New Topic: Acids and New Topic: Acids and AlkaliAlkali

2 important types of solutions are acids and alkali’sAcids taste sour Alkali taste bitter

We have also used many acids and alkalis in the lab this year.

Who can come up with the most?

LO: to list a number of household acids and the pH of numerous substances using pH paper

TASK: Make a list of all the acids and alkalis you have heard of before either in the lab or at home?

Making your own Indicator to test

everyday acids and alkalis

Washing powders dissolve in water to make alkaline solutions.

5.1b Identifying acids and alkalis

Alkalis are the chemical opposite of acids.They feel soapy.

Toothpaste helps protect teeth against acid erosion.

5.1b Identifying acids and alkalis

You probably use one alkaline substance every day – toothpaste.

Companies use huge amounts of it to make paper, detergents and aluminium for fizzy drinks cans.

5.1b Identifying acids and alkalis

Sodium hydroxide is an important alkali.

7E Acids and alkalis - Concentrated and dilute

Particle models of a concentrated acid and a weak acid.

Which sentence best describes which acid?

A. This acid has only a few acid particles compared to water particles.

B. This acid has a lot of acid particles compared to water particles.

Why is a dilute acid less hazardous than a concentrated acid?

concentrated acid weak acid

A dilute acid is less dangerous than a concentrated acid because there are less acids particles in a dilute acid.

Discuss these questions with your partner.

Be ready to feedback your ideas to the class

1. What is a strong acid?2. What is the keyword for strong acids?3. What is the opposite of a strong acid?4. What is the keyword for weak acids?5. How can make a strong acid weak?6. How can you make a weak acid strong?7. What does adding water to an acid do?

Time: 5 min

universal indicator

pH scale

An indicator is a dye which changes colour according to whether it is in an acidic or alkaline solution.

Indicators

Range of colours, tell us how strong acid or alkali is

1 2 14131211109876543

Strong acid Neutral Strong alkali

Weak acid Weak alkali

For example,

Making your own IndicatorApparatus Pestle and mortar

Filter paper and a filter funnel Red cabbage leaves

Boiling tube or conical flask Hot water

Method1 Put some red cabbage leaves into the mortar.2 Add a little hot water.3 Grind up the leaves so that you get as much of the colour out as possible.4 Filter the mixture and collect the liquid in a tube or flask.

universal indicatordemo

In your books, explain what I did and why the universal indicator changed colour

Practical: Safety with acids

http://uk.youtube.com/watch?v=s0CyLbiwHkg

How should spilled acids be cleaned up?

Part 2: Using your indicator

Apparatus•Red cabbage juice Dropping pipette•Spotting tile Substances to test

You will need the following results table: Copy the title and table into your book, then go around the class and test the everyday substances to see if they are acids, alkalis or neutral

Investigating the pH of everyday substances

METHODWear goggles and tie hair backIn your groups, put a few drops of each substance in the white

tray.Note down the name of each and your observations in the

table.Put a piece of indicator paper in the substance and record what

colour it goes.

Substance Colour with red cabbage indicator

Colour of pH paper and pH number

Acid/Alkali or neutral

Strong or weak

7E Acids and alkalis - Where are they found?

FALSE! The Latin word “acere” means “sour”. Acids have a sour or bitter taste.

 

7E Acids and alkalis - True or false?

True or False?

FALSE! Ethanoic acid is the chemical name for vinegar. Vinegar on pancakes -

YUCK! Most people prefer citric acid in lemon juice.

TRUE! Pure water is called neutral. In nature, rainwater is weakly acidic and seawater is weakly alkaline.

FALSE! They are called corrosive. Dangerous alkalis are sometimes called caustic.

FALSE! Only strong acids are dangerous. Weaker acids, like citric acid, are not harmful to skin.

TRUE! Arabic chemists used to make alkalis from the remains of plant ashes.

 

1. The word acid comes from the Latin word “acere” meaning “sweet”.

2. The word “alkali” comes from the Arabic “al-qily” which means “plant ashes”.

3. All acids are dangerous and can burn skin.4. Acids and alkalis that are dangerous to taste and touch are called caustic.

5. Pure water is not an acid or an alkali.6. The acid some people like to put on pancakes is called ethanoic acid.

Assessment feedbackHomework: Revise for Elements, compounds and mixtures test

Plenary learning log

Hazard!

Hazard!

Hazard!

Hazard Symbols

Hazard Symbols

Hazard symbols

1. What are hazard symbols?

2. What are they used for?

3. What colour are their background?

4. Why do we use them?

5. What are the advantages of using them instead of words?

Homework• Produce a leaflet on a famous scientistNote when and where they were bornWhat were they famous forWhat books or papers did they writeWhy was their work important?

Any other interesting facts about them and their work

Remember No CUT AND PASTE and make sure you understand everything you write

Post it notes

• 2 post notes

• On one, write 3 things you have liked the most about science last term

• On the other write down some things that you think could be better

Stick them on the board on your way out

Repro test

Combustion demo

• Write down your observations in your book

• Why did the money not burn?

Methane bubbles demo

• Write down any obserations in your book?

• Why did the bubbles rise?