CHM 117 MIDTERM

measured or exact value

18 m = M 2 avocados = E 3 teacups = E 1 ft = 12 in = E 144 g of sugar = M 2 cups of milk = M

calculate percent error

= (your value - real value)/real value x 100

Identify the observations that indicate an added solute is insoluble in water

A clear line appears between the added liquid and water after mixing and allowing to settle. The added solid settles to the bottom after mixing and allowing to settle. The combination of the solute and water appears cloudy after mixing and allowing to settle.

disposal of broken glass

Any broken glass should be swept up promptly and deposited in the special container for broken glass

How do you determine the last digit in any measured number on a non-digital instrument?

Estimate one digit past the smallest precisely known digit or marking

general guidelines

Food and beverages should not be consumed in the laboratory Do not return unused reagents to stock bottles. Dispose of excesses with other used chemicals

disposal of chemicals

For any laboratory using chemical solutions, you should designate a beaker or flask as your collection vessel for used and excess chemicals. At the end of the lab (or during the lab if the collection vessel has filled up), transfer the solutions from the collection vessel to the laboratory's designated spent chemicals container

safety when pouring liquids

Never pour liquids, particularly those that could cause eye injury, from above eye level

reaction with acid

Observe if bubbles and fizzing occur when hydrochloric acid is dropped on surface of mineral

Which signs are typically posted in areas of active lab work?

PPE, chemical storage, safety equipment, prohibit food and drink

volume of an irregular solid by water displacement

Place the object in the graduated cylinder, and record the resulting water volume as "b." Subtract the volume of the water alone from the volume of the water plus the object b=50, a=25: 50-25=25

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?

turn down stirring speed and move beaker to center of hot plate

reaction with iodine

turns purple or black

most accurate glassware

volumetric flask

if you get chemicals in your eyes

wash them out with water, alert instructor with any injuries

What are the best practices for safely handling waste in the lab?

wear PPE and check labels/instructions before disposal

Identify techniques to be used for accurate solution preparation using a volumetric flask.

Read the liquid volume at eye level from the bottom of the meniscus. After the solvent is added, stopper and invert the flask to mix the solution.

eye protection

Safety goggles must protect against chemical splashes. Goggles must (1) completely cover the eyes, (2) fit along the forehead, (3) provide indirect ventilation (i.e., ventilation will not allow a splash to reach your eyes)

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

Most chemicals can be cleaned up with a general spill kit, but a few chemicals require specialized spill procedures. For each substance listed, determine whether a general spill kit is sufficient or if a specialized spill kit is needed.

acetone - general mercury - special phosphoric acid - general hydroflouric acid - special methanol - general

physical or chemical property

density - P solubility - P color - P reactivity - C melting point - P flammability - C

What is the goal of qualitative analysis?

determining composition of substance

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

evenly distribute all of solution

shoes/footwear

feet must be covered

syring tips

sharps container

unused solid reagant

solid waste container

Solubility/reaction with water with powders

soluble, slightly soluble, and 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.

starting and stabilizing stir function, medium heat setting, turn up heat setting

splashes on skin

Chemical spills on the hands are particularly worrisome because of the potential for transferring chemicals to the eyes. You should wash your hands thoroughly at the end of any lab period involving potentially irritating chemicals, even if you do not recall getting chemicals on your hands.

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

Heating a crucible to remove water from a hydrate

What information is necessary to review in order to be considered familiar with the Safety Data Sheet (SDS) of a substance?

Identification and description of substance, Personal protection and first aid recommedations, Hazard warning, Handling, storage, and reactivity information

splashes on clothing

If a chemical is spilled on clothing, the clothing should be removed promptly because once the fabric has become soaked with a chemical, the chemical is held against the skin

major spills

In case of major spills, e.g, a large bottle of solution breaking and splattering a chemical solution over you, you should use the safety shower (Figure 4) located near the lab's doorway, removing clothing while showering

Which warning about iodine is accurate?

Iodine can stain the body and other surfaces

too high too low not affected too high

The conductivity probe is not rinsed after measuring an electrolyte solution, before measuring a non-electrolyte solution. The conductivity probe is not rinsed after measuring a non-electrolyte solution, before measuring an electrolyte solution. Several drops of an electrolyte solution are spilled out of the vial before a measurement is taken. Tap water rather than distilled water is used to clean the conductivity probe before measurement of a non-electrolyte solution.

Why do you need to record the temperature when making careful volume measurements of water?

The density of water depends on its temperature.

chemicals in eyes

Three eyewashes—two swivel units mounted on lab benches, and one pull-down eyewash located by the lab's main entrance

litmus test

blue = base red = acid

broken flask

box-lined with puncture resistant bag

Identify the common indicators that a chemical reaction has occurred

color change, bubbles, precipitate being formed, change in temp

In general, which characteristics are necessary for a location to be suitable for chemical storage?

cool, dry, dark

When using acids and bases, note that these substances are ___ Make every effort to avoid contact with ___ Be sure to wipe up any spills ___

corrosive, skin and lab surfaces, immeidately

macroscopic properties

crystal shape, color, etc.

dangling items

hair tied back, no dangling earrings

spills on floor

inform instructor and clean based on solution at hand

volume of a regular solid

length x width x height

When a vinegar and oil salad dressing separates into two layers, the oil floats on top of the vinegar. The density of the oil ___ the density of the vinegar.

less than

Identify the precautions to take with exits in the lab.

locate exits prior to lab, do not block door with exit sign

What is the main precaution to take if a Gas Cylinder sign is present in the lab?

make sure it is restrained but keep safe distance from it

density

mass/volume

conductivity

material's ability to allow heat or electric charges to flow

volumetric

measure one specific volume of liquid, great accuracy

graduated

measuring range of volumes of liquid

titrant solution

nalgene bottle with cap

Most laboratory chemical spills are cleaned up in a similar manner, but acid and base spills require an extra step. What is this extra step?

neutralize the spill before cleaning it up

clothing

no loose sleeves

Suppose you mix a solid into water and not all of it dissolves. This is ___ because ___

not a sign of chemical reaction, undissolved solid is not new substance

To isolate a single variable when rearranging equations, move all other variables to the ____ of the equation by using ___ on them and remembering to perform that operation Make sure the rearrangement has the target variable ____

other side, opposite function, on both sides of the equation in numerator not denominator