CHM 123 Lab Exam 1

How to experimentally find the formula of a hydrate

1) find moles of anhydrous (dried) sample from the mass 2) find mass of waters of hydration lost by taking the original mass of beaker and sample-mass of beaker and dried sample. then convert mass to moles 3) finally, do (mole of H20 lost)/(mole of hydrate sample)... this number will give you the number of waters of hydration and then you stick it after the original hydrate formula ex: BaCl2 * 1H20

In case of accidental contact with chemicals, how long should the eyes be flushed at the eyewash station?

15 minutes

Calibration Curve

A graph showing the value of some property versus concentration of analyze. When the corresponding property of an unknown is measured, its concentration can be determined from the graph. In this lab, density and concentration are used for the curve

Name the following hydrates: 1) CoSO4·4H2O 2) Zn(NO3)2·8H2O 3) Ti(OH)4·H2O

1) cobalt (II) sulfate tetrahydrate 2) zinc nitrate octahydrate 3) titanium hydroxide monohydrate

Outlier

A value much greater or much less than the others in a data set, if density is much different from others or exclude the measurement from the average as an outlier to improve precision

How many decimal places should be reported when using each measuring equipment? Analytical balance Graduated Cylinder Buret Pipet Thermometer

Analytical Balance- 4 Graduated Cylinder- 1 Buret- 2 Pipet- 2 Thermometer- 1

hygroscopic

Anhydrous compounds that absorb water vapor from the air

Determine when to put on disposable gloves for work in the lab. options: -After setting up all the glassware but before handling chemicals -After cleaning all the glassware for the experiment -Before entering the laboratory room -Before handling any glassware or chemicals for the experiment

Before handling any glassware or chemicals for the experiment

A student removes a chemical sample from a reagent bottle to be used in an experiment. What should be done with any excess chemical remaining from this sample after the experiment is complete? -Conduct a second trial of the experiment with the excess chemical. -Check and see if anyone else can use the chemical. If not, discard in the proper waste container. -Discard the chemical down the sink under running water. -Clean a spatula thoroughly, then use it to add the chemical back into the reagent bottle

Check and see if anyone else can use the chemical. If not, discard in the proper waste container.

What are the best practices for safely handling waste in the lab? Select one or more: -Check labels or instructions before any disposal. -Place any paper towels from the clean-up in the trash. -Always wear appropriate Personal Protective Equipment. -Remove gloves for better manipulation of the waste containers.

Check labels or instructions before any disposal., Always wear appropriate Personal Protective Equipment.

Which is the correct formula for the hydrate: chromium(II) phosphate pentahydrate: Cr2(PO3)3·5H2O CrP4·5H2O Cr3(PO4)2·5H2O CrPO4·H2O Cr2PO4·5H2O

Cr3(PO4)2*5H20

How to experimentally determine the numbers of waters of hydration present in a hydrate

Find the difference in mass between the hydrate and the anhydrous salt (hydrate that has been heated) which gives the mass of the waters of hydration lost to evaporation. Then convert to moles

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

Salt

an ionic compound that forms as a product of a reaction between an acid and a base

A careless student grabbed 0.5 M NaCl instead of 0.5 M CaCl2 to test the supernatant solution. What is the likely result of this error? -There will be no effect because any chloride salt will work for this test. -CaCl2 will mistakenly be identified as the limiting reactant. -If K2C2O4 is the excess reactant, it will not be detected. -If CaCl2 is the excess reactant, it will not be detected.

If K2C2O4 is the excess reactant, it will not be detected.

How to determine whether a hydrate is efflorescent

If the change in mass after one hour of being left out is greater than 0.005g, the sample is efflorescent

Can you visually determine whether a salt is a hydrate or anhydrous?

No

how do you know when you have heated a hydrate sample to a constant mass

Once you heat the sample and it loses less than 0.003 grams during a single heating

It is often helpful to remember the acronym PASS when using a fire extinguisher. Fill in the word that corresponds with each letter to complete the steps needed for operation of this device.

PULL the pin AIM the nozzle at the base of the fire SQUEEZE the lever slowly SWEEP the spray from side to side over the fire.

Anhydrous Salt

Salt without water as a result of the waters of hydration being driven off as water vapor with heating

Which is the correct formula for the hydrate: tin(II) chloride trihydrate: SnCl2·H2O SnCl2·3H2O Sn2Cl·3H2O Sn2Cl·H2O TnCl2·3H2O

SnCl2*3H20

How to calculate the concentration of the sodium chloride solution using line of best fit from the Calibration Curve. Report as % NaCl w/v.

Substitute the average density of the unknown solution into the 𝑦-value (density) in the line of best fit from the Calibration Curve and solve for X (concentration)

What is the point of the digesting and cooling steps in the Limiting Reactant experiment?

The digestion + cooling steps allow the smaller solid particles to redissolve and then reprecipitate as larger particles, which are easier to filter.

A student was eager to finish and determined the mass of the CaC2O4·H2O precipitate before it was completely air-dried. How will this affect the reported mass of the excess reactant in the original solid mixture? -The mass of excess reactant would be too low because the precipitate mass is erroneously high. -The mass of excess reactant would be too high because the precipitate mass is erroneously high. -The mass of excess reactant would be too low because the precipitate mass is erroneously low. -The mass of excess reactant would be too high because the precipitate mass is erroneously low. -The mass of the excess reactant would be unaffected.

The mass of excess reactant would be too low because the precipitate mass is erroneously high.

Solute

The minor component of the solution

A student misread the directions and washed the precipitate with twice as much water as the instructions said to use. How will this affect the reported mass of the CaC2O4·H2O? -The reported mass of the CaC2O4·H2O would be too low because some of the precipitate would be lost. -The reported mass of the CaC2O4·H2O would be too high because some of the precipitate would be lost. -The percent limiting reactant would be unaffected because the precipitate is insoluble in water.

The percent limiting reactant would be unaffected because the precipitate is insoluble in water.

How would the reported "percent limiting reactant" in the solid mixture be affected by omitting the step in which the precipitate was digested? -The percent limiting reactant would be too low because some of the precipitate would be lost. -The percent limiting reactant would be too high because some of the precipitate would be lost. -The percent limiting reactant would be unaffected but the filtering step would take much longer.

The percent limiting reactant would be unaffected but the filtering step would take much longer.

Waters of Hydration

Water molecules that become incorporated within the crystal lattice of the salt.

While pulling an empty beaker off the shelf at the beginning of lab, it slips out of your hand onto the floor. What PPE?

closed-toed shoes

deliquescent

compounds absorb water to such an extent that they actually dissolve in the water that they take up

CuSO4 ⋅ 5 H2O name

copper (II) sulfate pentahydrate

Hydrate

crystalline compounds that have a specific number of water molecules trapped within the crystal lattice

In general, which characteristics are necessary for a location to be suitable for chemical storage? options: dark, dry, poorly-ventilated, warm, cool

dark, dry, and cool

Identify the step that is not recommended when responding to an emergency: -Alert your instructor. -Turn off equipment such as Bunsen burners and gas jets. -Gather your belongings. -Proceed calmly and listen for instructions.

gather your belongings

While picking up a buret, an unknown solution left by a previous solution drips onto your hand. What PPE?

gloves

While checking on a stirring solution, the solution splashes up towards your face. What PPE?

googles

efflorescent

hydrated compound that spontaneously loses waters of hydration when placed in a dry environment

A student didn't notice that the filter paper was slightly wet when determining its initial mass. How will this affect the reported mass of the limiting reactant? -The reported mass of limiting reactant would be too low because the precipitate mass is erroneously high. -The reported mass of limiting reactant would be too high because the precipitate mass is erroneously high. -The reported mass of limiting reactant would be too low because the precipitate mass is erroneously low. -The reported mass of limiting reactant would be too high because the precipitate mass is erroneously low. -The reported mass of the limiting reactant would be unaffected.

The reported mass of limiting reactant would be too low because the precipitate mass is erroneously low.

When drying a hydrate, if heating cycles are stopped before the sample reaches a constant mass will the calculated waters of hydration be too high, too low, or not effected?

Too low

Solution

a homogeneous (one phase) mixture of two components

Precision

a measure of how close repeated measurements are to each other

While transferring a solution from a flask to a beaker, the solution accidentally spills down the front of the lab bench. What PPE?

lab coat

What are the prefixes for the following? 1 water of hydration 2 waters of hydration 3 4 5 6 7 8

mono di tri tetra penta hexa hepta octa

If you drop or break glassware in lab, first ___________ Then, ________sweep aside small glass shardscarefully collect all the broken glassware Finally, place all that material into the______

pick up the glass pieces with gloved handsget thick gloves or dustpan sweep aside small glass shardscarefully collect all the broken glassware trashbroken glass containersolid waste container

excess reactant

reactant that is still present at the end of the reaction

limiting reactant

reactant that limits how much product can be made, and is therefore completely consumed

Move to the safety shower if you spill hazardous chemicals on your ____. Stand under the shower and ____ the lever. Remove clothing and continue flushing the area for ___ minutes.

skin or clothing pull 15

Accuracy

the degree of closeness of that measurement to its actual or true value

Solvent

the other component, which makes up the majority of the solution

How we determined limiting reactant expeimentally

the supernatant (leftover liquid) solution is tested for the presence of calcium ions and oxalate ions. Only one of these can be present, the one that corresponds to the excess reactant

Limiting reactant specific example

when adding a source of Ca to the supernatant solution, the formation of a precipitate means there was an excess of C2O4 which means that CaCl2 was limiting. when added a source of C2O4 to the supernatant solution, the formation of a precipitate means there was an excess of Ca which means that K2C2O4 was limiting.