Elements & Compounds
Which of the following is an example of a compound?
A) Helium (He)
B) Sodium (Na)
C) Carbon Dioxide (CO2)
D) Iron (Fe)
C) Carbon Dioxide (CO2)
Chemical changes happen due to a ______ ______.
chemical reaction
In aqueous solutions, water is always the solute or solvent?
solvent
Which of these would cause a solid solute to dissolve faster in an aqueous solution?
A) Increase the temperature of the solvent.
B) Increase the amount of solute in the solvent.
C) Increase the density of the solute.
D) Increase the size of particles of the solute.
A) Increase the temperature of the solvent.
Explain the difference between a compound & a molecule.
Molecule - any 2 (or more) atoms bonded together
Compound - 2 or more DIFFERENT atoms bonded together
Physical changes will change a substance's physical properties but not its ______.
Identity
Solutes must always be _____.
A) Insoluble
B) Saturated
C) Soluble
D) Concentrated
C) Soluble
Name the 3 factors of solute dissolution rate.
Temperature, agitation and surface area
What is the difference between a chemical symbol vs a chemical formula?
Chemical symbol - 1 or 2 letters, represent an element
Chemical formula - chemical symbols put together with subscripts to show which elements make up a compound and/or molecule
Name an indicator that can be for either a physical change or a chemical change depending on the cause.
Change in color
Ellen learned that honey is a saturated solution of glucose and fructose dissolved in water.
Which describe solute(s) and solvent(s) in the honey solution?
A) Fructose is the solvent and water is the solute.
B) Water is the solvent and glucose is the only solute.
C) Water is the solvent and glucose and fructose are the solutes.
D) Fructose is the solvent and water and glucose are the solutes.
C
Sugar is more soluble at higher temperatures. This is mainly because at higher temperatures —
A) Sugar and water molecules move slower and their interactions make the sugar molecules stay together longer
B) Sugar and water molecules move faster, and their interactions make the sugar molecules separate from one another
C) Water molecules spread out more, making more room for the sugar molecules
D) Water molecules actually come apart into separate atoms and react with the sugar
B) Sugar and water molecules move faster, and their interactions make the sugar molecules separate from one another
Can things be both a molecule or a compound? Explain your reasoning.
Yes. All compounds are molecules but not all molecules are compounds.
Jack mixed Substance A and Substance B together in a beaker. Both substances are liquids. When mixed together, Jack can see that a solid mass formed inside the beaker and there are bubbles forming in the liquid. When he touches the beaker it feels warm. What the reaction a physical or chemical change and what indicators did Jack see?
Chemical change; formation of a precipitate, formation of gas, change in energy
Describe how you can raise and lower concentration level of a solution.
adding more solute makes a solution more concentrated
adding more solvent makes a solution less concentrated
Think back to the sugar cube lab, what 3 things can you do to make a sugar cube dissolve in water as fast as possible?
crush the cube into a powder, heat up the water and stir quickly
Compare and contrast the formulas of these two compounds.
Nitrous acid: HNO2
Nitric acid: HNO3
Describe the similarities and differences between the compounds. Circle TWO correct answers.
A) Both compounds contain the same kinds of atoms.
B) Both compounds contain the same total number of atoms.
C) Nitrous acid contains fewer oxygen atoms than nitric acid.
D) Nitrous acid contains more nitrogen atoms than nitric acid.
A & C
List the indicators of a chemical change we discussed in class (5 total).
1. formation of a gas
2. production of an odor
3. formation of a precipitate
4. change in color
5. change in energy
Explain the difference between the following vocab terms: concentration, saturated, diluted
Concentration: how much solute have you dissolved in a given solvent
Saturated: a solution that is at or above the maximum amount of solute that can be dissolved in a solvent
Diluted: a solution that is below the maximum amount of solute that can be dissolved in a solvent
Explain the difference between how solute molecules spread through out a solvent for when the solvent is heated vs when the solvent and solute are agitated.
When heat is used, solute molecules gain energy and spread out on their own.
When you agitate the solute and solvent, the solute molecules are mechanically spread out in the solvent.