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Understand Neutralisation

Worksheet Overview

QUESTION 1 of 10

There are lots of times we need to get rid of an acid completely. Stomach aches are often caused by too much acid in the stomach. If a pond is too acidic, life will not thrive in it. Neutralisation an acid with an alkali is one way of doing this, but there are others. By looking at the patterns, and thinking about the ions involved, we can predict what will happen for each type of reaction. Remember that the thing that makes acids acidic is the presence of excess H+ ions. If we want to make the pH neutral again, we need to react these ions away. This involves one type of ion being oxidised (losing electrons) and one type of ion gaining electrons (being reduced).

Acid + base, or acid + alkali

A base is a chemical which reacts with an acid to make a salt and water, and nothing else. The most common bases are metal oxides and metal hydroxides. Some bases dissolve in water; these are given the special name alkali. Because alkalis dissolve in water, we can talk about them having a pH; the pH of alkalis is greater than 7. Acids contain hydrogen, and oxides contain oxygen, so we can react them to make water (in terms of ions, 2 H+ + O2- → H2O) . Similarly, reacting hydrogen with hydroxide produces water (in terms of ions, H+ + OH- → H2O).

No matter what the acid, base or alkali are, the reactions all follow the same pattern:

acid + base → salt + water

(for example, sulfuric acid + copper oxide →  copper sulfate + water)

acid + alkali → salt + water

(for example, nitric acid + sodium hydroxide →sodium nitrate + water)

Acid + metal

We can also react acid with metal. The products are a salt + hydrogen gas. The part of the acid which isn't hydrogen reacts with the metal to make a salt, leaving the hydrogen by itself. The ionic equation for the hydrogen is 2 H+ → H2. The hydrogen is reduced (it's gained electrons), and the metal is oxidised (it loses electrons).

acid + metal → salt + hydrogen

(for example, hydrochloric acid + magnesium → magnesium chloride + hydrogen)

Thinking about these reactions in terms of oxidation and reduction links them to the reactivity series. A metal will only react with acid if it is more reactive than hydrogen.

Acid + carbonate

The final reaction you need to know is what happens when we react acid with a carbonate compound. Carbonate is CO3, and hydrogen from the acid reacts with one of the oxygens to make water. That leaves CO2 left over, which is carbon dioxide. So we get

acid + carbonate → salt + water + carbon dioxide

(for example, nitric acid + calcium carbonate → calcium nitrate + water + carbon dioxide

The ionic equation for this type of reaction is 2 H+ + CO32- → H2O + CO2.

Naming the salt

All these reactions produce a salt. The rules for naming the salt are the same for all the reactions:

1.  Look at the name of the non-acid (the alkali / base / carbonate / metal). There will be a metal mentioned in the name, usually as the first word. Look at the examples in this introduction- copper oxide, sodium hydroxide, magnesium, calcium carbonate. That metal name will be the metal in the name of the salt, which is the first word in the name. Look at the salts made in the examples- copper sulfate, sodium nitrate, magnesium chloride, calcium nitrate.

2. Now look at the acid used, which will tell you what type of salt is produced. There are three you are expected to know:

nitric acid, which produces nitrates

sulfuric acid, which produces sulfates

hydrochloric acid, which produces chlorides

Check the examples again- they all follow this rule.

And that's it! The name of the acid, and the metal added let us predict the salt form. The compound the metal is in initially (alkali, base, pure metal, carbonate) tells us what else is produced.

 

Think about what happens when hydrochloric acid and potassium hydroxide react.

Pick half-equations to make the type-equation for this reaction.

What salt will be produced when we react sodium oxide with nitric acid?

Which would be produced when hydrochloric acid reacts with aluminium carbonate? Tick all the correct answers.

aluminium

aluminium hydrate

aluminium chloride

carbon dioxide

carbonate

water

hydrogen

Imagine reacting potassium metal with hydrochloric acid. Which of these statements is true? Tick all the right answers.

Hydrogen is reduced

Hydrogen gas is produced

Potassium hydrate is produced

Hydrogen is oxidised

Potassium chloride is produce

The ionic equation is H+ → H2O

Imagine that we add some unlabeled powder to a beaker of sulfuric acid, without bothering to check what it is. (Don't add unlabeled powers to acids yourself- it's potentially very dangerous!)

We see bubbles in the beaker, and make a blue solution, which we are fairly sure is copper sulfate.

How could we tell whether the powder was copper or copper carbonate?

test the gas with a glowing splint

test the gas with a lit splint

test the gas by bubbling it through limewater

Think about what happens when hydrochloric acid and potassium hydroxide react.

What is the name of the salt produced? Type in its name.

Think about what happens when hydrochloric acid and potassium hydroxide react.

Tick the correct statements in this list.

The ionic equation is H+ + OH- → H2O

Potassium is oxidised

The ionic equation is H+ + 2 OH- → H2O

The balanced equation is HCl + KOH → KCl + H2O

Potassium is reduced

The balanced equation is HCl + 2 KOH → KCl + H2

What are the chemical formulas of sodium oxide and sodium carbonate? The charges on individual ions are Na+, O2-, CO32-. (Remember the rule for ionic compounds).

The ionic equation is H+ + OH- → H2O

Potassium is oxidised

The ionic equation is H+ + 2 OH- → H2O

The balanced equation is HCl + KOH → KCl + H2O

Potassium is reduced

The balanced equation is HCl + 2 KOH → KCl + H2

If we react zinc with hydrochloric acid, we produce zinc chloride. If we try to react copper with hydrochloric acid, nothing happens. Fill in the gaps to explain why this is. Use these words (but you may need to use some words more than once, or some not at all).

copper

electrons

hydrogen

neutralisation

reactive

redox

unreactive

zinc

The ionic equation is H+ + OH- → H2O

Potassium is oxidised

The ionic equation is H+ + 2 OH- → H2O

The balanced equation is HCl + KOH → KCl + H2O

Potassium is reduced

The balanced equation is HCl + 2 KOH → KCl + H2

If we react zinc with hydrochloric acid, we produce zinc chloride. What are the ionic half-equations for this reaction?

Zn → Zn2+ + 2 e-

2 H+ + 2 e- → H2

2 Cl- →Cl2 + 2 e-

H2 → 2 H+ + 2 e-

Zn2+ + 2 e- → Zn

Cl2 + 2 e- → 2 Cl-

  • Question 1

Think about what happens when hydrochloric acid and potassium hydroxide react.

Pick half-equations to make the type-equation for this reaction.

CORRECT ANSWER
EDDIE SAYS
Potassium hydroxide dissolves in water, so it's an alkali. However, all alkalis are also bases, so this is an acid + base reaction. These always make a salt, water and nothing else.
  • Question 2

What salt will be produced when we react sodium oxide with nitric acid?

CORRECT ANSWER
sodium nitrate
EDDIE SAYS
Sodium comes from sodium oxide, and nitrate comes from nitric acid.
  • Question 3

Which would be produced when hydrochloric acid reacts with aluminium carbonate? Tick all the correct answers.

CORRECT ANSWER
aluminium chloride
carbon dioxide
water
EDDIE SAYS
The salt produced would be aluminium chloride, because hydrochloric acid gives chlorides (not hydrates!) and the metal in the carbonate is aluminium. The other products from acid + carbonate are carbon dioxide and water.
  • Question 4

Imagine reacting potassium metal with hydrochloric acid. Which of these statements is true? Tick all the right answers.

CORRECT ANSWER
Hydrogen is reduced
Hydrogen gas is produced
Potassium chloride is produce
EDDIE SAYS
Acid + metal makes salt plus hydrogen gas. The name of the salt is potassium (because that was the metal used) chloride (because we used hydrochloric acid). Hydrogen gains electrons, so is reduced, but the ionic equation needs 2 H+ ions. The reactions of acid with alkali metals are very violent; you can find videos of them online, but they are very dangerous to do.
  • Question 5

Imagine that we add some unlabeled powder to a beaker of sulfuric acid, without bothering to check what it is. (Don't add unlabeled powers to acids yourself- it's potentially very dangerous!)

We see bubbles in the beaker, and make a blue solution, which we are fairly sure is copper sulfate.

How could we tell whether the powder was copper or copper carbonate?

CORRECT ANSWER
test the gas with a lit splint
test the gas by bubbling it through limewater
EDDIE SAYS
Copper metal with acid would give hydrogen gas, and copper carbonate with acid would give carbon dioxide. We could see what the gas is by trying the squeaky pop test and the turning limewater milky tests.
  • Question 6

Think about what happens when hydrochloric acid and potassium hydroxide react.

What is the name of the salt produced? Type in its name.

CORRECT ANSWER
potassium chloride
EDDIE SAYS
The alkali is potassium hydroxide, so take potassium from there. The acid is hydrochloric acid, so take chloride from there.
  • Question 7

Think about what happens when hydrochloric acid and potassium hydroxide react.

Tick the correct statements in this list.

CORRECT ANSWER
The ionic equation is H+ + OH- → H2O
The balanced equation is HCl + KOH → KCl + H2O
EDDIE SAYS
The ionic equation highlights the key change in the reaction. For all reactions between acid and hydroxide, this involves the hydrogen and hydroxide ions. The potassium ion doesn't change; it's +1 at the start and +1 at the end. That's why it doesn't appear in the ionic equation.
  • Question 8

What are the chemical formulas of sodium oxide and sodium carbonate? The charges on individual ions are Na+, O2-, CO32-. (Remember the rule for ionic compounds).

CORRECT ANSWER
EDDIE SAYS
Remember that for ionic compounds, the total charge needs to cancel. Since Na is +1 and O is -2, we need two sodiums for each oxygen. Draw out the dot-and-cross diagram if you\'re not convinced. In the same way, Na is +1 and CO3 is -2, so we need two sodiums for each carbonate.
  • Question 9

If we react zinc with hydrochloric acid, we produce zinc chloride. If we try to react copper with hydrochloric acid, nothing happens. Fill in the gaps to explain why this is. Use these words (but you may need to use some words more than once, or some not at all).

copper

electrons

hydrogen

neutralisation

reactive

redox

unreactive

zinc

CORRECT ANSWER
EDDIE SAYS
Metal + acid is a redox reaction, so it has parallels with displacement reactions. Electrons go from the more reactive metal to the less reactive one (hydrogen is as a sort-of metal here). Zinc is reactive enough to do this, but copper isn't.
  • Question 10

If we react zinc with hydrochloric acid, we produce zinc chloride. What are the ionic half-equations for this reaction?

CORRECT ANSWER
Zn → Zn2+ + 2 e-
2 H+ + 2 e- → H2
EDDIE SAYS
The zinc is oxidised (it loses electrons, and ends up in the compound) and the hydrogen is reduced (it gains electrons, and moves out of the compound). The chloride isn\'t involved in the electron transfer at all.
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