Acids and Bases

By the end of today’s class you should be able to: Explain what an indicator is Know that litmus paper is an indicator

An indicator An indicator is chemical that changes colour if it is in an acid or a base Litmus paper is an indicator.

How litmus paper works.. Red litmus stays red Red litmus turns blue Blue litmus turns red Red litmus turns blue Blue Litmus stays blue Red litmus stays red Blue Litmus stays blue

Doing the litmus test Substance tested What happened to red litmus What happened to blue litmus Is it acid/ base or neutral

Litmus test experiment The results for the litmus tests are: Tube 1. The solution is an alkali which turns blue when red litmus is added to it and remains blue when blue litmus is added to it. Tube 2. The solution is an acid which remains red when red litmus is added to it and turns blue when red litmus is added to it. Tube 3. The solution is water which remains red when red litmus is added to it and remains blue when blue litmus is added to it.

By the end of today’s class you should be able to: Name some common AND lab acids and bases Know what the pH scale is and how it works

What is an acid? Acids are a group of chemicals. What do you know about acids? Are all acids dangerous?

Some common acids used in the laboratory are: Hydrochloric Acid (HCl) Sulfuric Acid (H2SO4)

What is a base? everyday alkalis Bases are another group of chemicals. Examples… everyday alkalis

Some common bases used in the laboratory are: Sodium hydroxide - NaOH Limewater – Calcium hydroxide - Ca(OH)2 Bases that are soluble in water are called alkalis.

Can you… Explain what an indicator is? Give an example of an indicator? Use litmus paper to test a variety of solution and classify these as acidic, basic or neutral? Name some common acids and bases?

Learning objectives for today.. What the PH scale is How universal indocator Learn what a neutralisation reaction is

Indicators: how acidic or basic? Litmus will tell you whether a solution is acidic or basic: what it won’t tell you is how acid or basic. Universal indicator is an indicator that tells us how strong an acid or base is.

Indicators: the pH scale The pH scale is a scale that runs from 0 to 14 which tells you how acidic or how basic something is. pH7 is neutral pH 1 is strongly acid pH14 is strongly basic 1 2 14 13 12 11 10 9 8 7 6 5 4 3 Strong acid Neutral Strong bases Weak acid Weak Bases

Doing the universal indicator test Substance tested What is its pH? What type of substance is it?

What type of substance? 7 Are these substances acidic or alkaline? Are they weak or strong? Substance pH Description of acid/alkali soda water 6 car battery acid 1 soap 8 washing soda 10 stomach acid 2 oven cleaner 14 vinegar 4 very weak acid very strong acid very weak alkali weak alkali strong acid very strong alkali weak acid alkali acid 1 2 14 13 12 11 10 9 8 7 6 5 4 3

The PH scale

Learning check: Can you.. Tell what universal indicator is used for? Explain the difference between universal indicator and litmus paper? Explain what the pH scale is?

What is the pH?

Learning objectives To learn about what happens in a neutralisation reaction

? What happens when an acid and an alkali are mixed? Mixing an acid and a base causes a chemical reaction.

The chemical reaction between an acid and a base is called neutralisation. acid base a salt water The pH value of the reaction mixture will turn to 7

When an acid is mixed with a base they react with each other form a salt and water. This is called a neutralisation reaction. The things that are made are called products The things that react are called reactants Acid + Base Salt + Water

Examples of neutralisation reactions The vinegar neutralises the wasp sting!

Learning check.. What is a neutralisation reaction? What is made during a neutralisation reaction? What is the chemical formula of hydrochloric acid? What is the chemical formula of sodium hydroxide? Give one example of a neutralisation reaction

By the end of the lesson you should be able to: Know what a burette and pipette are used for and how they are used Learn the word equation and chemical equation for a neutralisation reaction between sodium hydroxide and hydrochloric acid Know how to titrate HCl against NaOH and prepare a sample of sodium chloride salt.

A Neutralisation reaction: The reaction in words (A word equation): Hydrochloric acid + Sodium Hydroxide Sodium Chloride + Water HCl + NaOH NaCl + H2O The reaction in chemical formulas (A chemical equation):

Homework Draw diagrams of the four main steps in the experiment into notes copy Filling pipette, Filling burette, Titration, Evaporating water to get salt

Measure out 25cm3 of sodium hydroxide into the conical flask. 2 Measure out 25cm3 of sodium hydroxide into the conical flask! 2. Add some indicator to the solution

3. Fill up the burette with hydrochloric acid (HCl) to the zero level.

Start the titration! Do the titration once roughly, twice more and then finally without an indicator.

Finally repeat the titration without using an indicator!

Evaporation will separate the salt and water!

Acids and Bases neutralisation Acids react with bases called carbonates to produce a salt, carbon dioxide gas and water. This is also a neutralisation reaction. Acid + Carbonate  Salt + Carbon dioxide + Water

A different type of neutralisation reaction Acid + Carbonate  Salt + Water + Carbon dioxide Hydrochloric acid + calcium carbonate  Calcium chloride + Water+ Carbon dioxide HCl + CaCO3  CaCl2 + H2O + CO2