Topic 3 - Electrolysis

When added to water, which ions do acids produce?

Hydrogen.

Which ions make aqueous solutions acidic?

Hydorgen.

When added to water, which ions do alkalis produce?

Hydroxide.

Which ions make aqueous solutions alkaline?

Hydroxide.

Are hydrogen ions positive or negative?

Positive.

Are hydroxide ions positive or negative?

Negative.

Describe what the numbers on the pH scale indicate.

• Acid = 0-6.

• Alkali = 8-14.

• Neutral = 7.

What can be used to measure pH?

Universal indicator and pH probe/meter.

Name a piece of equipment that could be used to measure the pH of a substance more accurately than the universal indicate a paper.

pH meter or probe.

Name 4 indicators that can be used to determine the acidity or alkalinity of a substance.

• Universal Indicator.

• Methyl Orange.

• Litmus Paper.

• Phenolphthalein.

Give the colour of methyl orange in acids, neutral and alkalis.

• Red in acids.

• Yellow in alkalis.

• Yellow/orange in neutral.

Give the colour of litmus paper in acids, neutral and alkalis.

• Red in acids.

• Purple in neutral.

• Bue in alkalis.

Give the colour of phenolpthalein in acids, neutral and alkalis.

• Colourless in acids and neutral.

• Pink in alkalis.

Describe how to use a universal indicator to test the pH of a substance.

• Add a few drops of universal indicator solution to the substance.

• Check the colour against a colour chart to determine the pH value.

Suggest a problem with using universal indicator to test for the pH of a solution.

The colour of the solution is matched to pH colour chart so may be subjective and doesn’t provide an exact pH value.

Why is universal indicator not used to measure pH during titrations?

It does not give a sharp colour change which is required to identify the end-point.

Why would litmus paper not be a suitable indicator in an experiment?

Litmus paper only shows if the solution is acidic / alkaline, not how acidic or alkaline it is.

Describe the colour change seen at the end points of this titration.

Red to yellow.

Explain two detail details that could be added to this method to ensure an accurate result is obtained.

• Use a white tile to make it easier to see exactly when the colour change of indicator takes place.

• Wash inside burette/pipette with appropriate solution before titration to ensure they are not contaminated.

Acid X has a pH of 1. What can be said about the concentration of hydrogen ions in acid X?

High concentration of hydrogen ions, making it a strong acid.

Alkali X has a pH of 8.5. What can be said about the concentration of hydroxide ions in alkali X?

Low concentration of hydroxide ions, making it a weak alkali.

The higher the concentration of hydrogen ions in a solution, the ____ the pH.

Lower.

The higher the concentration of hydorxide ions in a solution, the ____ the pH.

Higher.

What is the difference between strong and weak acids?

• Strong acids ionise/dissociate completely in aqueous solutions whereas weak acids only partially ionise/dissociate in aqueous solutions.

• Weak acids have fewer hydrogen ions/lower concentration of hydrogen ions than strong acids.

An acid completely dissociates in water. How can this acid be described?

Strong acid.

An acid only partially dissociates in water. How can this acid be described?

Weak acid.

Will a strong or weak acid of equal concentrations have more hydrogen ions in a solution?

Strong.

Strong acids have a pH between ___.

0-3.

Weak acids have a pH between ___.

4-6.

What does the ⇌ symbol indicate in the dissociation of an acid?

The acid is weak because it only partially dissociates.

Give examples of strong acids.

Hydrochloric acid, nitric acid, sulphuric acid.

Give examples of weak acids.

Ethanoic acid, citric acid, carbonic acid.

Do strong or weak acids have reversible reactions?

Weak acids.

What is the difference between a dilute and concentrated solution?

Dilute solution contains a small amount of solute in a given volume of solution whereas a concentrated solution contains a large amount of solute in a given volume of solution.

What is the difference between a dilute and concentrated acid?

Dilute acids contain a small amount of acid in a given volume of solution whereas concentrated acids contain a large amount of acid in a given volume of solution

If p H decreases by one unit, what happens to the concentration hydrogen ions?

Increases by a factor of ten.

If p H increases by one unit, what happens to the concentration hydrogen ions?

Decreases by a factor of ten.

How many times greater is the concentration of hydrogen ions in a solution of pH 4 and pH 6?

100 times.

If a hydrogen ion concentration in a solution of pH 5 increases by a factor 1000, what is the new pH?

pH 2.

1cm cubed of hydrochloric acid of pH 2 is made up to a volume of 10 cm cubed with distilled water. State the pH of the new solution.

pH 3.

What is the pH of this acid?

6.

What is the pH of distilled water?

pH 7.

What is a base?

A substance that can neutralise an acid to form a salt and water.

What type of base is an alkali?

Soluble base.

What is a name for soluble bases?

Alkalis.

Alkalis are insoluble bases. True or false?

False.

Alkalis are soluble bases. True or false?

True.

Are metal oxide soluble or insoluble bases?

Insoluble.

What are the common forms of bases?

Oxides, hydroxides or carbonates of metals.

Which substances can act as bases in acid base reactions?

Metal oxides, hydroxides and carbonates.

Why are metal oxides normally bases rather than alkalis?

Metal oxides are normally insoluble whereas alkalis are soluble.

Do all metals react with dilute acids?

No only those above hydrogen in the reactivity series.

Only metals above ____ in the reactivity series react with dilute acids.

Hydrogen.

State the reaction that occurs between a base and acid.

Base + Acid → Salt + Water.

What are the products when an acid reacts with a base?

Salt + Water.

State the reaction that occurs between a metal and acid.

Metal + Acid → Salt + Hydrogen.

What are the products when an acid reacts with a metal?

Salt + Hydrogen.

State the reaction that occurs between a metal carbonate and acid.

Metal Carbonate + Acid → Salt + Water + Carbon Dioxide.

What are the products when an acid reacts with a metal cabonate?

Salt + Water + Carbon Dioxide.

Effervescence is released when acid reacts with what? Why?

Acid reacts with metal carbonate because it forms carbon dioxide.

Why is effervescence produced when an acid reacts with metal carbonate?

They produce carbon dioxide when they react.

State the reaction that occurs between a metal oxide and acid.

Metal Oxide + Acid → Salt + Water.

What are the products when an acid reacts with a metal oxide?

Salt + Water.

State the reaction that occurs between a metal hydroxide and acid.

Metal Hydroxide + Acid → Salt + Water.

What are the products when an acid reacts with a metal oxide?

Salt + Water.

What is a neutralisation reaction?

A reaction that occurs when an acid reacts with a base to form salt and water.

What is the ionic equation for a neutralisation reaction?

H⁺(aq) + OH⁻(aq) → H2O(l).

Give a reason why adding hydroxide ions to an acid leads to an increased pH.

Hydroxide ions react with hydrogen ions and reduce hydrogen concentration increasing pH.

Which salt does hydrochloric acid form?

Chloride.

Write the formula for hydrochloric acid.

HCl.

Write the formula for the ion of chloride salt.

Which salt does sulfuric acid form?

Sulfate.

Write the formula for sulfuric acid.

H2SO4.

Write the formula for the ion of sulfate salt.

Which salt does nitric acid form?

Nitrate.

Write the formula for nitric acid.

HNO3.

Write the formula for the ion of nitrate salt.

Which products are formed when sodium hydroxide reacts with hydrochloric acid?

Sodium chloride + Water.

Which salt is formed when magnesium reacts with sulfuric acid?

Magnesium sulfate.

Which salt is formed when zinc oxide reacts with nitric acid?

Zinc nitrate.

Which salt is formed when calcium carbonate reacts with hydorchloric acid?

Calcium chloride.

Write the word equation for when sodium carbonate and sulfuric acid react.

sodium carbonate + sulfuric acid ⟶ sodium sulfate + water + carbon dioxide

A student adds marble chips to dilute hydrochloric acid. Marble chips contain calcium carbonate. Write the word equation for this reaction.

calcium carbonate + hydrochloric acid ⟶ calcium chloride + water + carbon dioxide

A student adds marble chips to dilute hydrochloric acid. Marble chips contain calcium carbonate. What type of reaction is this?

Neutralisation.

A student adds marble chips to dilute hydrochloric acid. Marble chips contain calcium carbonate.

Why would there be fizzing during the reaction and once the fizzing stops, why would there still be some marble chips left?

There would be fizzing as carbon dioxide is produced and there would still be marble chips left as they are in excess (not enough acid to react with all marble chips).

State two observations that would show the reaction has finished.

• No more bubbles/fizzing.

• Solid copper carbonate remains at the bottom of the flask.

Describe hoe you would obtain a solution of copper sulfate from the mixture and how you would obtain pure, dry copper sulfate crystals from this solution.

• Filter mixture. Place in filter paper in filter funnel and collect copper sulfate solution in conical flask.

• Pour solution into evaporating basin.

• Crystallise solution by heating with a Bunsen burner.

• When crystals form along the edge, remove from heat and allow to cool and crystallise.

• Filter crystals, dry between filter papers and then leave in a warm place like windowsill.

During a reaction between powder copper carbonate and dilute nitric acid, the powder completely disappears. State what can be deduced about the amount of acid used.

Acid is in excess/

Describe what you would observe when copper carbonate powder reacts with dilute sulfuric acid.

• Powder disappears.

• Effervescence/bubbles/fizzing.

State how you would change the method to improve accuracy.

• Use a measuring cylinder/pipette/burette to measure out hydrochloric acid.

• Use a balance to measure out base.

What happens when ammonia reacts with water?

Hydroxide ions form.

Aqueous ammonia is the same as ____.

Ammonium.

What is the chemical test for hydrogen?

Hold a lit burning splint at the open end of a test tube containing a gas. If hydrogen is present, it burns with a squeaky pop released.

In a test from hydrogen, what happens if hydrogen is present?

A squeaky pop is released.

A sample of hydrogen is mixed with air and ignited. State what would happen.

Squeaky pop released.

Pick A, B, C and D.

C.

What is the chemical name for limewater?

Calcium hydroxide.

What is a solution of sodium hydroxide called?

Limewater.

What is the test for carbon dioxide?

Bubble carbon dioxide through an aqueous solution of calcium hydroxide (limewater). If carbon dioxide is present, lime water turns to cloudy/milky.

In a test for carbon dioxide, what happens if carbon dioxide is present?

Lime water turns to cloudy/milky.