Exam Study Guide
Goggles must be kept OVER YOUR EYES until Mr. Leeds says to put them away *Even if you are already finished and cleaned up
Report ALL accidents/spills to Mr. Leeds immediately
Try your best to use common sense
In Case of Emergency
Nurse: ext: 2828
Safety equipment in classroom
Never taste chemicals (even if they look yummy!)
Always WAFT liquids to detect odor
NEVER WAFT SOLIDS/POWDERS!
Avoid touching chemicals
Always wash hands with soap and water after lab
If chemicals touch skin: flush skin with water for 1 minute AND notify Mr. Leeds
Hot glass and cold glass look the same
Never use chipped or broken glass- tell Mr. Leeds and dispose of broken glass in proper trash
Never use force to remove or insert glass
Roll up sleeves, put UP long hair, NOT just pull back (or you cannot do lab)
Never walk away from a lit burner
Never point the open end of a hot test tube at yourself or someone else
Do not look down into a test tube/beaker while it is being heated
Make sure burner is capped and flame is out when done
End of Experiment
CLEAN-UP AREA & MATERIALS COMPLETELY!!!! (Or you LOSE points)
Make certain that burner is out if one was used
Keep goggles on (over eyes) until Mr. Leeds says to put them away.
Reaction in a Bag
- The purpose of the lab is to record the observations that occur when multiple chemical substances are combined and to use them to understand the reactions of the chemicals.
- Heat = A + Liquid
- Cold = B + Liquid
- Gas = A + B + Liquid
- Experimental error- if there is a whole or a rip in the bag you would not know there is gas being produced.
- The red liquid is phenol red
- pH scale- Measures acidity, goes from 0-14, 0-6 is acidic, 7 is neutral, and 8-14 is alkaline
- Below 7 is yellow and above 7 is pink
- 2 Solids- Calcium chloride (Calcium + Chloride) is acidic and hydrotropic (absorbs and is attracted to water). It is used in canned veggies, electrolytes in sports drinks, and to flavor pickles (salty flavor). Sodium Bicarbonate (Baking soda) is not acidic and is used in baking, toothpaste, laundry detergent
Observation- information obtained by the senses- often by direct measurement.
Inference- a conclusion based upon known observations.
Hypothesis- A proposed solution to a scientific problem.
Control Group- the group that is the standard for comparison in any experiment.
Experimental Group- the group receiving the variable being tested. Control Factors- the variables that are held constant. They are the same
for both the control group and the experimental group.
Indicator- a substance used to show the presence of another substance.
Volume- the amount of space something occupies. True of solids, liquids, and gases.
Volume Displacement Technique- quick and easy way to determine the volume of a solid or gas.
Mass- the amount of matter in a substance (true of solids, liquids, and gases)
Meniscus- the curved portion of a liquid when in a container. Must read the bottom of the meniscus- at eye level- for proper measurement.
1.1 Heating Baking Soda
- The purpose of the lab is to observe and record the reaction that occurs when baking soda is heated.
- Experimental error 1- If there was a small crack in the test tube or rubber tubing. Experimental error 2- If the stopper is not snug.
- There is the same amount of gas as there is baking soda because the gas comes from the baking soda.
- Droplets and moisture come from the baking soda.
- During the tea experiment the liquids are not the same. Their colors are different.
- Control Group- unheated test tube
- Experimental group- heated test tube
- Indicator- tea (showed that heated is no longer baking soda)
- Variable- a category you try to measure
- Independent variable- cause a change in the dependent variable (temperature)
- Dependent variable- color of tea
- Control factors- same type of tea, same amount of baking soda, same amount of tea, same size test tube, same stirring time
Always start from the zero mark not the end of the ruler.
Be as precise as possible.
Make sure the ruler is straight when measuring.
Always zero balance before using.
Add or remove weight until the two lines meet at the zero mark. Then use the weights on the scale to see how much mass the object has.
Unit of measurement: cm3 (cubic centimeters)
Volume l x w x h (a x b x c)
Standard unit of length = meter (m)
1 centimeter (1 cm) = .01
100cm = 1m
Unit Cube- a small cube 1 cm on each side
Volume of Liquids:
Use a graduated cylinder to measure volume. *Always check the intervals or scale.
Units = milliliters (mL) or cm3
One milliliter = one centimeter
Read the water level from the bottom of the meniscus.
1.4 Measuring Volume by Displacement of Water
- Purpose- to use the displacement of water method to see the volume of dry sand that is sand and air space
- Experimental Errors: Sand sticks to sides of wet cylinder --> Volume of sand and water would be too high. Pour water into sand (water sits on top of sand because the air spaces don't allow water to filter down)
- No matter how much dry sand you have, there is always around 40% of water.
- Volume of sand and water - volume of water = volume of sand alone
- Volume of dry sand (air) - volume of sand alone = volume of air
- Volume of air divided by dry sand = Fraction of sand that is air
1.6 The Equal-Arm Balance
- Beqa: ancient standard mass used in Egypt
Earliest balance found in Egypt (approx. 7,000 years old)
standard unit grams (1g)
1 kilogram (1kg) = 1,000g
1 kilogram = 2.2 pounds (lbs.)
1.8 The Sensitivity of a Balance
- Purpose: To see if you mass the same object repeatedly will the mass remain the same. Also, to see how different the masses of two objects must be for our balance to detect the difference.
- Mass of Penny
Before 1982: 95% copper 5% zinc
After 1982: 2.5% copper 97.5% zinc
1943: Mad of steel and zinc
Sensitivity of Balance- the lightest mass that you can expect the balance to detect.
∆: Delta (change)
∆M: Change in Mass
Ending mass - initial mass of stopper = ∆M
∆M divided # of yeses = sensitivity of Balance
Chapter 1 Test
- During the Heating Baking Soda Experiment a lab group does not realize that they have a hole in their rubber tubing. How will this affect their understanding of the lab?
The group will not know that the gas being produced from the baking soda will eventually push the water from the bottle into the container because the gas will escape through the crack.
2. During the Reaction in a Bag Experiment a lab group does not realized that there is a hole in their zip lock bag. How will this affect their understanding of the lab.
The gourd will not realize that if they mix solid A + Solid B + Liquid a gas will be produced and expand the bag because it will escape through the hole.
3. For the Measuring Volume by Displacement of Water Experiment Mr. Leeds assigned lab groups different amounts of dry sand to begin the lab. Why did he dot this?
He wanted to show it doesn't matter how much sand you start with there will always be around 40% of air space in-between the sand particles.
2.1 The Mass of Dissolved Salt
- Purpose: To see if the mass of salt decreases when salt dissolves in water.
- Mi: Initial mass
- Mf: Final mass
Not drying off the cap --> water in Mi not there for Mf
Remove cap before Mf --> spillage/leakage
Not shaking long enough --? not dissolved
Cap not on tightly --> spillage/leakage
Spill salt when pouring into bottle
2.4 The Mass of Ice and Water
- Purpose- To distinguish if the mass of ice will increase, decrease, or stay the same when it melts.
- Condensation on bottle: comes from warm water vapor in the air (humidity). When it touches cool surface of bottle it turns from gas to liquid.
not wiping off condensation --> gain mass
bottle is wet during Mi
shaking the bottle --> lose mass
2.5 The Mass of Copper and Sulfur
- Purpose- to see if the total mass increases, decreases, or stay the same when copper and sulfur are heard together.
- Melting pt. of copper 1,100 degrees C (2000 degrees F)
- Melting pt. of sulfur 112 degrees C (235 degrees F)
- Yellow Smoke: water in sulfur turns to vapor (gas) and rises in test tube
- When it cools: Sulfur bonds with copper forms copper sulphide
- Experimental Errors:
Rubber sheet can have a hole-->gas could escape
Sheet is not tight on test tube-->gas could escape
Sulfur sticks to sides of test tube-->doesn't react
Clean pan between Mi and Mf
2.6 The Mass of a Gas
- Purpose- To see if the mass will increase, decrease, or stay the same when a solid and liquid produce a gas.
- Experimental Errors:
Cap is not tight or not quick enough-->loss of mass
Water in the pan during the Mi-->loss of mass
Cap is wet during Mi-->loss of mass
Touch tablet after Mi-->loss of mass
- Alka-Seltzer: Antacid + pain reliever:
Aspirin, citric acid, sodium bicarbonate
Sodium bicarbonate produces gas
2.7 The Conservation of Mass
- Closed system- a space where nothing can leave or enter.
- Law of Conservation of Mass- In a closed system mass will remain constant, regardless of the actions of the processes inside the closed system.
Chapter 2 Test
- Describe a possible error (specific to the lab) discussed in class, which could lead to a loss in mass during the Mass of a Gas lab.
If you touch the alma-seltzer while putting it into the bottle.
2. Describe a possible error (specific to the lab) discussed in class, which could lead to a loss in mass during the Mass of Copper and Sulfur lab.
If there was a hole in the sheet.
3. During an experiment of Ice and Water a gain in mass is noted by a lab group. Give a possible error (specific to the lab), discussed in class, as to how this gain in mass could have occurred.
If you didn't wipe off the condensation on the bottle between the Mi and Mf.
4. During the ice and water lab a lab group forgot to put the cap on their bottle. BY the time they realized their mistake some condensation had already formed on the outside and inside of the bottle. They should:
Start the lab over
5. In all four experiments from Chapter 2 the common theme involved investigating changes in mass of different states of matter. You know that in all the labs there should be no change in mass because:
Law of conservation of mass.
6. You are working in a class with no air conditioning, it is 90 degrees F. Your lab is to take the mass of water (that is 65 degrees F) in a small plastic bottle with a cap on, then place the bottle in a walk-in freezer allowing the liquid to solidify, then re-mass the bottle while in the freezer. What is a possible error you should be aware of:
Condensation may form on the outside of the bottle during the Mi and then freeze
7. A lab group dissolves 2g of salt into 8cm3 of water in a beaker with not cover. After a few days all of the water has evaporated. What will remain in their beaker?
2g of salt
- Property of an object- does not tell you what it is made out of.
- Property of a substance- this helps you identify what the object is made out of.
3.2 Mass and Volume
- Purpose- To see if the max of a 1cm3 object will depend on its shape or the substance it is made of.
- Experimental Errors:
Cylinder is wet when you mass-->add mass
Water splashes out of graduated cylinder-->volume less
Mass/volume same cylinder twice
Mass and Volume Notes
- Objects that are made of the same substance that have the same volume, will have the same mass (regardless of their shape). For example: long aluminum cylinder and short aluminum cylinder
- The mass of an object will double if its volume doubles.
- Objects that have the same volume but are made of different substances will not have the same mass. For example: aluminum and brass cylinders
Mass divided by volume equals density
3.5 The Density of a Solid
- Purpose- to utilize density to distinguish if 3 metal objects are made of the same substance.
- Experimental Errors:
Water splashes out of graduated cylinder
Find volume of rock before mass-->higher mass and higher density
Paint chipped off object
Measuring same side twice
3.6 The Density of a Liquid
- Purpose- To use density to compare 2 liquids to utilize if they are the same substance.
- Experimental Errors:
Not rinsing out cylinder between substances
Don't re-mass cylinder for first mass (empty)
Outside of cylinder is wet during mass empty
Dry out cylinder after mass empty
- Magnesium Sulfate = Epsom Salt
3.7 The Density of a Gas
- Purpose- to produce and collect a gas in order to accurately acquire the density of the gas.
- Experimental Errors:
Put foil back for Mf
Touching tablet after Mi-->Mf too small-->Mass decrease-->Density increase
Break surface of water with bottle-->Volume increase-->Density decrease
Stopper not on tight enough
Spilling water-->find volume of bottle-->Volume decrease-->Density increase
- Gas is carbon dioxide
Chapter 3 Test
- In order to calculate density, we found both the mass and volume of the liquid in the graduated cylinder because it is the most accurate method and we did not have to transfer liquid
- During the Density of a GAs lab the rubber tubing is incorrectly inserted near the bottom (mouth) of the bottle. This will cause less gas to collect in the bottle.
- If the error in #2 is made it will have the following affect: Volume decrease, density increase
- When calculating the density of a rock (irregular shape) it would be an experimental error to find the volume prior to massing
- When the alka-seltzer tablet is mixed with water, sodium bicarbonate within the tablet releases carbon dioxide.
- In the Density of a Gas lab a student forgets to include the foil for the Mf, the result is mass of gas increases, density increases.
- Epsom salt is the marketing name for which chemical compound: