Unit 3: Quantities in Chemical Reactions

Question 1

What unit is used to each type of compound in reference to number of moles?

a) Ionic
b) Covalent
c) Pure Elements

Answer 1

a) Formula Units
b) Molecules
c) Atoms

Question 2

What is the shortened number for the mol?

Answer 2

6.02 X 10²³

Question 3

What is the symbol for Avagadros Number?

Answer 3

N_A

Question 4

What is the equation for finding number of mols?

Answer 4

m

n= __

M

OR

formula units

n= _________

N_A

Question 5

What is the:

a) Coefficient
b) Base
c) Exponent

Answer 5

a) The number before the multiplication sign

5.67 X 10⁵

b) The number before the exponent (Always 10)
5. 67 X 10⁵
c) The small number above the base
5. 67 X 10⁵

Question 6

What 3 things must be true for a scientific notation to be correct?

Answer 6

1) The coefficient must be greater than or equal to 1 and less than 10
2) The base must be 10
3) The exponent must show the number of decimal places that the decimal need to be moved

Question 7

Which direction are postive and negative exponents moving?

Answer 7

Postive: Moving left

Example: 4321. → 4.321

4.321 X 10³

Negative: Moving right

Example: 0.25 → 2.5

2.5 X 10^-1

*HINT*

If original number was less than 1= -

If the original number was greater than 1= +

Question 8

What are the 5 Significant Digit rules

Answer 8

1) All digits that are not zero are significant

Example: 16.2 (3 Sig Digs)

2) Zeros between non zero digits are significant

Example: 103 (3 Sig Digs)

3) Zeros to the left of the first non zero digit are not significant. They only show placement of the decimal point

Example: 0.02 (1 Sig Dig)

4) Zeros to the right of a decimal point are significant if they are at the end of a number

Example: 16.0 (3 Sig Digs)

5) When a number ends in a zero or zeros that are not to the right of a decimal point, the ending zero may or may not be significant

Example:

160. (3 Sig Digs) OR 160 (2 Sig Digs)

Question 9

What are the 3 steps to add or subtract significant digits?

Answer 9

Step 1) Line up decimal numbers and add and subtract as normal

Step 2) Find the number in your adding or subtracting with the least number of sig digs after the decimal place

Step 3) Your answer should have the same number of sig digs to the right of the decimal as well.

Question 10

What are the 3 steps to multiply and divide sig digs?

Answer 10

Step 1) Multiply or divide the given values as normal

Step 2) Look at the number you multiplied or divided with the LEAST NUMBER OF TOTAL SIG DIGS

Step 3) Your answer should have the same number of total sig digs

Question 11

What are the 5 steps to calculate Molar Mass?

Answer 11

Step 1) Write MCompound Name =

M_H2O=

Step 2) Write the number of atoms as the coefficient of each element in brackets with “M” infront

M_H2O= [2( M_H) + (M_O)]

Step 3) Ensure to inculde units at the end g/mol!

M_H2O= [2( M_H) + (M_O)] g/mol

Step 4) Mutiply and add

18

Step 5) Write your final answer with units!

18 g/mol

Question 12

What is the equation to find Molar Mass?

Answer 12

m

M= ____

n

Question 13

What is the general formula for Percent Composition?

Answer 13

part

percent composition= ___________ X 100

whole

Question 14

What are the 3 steps to determine the Limiting Reagent?

Answer 14

6 PCl₃ + 6Cl₂ + P₄O₁₀ → 10POCl₃

Step 1) Use Stoicheometry to determine the number of moles of each compount in your reaction

7.27 mol : 14.1 mol : 3.53 mol

Step 2) Take each number of moles and divide it by the number of mols in your equation (Co-effcients)

7.27/ 6 : 14.1/6 : 3.52/1

Step 3) The smallest number calculated is the limiting and the rest are excess

1.21 : 2.35 : 3.52

Question 15

What is the general formula for percentage yield?

Answer 15

actual yield

percentage yield= ___________ X100%

theoretical yield