CHEM LAB EXAM 2 QUESTIONS AND
ANSWERS GRADED A+ 2025/2026
C2H6 + O2 --> CO2 + H2O - ANS 2C2H6+7O2⟶4CO2+6H2O
[2]C2H2+C2H2+ [5] O2⟶O2⟶ [4] CO2+CO2+ [2] H2OH2O - ANS [2]C2H2+C2H2+ [5]
O2⟶O2⟶ 4 CO2 + 2 H2O
Physical Change - ANS Change in state
Change in size
Tearing apart
Breaking into pieces
Grinding into powder
Dissolving
Chemical Changes - ANS Temperature increase*
Formation of gas bubbles*
Permanent color change
Formation of precipitate
Odor change
Change in pH
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,Law of Conservation of Matter - ANS atoms of matter are not created or destroyed during a
chemical reaction.
Oxygen (O2) - ANS is a colorless, odorless gas that supports combustion. A glowing wooden
splint will brighten or burst into flames when inserted into a container.
Hydrogen (H2) - ANS is a colorless, odorless gas that burns in air. Hydrogen is less dense than
air that can be captured in an inverted vessel, or in a test tube with a paper towel plug. A
mixture of hydrogen and air in a test tube will burn with a "pop" when exposed to a lit wooden
splint.
Carbon dioxide (CO2) - ANS is a colorless, odorless gas that does not burn in air or support
combustion. For that reason, it is used to extinguish fires. When dissolved in water, it forms a
mildly acidic solution containing carbonic acid, H2CO3(aq). A lit wooden splint will go out when
inserted into a container of carbon dioxide.
Composition (Combination) Reaction - ANS 𝐀 + 𝐁 ⟶ 𝐀𝐁
2 reactants 1 product
Decomposition Reactions - ANS AB ⟶ A + B
1 reactant 2 products
Single Replacement Reactions - ANS A + BC ⟶ B + AC
element + compound ⟶ Element + compound
Double Replacement Reactions - ANS AB + CD ⟶ AD + CB
2 compounds + 2 New Compounds
Combustion Reactions - ANS C_H_ + O2 ⟶ xCO2 + H2O
Fuel + Oxygen ⟶ Carbon Dioxide + Water
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, Percent recovery formula - ANS (Product mass)/(initial mass) x 100
How should the mass of copper metal at the end of the reactions compare to the starting mass
of copper? - ANS The produced mass of copper should equal the starting mass of copper.
What does a percent recovery of more than 100% likely indicate? - ANS The product still
contains some water.
Decomposition Example using copper - ANS Cu(OH)2(s)Δ−→CuO(s)+H2O(g)
Decanting - ANS The process of separating a liquid/solid mixture by slowly pouring the liquid
component into a new vessel as the solid settles to the bottom of the original vessel.
What is the purpose of stirring a solution while it is being heated? - ANS To help evenly
distribute heat throughout the solution
When working in a fume hood, what is the best position of the hood sash? - ANS As low as
possible, no more than halfway up
When testing the pH of a solution with pH paper, dip _________
in the solution. Add a _______ of the solution to the paper.
Compare the _____ of the pH paper to the scale that appears on the container. - ANS 1.
Stiring Rod
2. Drop
3. Color
Determine when you should remove your goggles in the lab room. - ANS When everyone in
the room is done handling any chemicals or glassware.
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
ANSWERS GRADED A+ 2025/2026
C2H6 + O2 --> CO2 + H2O - ANS 2C2H6+7O2⟶4CO2+6H2O
[2]C2H2+C2H2+ [5] O2⟶O2⟶ [4] CO2+CO2+ [2] H2OH2O - ANS [2]C2H2+C2H2+ [5]
O2⟶O2⟶ 4 CO2 + 2 H2O
Physical Change - ANS Change in state
Change in size
Tearing apart
Breaking into pieces
Grinding into powder
Dissolving
Chemical Changes - ANS Temperature increase*
Formation of gas bubbles*
Permanent color change
Formation of precipitate
Odor change
Change in pH
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,Law of Conservation of Matter - ANS atoms of matter are not created or destroyed during a
chemical reaction.
Oxygen (O2) - ANS is a colorless, odorless gas that supports combustion. A glowing wooden
splint will brighten or burst into flames when inserted into a container.
Hydrogen (H2) - ANS is a colorless, odorless gas that burns in air. Hydrogen is less dense than
air that can be captured in an inverted vessel, or in a test tube with a paper towel plug. A
mixture of hydrogen and air in a test tube will burn with a "pop" when exposed to a lit wooden
splint.
Carbon dioxide (CO2) - ANS is a colorless, odorless gas that does not burn in air or support
combustion. For that reason, it is used to extinguish fires. When dissolved in water, it forms a
mildly acidic solution containing carbonic acid, H2CO3(aq). A lit wooden splint will go out when
inserted into a container of carbon dioxide.
Composition (Combination) Reaction - ANS 𝐀 + 𝐁 ⟶ 𝐀𝐁
2 reactants 1 product
Decomposition Reactions - ANS AB ⟶ A + B
1 reactant 2 products
Single Replacement Reactions - ANS A + BC ⟶ B + AC
element + compound ⟶ Element + compound
Double Replacement Reactions - ANS AB + CD ⟶ AD + CB
2 compounds + 2 New Compounds
Combustion Reactions - ANS C_H_ + O2 ⟶ xCO2 + H2O
Fuel + Oxygen ⟶ Carbon Dioxide + Water
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, Percent recovery formula - ANS (Product mass)/(initial mass) x 100
How should the mass of copper metal at the end of the reactions compare to the starting mass
of copper? - ANS The produced mass of copper should equal the starting mass of copper.
What does a percent recovery of more than 100% likely indicate? - ANS The product still
contains some water.
Decomposition Example using copper - ANS Cu(OH)2(s)Δ−→CuO(s)+H2O(g)
Decanting - ANS The process of separating a liquid/solid mixture by slowly pouring the liquid
component into a new vessel as the solid settles to the bottom of the original vessel.
What is the purpose of stirring a solution while it is being heated? - ANS To help evenly
distribute heat throughout the solution
When working in a fume hood, what is the best position of the hood sash? - ANS As low as
possible, no more than halfway up
When testing the pH of a solution with pH paper, dip _________
in the solution. Add a _______ of the solution to the paper.
Compare the _____ of the pH paper to the scale that appears on the container. - ANS 1.
Stiring Rod
2. Drop
3. Color
Determine when you should remove your goggles in the lab room. - ANS When everyone in
the room is done handling any chemicals or glassware.
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
