Chemistry: Acids, Reactions and the Periodic Table
Acids, reactions and the periodic table, in 13+ Chemistry, covers the pH scale, how acids react with metals and with carbonates, and how a metal's position affects how vigorously it reacts with acid.
Before you start
Make sure you're comfortable with these topics first:
Method
- Learn the pH scale from 0 to 14: acids have a pH below 7, alkalis have a pH above 7, and a neutral substance (such as pure water) has a pH of exactly 7.
- Learn the colours universal indicator turns across the pH scale, from red for a strong acid, through green for neutral, to purple for a strong alkali; litmus is a simpler indicator that just turns red in acid and blue in alkali.
- Learn the general word equation for neutralisation, acid + alkali produces salt + water, and be able to name the salt produced: hydrochloric acid produces chloride salts, sulfuric acid produces sulfate salts, and nitric acid produces nitrate salts.
- Learn the general word equation for a metal reacting with an acid, acid + metal produces salt + hydrogen, and know the standard test for hydrogen gas: hold a lit splint at the mouth of the test tube; a positive result is a squeaky pop.
- Learn the general word equation for a carbonate reacting with an acid, acid + carbonate produces salt + water + carbon dioxide, and know the standard test for carbon dioxide gas: bubble it through limewater; a positive result is the limewater turning cloudy (milky).
- Know how to compare the reactivity of different metals with a dilute acid practically: add an equal-sized piece of each metal to the same volume and concentration of acid, and time how long it takes to collect a fixed volume of gas (for example 20 cm^3, using a gas syringe or an upturned measuring cylinder filled with water); a shorter collection time means a more reactive metal. A common source of error is using metal pieces of different sizes or shapes, since this changes the surface area exposed to the acid and makes the comparison unfair.
- Use the periodic table to identify metals (found on the left and in the middle) and non-metals (found on the right); only metals react with dilute acid to produce a salt and hydrogen gas, so this reaction can itself be used to help identify whether an unknown element is a metal.
- When naming a salt, take the first part of the name from the metal (or the metal in the alkali used) and the second part from the acid used, following the pattern learned above.
Worked example
A pupil adds a small piece of magnesium ribbon to a test tube of dilute hydrochloric acid. Bubbles of gas are produced. (a) Name the gas produced. (b) Describe a test to confirm the identity of this gas. (c) Name the salt formed in this reaction.
- Recall the general word equation: acid + metal produces salt + hydrogen, so the gas produced when a metal reacts with an acid is hydrogen.
- To confirm this, collect a sample of the gas and hold a lit splint at the mouth of the test tube.
- If the gas is hydrogen, it burns rapidly with a squeaky pop as it reacts with oxygen in the air.
- To name the salt, combine the name of the metal (magnesium) with the acid's salt-name (hydrochloric acid produces chloride salts).
- Final answer: (a) hydrogen; (b) hold a lit splint at the mouth of the test tube, and a squeaky pop confirms hydrogen; (c) magnesium chloride.
Practice questions
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Q1State whether a solution with pH 3 is acidic, neutral, or alkaline.Show answer
Answer: Acidic
Q2State the colour universal indicator turns in a strong alkali.Show answer
Answer: Purple (violet/dark blue)
Q3Complete the word equation: hydrochloric acid + sodium hydroxide produces ___ + ___.Show answer
Answer: Sodium chloride + water
Q4Name the salt produced when zinc reacts with sulfuric acid.Show answer
Answer: Zinc sulfate
Q5Describe the test for carbon dioxide gas, and state the positive result.Show answer
Answer: Bubble the gas through limewater; the limewater turns cloudy (milky) if carbon dioxide is present
Q6A student adds a piece of unknown grey solid to dilute acid and no bubbles are produced, even after several minutes. Suggest whether the solid is a metal or a non-metal, and explain your reasoning.Show answer
Answer: Non-metal, because metals react with dilute acid to produce hydrogen gas (seen as bubbles), and no reaction was observed here
Q7Name the acid that produces nitrate salts.Show answer
Answer: Nitric acid
Exam-style questions
Written in the style of a 13+ Common Entrance exam paper, with a full mark scheme.
A student reacts calcium carbonate (marble chips) with dilute hydrochloric acid. (a) Write a word equation for this reaction. (b) Name the gas produced. (c) Describe the test for this gas and state the positive result. (d) Name the salt produced.
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A pupil tests the pH of four unknown solutions using universal indicator: Solution W turns red, Solution X turns green, Solution Y turns purple, Solution Z turns orange. (a) State which solution is neutral. (b) State which solution is the strongest acid. (c) Put all four solutions in order of increasing pH, lowest pH first. (d) A few drops of Solution Y are added to Solution W until the mixture turns green. Name the type of reaction that has taken place.
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A technician has three unlabelled metals: copper, magnesium and zinc. She adds each metal to a test tube of dilute hydrochloric acid and times how long it takes to collect 20 cm^3 of gas. Metal: copper, magnesium, zinc. Time to collect 20 cm^3 of gas: no gas collected, 8 seconds, 45 seconds. (a) Identify which metal did not react with the acid. (b) State which of the two reacting metals is more reactive, and explain how the results show this. (c) Name one piece of apparatus, other than a stopwatch, that could be used to collect and measure the volume of gas produced.
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Free printable worksheet
Want more practice on paper? Download the chemistry: acids, reactions and the periodic table worksheet pack - 15 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 7 of 13+ Science Workbook, the whole course as one free printable PDF.
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