Mid-term Examination review
Observation - is information collected through the five senses. Inference - an interpretation or explanation of an observation. Physical change - occur when objects undergo a change that does not change their chemical nature. Involves a change in physical properties Examples of physical properties include: texture, shape, size, color, odor, volume, mass, weight, and density Chemical Change - substances are changed chemically and display different chemical properties after the change. * A chemical change is irreversible. Law of Conservation of Mass - In a chemical reaction, the mass of the products equals the mass of the reactants. (what you start with is what you will end with). Reactants - the starting substances in a chemical reaction
Products - the substances that are formed after a reaction.
Accuracy - The measure of how close a measurement comes to the actual or true value of whatever is measured.
Precision - The measure of how close a series of measurements are to one another. Matter – anything that takes up space and has mass.
Standard temperature and pressure = 0° Celsius at 1 atmosphere of pressure. Atmosphere is a unit for measuring pressure
Avogadro’s number = 6.02 x 1023
volume of 1 mol of any gas at STP = 22.4 L
Ion- atoms or groups of atoms that have a positive or negative charge Anion- negatively charged ion
Cation- positively charged ion
Molecules- small, electrically neutral “units”; maintain the properties of that substance Formula unit- the lowest whole number ratio of ions in an ionic compound Products are on the right side of the yield sign
Reactants are on the left side of the yield sign
Coefficients are the whole numbers that we place in front of a substance to balance an equation.
We correctly write the Nobel gases (such as oxygen and chlorine) with a 2 subscript (Cl2 02)
A precipitate is a solid that forms during a double replacement reaction.
The laws of conservation of matter and the law of conservation of energy state that no matter or energy can be created or destroyed.
The activity series is used when solving single-replacement reactions and tells you which elements will take the place of another. The higher element takes place of the lower element.
When balancing a chemical equation, always balance metals first.
When balancing a chemical equation you change the coefficient of the substance.
The state of an element in an equation may be given with a symbol. These symbols include;
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous
Only during combination reactions do we have a single product.
To find Density
D = Mass – Volume
To find Mass
M = D x V
To find Volume
V = M - D
Percent Error = / experimental value – accepted value / X 100 accepted value
Remember, the experimental value is what someone finds out after doing an experiment. The accepted value is what is supposed to happen. When you subtract the experimental value minus the accepted value, you will always end with a positive number because it is the absolute value.
If a decimal point is present – Start at the furthest left of the number and move right until you hit the first non-zero number. That number and all the rest of the numbers to the right (including zeros) of the first one are counted as significant figures.
Example: 8.6010 – there are 5 sig. Figs. (8,6,0,1,0)
If a decimal point is not present – Start at the furthest right of the number and move left until you hit the first non-zero number. That number and all the rest of the numbers to the left (including zeros) of the first one are counted as significant figures.
Example: 430001000 – there are 6 sig. Figs (4,3,0,0,0,1)
Many elements found in nature exist as compounds
2 main types of compounds:
Properties of Compounds
Molecular (Covalent) Compounds
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