Chapter 3 4th meetings

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Multiple Choice

Let's recall!

which one of these are the limiting reagent?

• bread 🍞

• cheese 🧀

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The actual number of each atoms present in a molecule.

​Molecular formula

The simplest-whole number-ratio of:
The atoms present in one molecule.

​Empirical formula

Draw

Determine the empirical formula of:

a. hydrazine = N₂H₄

b. octane = C₈H₁₈

c. benzene = C₆H₆

d. ammonia = NH₃

The empirical formula can be found by determining the mass of each element present in a sample of the compound

​Calculating EF part 1

Determine the empirical formula of a compound that contains 10 g carbon and 80 g of hydrogen.

Elements	Hydrogen	Oxygen
Mass of each element (g)	10	80
Atomic mass (Ar)	1.0	16.0
Moles = mass / Ar	10/1.0=10	80/16.0=5
Ratio (divide by smallest value)	10/5 = 2	5/5 = 1

​So, the empirical formula of the compound is H₂O

Draw

Experimental results show that a compound contains 248.46 g Sn and 19.54 g N. What is the empirical formula of this compound?

(Ar Sn = 118.71, N = 14.01)

Draw

Experimental results show that a compound contains 30.74 g Cu and 2.26 g N. What is the empirical formula of this compound?

(Ar Cu = 63.55 , N = 14.01)

The empirical formula can be found by determining the percentage of each element present in a sample of the compound

​Calculating EF part 2

Determine the empirical formula of a compound that contains 85.7% carbon and 14.3% hydrogen!

Elements	Carbon	Hydrogen
Mass of each element (%)	85.7	14.3
Atomic mass (Ar)	12.0	1.0
Moles = mass / Ar	85.7/12.0 = 7.14	14.3/1.0 = 14.3
Ratio (divide by smallest value)	7.14 / 7.14 = 1	14.3 / 7.14 = 2

​So, the empirical formula of the compound is CH₂

Draw

What is the empirical formula of a compound that is 40.20% Li and 59.80% P?

(Ar Li = 6.94 , P = 30.97)

Draw

What is the empirical formula of a compound that is 41.29% Cd and 58.71% Br?

(Ar Cd = 112.41, Br = 79.90)

​Calculating Molecular Formula

Reorder

Reorder the step to do this worked example!

The empirical formula of X is C₄H₁₀S and the relative formula mass (Mr) of X is 180.

What is the molecular formula of X?

(Ar C : 12, H : 1, S : 32)

1

2

3

• 1
• 2
• 3

Draw

The empirical formulae and molar masses of three compounds, A, B and C, are shown in Table.

Calculate the molecular formula of each of these compounds.

​Cation

Anion

​Ions that contain more than one type of atoms are called, compound ions.
Here is some common compound ions and 2 metal ions that we should learn:

Match

Match the Ion and the formula!

• Zinc

• sulfate

• nitrate

• carbonate

• ammonium

Zn²⁺

SO₄^2-

NO₃^-

CO₃^2-

NH₄⁺

• Zn²⁺

• SO₄^2-

• NO₃^-

• CO₃^2-

• NH₄⁺

• Formula of Covalent Compounds:

  • You can determine the formula of a covalent compound from the number of electrons needed to achieve the stable electronic configuration of a noble gas.

• General Rules for Covalent Bonding:

  • Carbon atoms (C): Form four bonds with other atoms.

  • Hydrogen atoms (H) & Halogen atoms (e.g., F, Cl, Br, I): Form one bond.

  • Oxygen atoms (O): Form two bonds.

  • Examples:

    • Water (H₂​O): Follows these rules, with H forming one bond and O forming two bonds.

    • Methane (CH₄​): Each carbon atom bonds with four hydrogen atoms.

• Note: There are many exceptions to these rules.

• Ionic compound made from atoms that do "give n take" of e^-

• Covalent compound made from atoms that do "sharing" of e^-

• All the atoms gather and make compound to reach the stability (8e^-)

​!

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Click here to do some balancing chemical equation

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