Chem Fall Midterm Exam 1st Sem

Question 1

Pure substance

Answer 1

Substance that can only be broken down chemically

Question 2

Element

Answer 2

Pure substance consisting of one type of Atom

Question 3

Compound

Answer 3

Two or more atoms chemically bound together

Question 4

Mixture

Answer 4

Two or more pure substances that can be separated, physically

Question 5

Homogenous

Answer 5

Consistent throughout

Question 6

Heterogeneous

Answer 6

Different throughout

Question 7

Scientific notation

Answer 7

x10-e: og placement moved from left to right (made bigger)
x10e: og placement from right to left (made smaller)

Question 8

Significant figure rules

Answer 8

1. All non-zero numbers ARE significant. The number 33.2 has THREE significant figures because all of the digits present are non-zero.
2. Zeros between two non-zero digits ARE significant. 2051 has FOUR significant figures. The zero is between a 2 and a 5.
3. Leading zeros are NOT significant. They’re nothing more than “place holders.” The number 0.54 has only TWO significant figures. 0.0032 also has TWO significant figures. All of the zeros are leading.
4. Trailing zeros to the right of the decimal ARE significant. There are FOUR significant figures in 92.00.

92.00 is different from 92: a scientist who measures 92.00 milliliters knows his value to the nearest 1/100th milliliter; meanwhile his colleague who measured 92 milliliters only knows his value to the nearest 1 milliliter. It’s important to understand that “zero” does not mean “nothing.” Zero denotes actual information, just like any other number. You cannot tag on zeros that aren’t certain to belong there.

5. Trailing zeros in a whole number with the decimal shown ARE significant. Placing a decimal at the end of a number is usually not done. By convention, however, this decimal indicates a significant zero. For example, “540.” indicates that the trailing zero IS significant; there are THREE significant figures in this value.
6. Trailing zeros in a whole number with no decimal shown are NOT significant. Writing just “540” indicates that the zero is NOT significant, and there are only TWO significant figures in this value.
7. Exact numbers have an INFINITE number of significant figures. This rule applies to numbers that are definitions. For example, 1 meter = 1.00 meters = 1.0000 meters =
   1.0000000000000000000 meters, etc.

So now back to the example posed in the Rounding Tutorial: Round 1000.3 to four significant figures. 1000.3 has five significant figures (the zeros are between non-zero digits 1 and 3, so by rule 2 above, they are significant.) We need to drop the final 3, and since 3 < 5, we leave the last zero alone. so 1000. is our four-significant-figure answer. (from rules 5 and 6, we see that in order for the trailing zeros to “count” as significant, they must be followed by a decimal. Writing just “1000” would give us only one significant figure.)

8. For a number in scientific notation: N x 10x, all digits comprising N ARE significant by the first 6 rules; “10” and “x” are NOT significant. 5.02 x 104 has THREE significant figures: “5.02.” “10 and “4” are not significant.

Question 9

Mass, density, volume formula

Answer 9

M=DxV
D=M/V
V=M/D

Question 10

Percent error

Answer 10

(Theoretical-actual)/actual x100

Question 11

Bohr model

Answer 11

Orbit 1: 2 electrons
Orbit 2: 8 electrons
Orbit 3: 8 electrons

Question 12

Q=MCT2-T1

Answer 12

Q: heat energy (joules/calories)
M:mass (kg/g)
C:specific heat (cal/gc)
T2-T1:change in temperature (c/*f)

Question 13

Endothermic reaction

Answer 13

Energy is absorbed, cold to the touch

Question 14

Exothermic reaction

Answer 14

Energy leaves/exits, warm to touch

Question 15

Ion

Answer 15

Different number of electrons (atom with charge)

Question 16

Cation

Answer 16

Positive, gives up electrons

Question 17

Anion

Answer 17

Negative, accepts electrons

Question 18

Valance electrons

Answer 18

Electrons farthest away from nucleus

Question 19

Transition metal

Answer 19

Metallic elements (central blocks), shows variable variance

Question 20

Polyatomic ion

Answer 20

Groups of atoms Covalently bonded together, but the group of atoms as a whole has a charge

Question 21

Do alkali metals gain or lose electrons

Answer 21

Gain

Question 22

Do you halogens gain or lose electrons?

Answer 22

Lose

Question 23

What happens in an alpha decay?

Answer 23

Atomic mass loses four, atomic number loses two

Question 24

What happens in beta decay?

Answer 24

Atomic number gains one

Question 25

Atomic radius

Answer 25

Total distance from Atoms nucleus to outer most orbital of electron. Increases down and to the left.

Question 26

Ionization energy

Answer 26

Energy required to remove an electron from an atom or anion, Increases up into the right

Question 27

Electronegativity

Answer 27

Ability of Adam to attract electrons. Increases up into the right.