2.1 a/b: Module 2: Quantitative Relationships in Chemistry

Module 2: Quantitative Relationships in Chemistry

Year 11

Syllabus dot points

• 2.1 a/b

  conduct practical investigations to observe and measure the quantitative relationships of chemical reactions, including but not limited to: – masses of solids and/or liquids in chemical reactions – volumes of gases in chemical reactions (ACSCH046)

  relate stoichiometry to the law of conservation of mass in chemical reactions by investigating: – balancing chemical equations (ACSCH039) – solving problems regarding mass changes in chemical reactions (ACSCH046)

What we will cover

• Module 2 overview

• ​law of conservation of mass

• ​balancing chemical equations

• relative atomic mass ​

• ​relative molecular weight

Module 2 Overview ​

• numbers in chemical reactions

• ​law of conservation of mass

• ​the mole - quantitatively discussing reactions - why things react the way they do

• ​concentration

• gas laws ​

Open Ended

In your own words, what is the Law of Conservation of Mass?

​Law of Conservation of Mass

​Matter cannot be created or destroyed, merely changed from one form to another.

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​In any chemical reaction, mass is conserved, meaning:

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mass of reactants = mass of products ​

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Meaning that in a chemical equation, it must be balanced. I.e. the same amount and types of atoms on the reactants and products ​

​Chemical Equation

Write out the formula (after forming them through ionic and covalent rules), then determine the coefficients through balancing the equation. ​

Multiple Choice

What is the total number of atoms present in 5Na₃PO₄?

• 5

• 55

• 40

• 8

Multiple Choice

Is the following equation balanced?

Al + O₂ ---> 2Al₂O₃

• YES

• NO

Multiple Choice

Balance this equation:

H₂ + Cl₂ ---> HCl

• It is balanced.

• H₂ + Cl₂ ---> 2HCl

• 3H₂ + Cl₂ ---> 6HCl

• H₂ + 3Cl₂ ---> 6HCl

Multiple Choice

Balance the following equation:

___ H₂+ ___ O₂→___ H₂O

• 1, 1, 3

• 2, 2, 2

• 1, 2, 1

• 2,1, 2

​Relative Atomic Mass

The mass of an atom is a useful way to differentiate between elements, however, they are so small it is too difficult to measure. So we use a relative scale instead to determine relative atomic mass (that we see on the Periodic Table). ​

​Chemists determined this in relation to a carbon-12 atom.

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The number on the PT is an average atomic mass, because it takes into account the existence of isotopes. ​

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​Relative Molecular Weight

A measure (still not the exact mass) of a molecule, using the relative atomic mass on the PT. ​

​Sometimes called relative formula mass, molar mass etc. All using the same procedure.

Fill in the Blank

What is the relative molecular mass of H₂O?

Fill in the Blank

What is the relative molecular mass of ammonium sulfate, (NH₄)₂SO₄?

Next up​

• The mole concept

• Calculations involving the mole ​

• percentage composition and determining empirical formula ​