Exam Study Guide
For every lab
· Goggles must be over your eyes until Mr. Leeds say 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 equiptment in classroom
· Fire extinguisher
· Fire blanket
· Eye wash/shower
· Never taste chemicals
· Always waft liquids to detect odor
· Never waft solids or powders
· Avoid touching chemicals
· Always wash hands with soap and water after lab
· If chemicals tough 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
· 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 the 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 and materials completely
· Make certain tat burner is out if one was used
· Keep goggles on (over your eyes) until Mr. Leeds says to put them away
Lab: Reaction in a bag
1. Red Liquid
- Phenol red
- Used as a ph indicator
- Ph scale: measures acidity; goes from 0-14; below 7- acid, above 7, alkaline, 7- neutral; lemon juice- 1.5; tums- 10
- Below 7 turns yellow
- Above 8 turns pink
2. Calcium chloride (A)
- Hydro-tropic (absorbs water/attracted to water) – uses: canned veggies- keeps from getting mushy, electrolyte in sports drinks, used to flavor pickles
3. Sodium bicarbonate – baking soda (B)
- Baking soda
- Not acidic
- Uses: baking, laundry detergent, toothpaste
Lab: Heating Baking Soda
- No visible changes occur to the baking soda after being heated.
- While being heated, the top of the test tube was foggy and misty, and condensation was occurring.
- Water gets pushed out of the bottle while baking soda is being heated. In the lab done in the textbook with no baking soda, the bottle does not fill with gas.
- The gas came from the baking soda (we know this because no gas was produced in the same lab without the baking soda).
- Water droplets at the top of the test tube came from the gas being emitted from the baking soda because the hot gas touches the sides of the top of the less-hot test tube.
- Heated baking soda + tea = darker color (brown), dissolved
- Unheated baking soda + tea = lighter color (tan), did not dissolve
- The heated baking soda and unheated baking soda are not the same. We know this because the unheated beaker was just baking soda and tea, so the heated would be the same color if they were the same substance.
- Control group: unheated baking soda + tea
- Experimental group- heated baking soda + tea
- Indicator: tea (it showed that the heated test tube was not baking soda)
- Variables: a category you try to measure
- Independent variable (causes a change in the dependent variable): temperature (heat)
- Dependent variable: tea color
- Control factors (things we can control in the lab): same type of tea, same amount of baking soda, same amount of tea, same size test tube, same amount of stirring time
- Experimental errors: hole in tubing --> won't see gas fill bottle : stopper not snug --> won't see gas fill bottle ; not cleaning stirring rod --> contaminate
- Extra question: Condensation more or less than the amount of baking soda? - Less, the condensation comes from the baking soda, and it cannot produce more than itself.
Volume (and length) Notes
- Unit of measurement: cm3 (cubic centimeters)
- Volume = L x W x H
- Ex: box with 1cm3 cubes can fit 5 for width, 2 for length, and 3 for height, with a space of 0.5 cubes remaining at the top. Volume would be 5 x 2 x 3.5 = 35.
- Standard unit of length: meter (m)
- 1 centimeter (1 cm) = 0.01 m ; 100 cm = 1 m
- Unit cube- a unit cube 1 cm on each side
- Use a graduated cylinder to measure volume of liquids (always check intervals on scale)
- Units = millimeters (mL) or cm3
- 1 mL = 1 cm
- Divisions of graduated cylinders: 10 mL- 0.2 mL divisions; 25 mL- 0.5 mL divisions; 50 mL- 1.0 mL divisions; 100 mL- 1.0 mL divisions
Single Pan Zero Balance Notes
2. Always "zero balance" before massing.
- push riders to zero (left)
- use adjustment knob if needed
3. Never switch pans.
4. Pick up balance by red part only.
5. Don't zero balance when done
Also, estimate to thousandths place because zero balance goes to hundredths place.
3. 50 mL graduated cylinders hold 50 cubic cm of water.
4. If box A has a a greater volume than box B, but its length is shorter, than its width and/or height is longer than box B's.
5. If a stone is dropped into a graduated cylinder, and the water lever raises from 25 cubic cm to 32 cubic cm, then the stone is 7 cubic cm. (displacement of water)
6. a) cube with 2 cm along each edge- 8 cubes
b) cube with 3 cm along each edge- 27 cubes
c) volumes of both- 8 cubic cm, 27 cubic cm
7. 30 x 15 x 10 = 4500 cubic cm
25 x 15 x 16 = 6000 cubic cm
8. Why volume divisions on a cone are spaced differently- the surface of the water is smaller at the bottom, so you need the depth the make up for it. You don't need the depth at the top because the surface is larger
9. a) arrow 1 = 1.2 cm
arrow 2 = 3.8 cm
we cannot round to the hundredths place because we are given up to the ones place, and we can only estimate one more position than given
b) arrow 3 = 1.66 cm
arrow 4 = 2.52 cm
arrow 5 = 4.50 cm
we cannot round to the thousandths place because we are given up to the tenths place, and we can only estimate one more position than given
c) We should report the positions of the arrows in part (b) to the nearest hundredth cm instead of tenth of a cm because we are able to estimate one more position than given and it would be more accurate.
10. a- 0.1 cubic cm ; b- 0.2 cubic cm
11. a- 4.0 cubic cm ; b- 1.30 cubic cm
12. 12 cm: 11.5 - 12.4 cm
12.0 cm: 11.95 - 12.04 cm
12.00 cm: 11.995 - 12.004 cm
13. The advantage of making graduated cylinders taller and narrower, rather than shorter and wider, is that they are easier to read. The lines are further apart because there's more depth due to the lack of surface.
Lab: Measuring Volume by Displacement of Water
- sand sticks to sides of wet cylinder - volume decreases
- pour water into sand- water sits on top of sand b/c the air spaces don't allow water to filter down
- Lab groups were instructed to use different amounts of sand because it does not matter how much dry sand you begin with, all groups have approximately 40% air space.
- Since sugar dissolves in water, use a non water-based liquid to measure volume of sugar
- Since cork floats in water, use a weight to submerge the cork (must take into account the volume of the weight)
- To find volume of sand alone, subtract the volume of the water from the volume of the sand and water.
- To find the volume of the air space, subtract the sand alone from the dry sand.
- To find the percentage of dry sand that is sand, divide sand alone by dry sand (and multiply by 100).
- If many people mass the same object, and one person gets a mass different by more than 0.02g, then that person has made an error because their mass is off by more than the sensitivity of the balance.
Mass Notes and BQ's
- Beqa- ancient standard mass
- Earliest balance found in Egypt approx. 7,000 years ago
- 1 kg = 2.2 lbs
18. If equal arm balance is horizontal, objects have the same mass.
20. Solid foods usually measured by mass, liquids usually measured by volume.
22. It is better to mass a person with a single pan balance rather than an equal arm balance because you would have to have something of equal mass to the person and put it on the balance to make it accurate
34. It is better to measure fuel oil and gas for cooking by volume because you would have to measure the weight of the gas if you did it by volume. It takes longer, you would need a scale, and it is less safe. Fuel oil is a liquid and has no air spaces, so it is more efficient to measure by volume. Coal is a solid and has air spaces, so it would be more accurate and take less time to measure it by its mass.
Lab: Sensitivity of a Balance
- Sensitivity- the lightest mass you can expect a balance to detect (margin of error when you mass something)
- Divide change in mass by # of yeses to find sensitivity
- Better to use groups of squares with a larger mass because there will be more change in mass at the end. The results are more accurate, and the balance reading may not have changed or changed enough if the pieces were too small.
- Mass of penny: before 1982- 95% copper and 5% zinc, after 1982- 2.5% copper and 97.5% zinc
- 1943- pennies made of steel and zinc b/c copper was needed for bullets
Lab: Mass of Dissolved Salt
- Cleaning pan between Mi and Mf- lose mass
- Outside of bottle is wet during Mi- lose mass
- Spill salt when pouring into bottle- lose mass
- Cap not on tightly/spillage or leakage- lose mass
- Take into consideration the sensitivity of a balance
- Must subtract Mi from Mf to be more accurate/know whether there was an increase or decrease
- Do not need to know individual masses of water and salt because they are not dependent on the change in mass
- To get the salt back, allow water to evaporate
- Histogram rule- if a number is on the line, move it to the right
- Tip: before drawing the line, find the lowest and highest points and determine your range
- Histograms with smaller are not necessarily better because they may not take into consideration the sensitivity of a balance
Lab: The Mass of Ice and Water
- Not wiping condensation before Mf- gain mass
- Bottle is wet during Mi- lose mass
- Condensation on the bottle comes from warm water vapor in the air (humidity) when it touches the cool surface of the bottle it turns from gas to liquid
Lab: Mass of Copper and Sulfur
- cleaning pan between Mf and Mi- lose mass
- hole in rubber sheet/sheet not sealed on test tube, gas escapes- lose mass
- smoke comes from water in sulfur turning to vapor and rising in the test tube
- when it cools, sulfur liquid bonds to copper and forms copper sulfide
Lab: Mass of a Gas
- ring of water in pan after Mi, water evaporates- lose mass
- cap is wet, alka-seltzer reacts during Mi- lose mass
- cap not tight enough, gas escapes- lose mass
- touch alka seltzer after Mi- lose mass
- alka-seltzer: aspirin, citric acid, and sodium bicarbonate (sodium bicarbonate releases the gas)
Chapter 2- extra
- Law of conservation of mass- in a closed system, mass will remain constant, regardless of the actions of the process inside the closed system
- open systems can have changes in mass (ex: beaker, graduated cylinder)
- if condensation forms on inside of open beaker, cylinder, etc, then you must start lab over bc/ condensation came from outside factors and the condensation could potentially drip into your experiment
Chapter 3 Intro
- property of an object: does not tell you what it is made out of
- property of a substance: helps identify what an object is made of
- vocab link: http://elearning.pinecrest.edu/course/50053699/materials/gp/74318089
Lab: Mass and Volume
- cylinder is wet- gain mass
- water splashes out of cylinder when measuring volume- lose volume
- objects made out of the same substance will have the same mass if they have the same volume, and vice versa
- Density = mass / volume
- unit: g/cm3
Lab: Density of a Solid
- find volume of rock before massing it, rock gets wet- gain mass
- paint chipping on objects- lose mass
- rocks have different densities because rocks are made of many substances
- objects with the same density have the same mass if their volumes are the same
- mass and volume (separately) are not dependent on density
Lab: Density of a liquid
- outside of graduated cylinder is wet during one of the massings- gain mass
- magnesium sulfate: epsom salt
Lab: Density of a Gas
- spill water when measuring vol.- volume decreases, density increases
- do not push tubing up in bottle far enough, some gas dissolves- volume decreases, density increases
- forget foil in Mf- mass increases, density increases
- touch tablet after Mi- mass increases, density increases
- gas was carbon dioxide