CHEM 1121 L Midterm

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

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

A hydrometer

An instrument for determining the density of a liquid relative to that of water.

When should lab participants look at the Safety Data Sheet (SDS) of a substance?

Before using the substance

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.

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

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.

What needs to be included in the label for each axis of a graph?

Name of quantity displayed on axis Units of quantity displayed on axis

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.

Percent Recovery

final/initial x 100%

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

Coulombs

the product of current, in Amps, and time, in seconds.

Under what conditions should a student inform the instructor of a lab injury?

The instructor must be informed of all laboratory injuries

What is the oxidation number for copper in CuSO4?

The oxidation number of the polyatomic ion, SO4, is −2, therefore the oxidation number of copper is +2.

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

What is the charge delivered by a current with an average of 0.63 A over 37.8 minutes?

37.8 M x 60 s x 0.63 A 1428.84

What information does not need to be included a chemical waste label?

A description of the experiment the chemicals were used for

Which compounds could be represented by the empirical formula CH2?

C3H6 C2H4 C8H16

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

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

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

Dry Dark Cool

For each described liquid, determine the behavior of a hydrometer calibrated around the density of pure water. Liquid less dense than water Liquid with the same density as water Liquid more dense than water

Float lower than water Float same position as water Float higher than water

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.

Identify the step that is not recommended when responding to an emergency.

Gather your belongings.

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.

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

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

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.

Calculate the moles of ammonia present in a 1.965 g sample if the molar mass of ammonia is 17.030 g/mol.

g/molar mass 0.1154 mol

The purpose of the best-fit line on an experimental scatterplot is to ___. The best-fit line allows us to ___

to identify any linear trend in scattered data predict behavior between measured data using its slope

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.

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.

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

How many electrons were transferred if the total charge of a process is 734.3 C?

To determine the number of electrons in a process, divide the total charge by the charge of each electron, 1.602×10−19 C. 4.584e+21 electrons

Identify the true statements describing the experimental set-up in the Measuring Avogadro's Number experiment.

he plastic spacer should be placed between the two strips of metal. The metal strip with the red lead is the one that should have its mass measured.

A concentrated salt solution has a mass of 5.27 g for a 5.00 mL sample. What is the specific gravity of this solution?

m/v Specific gravity is equal to the density of the substance divided by the density of water. Divide by 1.00 g/mL to obtain the specific gravity. Note that the units cancel, and the answer is unitless. 1.05

Determine which items of personal protective equipment (PPE) you will likely use in a general chemistry lab.

nitrile gloves, a labcoat, and safety goggles.

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.

P- Pull the pin A- Aim the nozzle at base of fire S- Squeeze the lever slowly S- Sweep the spray from side to side over the fire

All lab participants must remain prepared to use safety equipment in case of emergency. Identify the components of effective preparation.

Knowing what safety equipment is available Being familiar with how safety equipment is used Understanding where the safety equipment is located

How should students prepare to use chemicals in the lab?

Locate the spill kits and understand how they are used. Become familiar with the chemicals to be used, including exposure or spill hazards.

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.

Which is NOT a good source of information about the hazards that affect waste disposal in a chemistry lab?

Your lab partner

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 2.72 mL. After running the titration and reaching the endpoint, you read the base titrant volume as 24.12 mL. What volume of base was required for the titration?

Final Volume - Initial Volume 21.40 mL

Determine when to put on disposable gloves for work in the lab.

Before handling any glassware or chemicals for the experiment