Stoichiometry

Question 0

What is an excess reagent?

Answer 0

The reagent that is present in larger quantities than necessary

Question 1

What is a limiting reagent?

Answer 1

The reactant that determines how much product can be formed

Question 2

What is predicted or theoretical yield?

Answer 2

The expected amount of product

Question 3

What is experimental or actual yields?

Answer 3

The quantity of the product actually obtained

Question 4

How likely is it for the predicted and experimental yields to be the same?

Answer 4

Extremely rare

Question 5

How do you do calculations for limited and excess reagents?

Answer 5

1. Calculate the moles of each reactant
2. Divide the moles of that reactant by its coefficient
3. The lower number is the limiting reagent
4. Use this as moles given

Question 6

What factors affect experimental yields?

Answer 6

1. Competing reactions
2. Reaction is very slow
3. Collection and transfer methods
4. Reactant or product purity
5. Reaction doesn’t go to completion

Question 7

What are competing reactions?

Answer 7

When two chemicals react to give different products

Question 8

What is an ideal percent yield?

Answer 8

As close to 100% as possible

Question 9

How is percent yield calculated?

Answer 9

%yield = (actual yield/predicted yield) x 100

Question 10

When the percent error is closer to zero, is it better or worse?

Answer 10

Better

Question 11

How do you calculate percent error?

Answer 11

%error=(actual-predicted)/predicted x 100

Question 12

What is a titration?

Answer 12

A procedure used to find the volume of substances so you can calculate the concentration

Question 13

What is standardization?

Answer 13

When a solution of known concentration, a standard solution, is reacted with a solution of unknown concentration

Question 14

What types of chemicals need to be standardized and why?

Answer 14

Strong acids and strong bases because their concentrations will change over time

Question 15

What is a titrant?

Answer 15

A solution that is transferred from a precisely marked tube called a burette to a flask containing the sample and an indicator

Question 16

Why is an indicator used?

Answer 16

Because a sudden change in color indicates the completion of the reaction

Question 17

What is the endpoint?

Answer 17

The point where the titrant reacts completely with the sample

Question 18

What is the equivalence point?

Answer 18

The volume needed to reach the endpoint

Question 19

What is a pH titration curve?

Answer 19

A plot of the pH versus the volume of titrant added

Question 20

How are titration curves shaped?

Answer 20

They are S-shaped

Question 21

What happens when a strong monoprotic acid is titrated with a strong monoprotic base?

Answer 21

The equivalence point will always have a pH of seven at 25°C

Question 22

What does the first point on the curve indicate?

Answer 22

The pH of the sample

Question 23

What is the buffer region

Answer 23

The pH changes very gradually at first

Question 24

What happens to the rate of change as the point is approached?

Answer 24

The pH changes very rapidly

Question 25

What is stoichiometry?

Answer 25

The study of the relative quantities of reactants and products in a chemical reaction

Question 26

How do you find the moles of a substance when given the moles of another substance in the chemical reaction

Answer 26

NW = NG x W/G

Question 27

What does gravimetric mean?

Answer 27

Mass measurements

Question 28

How do you find moles using mass and molar mass?

Answer 28

n = m/M

Question 29

When can you use the law of combining volumes?

Answer 29

When the pressure and temperature conditions are constant for both the reactants and products

Question 30

What is the ideal gas law?

Answer 30

PV = nRT