Quantitative Chemistry

Question 1

What does the Law of Conservation of Mass state?

Answer 1

No matter is lost or gained during a chemical reaction.

Question 2

In a balanced chemical equation, what must be true about the mass of reactants and products?

Answer 2

The total mass of the reactants is equal to the total mass of the products.

Question 3

What is a precipitation reaction?

Answer 3

A reaction in which two solutions react to form an insoluble solid called a precipitate.

Question 4

What happens to the mass of a reaction flask if a gaseous product escapes?

Answer 4

The total mass of the reaction flask will change as product mass is lost.

Question 5

True or False: The total amount of matter before and after a reaction is the same.

Answer 5

True

Question 6

If there is no subscript number after an element in a chemical formula, what does it signify?

Answer 6

There must be one of that particular element.

Question 7

What does a subscript number after brackets indicate in a chemical formula?

Answer 7

That number belongs to all the elements inside the bracket.

Question 8

Which non-metals must be written as molecules?

Answer 8

• H2
• N2
• O2
• F2
• Cl2
• Br2
• I2

Question 9

How do you balance a chemical equation?

Answer 9

Ensure the same number of atoms of each element on both sides of the equation.

Question 10

What is the relative atomic mass symbol?

Answer 10

Ar

Question 11

What does the symbol Mr refer to?

Answer 11

The total mass of the molecule.

Question 12

How do you calculate the relative formula mass (Mr) of a substance?

Answer 12

Add up the relative atomic masses of all the atoms present in the formula.

Question 13

What is the formula to calculate the percentage by mass of an element in a compound?

Answer 13

% mass of an element = (r × number of atoms of the element) / Mr of the compound × 100

Question 14

What is the equation for percentage composition?

Answer 14

Percentage Composition = (total mass of element / mass of compound total) × 100

Question 15

True or False: The total mass of a reaction flask will decrease if a gaseous product escapes.

Answer 15

True

Question 16

What happens to the mass of the reaction flask when a metal reacts with oxygen?

Answer 16

The mass of the oxide produced is greater than the mass of the metal you started with.

Question 17

What is produced when metal carbonates thermally decompose?

Answer 17

Carbon dioxide gas

Question 18

What type of error occurs due to faulty experimental procedures?

Answer 18

Systematic errors

Question 19

What is the difference between random errors and systematic errors?

Answer 19

Random errors vary in direction, while systematic errors always pull results in the same direction.

Question 20

What is the uncertainty for a thermometer that reads to 1°C?

Answer 20

+0.5°C

Question 21

How is uncertainty calculated for digital instruments?

Answer 21

The uncertainty is taken as the smallest division on the scale.

Question 22

What is the uncertainty for an electronic balance that reads to 0.01 g?

Answer 22

+0.01 g

Question 23

How can uncertainty in results be estimated from repeated experiments?

Answer 23

Uncertainty is ± half of the range of results.

Question 24

Fill in the blank: Uncertainty can arise from __________ judgment of the experimenter.

Answer 24

subjective

Question 25

What is a common source of uncertainty in titration experiments?

Answer 25

Judging the end point by looking at the color of the indicator.

Question 26

What should be done when uncertainties are difficult to quantify?

Answer 26

Comment on them as a source of error in an evaluation.

Question 27

What is the mole and its symbol?

Answer 27

The mole, symbol mol, is the SI unit of amount of substance.

Question 28

How many particles are in one mole of a substance?

Answer 28

One mole contains 6.02 x 10^23 particles, known as the Avogadro Constant.

Question 29

What does one mole of sodium (Na) contain?

Answer 29

One mole of sodium contains 6.02 x 10^23 atoms of sodium.

Question 30

What does one mole of hydrogen (H2) contain?

Answer 30

One mole of hydrogen contains 6.02 x 10^23 molecules of hydrogen.

Question 31

What is the mass of 1 mole of a substance called?

Answer 31

The mass of 1 mole of a substance is known as the molar mass.

Question 32

How is the molar mass of an element determined?

Answer 32

For an element, it is the same as the relative atomic mass written in grams.

Question 33

How is the molar mass of a compound determined?

Answer 33

For a compound, it is the same as the relative molecular or formula mass in grams.

Question 34

What is the formula for converting between moles, mass, and molar mass?

Answer 34

The formula is: Moles = Mass / Molar Mass.

Question 35

What can chemical/symbol equations be used to calculate?

Answer 35

They can be used to calculate the moles and mass of reactants and products.

Question 36

What is the process to balance a chemical equation using masses?

Answer 36

Convert masses to moles, find the molar ratios, and then write the balanced equation.

Question 37

True or False: One mole of any element is equal to the relative atomic mass of that element in grams.

Answer 37

True.

Question 38

Fill in the blank: The mass of a substance can be calculated using the formula _______.

Answer 38

Mass = Moles x Molar Mass.

Question 39

What do you need to do if the resulting numbers from mole calculations are uneven?

Answer 39

Multiply all of the numbers by the same number to find the smallest whole number for the coefficients.

Question 40

How do you calculate the number of moles for an element?

Answer 40

Divide the mass of each element by its relative atomic mass (Ar) ## Footnote For example, for hydrogen: 10 g / Ar(H) = 10.

Question 41

What is a limiting reactant?

Answer 41

The reactant that is used up first in a reaction, limiting the amount of product formed.

Question 42

What happens to the reaction when the limiting reactant is completely used up?

Answer 42

The reaction cannot continue.

Question 43

What is a solute?

Answer 43

A solid substance that dissolves in a liquid.

Question 44

What is a solvent?

Answer 44

The liquid in which a solute dissolves to form a solution.

Question 45

What does concentration refer to?

Answer 45

The amount of solute in a specific volume of solvent.

Question 46

What is the formula for calculating concentration?

Answer 46

Concentration (g/dm³) = mass of solute (g) / volume of solution (dm³)

Question 47

1 dm³ is equivalent to how many cm³?

Answer 47

1000 cm³

Question 48

How do you convert from cm³ to dm³?

Answer 48

Divide by 1000.

Question 49

How do you convert from dm³ to cm³?

Answer 49

Multiply by 1000.

Question 50

What is yield in the context of a chemical reaction?

Answer 50

Yield is the term used to describe the amount of product you get from a reaction.

Question 51

Why is it rare to achieve 100% yield in a chemical process?

Answer 51

* Some reactants may be left behind in the equipment * The reaction may be reversible * Products may be lost during separation and purification * Side reactions may occur * Products can be lost during transfer

Question 52

What is the difference between actual yield and theoretical yield?

Answer 52

* Actual yield: recorded amount of product obtained * Theoretical yield: amount of product that would be obtained under perfect conditions

Question 53

What does the percentage yield compare?

Answer 53

The percentage yield compares the actual yield to the theoretical yield.

Question 54

What is the equation to calculate percentage yield?

Answer 54

percentage yield = (actual yield / theoretical yield) × 100

Question 55

If a student prepared 1.6 g of copper(II) sulfate while the theoretical yield is 2.0 g, what is the percentage yield?

Answer 55

Percentage yield = 80%

Question 56

What are the steps to calculate theoretical masses of products?

Answer 56

* Write out the balanced equation * Convert the given mass of reactant(s) into moles * Use the coefficients in the equation to deduce moles of product(s) * Convert moles of product into mass

Question 57

In the reaction Zn + CuSO4 → Cu + ZnSO4, if 6.5 g of zinc is added, how many moles of zinc does it yield?

Answer 57

0.1 mol

Question 58

What is the maximum mass of copper that could be formed from 0.1 moles of zinc?

Answer 58

6.35 g

Question 59

What is atom economy?

Answer 59

Atom economy studies the amount of reactants that get turned into useful products.

Question 60

What is the formula for calculating atom economy?

Answer 60

Atom economy = (total Mr of desired product / total Mr of all reactants) × 100

Question 61

Calculate the atom economy for the reaction CH4 + H2O → CO + 3H2.

Answer 61

17.6%

Question 62

What factors should companies consider when choosing a reaction pathway?

Answer 62

* Atom economy * Percentage yield * Rates of reaction * Equilibrium position

Question 63

True or False: High percentage yields and fast reaction rates are desirable attributes in industrial chemical processes.

Answer 63

True

Question 64

What can improve the atom economy of a reaction?

Answer 64

Selling or reusing waste products.

Question 65

Fill in the blank: The actual yield and percentage yield can only be determined by _______.

Answer 65

[experiment]

Question 66

What is one common error when calculating percentage yield?

Answer 66

Dividing the theoretical yield by the actual yield instead of the other way around.