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Practical videos | 14–16 years
- 1 Access free videos to support your teaching
- 2 Paper chromatography
- 3 Rates of reaction
- 4 Simple distillation
- 5 Enthalpy change of combustion
- 6 Conservation of mass
- 7 Electrolysis of aqueous solutions
- 8 Halogen displacement reactions
- 9 Identifying ions
- 10 Preparing a soluble salt
- 11 Reactivity series of metals
- 12 Simple titration
- 13 Temperature change (neutralisation)
- 14 Potable water
Conservation of mass
- Five out of five
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Investigate conservation of mass with two experiments exploring the concept
This video presents two experiments, the first is the reaction of magnesium with oxygen and the second is the reaction of calcium carbonate with hydrochloric acid.
Chapter titles: 00:09 Introducing conservation of mass; 01:29 Reaction of magnesium and oxygen; 04:31 Reaction of calcium carbonate with hydrochloric acid; 05:54 Calculating the change in mass; 07:20 Open and closed systems.
Download additional resources
Supporting resources booklet including pause-and-think questions with answers, teacher notes, intended outcomes, follow-up worksheets and structure strips. Plus technician notes and integrated instructions . Editable versions of all worksheets, results tables and the intended outcomes are provided.
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- Teacher notes
Full teacher notes are available in the supporting resources booklet , including ideas for how to use this video and the supporting resources as part of your teaching.
Notes on running the practical experiments
Two practical experiments are included in the video:
- the reaction of magnesium with oxygen
- the reaction of calcium carbonate with hydrochloric acid
Technician notes and integrated instructions are offered for both experiments.
The reaction of magnesium with oxygen takes around 30–45 minutes, depending on the competence of the class. To fit both activities into one hour in the laboratory it is possible to run both experiments concurrently. Once the crucible is being heated over a roaring blue flame in the first experiment, learners can begin the calcium carbonate with hydrochloric acid reaction. You should be able to complete the reaction in the conical flask before the magnesium has fully reacted. Learners can measure change of mass and clear away their glassware while waiting for the crucible to cool.
Procedure for the reaction of magnesium with oxygen
1. Take a piece of magnesium about 10–15 cm long. Twist it into a loose coil.
2. Put the magnesium inside the crucible and place the crucible with the lid on a mass balance. Record the total mass of the magnesium, crucible and lid.
3. Set up the Bunsen burner on the heat resistant mat with the tripod. Place the pipe clay triangle over the tripod, ensuring that it is secure. Place the crucible containing the magnesium in the pipe clay triangle and put the lid on.
4. Light the Bunsen burner and begin to heat the crucible. It is best to start with a gentle blue flame, but you will need to use a roaring flame (with the air hole fully open) to get the reaction to go.
If you are going to complete the reaction of magnesium with oxygen and the reaction of calcium carbonate with hydrochloric acid concurrently, begin the second procedure here. You must make sure you continue to monitor the crucible and Bunsen burner.
5. Once the crucible is hot, gently lift the lid with the tongs a little to allow some oxygen to get in. You may see the magnesium begin to flare up. If the lid is off for too long then the magnesium oxide product will begin to escape. Avoid this.
6. Keep heating and lifting the lid until you see no further reaction.
7. Turn off the Bunsen burner and allow the apparatus to cool.
8. Place the crucible with lid containing the product onto a mass balance. Record the total mass of the crucible, lid and product.
Procedure for the reaction of calcium carbonate with hydrochloric acid
1. Measure out 20 cm 3 of hydrochloric acid in a measuring cylinder.
2. Place the 20 cm 3 hydrochloric acid into a 250 cm 3 conical flask.
3. Place this onto a mass balance. While the conical flask is still on the mass balance, add 2–3 marble chips to the top-pan. Record the total mass of the flask, acid and marble chips.
4. Add the marble chips to the conical flask.
5. Gently swirl the flask.
6. Record the mass after 3 minutes (or before if there is no more fizzing).
Learners will need to have a clear understanding of the following scientific terminology:
- conservation of mass
An example Frayer model for the term ‘conservation’ is included in these resources. You can find more examples, and tips on how to use Frayer models in your teaching here.
Prior knowledge
Learners should be familiar with the particle model of matter from their 11–14 learning. They should be able to describe how the arrangement of particles changes as a substance moves between different states.
Learners should also be able to use the periodic table to identify symbols for elements and suggest formula for compounds. Learners should be confident writing word and symbol equations;
There are some questions included which ask learners to balance equations and add state symbols. Depending on where conservation of mass occurs in your scheme of work your learners may not have come across this yet. Adapt the questions to make them relevant to the stage and level that you are at.
Some of the challenge tasks require knowledge from other topics. It would be useful for learners to be able to recall the products of acid base reactions, in particular the general equation:
metal carbonate + acid → a salt + water + carbon dioxide
Common misconceptions
Learners sometimes get unconvincing results when heating magnesium in a crucible. It is worth evaluating what they have done as there are several reasons why their results may be disappointing:
- the magnesium oxide product may escape as they lift the lid
- not all the magnesium may have reacted (the product may still look a bit grey rather than white)
- they may have prodded the product with their splint so not all of it got weighed (more common than you might expect)
- not taring the balance correctly when measuring the mass
- having the magnesium coiled too tightly so that not all of it reacts
Some learners think that gases have no mass and that substances in their solid state have a greater mass than in their liquid form, confusing density with mass. Use carefully structured demonstrations to address these misunderstandings before introducing chemical changes that appear to violate the law of conservation of mass. Some examples of demonstrations can be found in the article How to teach conservation of mass .
Diagnostic multiple-choice questions are a great way to explore learners’ reasoning behind their answers. Best Evidence Science Teaching resources provide a great starting point to explore their ideas about conservation of mass. Learners are given a question and multiple plausible explanations for an observation. They then choose and justify which explanation they agree with. You can also provide learners with thought experiments and ask them to provide their own explanations (see the thinking questions resource). Read more about diagnostic questioning and access Best Evidence Science Teaching resources on the topic of particles and structure .
Conservation of mass: supporting resources
Conservation of mass: integrated instructions, conservation of mass: technician notes_1, conservation of mass: pause-and-think questions, conservation of mass: intended outcomes, conservation of mass: follow-up worksheet, conservation of mass: structure strips, conservation of mass: printable results tables, frayer model: conservation.
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Access free videos to support your teaching
Paper chromatography
Rates of reaction
Simple distillation
Enthalpy change of combustion
Electrolysis of aqueous solutions
Halogen displacement reactions
Identifying ions
Preparing a soluble salt
Reactivity series of metals
Simple titration
Temperature change (neutralisation)
Potable water
- 11-14 years
- 14-16 years
- Practical experiments
- Technician notes
- Compounds and mixtures
- Properties of matter
Specification
- The law of conservation of mass states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
- Recall and use the law of conservation of mass.
- 1.47 Explain the law of conservation of mass applied to: a closed system including a precipitation reaction in a closed flask
- 1.47b Explain the law of conservation of mass applied to: a non-enclosed system including a reaction in an open flask that takes in or gives out a gas
- 1.47a Explain the law of conservation of mass applied to: a closed system including a precipitation reaction in a closed flask
- C5.3.1 recall and use the law of conservation of mass
- C5.2.1 recall and use the law of conservation of mass
- C1.3k recall and use the law of conservation of mass
- C1.3i recall and use the law of conservation of mass
- Equations, involving formulae, can be written to show the reaction of metals with oxygen, water, and dilute acids: metal + oxygen → metal oxide
- Given a balanced equation, the mass or number of moles of a substance can be calculated given the mass or number of moles of another substance in the reaction
- a metal carbonate + an acid → a salt + water + carbon dioxide
- 2H⁺(aq) + CO₃²⁻(aq) → H₂O(l) + CO₂(g) for aqueous metal carbonates
- (k) chemical reactions as a process of re-arrangement of the atoms present in the reactants to form one or more products, which have the same total number of each type of atom as the reactants
- (l) colour changes, temperature changes (exothermic/endothermic) and effervescence as evidence that a chemical reaction has taken place
- (m) how to represent chemical reactions using word equations
- (n) how to represent chemical reactions using balanced chemical equations where the total relative mass of reactants and products is equal
- 2.1.2 describe the reactions, if any, of the above metals with the following and describe how to collect the gas produced, where appropriate: air; water; and steam;
- 1.5.5 construct word equations to describe the range of reactions covered in this specification; and
- 1.5.6 recognise that in a chemical reaction no atoms are lost or made but they are rearranged, and as a result we can write balanced symbol equations showing the atoms involved.
- 1.5.7 write balanced symbol equations for all reactions covered in this specification and for unfamiliar chemical reactions when the names of the reactants and products are specified;
- 2. Develop and use models to describe the nature of matter; demonstrate how they provide a simple way to to account for the conservation of mass, changes of state, physical change, chemical change, mixtures, and their separation.
- Concentration. Particle size.
- Household acids and bases (two examples of each).
- Acids, bases and salts. Neutralisation - formation of a salt from an acid and a base.
- Law of conservation of mass.
- Using the octet rule to predict the formulas of simple compounds - binary compounds of the first 36 elements (excluding d-block elements) and the hydroxides, carbonates, nitrates, hydrocarbonates, sulfites and sulfates of these elements (where such…
- 3.3 The Mole
- Empirical and molecular formulas.
- Chemical equations. Balancing chemical equations. (Simple examples.)
- Calculations based on balanced equations using the mole concept (balanced equations will be given for all calculations).
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