General Chemistry Midterm
Name:_______________________________
Part I Vocab:
Matter :anything that takes up space and has mass
Compound: a chemical combination of two or more different elements joined in a fixed proportion
Element: a substance that cannot be broken down into simpler substances
Density: the amount of matter in a given unit of volume
Heterogeneous mixture: a combination of substances that are not chemically combined and that does
not have uniform composition
Homogeneous mixture A combination of substances that are not chemically combined but has
uniform composition throughout
Filtration a technique that uses a porous barrier to separate a solid from a liquid
Chromatography A technique that is used to separate the components of mixture based on the
components’ ability to be drawn across the surface of another material
Distillation A technique that can be used to physically separate most homogeneous mixtures based on
the differences in the boiling points of the substances
Chemical property / change The ability of a substance to react with another substance
Physical property / change A type of change that does not alter the substance’s chemical composition
Atomic number Number of protons in the nucleus of an atom
Mass number Number of protons and neutrons in an atom
Isotope Atoms of the same element that have different numbers of neutrons
Nonmetal an element that does not conduct electricity or heat, is brittle when solid or a gas at room
temperature
Metal Metal An element that is solid at room temp, a good conductor of heat and electricity, are
shiny, ductile and malleable
Metalloid An element that has physical and chemical properties of both metals and nonmetals
Ductile Capable of being drawn out into a wire
Malleable Able to be hammered into a sheet
Ion An atom or group of atoms with a positive or negative charge
Sublimation : the process by which the particles of a solid escape and form a gas
Condensation: the process by which gaseous particles come together to form a liquid or sometimes a
solid
Freezing: the temperature at which a liquid becomes a crystal lattice
Melting: The temperature at which a crystal lattice becomes a liquid
Synthesis reaction: a reaction in which two or more substances react to form one product
Decomposition reaction A single compound breaks down into two or more substances
Combustion reaction An exothermic chemical reaction that occurs when a substance reacts with oxygen
Single replacement reaction A chemical reaction in which the atoms of one element replace the atoms of
another element in a compound
Double replacement reaction – a chemical reaction in which the ions of two substances are exchanged and
produces a solid, gas or water
Part II: Describe the following
1. Atomic theory - All matter is made of atoms. Atoms cannot be divided by chemical means. All atoms of the
same element have the same number of protons.
2. Atomic structure (use protons, neutrons, electrons) Positively charged protons and neutral neutrons are found
in the nucleus of an atom and make up the bulk of the atoms mass. Much smaller negatively charged
electrons orbit the nucleus in energy levels and make up the volume of the atom.
3. Law of conservation of mass: Matter cannot be created nor destroyed.
4. The difference between an observation, hypothesis and conclusion An observation refers to information gained
through the senses. A hypothesis is an educated guess that has not been tested. A conclusion is an
explanation for a phenomenon that has been tested.
5. Democritus’s contribution to the atomic theory: Democritus was the first person to suggest that matter was
made up of tiny particles that he called “atoms”.
6. Difference between a qualitative observation and a quantitative observation. A qualitative observation is a
description consisting of words. A quantitative observation is a description consisting of measurements.
7. Difference between the independent and dependent variables. The independent variable is what is being
manipulated by the tester in the experiment and the dependent variable is the outcome or what is measured
as a result of the independent variable.
Part III: Know the following information: (worksheets in class and problems listed below)
1. How to name ionic and molecular compounds.
2. How to balance and classify chemical reactions.
3.. How to calculate density. D = mass / volume (g/ml)
Part IV: Solve the following problems:
1. A 5mL sample of water has a mass of 5g. What is the density of water?
5g ÷ 5 ml = 1 g/ml
2. A cube of aluminum with volume = 5 cm3 has a mass of 20g. What is the density of aluminum?
20g ÷ 5 cm3 = 4 g/cm3
3. What is the volume of a sample that has a mass of 20g and density of 4 g/mL?
Density = mass / volume, so volume = mass / density, so
Volume = 20g ÷ 4 g/mL = 5 mL
4. What is the atomic number for the following elements?
a. at atom with 37 electrons
37
b. an atom with 72 protons
72
c. an atom with 1 electron
1
d. an atom with 6 neutrons and a mass number of 12
12-6=6