Predicting and Identifying Reactions | OCR GCSE Combined Science Chemistry, Higher tier (J250)
Predicting and Identifying Reactions
- 53 questions
- 4 subtopics
Predicting and Identifying Reactions is examined in Paper 10 (Chemistry), except the tests for oxygen, hydrogen, carbon dioxide and chlorine, which the specification places in Topic C3 and examines in Paper 9 (Chemistry).
It covers Groups 1, 7 and 0 and why they behave as they do; predicting reactivity from the Periodic Table; reactivity of metals with water and acids; and the tests for oxygen, hydrogen, carbon dioxide and chlorine.
Sample questions from Predicting and Identifying Reactions
Answer each one closed book first, then open the answer.
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Groups 1, 7 and 0, and why they behave as they do
In what form do the elements of Group 7 exist?
Show the answer
As diatomic molecules of two atoms sharing a pair of electrons, such as Cl₂ and Br₂. -
Groups 1, 7 and 0, and why they behave as they do
How many outer electrons does a halogen atom have, and what ion does it form?
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Seven outer electrons, and it gains one more electron to form a 1− ion. -
Predicting reactivity from the Periodic Table
Predict the formula of the compound formed between potassium and iodine.
Show the answer
KI, because potassium loses one electron and iodine gains one. -
Predicting reactivity from the Periodic Table
An unknown element is a soft metal that is stored under oil and fizzes vigorously on cold water. Which group does it belong to?
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Group 1. -
Reactivity of metals with water and acids
Compare how magnesium reacts with cold water and with steam.
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It reacts extremely slowly with cold water, but burns vigorously in steam to form magnesium oxide and hydrogen. -
Reactivity of metals with water and acids
A grey metal is left in blue copper sulfate solution and becomes coated in a pink-brown layer as the solution fades. What does this show?
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The grey metal is more reactive than copper, because it has displaced copper from the solution. -
Tests for oxygen, hydrogen, carbon dioxide and chlorine
Describe the test for chlorine and its positive result.
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Hold damp blue litmus paper in the gas; chlorine turns it red and then bleaches it white. -
Tests for oxygen, hydrogen, carbon dioxide and chlorine
What does chlorine gas look and smell like?
Show the answer
It is a pale green gas with a sharp, choking smell.
The 4 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Groups 1, 7 and 0, and why they behave as they do | The physical properties of the Group 1 metals and their reaction with water, the states, colours and diatomic molecules of chlorine, bromine and iodine, why the noble gases are unreactive and their properties, the outer electrons and ions of Groups 1 and 7, why reactivity rises down Group 1 and falls down Group 7, predictions for rubidium and astatine, halogen displacement, and noble gas boiling points. | 16 |
| Predicting reactivity from the Periodic Table | Where metals and non-metals sit, why a group reacts alike, caesium in water, the formulae of potassium iodide and calcium chloride, chlorine displacing iodine, why argon does not react, and recognising a Group 1 metal. | 11 |
| Reactivity of metals with water and acids | Why metals form positive ions when they react with water or acid, the products with acid, why potassium reacts faster than calcium, the metals that react with cold water, magnesium with steam, why copper does not react with acid while zinc and iron react slowly, ordering metals by fair tests and displacement, the temperature rise, cleaning with emery paper, and aluminium's oxide layer. | 16 |
| Tests for oxygen, hydrogen, carbon dioxide and chlorine | The tests and positive results for oxygen, hydrogen, carbon dioxide and chlorine, why the litmus paper must be damp, what turns limewater milky, telling oxygen from hydrogen with a splint, what chlorine looks and smells like and why it is tested in a fume cupboard, and identifying a gas from its test results. | 10 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR GCSE Combined Science Chemistry, Higher tier Active Recall Guide
Every topic, not just this one. 916 questions with their answers.