Honors - Unit 4 - Chemical Quantities

Question 1

Empirical Formula

Answer 1

Empirical Formula - A formula that gives the simplest whole-number ratio of atoms in a compound.

Question 2

Dimensional Analysis

Answer 2

A method of mathmatical analysis which involves converting between units.

Question 3

Percent Composition

Answer 3

The amount of a given element in a compound.

Question 4

Scientific Notation

Answer 4

A way of expressing really large or really small numbers.

Question 5

Negative Exponents in Scientific Notation

Answer 5

Negative Exponents in Scientific Notation mean you should move the decimal to the left to change the number to standard notation.

Question 6

Turning Standard Notation into Scientific Notation

Answer 6

If the number is greater than 1, the exponent will be positive.

If the number is less than 1, the exponent will be negative.

Question 7

The Mole

Answer 7

A unit of measure.

1 mole = the atomic mass of an element

and

1 mole = 6.02 E23 atoms, particles, molecules, units, etc.

Question 8

Positive Exponents in Scientific Notation

Answer 8

Postive Exponents mean move the decimal to the right when changing a number to standard notation.

Question 9

Significant Figures

Answer 9

All the digits in a measurement that are known with certainty plus a last digit that must be estimated.

Question 10

Rules for Multiplying and Dividing with Significant Figures

Answer 10

The result has the same number of significant figures as the factor with the fewest significant figures.

Question 11

Rules for Adding and Subtracting with Significant Figures

Answer 11

The result has the same number of decimal places as the number with the fewest decimal places.

Question 12

How many atoms are in 2.7 moles of iron?

Answer 12

2.7 moles Fe x (6.02x10²³ atoms Fe/1 mole Fe) =

1.6 x 10²⁴atoms Fe

Question 13

How many moles are in 3.67 x 10²⁴ molecules of SO₂?

Answer 13

3. 67 x 10²⁴ molecules SO₂ x (1 mole SO₂/6.02x10²³ molecules SO₂)=
4. 10 moles SO₂

Question 14

9.08 g of Al₂0₃ is equal to how many moles?

Answer 14

9.08 g Al₂0₃ x (1 mole Al₂0₃/101.96 g Al₂0₃) = 0.0890 moles Al₂0₃

Question 15

What mass of copper (II) sulfide is equal to 4.79 x 10²² atoms?

Answer 15

4. 79 x 10²² atoms CuS x (1 mole CuS/6.02x10²³ atoms CuS) x (95.61 g CuS/1 mole CuS) =
5. 61 g CuS

Question 16

What is the percent composition of oxygen in CuSO₄?

Answer 16

mass of CuSO₄= 63.546 + 32.065 + 4(15.999) = 159.7 grams

Mass of oxygen = 4(15.999) = 64 grams

(64/159.7) x (100%) = 40.1. %O

Question 17

A compound contains 21.6 g of silver and 3.21 g of sulfur, what is the percent composition?

Answer 17

21.6/(21.6+3.21) = 87.1% Ag

3.21/(21.6+3.21) = 12.9%S

Question 18

Scientific Notation Example

Answer 18

Scientific notation (exponential notation) represents very large or very small numbers as powers of ten.

Question 19

To convert a number greater than 1 to scientific notation?

Answer 19

The original decimal point is moved n places to the left, and the resulting number is multiplied by 10^n.

Question 20

To convert a number less than 1 to scientific notation?

Answer 20

the original decimal point is moved n places to the right, and the resulting number is multiplied by 10^-n.

Question 21

Significant Figure Rules for Addition and Subtraction:?

Answer 21

The answer of a calculation based on measurements cannot have greater significance than any of the measurements that produced the answer.

The least certain measurement (fewest decimal places) limits the certainty of the calculated answer.

*Line up the decimal points and report the answer based upon the fewest decimal places.

Question 22

Significant Figure Rules for Multiplication and Division:?

Answer 22

The calculated answer can be no more precise than the least precise number from which the answer is derived.
The least precise number is the one with the fewest sig figs.

Question 23

Rules for Rounding Off Numbers?

Answer 23

1. When the leftmost number removed is less than 5, the preceding number is left unchanged.
   Ex: Round 45.2624 to four significant digits: 45.26

2. When the leftmost digit removed is 5 or greater, the
   preceding number is increased by 1.
   Ex: Round 3.75 to two significant figures: 3.8

Question 24

Rules for Significant Figures?

Answer 24

1) ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant.

2) LEADING zeroes are NEVER significant
3) Zeroes CAPTURED between non-zero numbers are ALWAYS significant.
4) TRAILING zeroes without a decimal are NEVER significant
5) TRAILING zeroes with a decimal are ALWAYS significant.
6) When using SCIENTIFIC NOTATION all digits in front of “x 10‾³” or “E-3” are ALWAYS significant

Question 25

Subscripts

Answer 25

Small numbers to the lower right of chemical symbols. Represent the number of atoms of each element in a molecule.

0₂

Question 26

Coefficients

Answer 26

The large numbers in front of chemical formulas. Represent the number of molecules of the substance in the reaction.

2Cl

Question 27

Diatomic Molecule

Answer 27

If these elements appear by themselves in an equation, the must be in pairs with the subscript 2.

Question 28

Scientific Notation in TI-84 and class calculators

Answer 28

(Number) 2nd EE (Exponent)

Hint: negative button is not the minus button

Question 29

What do significant figures show?

Answer 29

Precision

Question 30

Are digits 1-9 “significant” or “not significant”?

Answer 30

Significant

Question 31

Are zeros between significant digits “significant” or “not significant”?

Answer 31

Significant

Question 32

Are zeros before significant digits “significant” or “not significant”?

Answer 32

Not Significant

Question 33

Are zeros after a decimal and after a significant digit “significant” or “not significant”?

Answer 33

Significant

Question 34

When adding and subtracting with Significant Figures, ___________________.

Answer 34

keep the least number of decimal places

Question 35

When multiplying and dividing with Significant Figures, ___________________.

Answer 35

round to least number of sig figs

Question 36

Are zeros after a decimal and before a significant digit “significant” or “not significant”?

Answer 36

Not Significant

Question 37

Convert the following into standard notation:
4.386 x 10⁷

Answer 37

43,860,000

Question 38

Convert the following into standard notation:
4.39 E-7

Answer 38

0.000000439

Question 39

Convert the following into standard notation:
3.7 x 10⁻⁵

Answer 39

0.000037

Question 40

Steps for finding Empirical Formula from percent composition

Answer 40

Question 41

Answer 41