Introducing chemical reactions (C3.1) | OCR GCSE Combined Science A (Gateway Science) — Chemistry — Higher (J250)

C3.1 Introducing chemical reactions

Summary A chemical equation represents, in symbolic terms, the overall change in a chemical reaction. New materials are formed through chemical reactions but mass will be conserved. This can be explained by a model involving the rearrangement of atoms. Avogadro gave us a system of measuring the amount of a substance in moles. Underlying knowledge and understanding Learners should be familiar with chemical symbols and formulae for elements and compounds. They should also be familiar with representing chemical reactions using formulae and equations. Learners will have knowledge of conservation of mass, changes of state and chemical reactions.

Common misconceptions Although learners may have met the conservation of mass they still tend to refer to chemical reactions as losing mass. They understand that mass is conserved but not the number or species of atoms. They may think that the original substance vanishes ‘completely and forever’ in a chemical reaction.

Reference	Mathematical learning outcomes	Maths skills
$CM3.1i$	$arithmetic computation and ratio when determining empirical formulae, balancing equations$	$M1a, M1c$

Learning outcomes	To include	Maths	Working scientifically
$C3.1a use chemical symbols to write the formulae of elements and simple covalent and ionic compounds$		$M1a, M1c$	$WS1.4a$
$C3.1b use the names and symbols of common elements and compounds and the principle of conservation of mass to write formulae and balanced chemical equations and half equations$		$M1a, M1c$	$WS1.4c$
$C3.1c use the names and symbols of common elements from a supplied Periodic Table to write formulae and balanced chemical equations where appropriate$	$the first 20 elements, Groups 1, 7, and 0 and other common elements included within the specification$
$C3.1d use the formula of common ions to deduce the formula of a compound$		$M1a, M1c$
$C3.1e construct balanced ionic equations$		$M1a, M1c$
$C3.1f describe the physical states of products and reactants using state symbols (s, l, g and aq)$
$C3.1g describe tests to identify selected gases$	$oxygen, hydrogen, carbon dioxide and chlorine$
$C3.1h recall and use the definitions of the Avogadro constant (in standard form) and of the mole$	$the calculation of the mass of one atom/molecule In recognition of IUPAC’s review, we will accept both the classical (carbon-12 based) and revised (Avogadro constant based) definitions of the mole in examinations from June 2018 onwards (see https://iupac.org/ new-definition-mole-arrived/)$	$M1b, M1c$	$WS1.4b, WS1.4c, WS1.4d, WS1.4f$
$C3.1i explain how the mass of a given substance is related to the amount of that substance in moles and vice versa$		$M1c, M2a$	$WS1.4b, WS1.4c$
$C3.1j explain how the mass of a solute and the volume of the solution is related to the concentration of the solution$		$M1b, M1c$	$WS1.3c, WS1.4a, WS1.4c$
$C3.1k recall and use the law of conservation of mass$			$WS1.4c$
$C3.1l explain any observed changes in mass in non- enclosed systems during a chemical reaction and explain them using the particle model$			$WS1.1b, WS1.4c$
$C3.1m deduce the stoichiometry of an equation from the masses of reactants and products and explain the effect of a limiting quantity of a reactant$		$M1c$	$WS1.3c, WS1.4c, WS1.4d, WS1.4f$
$C3.1n use a balanced equation to calculate masses of reactants or products$		$M1c$	$WS1.3c, WS1.4c$

Learning outcomes

To include

Maths

Working scientifically

Practical suggestions

C3.1a use chemical symbols to write the formulae of elements and simple covalent and ionic compounds

M1a, M1c

WS1.4a

C3.1b use the names and symbols of common elements and compounds and the principle of conservation of mass to write formulae and balanced chemical equations and half equations

M1a, M1c

WS1.4c

C3.1c use the names and symbols of common elements from a supplied Periodic Table to write formulae and balanced chemical equations where appropriate

the first 20 elements, Groups 1, 7, and 0 and other common elements included within the specification

C3.1d use the formula of common ions to deduce the formula of a compound

M1a, M1c

C3.1e construct balanced ionic equations

M1a, M1c

C3.1f describe the physical states of products and reactants using state symbols (s, l, g and aq)

C3.1g describe tests to identify selected gases

oxygen, hydrogen, carbon dioxide and chlorine

C3.1h recall and use the definitions of the Avogadro constant (in standard form) and of the mole

the calculation of the mass of one atom/molecule In recognition of IUPAC’s review, we will accept both the classical (carbon-12 based) and revised (Avogadro constant based) definitions of the mole in examinations from June 2018 onwards (see https://iupac.org/ new-definition-mole-arrived/)

M1b, M1c

WS1.4b, WS1.4c, WS1.4d, WS1.4f

C3.1i explain how the mass of a given substance is related to the amount of that substance in moles and vice versa

M1c, M2a

WS1.4b, WS1.4c

C3.1j explain how the mass of a solute and the volume of the solution is related to the concentration of the solution

M1b, M1c

WS1.3c, WS1.4a, WS1.4c

C3.1k recall and use the law of conservation of mass

WS1.4c

C3.1l explain any observed changes in mass in non- enclosed systems during a chemical reaction and explain them using the particle model

WS1.1b, WS1.4c

C3.1m deduce the stoichiometry of an equation from the masses of reactants and products and explain the effect of a limiting quantity of a reactant

M1c

WS1.3c, WS1.4c, WS1.4d, WS1.4f

C3.1n use a balanced equation to calculate masses of reactants or products

M1c

WS1.3c, WS1.4c

Introducing chemical reactions

Next Steps

Learning Objectives