football field is 120 yards by 53.333 yards. What is the area of the football field in acres if 1 acre=43560 ft2? Use correct significant figures when answering this question.
1.3 Note that you should not round your answer to the correct significant figures until the end of the calculation. Start by converting the measured distances from yards to feet by remembering that 1 yard=3 feet. Then calculate the area of the field in square feet. Finally, convert area in square feet to acres.
Knowing that one day is 24 hours and one hour is 60 minutes, how many minutes are in 8.8 days?
13000 The conversion factor should be made from the equivalence between the two units involved. The conversion factor should be set up so that the units of the starting measurement are on the bottom to cancel and give the new units on top. Then, perform the calculation by multiplying the starting value by the number on top of the conversion factor and dividing by the number on the bottom. This conversion requires two conversion factors, one relating days and hours and one relating hours and minutes. 8.8 days×24 hours/1 day×60 minutes/ 1 hour Note that because 24 and 60 are numbers defining units, the numbers are considered infinitely significant and do not affect significant figures in the answer.
In case of accidental contact with chemicals, how long should the eyes be flushed at the eyewash station?
15 minutes Individuals who experience chemical contact with the eyes should proceed to the eyewash station immediately. Rinsing the eyes at the eyewash station is the best approach towards eliminating as much of the chemical as possible, minimizing the risk of serious eye damage. The water in the eyewash station should run for 15 minutes. It is important to continue flushing the eyes for this duration of time even if the irritation has already subsided. After this point, the affected eye(s) may be evaluated and further action may be taken if necessary.
Perform the calculation, rounding your answer to the proper number of significant figures. 0.125 + 4.09 + 13.0065 =
17.22 The mathematical operation in the question is addition so follow the significant figure rules for addition/subtraction, which look at the digits past the decimal point. The number 4.09 has the fewest digits past the decimal point, so the answer can have only two digits past the decimal point. When performing the calculation, the answer appears as 17.2215 but you should round it to 17.22.
What is the correct reading of the volume in the pictured buret?
17.32 mL Determine the volume in the buret based on the bottom of the meniscus. Note that volume markings increase going down the buret. Therefore, with the meniscus below the 17 mL line, the correct volume is greater than 17 mL. The bottom of the meniscus falls slightly below the third tick mark below 17 mL, which corresponds to 17.3 mL. Therefore, a good estimate of the volume is 17.32 mL. You should always report the reading with one estimated digit past the smallest marking by noticing where the bottom of the meniscus falls between the tick marks.
Suppose you are titrating an acid of unknown concentration with a standardized base. At the beginning of the titration, you read the base titrant volume as 2.95 mL. After running the titration and reaching the endpoint, you read the base titrant volume as 21.94 mL. What volume, in mL, of base was required for the titration?
18.99 mL To find the volume of titrant used in any titration, subtract the starting volume reading from the final volume reading. The difference between the two readings is the amount of titrant dispensed during the titration. The calculated volume will be an accurate measurement of the titrant required as long as each reading was made as accurately as possible with the meniscus at eye level.
Complete the electron configuration of a calcium atom by selecting the correct orbitals.
1s2 2s2 2p6 3s2 3p6 4s2 Remember the blocks of the periodic table and fill them up through to the given element. You only need to pass through the s and p blocks, which have energy levels matching the row number.
Consider each possible structure of carbon dioxide, CO2. Determine whether the structure is correct and justify your decision.
24 electrons needed−16 electrons available=82=4 bonds in the structure24 electrons needed−16 electrons available=82=4 bonds in the structure The only structure with four bonds is the correct one, with two double bonds. The structure with two single bonds and no lone pairs on the carbon atom has the right number of electrons, but the carbon does not have an octet. The structure with two single bonds and two lone pairs on the carbon atom has an octet on each atom, but there are 20 electrons drawn, not the 16 available.
Choose the best graduated cylinder to make each measurement in a single use.
5.75 mL of a sucrose solution - A 10 mL graduated cylinder with markings every 0.1 mL 18.5 mL of a NaClNaCl solution- A 25 mL graduated cylinder with markings every 1 mL 36 mL of water- A 50 mL graduated cylinder with markings every 10 mL
Perform the calculation, rounding your answer to the proper number of significant figures. 6.16 - 0.00086 =
6.16 The mathematical operation in the question is subtraction so follow the significant figure rules for addition/subtraction, which look at the digits past the decimal point. The number 6.16 has the fewest digits past the decimal point, so the answer can have only two digits past the decimal point. When performing the calculation, the answer appears as 6.15914 but you should round it to 6.16.
Using the letters on the image, identify the significance of each section on the NFPA diamond.
A -Health B -Flammability C-Reactivity D-Special Hazards The NFPA diamond may appear on a chemical container or in its storage area. The blue section provides health hazard information, the red section provides information about its fire hazard, the yellow section provides information about its reactivity hazard, and the white section includes codes to indicate any special hazards, such as being an acid. A rating of 0 is stable whereas a rating of 4 is the most hazardous in each area.
What information does not need to be included a chemical waste label?
A description of the experiment the chemicals were used for
In a liquid with the same density as water -Float in the same position as pure water In a liquid that is more dense than water -Float higher than position in pure water In a liquid that is less dense than water -Float lower than position in pure water
A hydrometer is based on buoyancy, which uses differences in density to determine floating. Buoyancy is responsible for the floating of a lower density object on a liquid that is higher density. A hydrometer creates a density comparison between a sample and a standard, pure water in this case. If a liquid is more dense than water, the hydrometer will be lifted up more than in pure water and will float higher. If a liquid is less dense than water, the hydrometer will not be lifted as much as in pure water and will float lower.
A hydrometer is a tool used to measure the density of a liquid relative to that of water.
A hydrometer is used to measure the density of a liquid relative to the density of water, or relative density. This density ratio is typically expressed without units.
When a vinegar and oil salad dressing separates into two layers, the oil floats on top of the vinegar. The density of the oil is less than the density of the vinegar
A lower density substance will float on a substance that has a higher density. For example, something will only float on water if its density is less than that of water.
Determine whether each observation generally corresponds to a physical change or a chemical change. A chemical change involves the creation of at least one new substance whereas physical changes are alterations to the starting substance. The formation of bubbles or a precipitate clearly indicates that a new substance has been created and a chemical reaction has occurred. An inherent color change or change in temperature indicates changes to the chemical makeup of the substance, even if the new substances are not visible. Note that external changes to color, such as applying paint, or to temperature, such as heating on a hot plate, are physical changes. These external changes are alterations to the starting substance. A phase change, such as melting or boiling, or a solid being dissolved are signs of physical changes, not chemical reactions. In both cases, the original substance is still present, just in a different form.
A solution heats up upon mixing with another. -Chemical change The color of a substance changes over time. -Chemical change A liquid freezes into a solid. -Physical change Bubbles are produced upon mixing two solutions. -Chemical change A solid dissolves into water. -Physical change A precipitate is formed from two solutions. -Chemical change
Using the letters on the image, identify each component of the Bunsen burner.
A-Barrel B-Air inlet C-Gas inlet D-Gas regulator In a Bunsen burner, the gas flows through a hose connected to the gas inlet and through the barrel up to the top where the flame will be once lit. The air inlet around the barrel controls how much oxygen from the air is mixed with the gas. The gas regulator at the bottom controls the amount of gas that travels up through the barrel.
To convert between units, you need to know the relationship between units. For example, one mile equals 5280 feet. This relationship can now be used as a conversion factor, set up as required by the question. For each conversion, choose the correct arrangement of the conversion factor and complete the calculation. 1. Convert 7860 feet to miles 7860 feet×( A )/( B ) 7860 feet= 2. Convert 0.565 miles to feet 0.565 miles×( C )/( D ) 0.565 miles=
A: 1 mile B: 5280 feet 7860 feet=1.49 miles C=5280 feet D=1 mile 0.565 miles=2980 feet
An ion is a charged version of an atom that is formed by losing or gaining electrons compared to the atom.
An atom is the neutral basis of the element because the number of protons and electrons is equal. When an atom loses or gains electrons, the number of protons and electrons are no longer equal and the ion becomes charged.
Which formula is not an example of an ionic compound?
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. Metals are generally on the left side of the periodic table whereas nonmetals are on the right. Elements that can act as both are called metalloids.
Choose the most appropriate task for each pictured piece of glassware.
Beakers should be used mostly to temporarily hold chemicals. Beakers have spouts to help pour liquids into other glassware, such as burets. Although beakers have volume measurement lines, they have low accuracy and should only be used for approximate measurements. The Erlenmeyer flasks have a conical shape that acts to contain any splashes. Therefore, Erlenmeyer flasks are useful to hold reaction mixtures that are being stirred or to act as collection vessels under a funnel or buret. Like beakers, the volume markings should only be used for approximate measurements. The graduated cylinder is used for more careful volume measurements. Because it has multiple volume markings, many different volumes can be measured with a graduated cylinder to a reasonable accuracy.
Read each statement regarding food and beverages in the lab and determine if each is true or false.
Beverages are allowed in lab as long as they are in containers with lids.- False Tobacco products of all kinds are prohibited in lab. -True Food items should not be brought into the lab. -True Chewing gum is okay in the lab as long as you don't blow bubbles. -False
What are the best practices while sharing a lab balance with other students?
Brush off any chemical dust around the balance after each use. Alert your TA or instructor about any issues with the balance. Do not Tare a balance when you will be stepping away from the balance. Instead, write down the mass of any glassware or weighing vessels before leaving the balance. Tare weighing vessels only when you are going to continue using the balance immediately. When sharing a balance with others, work carefully to avoid making any messes for other users to deal with. Use vessels such as weigh boats rather than placing any materials directly on the balance. Make sure to clean up any mess that you make after each use. If you find any issues with the balance, such as not being properly stabilized, let a TA or instructor know so that the problem does not go ignored for others
Determine whether each of the properties described applies to volumetric or graduated glassware.
Capable of measuring a range of volumes of liquid- graduated Designed to measure one specific volume of liquid -volumetric Used for applications in which great accuracy is needed double_arrowvolumetric 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.
A student removes a chemical sample from a reagent bottle to be used in an experiment. What should he do with any excess chemical remaining from this sample after the experiment is complete?
Check and see if anyone else can use the chemical. If not, discard in the proper waste container. Once a chemical has been removed from a reagent bottle, it may become contaminated by residue on tools, containers, or other lab surfaces. In order to prevent possible safety risks or unintended chemical reactions, substances that are removed from a reagent bottle must never be added back into the bottle. If excess chemical is left over after it is needed in an experiment, it can be shared with another student or discarded in the proper waste container.
When using a properly stabilized balance, how should you ensure that you get the most accurate mass reading possible
Close the side shields on the balance during reading. Measure the mass of the sample at room temperature. To get the most accurate readings, you should diminish any unusual environmental factors, such as abnormal temperatures or air currents. Measure samples at room temperature to avoid convection currents from a heated sample affecting the reading. Close the side shields on any balance that has them while making a measurement to decrease impact from any air flow. Your sample should be placed in the middle of the balance pan. A properly stabilized balance will be balanced with this ideal placement. The balance should also be stabilized on the table without you leaning on it. Leaning on the table might actually destabilize the balance.
Mass is conserved in an experiment if the sum of the individual component masses equals the mass of the mixture of the components.
Conservation of mass means that all the mass you start with is still present. Thus, if the mass of the mixed components equals the sum of the masses of each individual component, mass is conserved.
To determine a covalent compound formula from a compound name, start by identifying the symbol for each element in the compound. Then, use the prefixes from the name to determine the subscripts necessary to match the number of each element in the name.
Covalent compounds are held together by shared electrons in covalent bonds. The same elements can combine in multiple covalent arrangements. Therefore, the name of a covalent compound communicates the number of each element with prefixes and the formula can be determined by using the numerical translation of the prefix as each element's subscript.
A 7.298 g sample of copper reacts with oxygen, forming a copper oxide. The final mass of the copper oxide is 8.217 g. What is the formula of the copper oxide?
Cu2O Divide the mass of the copper sample by the atomic mass of copper (63.546 g/mol) to find the number of moles. Subtract the mass of the copper from the mass of the copper oxide to find the mass of oxygen. Divide this mass by the atomic mass of oxygen (15.999 g/mol) to find the number of moles of oxygen. Find the mole ratio of Cu to O
Consider the trendline on a graph of Mass vs. Volume of a solid or a liquid. What information can be obtained about the substance from the slope of this line?
Density Recall that the formula for a trendline is y=mx+b, where y represents the value on the y-axis, x is the value on the x-axis, m is the slope, and b is the intercept, which should be 0 on a Mass vs. Volume graph. The slope is therefore equal to y divided by x, or mass divided by volume. This value is equal to the density of a substance.
The equation to calculate density is D=m/V, where D is the density, m is the mass, and V is the volume.
Density is the mass of a substance per unit of volume. Density can describe a mixture, such as a solution, or a pure substance
Review the Safety Data Sheet (SDS) (click the SDS icon below) for hydrogen peroxide, then identify the best course of action for each type of chemical exposure.
If inhaled-Move person to fresh air. If swallowed-Rinse mouth with water. In case of skin contact-Take off any contaminated clothing and rinse thoroughly In case of eye contact-Rinse with water for 15 minutes.
If you drop or break glassware in lab, first get thick gloves or dustpan . Then, carefully collect all the broken glassware. Finally, place all that material into the broken glass container.
If you break glassware in lab, you need to protect yourself during the cleanup and dispose of the glass appropriately. Before approaching the broken glass, find thicker gloves or a dustpan. Do not handle broken glass with regular lab gloves as the glass can easily cut through the thin material. Then, use the gloves or dustpan to carefully collect the glass. Make sure to gather all the small pieces of glass as well. The dustpan can be particularly helpful to ensure that all the glass is caught, rather than being swept aside for someone to accidentally find later. Finally, put the broken glass into the broken glass container, which has a puncture resistant bag to avoid rips or injuries. Broken glass should never be put in regular trash or solid waste. Although you should be trained for most clean up procedures, if you are ever uncomfortable with a situation, it is better to ask your instructor.
Determine the number of significant figures in each measurement. Then, choose the representation of the number where x is in place of the estimated digit from the measurement.
In 14.8 m, there are 3 significant figures. All the digits are non-zeros and are significant. In $10.25, there are 4 significant figures. The only zero in the measurement is between two non-zero digits and is, therefore, significant. In 0.05 L, there is only 1 significant figure. Neither zero is significant because they both appear to the left of all the non-zero digits. In 1.000 g/mL, there are 4 significant figures. All the zeros are significant because they appear to the right of the non-zero digit and there is a decimal point present. In 6200 cm, there are 2 significant figures. The zeros are not significant because they appear to the right of non-zero digits but there is no decimal point present. In 403 kg, there are 3 significant figures. The zero is significant because it appears between two non-zero digits. In all the measurements, the last significant digit, whether a zero or not, is the estimated digit.
Read the Safety Data Sheet (click SDS icon below) of hydrogen peroxide to identify the recommended way to store this substance.
In a tightly closed container in a dry and well-ventilated place
Changing gloves often will minimize the spread of chemicals. To properly remove gloves, first, grasp the exterior of one glove with a gloved hand, and then, peel off the first glove . Then insert a bare finger between the interior edge of the second glove and the skin, and remove the second glove.
It is important to change gloves as often as necessary when working with chemicals in a laboratory. Changing gloves often will minimize the spread of chemicals and the risk of contamination to lab equipment and other stock chemicals. To properly remove gloves, first, grasp the exterior of one glove at the wrist with the other gloved hand, and peel it off. Then insert a bare finger between the interior edge of the second glove and the skin, and remove the second glove being careful to avoid touching the exterior of the glove with bare hands.
Determine whether or not each chemical formula is an empirical formula
K2C2O4-Not an empirical formula NaMnO4- Empirical formula Ba3(PO4)2- Empirical formula CaCO3- Empirical formula C6H12O6- Not an empirical formula
A-Funnel B-Primary container C-Waste label D-Secondary container
Liquid waste should be added into the appropriate primary waste container using the funnel. Containers that directly hold the waste are the primary containers. This set-up shows primary containers for both organic and aqueous liquid waste. You will need to know which type of waste you are handling to choose the correct container. The funnel in each container reduces accidental spills and splashes of the waste chemicals. The secondary container around the primary waste containers can catch any possible splashes or spills that escape the funnel. No waste should be directly added to the secondary container. When the waste containers are actively being used, the liquid waste containers need to have waste labels on them. A complete waste label should identify the type of waste as shown, but also the chemicals being added to the container and their relative amounts.
What practice will not help you make an accurate volume reading on a buret at the beginning of a titration?
Make sure that the meniscus starts exactly at 0.00 mL. Explanation When reading the volume of titrant in a buret at the beginning of a titration, make sure to have the top of the liquid at eye level. You don't want an angled view to change your perspective of where the volume aligns compared to the markings. In particular, you need to align the bottom of the meniscus (curved top of the liquid) with the volume marking. The most accurate readings will only be possible when the volume level falls within the marked range on the buret. Thus, your interpretation of the volume alignment with the marking has the wiggle room to estimate the last digit of the reading above or below the marking.
Which of the following compounds requires a Roman numeral in its name?
MnO2 The Roman numeral in the name of the compound indicates the charge of a cation. It is only necessary if the metal element can form cations with multiple different charges. In general, you are looking for a transition metal cation in the compound as most of the transition metals can have many different oxidation states or charges. Therefore, MnO2MnOX2 is the compound that needs a Roman numeral in its name. The cation comes from manganese, which can have multiple different oxidation states. The name of MnO2MnOX2 is manganese(IV) oxide, where the Roman numeral "IV" indicates that the cation present is Mn4+MnX4+ . The charge of the cation can be determined by knowing the -2 charge of the oxygen ion and knowing the formula, which contains the ions in the ratio necessary for a neutral unit. The other compounds are all examples of other ionic compounds, as demonstrated by the presence of metal elements combined with a non-metal element or an anionic polyatomic ion. The cation in each of these compounds comes from an element that only has one stable ionic charge, so the charge does not need to be indicated in the name. The correct name of MgCl2MgClX2 is magnesium chloride, the correct name of Al(NO3)3Al(NOX3)X3 is aluminum nitrate, and the correct name of Na2ONaX2O is sodium oxide.
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. The best choice to stabilize a tipping buret set-up is to move the buret to a ring stand with a larger base. The demands of the experiment determine the size of the buret, so you will likely not be able to change the size of the buret to stabilize the set-up. Adding another buret to the ring stand involves another piece of glassware that is not necessary. This puts an expensive buret at risk for breaking without it even being used. You should never plan to stabilize something in the lab with your hands. You might splash chemicals on your hands and you will not be as stable as the intended equipment.
Which signs are typically posted in areas of active lab work?
Personal protective equipment (PPE) sign Sign prohibiting food and drink Safety equipment signs Chemical storage signs
In the context of a balanced chemical equation, a subscript is a number to the lower right of an element or ion within formula and it applies to only the part of the formula it follows. A coefficient is a number to the left of a formula and it applies to the entire formula it precedes. Only coefficients should be added or changed when balancing chemical equations.
Subscripts are part of formulas and represent the number of elements or ions within a formula. They only apply to the element or ion they are connected to. Subscripts are not changed when balancing a chemical equation. Coefficients are added while balancing chemical equations. They act as multipliers for the whole formula that they are in front of.
An empirical formula is the simplest ratio of elements in any compound, whether it be ionic or covalent. Therefore, there is no use of predicted charges in determining an empirical formulas. The ratios in a formula are in terms of moles, or number, rather than mass because each element has a different mass. The first step in determining a formula from masses is to convert from mass to moles. Then, to find the ratio between elements, divide the moles of each element by the smallest number of moles present. The ratio dictates the subscript in the empirical formula.
Suppose you are given the mass of each element in a compound sample. To calculate the empirical formula, start by converting the mass of each element to moles using each element's molar mass. Then, calculate the ratio between the elements by dividing the moles of each element by the smallest number of moles present.
When using the Tare function on a balance, start by placing the glassware on the balance. Then, press the Tare/Zero button to cancel out that mass. Finally, add your sample to the glassware and record the mass of your sample.
The Tare/Zero button on a balance allows you to zero out the balance with something on it so that only the mass of the sample appears on the balance. You need to start by putting the glassware or weighing vessel on the balance, using the Tare/Zero function, and then add the sample. Make sure not to press the Tare/Zero button after adding the sample or its mass will also be zeroed out.
A mile is defined as 5280 feet. This number is an exact number which means that it has infinite significant figures.
The definition of a unit is an exact number. An exact number has infinite significant figures, which means that it will not limit significant figures in any calculation.
Suppose you mix two solutions in a test tube and the test tube becomes hot. This is a sign of a chemical reaction because chemical changes can release heat.
The heat generated in the test tube is a sign of a chemical reaction. Chemical reactions can either generate or consume heat. The mixture of the two solutions caused an exothermic reaction that released heat. Note that if an external heat source is applied, heat does not indicate a chemical reaction but rather leads to a physical change to the starting substance. Heat is only a sign of a chemical reaction when it is generated by the substances reacting.
Under what conditions should a student inform the instructor of a lab injury?
The instructor must be informed of all laboratory injuries. Students must inform their instructor of all injuries that occur in lab. Instructors are best suited for evaluating injured students and following first aid or emergency protocol when necessary. Even if an injury appears minor or familiar, the presence of chemicals in the lab may cause the body to respond in unexpected ways. Instructors should be familiar with the chemicals used, and are prepared to respond accordingly.
For each atom, determine how many dots should be drawn around the element symbol in the Lewis structure for a lone, neutral atom. The Lewis structure of an oxygen atom should have 6 dots drawn around the symbol O. The Lewis structure of a calcium atom should have 2 dots drawn around the symbol Ca. The Lewis structure of a nitrogen atom should have 5 dots drawn around the symbol N. The Lewis structure of an aluminum atom should have 3 dots drawn around the symbol Al. The Lewis structure of a fluorine atom should have 7 dots drawn around the symbol F.
The number of dots corresponds to the number of valence electrons around the atom. The number of valence electrons is the group number for Groups 1 and 2 on the periodic table and the group number minus 10 for Groups 13 through 18.
To measure out a volume of liquid, start by choosing the appropriate graduated cylinder and moving the bumper to the top of the graduated cylinder to protect it from breakage. Then, pour the liquid into the graduated cylinder until the bottom of the meniscus aligns with the desired volume marking when you look at the graduated cylinder from eye level.
The placement of the bumper at the top of the graduated cylinder will stop the glass cylinder from hitting the benchtop if it is knocked over. The proper way to read a graduated cylinder is to have the bottom of the meniscus line up with the volume marking when you view the graduated cylinder at eye level. Reading from above or below will lead to a reading that is too high or too low.
What should you do if your Bunsen burner does not light after a few tries with the striker?
Turn off the gas cock for 10 seconds before trying again. Not lighting right away is a common issue with Bunsen burners. There is no need to alert your instructor unless something is wrong with the set-up. You should try again to light the burner but you need to do it safely. Do not use matches to light the burner unless instructed to do so. Instead, turn off the gas cock for 10-15 seconds to allow the gas in the area to clear out. Then, open the gas cock and try again with the striker.
Identify which balance was used to make each mass reading.
The tolerance of a balance determines how many decimal places are included on the display. The last decimal place is estimated and accurate to ±1 in that decimal place. The balance with a tolerance of ±0.0001 g is the most accurate balance listed. It is capable of making mass readings with four decimal places, such as 4.0000 g. The balance with a tolerance of ±0.01 g is the least accurate balance listed. It is only capable of making mass readings with two decimal places, such as 5.43 g, but not the readings with more decimal places. Always record all the decimal places, including all zeroes, from a balance's display so as not to lose significant figures.
S2F10 - Disulfur decafluoride SF4- Sulfur tetrafluoride PBr5 - Phosphorus pentabromide ClO2- Chlorine dioxide PBr3 - Phosphorus tribromide
To name a covalent compound, name the first element and add any prefix for a subscript greater than 1. Then, name the second element, changing the ending to -ide, and add a prefix matching the subscript. The second element needs a prefix, even if there is only one in the formula.
When an alarm sounds in the laboratory, it is important to respond calmly and remain quiet. Listen for any other instructions, turn off any equipment in use, and be prepared to leave immediately.
When an alarm sounds, it is important to react quickly while being careful to fully consider the best course of action. Listen to any instructions given by the instructor, emergency personnel, or others with knowledge of the emergency situation, then proceed accordingly.
When should you start a new chemical waste container in the lab?
When the contents of the current container are a couple inches below the brim of the container A chemical waste container should be replaced with a new one when the level of chemicals in the container are a couple inches below the container's opening. This ensures that the container can still be capped off and closed. Thus, the waste container should not be filled all the way to the brim.
Identify the section in which each type of information can be found on a Safety Data Sheet.
chemical name and formula- Identification possible dangers and health effects -Hazards Identification recommendations in case of accidental contact with the chemical-First Aid Measures recommended personal protective equipment (PPE)-Exposure Controls/Personal Protection incompatibility or reactivity with other chemicals-Handling and Storage
