Acids and Alkalis

Can you think of some common, household acids and alkalis?

Acids AlkalisVinegarFruit Juice

Baking SodaIndigestion PowderOven Cleaner In Toothpaste

USES:

WASP STING IS ALKALINE IT IS NEUTRALISED BY VINEGAR AN ACID

•LIME AN ALAKLI IS ADDED TO ACIDIC SOIL

•VINEGAR IS USED AS A PRESERVATIVE

•AMMONIA IS USED AS A HOUSEHOLD CLEANER

COMMON LAB

ACIDS

ACID

FORMULA

COMMON LAB

ALKALIS

ALKALI

FORMULA

HYDROCHLORIC

(hydrogen chloride)

SODIUM

HYDROXIDE

SULPHURIC

(hydrogen sulphate)

POTASSIUM

HYDROXIDE

ETHANOIC AMMONIUM

HYDROXIDE

NITRIC

(hydrogen nitrate)

LITHIUM

HYDROXIDE

HCl(aq)

H2SO4(aq)

CH3COOH(aq)

HNO3(aq)

NaOH(aq)

KOH(aq)

NH4OH(aq)

LiOH(aq)

Laboratory Acids and Alkalis

Can you work out the FORMULAS from the name?You MUST remember the FORMULAS of these!!!

INDICATORS SUBSTANCES THAT CHANGE COLOUR WITH CHANGING pH

pH scale Used to measure acidity or alkalinity of SOLUTIONS

Scale runs from under 0 to above 14

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neutral 7 only

Anything under 7 is acidic

Anything above 7 is alkaline

Testing for Acids and Alkalis

The pH scale is based on the pH of pure water being =7When we measure the pH of a solution, we are measuring to what degree a solute has changed the pH of waterUniversal indicator to cover the whole range

Red pink orange green blue/green blue purple

Strong acid weak acid neutral weak alkali strong alkali

The pH Scale

1. Prepare a test solution

2. Add universal indicator (or drop onto pH paper)

3. Allow colour to develop

4. Compare with standard colour chart

Rules when testing pH

Testing for pH

Name of Solution pH Acid / Alkali / Acid

Follow the rules for “Testing pH” and test 5 different solutions

Non-metal Oxides

Name of oxide

Appearance of oxide

Universal indicator

Sulphur dioxide

Carbon dioxide

Oxides of nitrogen

Hydrogen oxide

Colourless, pungent gas

Colourless, odourless gas

Colourless or brownPungent gas

Colourless and odourless

RED

RED

RED

GREEN

Non-metal Oxides

Oxides of carbon and sulphur are prepared by burning sulphur and carbon in air.

Oxides of nitrogen are prepared by sparking air

RULE:Oxides of NON-METALS make ACIDIC SOLUTIONS

EXCEPTION:Oxide of HYDROGEN is NEUTRAL (water)

Starter question

Which of the following substances when dissolved in water would produce an acidic solution

1)Magnesium oxide

2)Hydrogen oxide

3)Ammonium hydroxide

4)Phosphorus oxide

Answer 4)

Explanation the rule is soluble non-metal oxides make acidic solutions

Metal Oxides

Experiment 1:1. Add a tiny quantity of CALCIUM OXIDE into a dimple tray2. Add a few drops of WATER3. Test the pH of the solution with UNIVERSAL INDICATOR

Name of OxideAppearance

of Oxide pH of solution

Metal Oxides

When a metal oxide reacts with water, the METAL HYDROXIDE is formed

eg Sodium oxide reacts and forms SODIUM HYDROXIDE

Na2O (s) + H2O (l) 2NaOH (aq)

Making Metal Oxides

Experiment 2:1. Ignite a little of MAGNESIUM RIBBON2. Allow magnesium to burn and form MAGNESIUM OXIDE3. Drop the white ash onto a dimple tray4. Check the pH of the SOLUTION

Write the balanced equation for making MAGNESIUM OXIDE:

RULE:Oxides of METALS make ALKALINE SOLUTIONS

HOWEVER:Like non-metal oxides, they must be SOLUBLE in water for them to change the pH of water

Metal Oxides

Today’s plan:• Looking at INSOLUBLE METAL OXIDES• AMMONIA GAS and its pH

THURSDAY 8th OCTOBER

Insoluble Oxides and Hydroxides

Experiment:1. Add a small quantity of copper (II) oxide to a test-tube2. Add approx 5ml of water3. Shake the tube and try and dissolve the solid4. Use a dropper to transfer a sample of the clear liquid to the spotting tile5. Check the pH with Universal Indicator

Some metal oxides (such as copper (II) oxide) are INSOLUBLE in water, as these don’t dissolve, they CANNOT alter the pH of water.

Ammonia

NH3(g) is ammonia gas

(covalently bonded compound)

When dissolved in water ammonium hydroxide is formedThe equation for the reaction when ammonia gas dissolves in water to form ammonium hydroxide

NH3(g) + H2O NH4OH(aq)

THIS SOLUBLE HYDROXIDE MUST BE AN ALKALI

Fountain Experiment

Summary Flow-chart

Starter Question

Put these four oxides in order of the one which will give the HIGHEST pH to the one that will give the LOWEST pH:

Hydrogen oxideMagnesium oxideCarbon dioxideCopper (II) oxide

(The flow-chart from last day will help you!!)

Acids

Name of acid Formula

Hydrochloric

Sulphuric

Nitric

Ethanoic

HCl (aq)

H2SO4 (aq)

HNO3 (aq)

CH3COOH (aq)

Which element is COMMON to all acids?

AcidsLooking at the formula of the acids – which type of BONDING would you expect?

Think……..Would you expect it to CONDUCT ELECTRICITY??

Experiment:1. Set up the circuit shown2. Use HYDROCHLORIC ACID and determine if it conducts3. Repeat with both SULPHURIC and NITRIC ACIDS

Acids

Acids are:Compounds which dissolve in water to give a pH less than 7

All acids contain the element HYDROGEN

Acid solutions are able to conduct electricity

Electrolysis of Acids

1. Set up apparatus as shown – using DIRECT CURRENT (DC)

2. Upturn a test-tube FULL OF WATER over each electrode

3. Turn on the power supply – set to 6V

4. Collect a tube-full of gas from one electrode.

5. Keep the tube inverted to prevent losing any gas.

6. Test the tube for HYDROGEN GAS.

7. Repeat for other electrode.

Experiment:

Electrolysis of Acids

Draw a labelled diagram of the apparatus used last day

Underneath your diagram copy the note below:Electrolysis is the breaking down of a compound using electricity.

When acids undergo electrolysis, HYDROGEN GAS is formed at the negative electrode.

Why does hydrogen form?

+ve -ve

H+

e-

H+

H+

H+H+

H+

e-e-

e-

HHH

Although acids are made up of non-metalsthey exist as IONS.

The hydrogen ions (H+) pick up electrons from the negative electrode and producehydrogen gas.

Ions in Acids

Name of Acid Formula Ions Present

Hydrochloric

Sulphuric

Nitric

Ethanoic

AlkalisThink!!What common alkalis have you come across before??How many can you name??

AlkalisCan you now put these into a table?Can you get their formula?Can you work out the IONS present?

Name of Alkali Formula Ions

The pH scale - dilutionExperiment:• Measure 10ml of acid into test-tube (A) – test pH

• Take 1ml of A and dilute with 9ml of water (B) – test pH

• Take 1ml of B and dilute with 9ml of water (C) – test pH

• Repeat for test-tubes D, E and F – testing pH of each

Results:Test-tube pH

The pH scale - dilution

Answer these questions in your NOTES jotter.Write in sentences – these will be your notes for this activity!!

• What happens to the ACIDITY as the ACID is diluted?• What is happening to the concentration of H (aq) ions?• What happens to the pH as the ACID is diluted?

+

The pH scale - dilutionExperiment (This is a repeat of yesterday’s using ALKALI):• Measure 10ml of ALKALI into test-tube (A) – test pH

• Take 1ml of A and dilute with 9ml of water (B) – test pH

• Take 1ml of B and dilute with 9ml of water (C) – test pH

• Repeat for test-tubes D, E and F – testing pH of each

Results:Test-tube pH

The pH scale - dilution

Answer these questions in your NOTES jotter.Write in sentences – these will be your notes for this activity!!

• What happens to the ALKALINITY as the ALKALI is diluted?• What happens to the concentration of OH (aq) ions?• What happens to the pH as the ALKALI is diluted?

-

H+(aq) and OH-

(aq) Ions

NEUTRAL solutions contain an EQUAL concentration of H(aq) and OH(aq) ions.

ACIDIC solutions contain a GREATER concentration of H(aq) than OH(aq) ions.

ALKALINE solutions contain a GREATER concentration of OH(aq)

than H(aq) ions.

+

+

+

-

-

-

Water

The chemical name for water is HYDROGEN OXIDE

The expected bonding is

From this bonding

COVALENT BONDING

WATER SHOULDN’T CONDUCT ELECTRICITY

Water DOES conduct electricity

For water to conduct, there MUST be charged particles

The charged particles present are IONS