Elements and Compounds
This is the smallest unit of an element that still has the properties of that element.
What is an atom
Using the periodic table, this element has the chemical symbol K.
What is potassium?
An ice cube melting into liquid water is this type of change.
What is physical?
In a mixture of salt and water, the salt is called this.
What is the solute?
Crushing a solid into smaller pieces decreases this, which makes it dissolve faster.
What is surface area?
This is the chemical symbol for sodium.
What is Na?
This is the number of hydrogen atoms in one molecule of H₂O.
What is 2?
Wood burning in a campfire is this type of change because of this evidence
What is a chemical change? (odor change, light being produced, color change, gas being produced)
In an aqueous solution, this substance is the solvent.
What is water?
Stirring or shaking a solution is called this, and it speeds up dissolving.
What is agitation?
Of O₂, Fe, NaCl, and He, this is the only compound.
What is NaCl?
(It has two different elements chemically combined.)
Sulfuric acid is 3H₂SO₄. Give the number of atoms of each element and the total.
What is 6 hydrogen, 3 sulfur, 12 oxygen = 19 atoms?
Name two signs (evidence) that a chemical change has taken place.
What are: gas bubbles, color change, precipitate (solid forms), temperature change, light given off, or odor? (any two)
This term describes the amount of solute dissolved in a given amount of solvent or solution.
What is concentration?
A sugar cube dissolves faster in hot water than in cold water. Explain why.
What is: particles in hot water move faster and collide with the solute more often and with more energy?
Compare an element and a compound in terms of the atoms they contain.
What is: an element has only one kind of atom, and a compound has two or more different kinds of atoms chemically combined in a set ratio?
Calcium hydroxide is 5Ca(OH)₂. This contains this many molecules
What is 5? (identified by the coefficient)
Cutting paper into small pieces is a physical change. Explain why.
What is: the paper changes size and shape, but no new substance forms, and it is still paper?
Adding more water to a strong juice concentrate is called this, and it causes the concentration to do this.
What is dilution, and the concentration decreases?
A student puts a sugar cube in 100 mL of cold water without stirring. A second student puts crushed sugar in 100 mL of hot water and stirs. Which sugar dissolves faster? Name the three factors that cause the difference, and identify the solute and the solvent.
The crushed sugar in hot, stirred water dissolves faster. The factors are surface area, temperature, and agitation. The solute is sugar and the solvent is water.
Classify O₂, H₂O, and Ne as an element or a compound, and tell which of them are molecules
What is: O₂ is an element and a molecule. H₂O is a compound and a molecule. Ne is an element made of single atoms, so it is not a molecule.
Aluminum sulfate is Al₂(SO₄)₃. Give the number of atoms of each element and the total.
What is 2 aluminum, 3 sulfur, 12 oxygen = 17 atoms?
One student stirs sugar into water. Another mixes baking soda and vinegar and sees bubbles. Which is a chemical change and how do you know?
What is the baking soda and vinegar? A new substance (carbon dioxide gas) formed. Sugar dissolving is physical because the sugar is still sugar.
A 100 mL sugar solution contains 20 g of sugar. Water is added to make 200 mL. What happens to the amount of sugar and to the concentration?
What is: the amount of sugar stays 20 g, but the concentration is cut in half (0.2 g/mL to 0.1 g/mL)?
Use particle ideas to explain how crushing, stirring, and heating each speed up dissolving.
What is: crushing exposes more solute to the solvent. Stirring moves dissolved particles away and brings fresh solvent to the solute. Heating makes particles move faster so they collide more?